UBC Theses and Dissertations

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UBC Theses and Dissertations

Molecular inner-shell excitation studied by electron impact Hitchcock, Adam Percival 1978

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MOLECULAR  INNER-SHELL EXCITATION  STUDIED BY ELECTRON IMPACT  by ADAH PERCIVAL B.Sc.  Hons,  HITCHCOCK  McMaster U n i v e r s i t y ,  1974  THESIS SUBMITTED IN PARTIAL FULFILLMENT THE  REQUIREMENTS  FOR  THE DEGREE OF  DOCTOR OF PHILOSOPHY in THE FACULTY OP GRADUATE STUDIES in  t h e Department o f CHEMISTRY  Be  accept to  THE  this  thesis  the required  A  d  a  m  p  conforming  standard  UNIVERSITY CF BRITISH June,  •(7)  as  COLUMBIA  1978  e r c i v a l Hitchcock, 1978  In p r e s e n t i n g t h i s  an  thesis  advanced degree at  further  fulfilment  of  the  freely  available  for  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f  by h i s r e p r e s e n t a t i v e s . this  thesis for  It  financial  gain s h a l l not  written permission.  Department The  of  C^JJ^^Y^^^^M  U n i v e r s i t y o f B r i t i s h Columbia  2075 Wesbrook P l a c e Vancouver, Canada V 6 T 1W5  Date  UIMML_  %l  ?  /?7%  this  study. thesis  my Department  i s understood that copying or  for  agree that  reference and  f o r s c h o l a r l y purposes may be granted by the Head of  of  requirements  the U n i v e r s i t y of B r i t i s h Columbia, I  the L i b r a r y s h a l l make it I  in p a r t i a l  or  publication  be al1 owed without my  ii  ABSTRACT  Electron provide  many  impact  and e l e c t r o n  useful  tools  physical  structure  electron  energy  describes of  the  of  matter.  loss  inner-shell low  examination  One  of  resolution  (EELS) .  of  is  interesting  spectroscopic  electron  energy  The  significant  also  of  experimental and  more  i t s  including  hydrocarbons  (C H X, 6  5  series of  this  4  (CH X,  2  6  X = F,  3  X = F, C l , Br,  2  2  of  C l , Br, I ) , the  4  the many  inner-shell  the  and has  technique  Improvements energy  related  and  resolution  molecules  of  have  a l l observable and  700 eV  and  C H ), 6  i n the  The m o l e c u l a r  unsaturated 2  that  foundation  between 50  (CH , C H , C H , C H  that  of m o l e c u l e s .  investigations  saturated,  thesis  molecules.  and  arrangements.  excitation structure  simplest  halides  on  application.  scanning  of several  studied  the  builds  is  of e x c i t a t i o n s  i n the  e x t e n s i o n s not only  flexible  inner-shell  occur  a p p a r a t u s have l e d t o h i g h e r  I SEE L s p e c t r a been  work  This  demonstrated  (ISEELS)  the  i n the Department o f  feasible  features  loss spectra  present  provided but  experimentally  of tools  gaseous  studies  C h e m i s t r y a t UBC by G.B. Wight h a v e technique  these  o f EELS t o s t u d i e s  electrons  technigues  the  spectroscopy  the application  Preliminary,  for  spectroscopic  6  in  aromatic  the  methyl  I ) , t h e monohalobenz enes chloromethanes  (CH Cl _ , x  4  x  x = 0 t o 4) and c h l o r o e t h a n e . A out  number  i n order  of s p e c i f i c to  assist  investigations  spectral  h a v e been  interpretations  carried and  to  i i i  further  understand  excitation  the  phenomena.  Isotopic  to  a i d the assignment  and  CH3Br  energy  (CD Br).  structure  have of  been  The  6  observations excitation In  techniques  FOM  theoretical  ion  have  in  Institute  An a t t e m p t  descriptions  excitation  features  coincidence  results  chloromethanes  and S F 6 .  been of in  and  made t o  the light ISEELS  4  phase  the  CH2CI2,  has l e d to inner-shell halides.  electron-ion  study  the  ionization was  the  studies  ionic of  a  performed Physics  in  alternate  characteristic both  fine  spectrum  evaluate  of  (CD )  transitions  and M o l e c u l a r  certain  and  of  studies, to  4  absorption  experiment  f o r Atomic has  in  used  gas  resolution  used  This  6  the  and the methyl  excitation  SF .  of CH  excitation  2p  ISEELS been  of  been  quadrupole  structure  the  following  2p electron  Amsterdam.  shell  to  has  spectra  experimental  vibrational  addition  fragmentation  the  electric  inner-shell  spectra  X-ray  the  the sulphur  improved  of  in  s p e c t r a .of N2/ C O , C 2 H 4  coincidence  at  in  Is  extended  reported  of  substitution  observation  of  Molecular  CCI4.  identified  SF .  sulphur  is  nature  the carbon  equivalent  (EXAFS)  and  CHCI3  of  The f i r s t  3  loss  physical  inner-  electronof  the  iv  TABLE OF  CONTENTS  Abstract T a b l e of  i i Contents  iv  Tables  ix  Figures  xii  Plates  xvi  Acknowledgements  Chapter  1:  xvii  Introduction  1  1.1  C h a r a c t e r i s t i c s of I n n e r - S h e l l  1.2  Electrons  1.3  Related  versus  Gas  Excitation  ...  Photons  Phase  8  Inner-shell  Studies  19  (XPS)  19  X-ray  1.3.2  Auger S p e c t r o s c o p y  23  1.3.3  X-ray  Emission  27  1.3.4  Ionic  Fragmentation  29  Inner-shell  Excitation  1.4.1  Electron  1.4.2  Photoabsorption  Chapter  2:  Theory  of  2.1  Electron  2.2  Bethe-Born  2.3  Generalized  2.4  Applications  Spectroscopy  .......  1.3.1  1.4  Photoelectrcn  3  in Solids  Energy L o s s  Fast  Energy  31 31 33  Electron  Impact  Loss Spectroscopy  Theory Oscillator  .  35 35 38  Strengths  to I n n e r - s h e l l  Excitation  41 45  V  2.4.1  Energy  L o s s and A n g u l a r  Dependence o f t h e Momentum 2.4.2 O p t i c a l l y Chapter  Transfer  45  Forbidden T r a n s i t i o n s  47  3: E x p e r i m e n t a l  50  3.1 The S p e c t r o m e t e r 3.1.1  50  The E l e c t r o n  Source  54  3.1.2 The M o n c e h r o m a t o r  56  3.1.3  60  The I n t e r a c t i o n  3.1.4 The E n e r g y  Region  Loss A n a l y s e r  61  3.1.5  Spectrometer  Control  3.1.6  Spectrometer  C o n s t r u c t i o n , Vacuum  System  and M a g n e t i c  3.2 S p e c t r o m e t e r 3.3 E n e r g y  Circuitry  .........  Shielding  64  68  Operation  71  Calibration  76  3.4 Sample P u r i t y  78  3.5 T h e E l e c t r o n - I o n C o i n c i d e n c e A p p a r a t u s  81  3.5.1 E l e c t r o n E n e r g y L o s s 3.5.2 E l e c t r o n - I o n C o i n c i d e n c e 3.5.3 Electron-Ion Coincidence C o i n c i d e n c e Mode)  (TAC Mode) .... (Fast  86  3.5.4 I o n A u t o c o r r e l a t i o n Chapter  4: T h e I n t e r p r e t a t i o n  Excitation 4.1  M.O.  87  of I n n e r - s h e l l  Spectra  89  Models  89  4.2 T h e E q u i v a l e n t C o r e 4.3 Ab I n i t i o Theorem 4.4 P o t e n t i a l  82 84  (Z + 1) A n a l o g y  Calculations  93  beyond Koopmans 95  Barrier  Effects  and t h e M.O.  Model 97  vi  4.5  The  Shape R e s o n a n c e  4.6  EX A FS  Model  106  4.7 V i b r a t i o n a l S t r u c t u r e sitions C h a p t e r 5: C a r b o n C H and C H 2  6  6  100  K-shell  in Inner-Shell  111  E x c i t a t i o n of C H , 2  5.2  Comparison  with  5.3  D e t a i l s of  the  Energy  Loss  2  4  the  Spectra SEY  Spectral  5.4 R e l a t e d E x p e r i m e n t a l Excited States  118  Spectra  125  Assignments  131  Studies  of the  K-shell 139  5.5 P r e d i c t i o n s o f t h e I o n i z a t i o n R a d i c a l s from, t h e Z + 1 A n a l o g y  Potentials  of 140  6: I s o t o p e E f f e c t s on the I n t e n s i t i e s i n tha E x c i t a t i o n S p e c t r u m o f Methane . . . . . . . . . . . . .  6.1  Introduction  6.2  Experimental  6.3  Vibronic 7:  The  143 143  Results  Coupling  144  Interpretation  148  Methyl Halides  7.1  Long  7.2  Carbon K - s h e l l  7.3  V i b r a t i o n a l Structure  7.4  C H , 116  Electron  Chapter  2  6  5.1  Chapter K-shell  Tran-  Range S c a n s  and  154  Continuum  Features  .....  Excitation  7.3.1  Isotope Studies  7.3.2  Assignment of  Halogen I n n e r - S h e l l  i n the of  155 160  C  Methyl  1s  Spectra  Bromide  ...  171  ......  171  V i b r a t i o n a l Modes  176  Spectra  177  7.4.1  Fluorine  1s  Excitation of  CH F  7.4.2  Chlorine  2p  E x c i t a t i o n of C H C 1  7.4.3  Chlorine  2s  Excitation of  CH Cl  7.4.4  Bromine  3d  Excitation of  CH Br  179  3  182  3  3  3  ........  186 189  vii  7.1.5 I o d i n e Chapter  4d E x c i t a t i o n o f C H I  8: T h e M o n c h a l o b e n z e n e s  8.1  Excitation  of Carbon  8.2  Excitation  of Halogen  199  1s E l e c t r o n s Inner-shell  C h a p t e r 9: i n n e r - s h e l l E x c i t a t i o n and Phenomena i n t h e C h l o r o m e t h a n e s 9.1  193  3  Carbon  200 Electrons  . 212  EXAFS-type 219  1s E x c i t a t i o n o f t h e C h l o r o m e t h a n e s .. 220  9.2 C h l o r i n e  2p E x c i t a t i o n  of C h l o r o -  e t h a n e and t h e C h l o r o m e t h a n e s  229  9.3 EXAFS F e a t u r e s  235  i n the Chloromethanes  9.4 C h l o r i n e 2s E x c i t a t i o n o f C h l o r o e t h a n e and the Chlcromethanes  246  9.5 C a r b o n  249  9.6  1s E x c i t a t i o n o f C h l o r o e t h a n e ........  Discussion  Chapter  10: ISEELS  253 Studies  10. 1 The P o t e n t i a l F  of S u l p h u r H e x a f l u o r i d e  Barrier  Interpretation  1 s , S 2 s and S 2p E x c i t a t i o n  10.2 A d d i t i o n a l  Features  . 258  of the • 260  Spectral Features  267  10.3 Rydberg T r a n s i t i o n s i n t h e S 2p S p e c t r u m ... 272 C h a p t e r 11: E l e c t r o n - i o n C o i n c i d e n c e S t u d i e s o f t h e I o n i c Fragmentation of SF ....280 11.1 A b s o r p t i o n O s c i l l a t o r S t r e n g t h s . . . . . . . . . . . . 283 6  11.2 I o n i c  Fragmentation  11.3 S e p a r a t i o n o f V a l e n c e - s h e l l and S 2p Components o f S F I o n i c F r a g m e n t a t i o n . . . . . . . . . . . 6  11.3.1 V a l e n c e - s h e 11 Component o f t h e Absorption O s c i l l a t o r Strength  288 296 296  11.3.2 V a l e n c e S h e l l and S 2p Components o f t h e Ion O s c i l l a t o r S t r e n g t h s ... 300 11.4 I o n O s c i l l a t o r S t r e n g t h s and D o u b l e Dissociative Ionization  306  viii  11.5  Discussion  C h a p t e r 12: High R e s o l u t i o n S t u d i e s Structure in Inner-shell Excitation  311 of  Vibrational 314  12. 1 N i t r o g e n  314  12. 2 C a r b o n  Monoxide  318  13: C o n c l u s i o n s  321  Chapter  References Citation  Index  ...323 345  ix  T A EL ES  1.1  Bibliography  o f gas  3.1  S o u r c e and s t a t e d  phase  purity  inner-shell  studies  14  o f t h e c h e m i c a l samples 79  5.1 A b s o l u t e e n e r g i e s (eV) , term v a l u e s and t e n t a t i v e a s s i g n m e n t s of peaks o b s e r v e d i n t h e C spectrum of C H  1s  5.2 A b s o l u t e e n e r g i e s {eV), t e r m v a l u e s and t e n t a t i v e a s s i g n m e n t s of peaks o b s e r v e d i n t h e C spectrum o f C H4  1s  5.3 A b s o l u t e e n e r g i e s (eV) , t e r m v a l u e s and t e n t a t i v e a s s i g n m e n t s o f peaks o b s e r v e d i n t h e C spectrum o f C H  1s  5.4 A b s o l u t e e n e r g i e s ( e V ) , t e r m v a l u e s and t e n t a t i v e a s s i g n m e n t s of peaks o b s e r v e d i n t h e C spectrum of C H  1s  2  132  6  133  2  6  2  134  6  2  135  5.5 P r e d i c t e d i o n i z a t i o n p o t e n t i a l s o f c o r e e q u i v a l e n t r a d i c a l s ( e n e r g i e s i n eV)  141  6.1 I s o t o p e e f f e c t on t h e i n t e n s i t y o f t h e K—»-3s t r a n s i t i o n i n t h e c a r b o n 1s s p e c t r u m o f methane ....  147  7.1 A b s o l u t e e n e r g i e s (eV) , t e r m v a l u e s , c o r r e l a t i o n s l o p e s and t e n t a t i v e a s s i g n m e n t s f o r t h e f e a t u r e s o b s e r v e d i n t h e C 1s e n e r g y l o s s s p e c t r a o f t h e methyl h a l i d e s  163  7.2 Peak s e p a r a t i o n s , w i d t h s , i n t e n s i t i e s and i s o t o p e s h i f t s d e r i v e d from the l e a s t - s q u a r e s a n a l y s i s o f f e a t u r e s 2-6 i n t h e C H B r and CD B r spectra  175  7.3 A b s o l u t e e n e r g i e s ( e V ) , t e r m v a l u e s and t e n t a t i v e assignments f o r f e a t u r e s observed i n t h e F 1s s p e c t r u m o f C H F  181  7.4 A b s o l u t e e n e r g i e s ' ( e V ) , t e r m v a l u e s and t e n t a t i v e assignments f o r f e a t u r e s observed i n the CI 2p and C l 2s e n e r g y l o s s s p e c t r a o f C H C l  184  7.5 A b s o l u t e e n e r g i e s ( e V ) , terra v a l u e s and t e n t a t i v e assignments f o r f e a t u r e s observed i n the Br 3d s p e c t r u m o f C H B r  191  3  3  3  3  3  X  7.6 A b s o l u t e e n e r g i e s (eV) , term v a l u e s a n d t e n t a t i v e assignments f o r f e a t u r e s observed i n the I 4d s p e c t r u m o f C H I  196  8.1 A b s o l u t e e n e r g i e s (eV) , t e r m v a l u e s and t e n t a t i v e assignments f o r f e a t u r e s observed i n the c a r b o n 1s e n e r g y l o s s s p e c t r a o f t h e monohalobenzer.es  202  8.2 E x p e r i m e n t a l and c a l c u l a t e d w i d t h s o f t h e C 1s—*-xt* t r a n s i t i o n s i n t h e m o n c h a l c b e n z e n e spectra  206  3  8.3 A b s o l u t e e n e r g i e s l e v ) , terra v a l u e s and t e n t a t i v e assignments f c r f e a t u r e s observed i n the e l e c t r o n e n e r g y l o s s s p e c t r u m o f C H C 1 i n t h e C l 2p and C l 2s r e g i o n s 214 6  5  8.4 A b s o l u t e e n e r g i e s (eV) , term v a l u e s and t e n t a t i v e assignments f o r f e a t u r e s observed i n the Br 3d s p e c t r u m c f C 6 H B r and the I 4d s p e c t r u m o f C H I  217  9.1 A b s o l u t e e n e r g i e s (eV) , t e r m v a l u e s a n d t e n t a t i v e a s s i g n m e n t s f o r c a r b o n 1s e x c i t a t i o n f e a t u r e s i n the CH C1 , CHCl and C C l electron energy l o s s s p e c t r a  222  9.2 A b s o l u t e e n e r g i e s ( e V ) , t e r m v a l u e s a n d t e n t a t i v e a s s i g n m e n t s f o r c h l o r i n e 2p and 2s e x c i t a t i o n f e a t u r e s i n t h e e l e c t r o n energy l o s s s p e c t r a o f c h l o r o e t h a n e and t h e c h l o r o m e t h a n e s  231  5  6  5  2  2  3  4  9.3 EXAFS a n a l y s i s o f f e a t u r e s o b s e r v e d i n t h e C l 2p continua of CH C1 , CHCl and CCI4 and t h e C 1s continuum of C C l 241 2  2  3  4  9.4 A b s o l u t e e n e r g i e s {eV) , t e r m v a l u e s a n d t e n t a t i v e assignments f o r C 1s e x c i t a t i o n f e a t u r e s of C H C1. A n a l y s e s o f t h e C H and C H C l C 1s s p e c t r a are l i s t e d f o r comparison  252  10. 1 E n e r g i e s (eV) and a s s i g n m e n t s f o r t h e f e a t u r e s o b s e r v e d i n t h e S 2s, S 2p and F 1s e n e r g y l o s s spectra of SF  262  2  5  4  3  6  10.2 S p i n - o r b i t s p l i t t i n g s , w i d t h s and i n t e n s i t y r a t i o s d e r i v e d from l e a s t - s g u a r e s f i t s to the 6aig and 2t2g p e a k s i n t h e S 2p e n e r g y l o s s s p e c t r u m .... 278 11.1 Peak a r e a s and i d e n t i f i c a t i o n the i o n a u t o c o r r e l a t i o n spectrum  of i o n p a i r s  from 293  xi  11.2 V a l e n c e - s h e l l , (S 2 p , 6 a i j ) s t a t e and S 2p c o n t i n u u m components o f S F i c n i c fragmentation 6  12.1 A n a l y s i s o f t h e v i b r a t i o n a l s t r u c t u r e K —*r-fr* t r a n s i t i o n s i n t h e N (N 1s) and CO energy l o s s s p e c t r a 2  in (C  ....  305  the 1s) 317  x i i  F I G U R E S  1.1 Binding energies versus inner-shells  natural  linewidths f o r 6  1.2 Comparison of constant-energy and constantwavelength resolution as a function of excitation energy  12  1.3 T i m e d i s t r i b u t i o n o f t h e g a s p h a s e e x c i t a t i o n s t u d i e s l i s t e d i n t a b l e 1.1  18  inner-shell  1.4 O r b i t a l d i a g r a m o f c o r e excitation, i o n i z a t i o n and c o r e - h o l e decay (Autoionizat ion, Auger, X-ray Emission)  20  2.1 A n g u l a r d e p e n d e n c e o f K f o r 2.5 k e V i n c i d e n t e l e c t r o n s a t e n e r g y l o s s e s o f 25 ( C u r v e A) a n d 250 eV ( C u r v e B)  46  2.2 A c o m p a r i s o n o f e l e c t r o n i m p a c t a n d p h o t o a b s o r p t i c n s p e c t r a c f argon i n t h e r e g i o n excitation  49  2  3.1 Schematic of t h e Inner-Shell Loss Spectrometer  Electron  Energy 53  3.2 O p t i m u m f o c u s s i n g v o l t a g e f o r m a x i m u m transmission through the analyser entrance 2.5 k e V i n c i d e n t e n e r g y a n d 2 5 eV a n a l y s e r energy 3.3 Schematic o f t h e ISEELS spectrometer t r o n i c s and data handling system  lens f o r pass 63  elec65  3.4 V a l e n c e - s h e l l e n e r g y l o s s s p e c t r u m (1.5 keV i m p a c t e n e r g y , A E = 0 . 0 3 eV)  o f CO  3.5 Valence-shell energy loss spectrum ( 2 . 5 k e V i m p a c t e n e r g y , A E = 0 . 08 e V )  of  3.6  Calibration  of C H 2  3.7 T h e e l e c t r o n - i o n (Amsterdam) 3.8  Configurations  4  (C 1s)  b y CO  73 CH I 3  74  (AB=0.5  eV)  ....  77  coincidence apparatus 81  f o r coincidence experiments  3.8. a E l e c t r o n - i o n o f - f l i g h t ' )  o f 2p  c o i n c i d e n c e TAC  mode  .....  85  ('time85  xiii  3.8.b E l e c t r o n - i c n coincidence 3.8.c  coincidence ('fast  mode')  85  Ion-ion coincidence ( i o n autocorrelation)  .  85  4.1 R a d i a l w a v e f u n c t i o n s f o r t h e K r 3d o r b i t a l a n d t h e e f c o n t i n u u m waves (€=0 a n d €=6 R y d b e r g s ) 5.1 The c a r b o n 1s e n e r g y l o s s s p e c t r u n o f e t h a n e (AE=0.5 eV FHHM) •  119  5.2 T h e c a r b o n 1s e n e r g y (AE=0. 5 eV FHHM)  120  l o s s spectrum  103  of e t h y l e n e  5.3 T h e c a r b o n 1s e n e r g y l o s s s p e c t r u m o f e t h y l e n e (AE=0.35 eV ( n a i n ) and 0.21 e ? ( i n s e r t ) FHHM) ...... 121 5.4 T h e c a r b o n 1s e n e r g y l o s s s p e c t r u a o f benzene (AE=0.6 eV ( a a i n ) and 0.36 eV ( i n s e r t ) FHHM) ....... 122 5.5 The c a r b o n 1s e n e r g y l o s s s p e c t r u a o f a c e t y l e n e (AE=0.6 eV ( a a i n ) a n d 0.4 eV ( i n s e r t ) FHHM)  123  5.6 The s y n c h r o t r o n e l e c t r o n and C H  yield  126  5.7 T h e s y n c h r o t r o n e l e c t r o n C H and C H  yield  2  6  6  spectra of CH  4  6  2  spectra of  C 2 H 4 ,  127  2  6.1 The c a r b o n 1s e n e r g y (AE=0.35 eV FHHM)  loss spectra  o f C H 4 and C D 4 145  7.1 L o n g r a n g e s c a n s o f CH3CI, C H B r and C H I between 50 and 35 0 EV  156  7.2 T h e e n e r g y l o s s s p e c t r u m excitation region  158  3  3  of C H I  7.3 S t r u c t u r e below t h e c a r b o n h a l i d e s (AE=0.25 eV FHHM)  3  i n t h e I 3d  1s IP i n t h e a e t h y l ,  161  7.4 C o r r e l a t i o n s between t h e c a r b o n 1s e x c i t a t i o n e n e r g i e s and i o n i z a t i o n p o t e n t i a l s i n t h e a e t h y l halides  165  7.5 T h e c a r b o n 1s e n e r g y C D B r (AE=0. 25 eV FHHM)  172  3  loss  spectra  o f CH3Br and  7.6 L e a s t s q u a r e s s i m u l a t i o n o f t h e C 1s e n e r g y l o s s s p e c t r a o f C H B r and C D B r i n the r e g i o n o f f e a t u r e s 2 to 6 173 3  3  xiv  7.7 T h e e n e r g y l o s s s p e c t r u m of C H 3 F o f F 1s e x c i t a t i o n (AE=1.0 eV FWHM) 7.8 T h e e n e r g y l o s s o f C I 2p e x c i t a t i o n  i n the  region 180  spectrum o f C H C l i n the (AE^0.35 eV FWHM)  region  7.9 T h e e n e r g y l o s s s p e c t r u m o f C H C l i n t h e o f c h l o r i n e 2s e x c i t a t i o n (Afi-1.0 eV FWHM)  region  3  182  3  187  7.10 T h e e n e r g y l o s s s p e c t r u m o f C H B r i n t h e o f b r o m i n e 3 d e x c i t a t i o n (AE=0.35 eV FWHM) 3  region 190  7.11 T h e e n e r g y l o s s s p e c t r u m of C H I i n t h e r e g i o n o f i o d i n e 4d e x c i t a t i o n (AE=0.35 eV FWHM)  194  8.1 E n e r g y l o s s s p e c t r a o f t h e m o n o h a l o b e n z e n e s and benz-ene i n t h e r e g i o n o f C 1 s e x c i t a t i o n (AE=0.35 eV FWHM)  201  8.2 T h e c o r r e l a t i o n between t h e K b i n d i n g e n e r g i e s and t h e e n e r g y l o s s o f peak 2 i n t h e c a r b o n 1s spectra o f t h e monohalobenzenes  204  3  2  8.3 The e n e r g y l o s s s p e c t r u m o f C H C l i n t h e r e g i o n o f C I 2p (AE = 0.35 eV FWHM) and C I 2 s (AE=0.6 eV FWHM) e x c i t a t i o n 213 6  5  8.4a T h e e n e r g y l o s s s p e c t r u m of CeHsBr i n t h e r e g i o n o f Br 3d e x c i t a t i o n (AE=0.35 eV FWHM)  216  8.4b T h e e n e r g y l o s s s p e c t r u m o f C H I i n t h e r e g i o n o f I 4d e x c i t a t i o n (AE=0.35 e V FWHM) 216 6  9.1 the  5  The e n e r g y l o s s s p e c t r a o f t h e c h l o r o m e t h a n e s i n r e g i o n o f C 1 s e x c i t a t i o n (AE=0.25 eV FWHM) ....  221  9.2 T h e e n e r g y l o s s s p e c t r a o f t h e c h l o r o m e t h a n e s and c h l o r o e t h a n e i n t h e r e g i o n o f C l 2p a n d C l 2 s e x c i t a t i o n (AE=0. 35 eV FWHM) .. 230 9.3  Long  range scan o f C C l  236  9.4 the  S t r u c t u r e i n t h e C l 2p i o n i z a t i o n c h l o r o m e t hanes  4  continua o f 237  9.5 EXRFS p l o t f o r t h e f e a t u r e s o b s e r v e d i n t h e C l 2p c o n t i n u a o f C H 2 C I 2 , C H C 1 and C C I 4 and the C 1s continuum of C C I 4 3  9.6  Structure  i n t h e C 1s c o n t i n u u m  o f CCI4  240  ........ 245  9.7 T h e e n e r g y l o s s s p e c t r u m o f C2H5CI i n t h e o f C 1s e x c i t a t i o n (AE=0. 5 eV FWHM)  region 250  XV  10. 1 The energy l o s s s p e c t r a o f S F i n t h e F 1 s , 6  S 2s and S 2p e x c i t a t i o n r e g i o n s  (AE=0.4 eV FHHM) .. 261  10.2 The m o l e c u l a r o r b i t a l scheme f o r S F  .......... 264  6  10.3 Extended energy range s p e c t r a o f S F i n t h e F 1s, S 2p and S 2s r e g i o n s 263 10.4a The p h o t o a b s o r p t i o n spectrum o f S F i n t h e S 2p r e g i o n showing t h e fiydberg s t r u c t u r e (NMH7 1) .. 273 6  6  10.4b The energy l o s s spectrum of S F i n t h e Rydberg r e g i o n o f t h e S 2p spectrum (AE=0.2 eV FWHM) 273 6  11.1 A b s o r p t i o n o s c i l l a t o r to 230 eV ..  s t r e n g t h f o r SF  e  from 5 285  11.2 A b s o r p t i o n o s c i l l a t o r s t r e n g t h f o r SF6 i n t h e S 2p r e g i o n (160 t o 230 eV) 286 11.3 I o n t i m e - o f - f l i g h t spectrum i n c o i n c i d e n c e 184 eV energy l o s s e l e c t r o n s  with  289  11.4 I o n a u t o c o r r e l a t i o n spectrum ( i n t e g r a t e d o v e r a l l energy l o s s e s o f 8 keV e l e c t r o n i m p a c t on S F 6 ) . 291 11.5a S F + i o n f r a c t i o n i n t h e S 2p r e g i o n by t i m e - o f - f l i g h t measurements 5  obtained  11.5b I o n o s c i l l a t o r s t r e n g t h f o r S F * i n the S 2p region 5  298 298  11.6a S 2p component of t h e a b s o r p t i o n o s c i l l a t o r s t r e n g t h compared t o the sum of t h e S 2p components o f the i o n o s c i l l a t o r s t r e n g t h s .................... 301 11.6b V a l e n c e - s h e l l component of t h e a b s o r p t i o n o s c i l l a t o r s t r e n g t h compared t o t h e sum o f t h e v a l e n c e - s h e l l components o f t h e i o n o s c i l l a t o r strengths  301  11.7 S 2p components o f t h e F + , S+, S F and SF + ion o s c i l l a t o r s t r e n g t h s compared t o the S 2p component o f t h e a b s o r p t i o n s c a l e d t o match t h e i o n o s c i l l a t o r s t r e n g t h s i n the S 2p continuum 30 3 2 +  2  12.1 V i b r a t i o n a l s t r u c t u r e i n t h e N 1 s — M r * t r a n s i t i o n o f N (AE=0.090 eV FWHM). The r e s u l t o f a l e a s t - s q u a r e s f i t o f s i x l o r e n t z i a n s i s shown 2  315  12.2 V i b r a t i o n a l s t r u c t u r e i n t h e C 1 s — • T r * t r a n s i t i o n o f CO (AE=0. 065 eV FHHM). The r e s u l t of a l e a s t - s q u a r e s f i t o f t h r e e l o r e n t z i a n s i s shown .... 319  xvi  PLATES  Plate  1:  Plate  2: C o m p l e t e I S E E L S  The  ISEELS  spectrometer experimental  52 arrangement  69  xvii  ACKNOWLEDGEMENTS I  would s i n c e r e l y l i k e  interest, of  my  e n c o u r a g e m e n t and  studies.  with  the  thanks are  I t has  other  members  due  Dr.  introducing  to  me  spectroscopy, interpret  the  der  Wiel,  electron-ion  and  both  would  also  many members o f elsewhere,  C.  This  J u n g e n , Dr.  W.H.E. Schwarz. providing  the  providing Wallbank  curve  This assistance electronic  very  helped  t h e s i s , and  to  on  of  electron  Dr.  and  M.J.  perform  van the  contributions  community,  both  stimulating others), M.B.  Dr.  Dr.  program  and  Drs.  a  number  of  D.C.  Merer,  Frost  M.S.  UBC  Professor  CD3Br,  spectra  Dr.  of  helpful  A.  R o b i n and  thank  at  and  of  XPS  in  t o J o h n Cook,  I  the  Special  helpful  addition,  fitting  and  6  (among  and  him  SF .  provided  CD4  his  course  record  to  helped  a c k n o w l e d g e the  Dehmer, Dr.  the  group.  intricacies  and  for  Banna Banna of  for for and the  studied. work of  could the  construction.  not  capable  workshops;  s p e c t r o m e t e r and the  was  who  scientific  J.L.  for recording  molecules  studies  includes  samples  the  this  have  In  research  Hood, who  suggested  the  who  his  halobenzene s p e c t r a , of  like  Brion  working with  of  and  C. E.  a pleasure  Pocock,  coincidence  discussions. Dr.  Mark  Dr.  throughout  experimental  portions  who  thank  assistance  Stephen  the  methane  proofread  the  to to  who  I  been  to  have b e e n staff  of  in particular,  provided  performed the Ed  mechanical  Gomm, who  much u s e f u l a d v i c e  without  the and  built  the  for details  of  x viii  Financial Canada  1967  exchange  support  from  T  wish  to  encouragement throughout this  thesis  Research C o u n c i l of  S c i e n c e s c h o l a r s h i p and from a  grant i s g r a t e f u l l y  Finally  a National  my  NATO  Scientific  acknowledged.  thank  Ilona  graduate  f o r h e r p a t i e n c e and  studies.  I  dedicate  t o her.  Whoever t h i n k s a f a u l t l e s s p i e c e t o see T h i n k s what n e ' e r was, n o r i s , n o r e ' e r s h a l l Alexander  be. Pope  1  CHAPTER  1  INTRODUCTION  "We s h a l l n o t c e a s e f r o m our exploration and the end of a l l our exploring w i l l be t o arrive where we started and know the place f o rthe f i r s t time" T.S. Eliot  In  recent  spectroscopic levels  of  subject  years  techniques  atoms i s  the  The  G.R.  (W74)  have  such  investigations. studies  impact  Electron to  ever  since  f i r s t  The  of  t h e early  vacuum  analysers of  inelastic  development  u n t i l  inner-shell  the  aspect  i n i t i a l  that  of  excitation  gas phase  thesis  this  studies  suitable  of  electron  technique  describes  inner-shell  spectroscopy states  Franck-Hertz  f o r  further  excitation  1960's  provided  of  (EELS) atoms  quantization  electron  scattering  technique  was  when  technical  and  e l e c t r o s t a t i c  the basis  spectroscopy.  and  by  summary  i n on  which  excitation  mercury  atoms.  relatively  slow  i n the  electron  growth  of early  usad  molecules  (FH14),  advances  f o r a rapid A  h a s been  experiment  energy  o f t h e EELS  production  electron  very  molecular  the excited  the classic  by  the  low-resolution  i s a  loss  demonstrated  processes  interest i n  techniques. energy  investigate  of  This  of  growing  fundamental  demonstrated  spectroscopy  a  involve A  pioneering,  loss  electron  which  investigation  energy  experimental  has been  and molecules.  process. Wight  there  energy  i n a l l EELS  areas  areas  studies  2  and is  a discussion given  which  i n W7U  provide  while  a  general  and  electron  M69,  TRK70,  BW77,  of applications number  loss  beam  electron  of  energy  electrons  Excitations electron  loss  i s  where  beam.  X  i s  c o l l i d i n g  available  spectroscopy  MS68,  WA74,  The p r o c e s s  electron  a n d X*  internal  energy  amounts  up  K68,  B69  r  B75, C75, KC76,  transitions  to  both  investigating There  absorption  i s  bound  the target  scattering) electron  o f  the  of  (171).  simulates  dipole  transitions  and/or  large  Under a  scattering  state,  incident  i st h e  produced electron  energy  energy,  e  into  losses,  occur  by  of  f o r every  and continuum  states.  Therefore  use  of  photoabsorption  o f atoms  and  loss  spectra  obtained  small  incident  electrons,  these  photon  dominant. angles  momentum  conditions, f i e l d  photounder  transfers  small  angle  the colliding and  A t low impact higher  (PA)  molecules.  r e l a t i o n s h i p between  involving  v i r t u a l are  as  including  energy  (i.e. fast  scattered  target,  quantitative  conditions  the  species.  the  the excitation  a  i n  target,  Kinetic  electron  t o the  and electron  experimental  molecular  process  i s an a l t e r n a t i v e  losses  be r e p r e s e n t e d  of the target.  excitation  'monoenergetic •  the target  i s the excited  energy  a  «»>X* «- e or  to the incident  accessible  may  • e  atomic  kinetic  t o excite  as energy  the  converting  to  (LSD68,  spectroscopy  used  are detected  X  for  are  t o electron  L74, LS74,  excitation  BH78). In  EELS  shell  reviews  studies  H73, BF74,  r  of  introductions  energy  B71  to valence  order  electric energies electric  3  multipole become  transitions  increasingly  energy  loss  important.  of atomic  phot oabsorpt ion.  and and  A  i s outlined  describe  some  present  also  spin In  spectroscopy  investigation  impact  and  i n chapter  photoabsorption  respect  electron  mors  complete  provides  quantitative 2  states  treatment  of  electron  the following  sections  of electron  as  than  of  inner-shell  comparison  technigues  a excited  while  features  a qualitative  processes  this  and m o l e c u l a r  essential  forbidden  applied  processes energy  to  loss  inner-shell  exci tation.  1.1  Characteristics  In  contrast  t o valence-shell  f o r  inner-shell  o r b i t a l  unambiguously excitation spectral  features  an  identified  energies  from  frequently  overlap  d i f f i c u l t .  The  somewhat  inner-shell atomic  lower  frequently atoms.  than  with  level, using  In this  are highly  molecular  either  types  of  50  eV,  o r b i t a l s  i d e n t i f i c a t i o n used  of  as  a  inner-shell  thesis.  Since  c h a r a c t e r i s t i c  inner-shell  nomenclature  thesis  of this  f o r  eV, t h e  Below  been  of the realm  f o r the purposes  50  different  has  be  since,  different  spectral  eV  i n i t i a l  usually  basis  of  c a n make  energies  can  separated.  promotions  of 50  the  approximately  are well  limit  excitation  labelled  energetic  d e f i n i t i o n  processes  core  transition  an  which  arbitrary  excitation  for  levels  Excitation  excitation,  associated  (core)  a r i s i n g  on  larger  structures  inner-shell  the  of Inner-Shell  s t r i c t l y  the X-ray  levels only (K, L  of are  correct 1 #  L  2 J  3  ,  4  M  1»  3d  M  2,3  i  M  ....)  except  4,5 >  •••)  notation i n  required  cases for  In  normally  a  an  processes  magnitude  characteristic  of  10  the  i n  different  a  principle  be  of  inner-shell  spectroscopy The shell  probe  (XPS  virtual  spectroscopic play  information value.  level,  Since  3p, levels i s  an  a  inner-shell  promoted  target, the  giving  to  giving should  Although  o r b i t a l  the  enviroments  rise  Why  same  the  i s  variations of  a  target,  continuum.  core  to  of  very up  atomic  (Sh73).  To  to level  a  good  chemical  s h i f t s  reflect  the  charge  on  (SNF67,  SNJ69,  Sh73) .  Such  shifts  can  from  the  see  section  structure  low i n  concerning inner-shell  also  of  the  onset  i n practice  X-ray  they  photoelec tron  i n  molecular  provide core  the  lying  electron target.  excitation  may  Aside orbitals  events  be are  of  excitations  reactions  orbitals  inner-  information  unoccupied  chemical  these  of  1.3.1).  these  levels  by  observed  can  since  roles  locations  continua, although  accurately  interest,  important  3s,  notation  interest?  atomic  spectra  interest  the  -  of  from  chemical  determined  discrete  chemical  removed  of  more  excitation  the  ionization  ionization  determined  of  binding energies  these  2p,  theory  i s either  energy  molecule  in  are  or  chemical  approximation, i n  the  group  electron  of  the  2s,  for inner-shall  picture  orbital  be  used  correct  inner-shell  of  occur  are  (1s,  discussion.  core  transitions,  such  atom  of  unoccupied  to  an  the  physics  one-electron  rise  in  schemes  purposes  event,  •discrete'  atomic  r  where  the  excitation  eV  o  from often  and of  thus  practical  localized  at  5  specific  atoms  of  an  the  spectral  be  electron  excitation  of  atoms  examined  techniques).  inner-shell  which  thesis,  There  studies.  resulting  has  a  are discussed of  very  excitation  of  a  short  l i f e t i m e . levels  formation  of neutral  than  the  ionization  in  an  given  uncertainty  uncertainty  states  energy  4. inner-shell  been  promoted, and  reason  According  of  such  from  energies  lifetime  thus  •discrete'  different  with  potential). this  reported  rapidly  fundamentally  core  i s  states  less  to  the  reflected which  i s  by:  r where  r  width) (-fi =  decays  excited  the  to  has  with  of  i n chapter  (For t h i s  principle,  i n  available  limitations  state  i s  highly-localized,  experiments  electron  can  ( e . g . by  aspects  detail  core  excited  the  Heisenberg  a  o r b i t a l s  photobsorption  only  the  in  highly  f i r s t  of  UV  examining  levels  excitation  are  t o  course, When  core  Unoccupied  extent  features  inner-shell  Additional  are relevant  are  excitation  orbital  by  spectral  of  the advantages  excitation.  excitation,  number  of  visible-UV-vacuum  i n i t i a l  s p a t i a l  investigated  energies a  and  valence-shell  or  However  be  molecule.  by  loss  energy-labelled  the  i n a  t h e energy  can  and  energy  this  o r b i t a l  intensities  from  different  also  in  molecule,  unoccupied  arising on  i n a  i s  and  t h e energy T  i s  6.582x10-1* Although  ~ 1 i / r  (1.1)  uncertainty  the  l i f e t i m e  of  (i.e. the the  natural  excited  linestate  eV»sec).  details  of  the decay  mechanisms  cause  large  l  variations  i n the  lifetimes  of different  core  hole  states.  6  the  decay w i d t h  energy  within  1.1  which  linewidth a  order  width of  carbon,  0.02  eV  nitrogen  J02 -\ O  Fig.  for  1.1  i  and  of  the  for  oxygen  1  • 500  i  of  2p  3/2  energies  i  1000  and  natural  energy  for  3d  The  5/2  ).  at  The  50  i s of  the  widths  for  Typical  i  1500  for  elements.  excitation  i  figure  is illustrated  states  K-shell  in  atom-identifying  second-row  L i 1s).  binding  in  binding  thus the  core-excited (e.g.  trend  l e v e l s (1s,  binding  increasing  is illustrated  general  number, and  energies  with  a function  inner-shell  inner-shell  K-shell  This  the  with atomic  of  minimum  subshell.  plots  of  variation  the  each  increases  (Hg69, KRK74) as  nuaber  nature  generally  Binding Energy-eV  eV  are  about  i  2000  Binding energies versus natural linewidth s f o r inner-shells. The w i d t h o f Ne was d e t e r m i n e d by monochromated XPS s t u d i e s w h i l e t h e level widths for the o t h e r s p e c i e s r e f e r t o t h e l i n e w i d t h s of d i s c r e t e c o r e - e x c i t a t i o n s as determined by highr e s o l u t i o n ISEELS.  7  0.1  eV.  0.3  ev  0.23  At  energies  [e.g.  eV  the  Me  features  lead of  to  requirement  natural  linewidth  considerably  less)  0.1  1  eV  considerations 50  and  1, 0 0 0  for  gross  of  the  is  becomes  =  870  eV)  0.3  eV  of  the  states.  cm-*)  of  .  above,  i d e n t i f i e d  will  Furthermore,  vibrational structure  order  0.3  Thus, the  as  eV  chemical  from  the  are  i s  a  at  most  linewidth  region most  effects  a  (preferably  the  spectral  being  i s  spectral  vibrational spacings  8,064  investigating  width  than  overlapping  observing  {BE  larger  electronic  since  minimum  linewidth  for  =  the  widths  outlined eV  keV  natural  different  (N.B.  1  Decay  minimum  eV  1s  (GSS74) ].  frequently  of  in  between rewarding  inner-  shell  excitation. In large  addition natural  inner-shell in  to  the  linewidths  excitation  nature.  For  decrease  i n  cross  (see  chapter  2  for  ISEELS  which  has  studies.  absorption  in  the  (the  extreme  very  d i f f i c u l t .  following  studies  are  impact  discouraged  These  the  regions and  are  problems  d i f f i c u l t i e s more  has  there  X-ray are  50  with  i s a  energy  very loss  been  the  development  of  techniques  between  by  experimental  probably  earlier  soft  imposed  increasing  This  experimental  spectral  other  studies,  with  details).  The  limitation  which  section  ultraviolet  section.  there  electron  rapid  factor  fundamental  for  and  regions)  discussed  photo-  1,000 are i n  eV also the  8  1.2  Electrons  In  versus  order  excitation  by  to  Only  sources  of  electron often due  i t s  gas  are  expensive  energy a  phase  solely  of  problem  with  soft  X-ray  diffraction because  of  incidence A  use  second  a  be  most  do  where  problem,  of  to  use  to  high  present  time  or  dedicated thus  even  other  the  with  a  d i f f i c u l t i e s  studies. of  and  soft  techniques  well  for  and  high  X-ray  g r a t i n g s and i s  X-ray  photons used  mechanically  successful soft  i s  f a c i l i t i e s  and  Hovever  r e f l e c t i v i t i e s  which  the  applications  work  r e f l e c t i v i t y  such  parasitic  At  diffraction  not  sources  increasingly  constructed  number  applied  diffraction  angles  being  alleviated.  crystal  surface The  are  inonochromation  gratings poor  often  photoabsorption  cannot  coefficients. presently  The  are  i s  studies  inconvenient  synchrotron.  source  efficient  X-rays  somewhat  radiation  i s being  d i f f i c u l t .  hard  the  rings  light  First, is  of  synchrotron  synchrotron occur  uses  used  However,  ( i i )  radiation  synchrotron  being  i s light  and  photoabsorption  are  studies.  usually  source  Bremstrahlung  phase  and  inner-shell  continuum  Bremstrahlung  applications  storage  to  latter  are  of  light  X-ray  Electron  continuum  radiation  soft  (i)  f o r gas  inner-shell  physics  number  use:  studies  continuum  of  intensity.  and  a  radiation.  use  useful  for  the  t c  low  a  detailed  types  synchrotron  produce  since  two  practical  d i f f i c u l t  to  perform  photoabsorption,  required. are  Photons  for ruled  soft  X-rays  absorption  monochromators  mirrors at  grazing  maximized.  particularly  severe  for  9  photoabsorption  studies  at  energies  of  i s contamination  of  ~300  eV  ( i . e . wave-  o lengths  of  optical of  A),  components  diffusion  Such in  ~U5  pump o i l s  deposits  the  with  can  carbon  or CO  s t r u c t u r e i n the  easily  mistaken f o r t r u e  problems  synchrotron et  thesis. are  This  seems t o  the  be  to the  and  largely  careful  the r a d i a t i o n  and  are  spectrum  studies  in  due  to  order  s e r i o u s i n the  maximum i n t e n s i t y  chapter  5  hard  X-ray  constructed  to  Achromatic  surface  g a s e s h a v e been  with  presence  light  - 9  torr)  K-shell  region.  molecules,  soft  work.  X-ray  photo-  higher  energy  p r o b l e m i s a l l the radiation since  higher  i n attempts  to cope  due  problem  is  order  selective with  being  radiation.  absorption this  the  usually  S p e c i a l monochromators are  or  be  This  continuum  reflectors  by  this  cannot  optical  of  This  source  discriminate against  used  deposits  in current  case of synchrotron  region.  of  (<10  carbon-containing  overlapping.  in this  the  clarified  (BBB78).  difficulty  the  in  Eberhardt  been  carbon  can  features.  of  such  t o the  limitation  is  which  encountered  has  required  in  experimental  temporally  corrections for structure  restricted  important  third  the  discussed  large interest  i s an  radiation  in  work  other  example).  spectral  were  monochromator,  avoided  absorption  more  of  studies  latter  g r a t i n g contamination  A  type  for  intense  absorption  yield  (HB77) as  in  completely  this  causing  and  decomposition  Even when u l t r a - h i g h vacuum c o n d i t i o n s  used  Due  X-rays  incident light  this  electron  ISEELS s t u d i e s  to  of  a l . (EH76) .  the  (frcm  absorb a l a r g e f r a c t i o n  variable  Severe  deposits  by  carbon K - s h e l l region  be  gratings  by  problem.  10  Thus,  for  studies  four-fold  in  larger  the  nitrogen  pressure  of  K-shell oxygen  region can  be  (~30  &),  added  to  a the  0  sample  to  absorb  r a d i a t i o n below  20  A  INSS69,  solutions  generate  their  own  the  photon  intensity  i n  spectral region  can  also  result  in  radiation  i f high  f i l t e r i n g  of  the  Finally, experiment becomes  higher  the  absorption  energy eV  at  400  The  problems  eV  cf  and  energy  technique  [although  cross The  section  basic  impact than  i s  -  a  the  and  kinetic  the  the  for  energy  transition by  i n  of  for  sufficient  photoabsorptio wavelength, to  high  resolution  intensity  i n  n i t  obtain  Since  A  eV  there  The  i s  a  highest  an  inner-shell  which  corresponds  180  (GKH77)  at  for  do  not  the  eV  energy  the  energy.  apply  the  inner-shell of  region,  X-ray to  the  does  but  Since  there  the  (see  chapter  are  by  impact  no  own  the  i n 2) ] .  electron  electron  between  i t s  decrease  excitation  incident  photoelectron  have  rapid  loss  potential difference  c o l l i s i o n  soft  method  particular  increasing  requirement  determined source  with  and  wavelength  of  0.03  limitations above,  limitations  interest  (NSS69).  discussed  inherent  i s  decrease  short  a  regions.  0.08  absorption loss  in  reported  spectrum  Such  CMT73).  d i f f i c u l t  yet  resolution  0.4  of  the  terms  expense  they  resolution obtainable.  resolution  synchrotron an  to  i n  wavelength the  since  required  resolution  more  at  of  (NSS69,  constant  shorter  limit  are  orders  the  gained  wavelength  only  pressures  usually  i n  always  practical  to  absorption  progressively  resolution is  total  since  i s  the  problems  HNI74).  larger  energy  i s  electron  problems  with  11  an  excitation  source  such  photoabsorption. technologies are  well  The  required  understood  Since process,  for examining  hard  X-rays.  electrons energy, loss  to  In  are the  the  carbon  in  specific  same  addition,  K-shell  caused  region, the  and  X-ray  experimental  electron  beams  non-resonant  regions  a  infrared  scattered  entire  energy  regions are  treated  suited  as  to  kinetic  i t i s free  such  be  constant  the  i s well  because  the  inelastically  spectral  impact  grating  i s a  from  analysed at  a l l  region  by  soft  experimental techniques can  i f  thus  energy  control  i s constant over  electron  in  and  scattering  spectral  resolution  Thus,  structure  any  optics  and  electron the  and  encountered  HR76).  retarded  spectrum  equally.  create  (S48,  essentially  are  electron  inelastic  used  as  to  studies  i n  from  problems  of  spurious  those  contamination i n photoabsorption  experiments. i.  The  most  absorption achieving With  seems  analysis, in  including The  nitrogen  K-shell  a  be  i t s  wavelength  several resolution  of  the  ISEELS  incident of  i n the  resolution  times i n the  better same  of of  than  (TKB76,  KTR77,  2  (at  0.006  U00 A  than  the  spectral  region  meV  have  nitrogen  eV)  75  A)  been  chapter K-shell  ineV i n  (KRT77)  (at ~31 best  constant  KRT77,  of  for  energies.  and  100  and  photo-  potential  electrons  resolution N  over  excitation  less  carbon  demonstrated  ISEELS  large  spectra  spectrum  of  demonstrated  at  resolutions  studies  regions.  to  to  selection  demonstrated 12)  advantage  higher resolution  energy  energy  important  i s  the  equal  which  i s  photoabsorption  (NSS69).  t-12.4  1000-q  or <  100-J  CD CD D CQ  D)  M240  CD C LU  i—i  0.001 F i g . 1.2  i i 1111|  0.01  1  i i i i 111|  Resolution  0.1  1—i  AA A  i i 1111|  1  1—i—i i 1111|  10  1—i  i i 1111  100  >o  12400  Wavelength resolution (AX) plotted against e x c i t a t i o n energy for fixed values of energy resolution (AE). The shaded area marks the excitation energies where the best electron impact resolution i s presently superior to the best photoabsorption resolution.  H to 1  13  A comparison resolution, and  which  electron  as  resolutions spectra  a  that  (i.e.  in  definite  resolutions  energy  shaded  resolution  the  above  and  ISEELS  region  of  natural  emphasized  this  the  figure),  list  is  field.  Bremstrahlung indicated. expected  from  field.  At  The  for  electron  expected  The l a r g e r  the  loss  only  number  of  the  photo-  i n table  region  have  to  reasonably  be  F i g . 1.3  recent  been  i s  a  excitation growth  in  of s y n c h r o t r o n ,  studies  number o f p h o t o a b s o r p t i o n  t h e much l a r g e r time,  inner-shell  i s given  contributions energy  is a  impact.  i m p a c t and  region.  I t c l e a r l y shows  and e l e c t r o n  this  there  o f gas p h a s e i n n e r - s h e l l  relative  lines  0.1 eV, t h e r e l a t i v e l y  i n t h e s o f t X-ray  o f t h e number  per year.  two  be a d e q u a t e t o o b t a i n  up t o 1977 f o r t h i s e n e r g y  histogram studies  o f gas phase  obtained  and  at energies  these  inner-shell excitation studies  Results  complete  of  the  are around  information.  1.1.  studies  linewidths  maximum  A bibliography  been  i n photoabsorption  o f 0.05 eV w i l l  absorption  have  highest  modest r e s o l u t i o n possible  (eV),  The  intersection  200 eV  In  corresponding to  a d v a n t a g e t o t h e use o f e l e c t r o n  smallest  excitation  1.2.  energy.  For excitation  g i v e n by t h e  in figure  AE  of e x c i t a t i o n  indicated.  photoabsorption  AA(&),  resolutions  function  the  comparing  i s presented  yet demonstrated  are  above  Since  of  in  loss  wavelength  values  plotted  i s helpful  energy  this figure, fixed  of c o n s t a n t - e n e r g y and c o n s t a nt-wa v e l e ngth  workers  two l a b o r a t o r i e s  are  also  studies i s in  this  are a c t i v e l y  TABLE  B I B L I O G R A P H Y OF GAS P H A S E  INN Eg-S HELL  STUDIES  ATOMS A.1.  Photoabsorption  A. 1. a R a r e Ne  1s  Ar  2p  Ar Kr  1s  3a  Kr Xe  1s 4d  Xe Xe Xe Xe  4p 3d 2s 2p  o f Atoms  Gases B18, Wu70 P34, WM69 P39, LBZ64 CM65, CM77a KE75 CM64, CM65, C76 D68 N6 8 N68  A. l . b  Ba54, L 6 5 , LZ63,  NSS68,  S63, Wu65, H77 , HKS69, CM64, CM75, GMK76,  E64, LBZ64, WM69, H K S 6 9 ,  i.  A.2  ISEELS  Ar  2p  Kr Xe  3d 4d  o f Atoms AG L 6 9 , W B 7 2 , W W T 7 6 , KTR77 A G L 6 9 , KTR77 A G L 6 9 , WW77, K T R 7 7  Metal  L i 1s Na 2 p , 2 s K 2p Ca 2 p Ca 3p Mn 3 p Fe 3p Zn 3s Ga 3d Ge 3 d Sb 3d , 3 p Sr Cd  3d,3p 3d  Sn Cs Ba  4d 4d 4d  Ba La Sm Eu Tl Hg Pb Pb  3d 4d 4d 4d 4f 4f ,5s 5d, 6s 4f  Atom V a p o u r s  SBE78 CGM7 1 M75 M76 CM77d CMM76 BSW77 CM74a CM77b CM77e MC75a, CM77a MC75b, CMT72, CM77a CM77e PRS75, CM74b, ELS75 CM 7 4 b R7 7 R77 MC76 CM 7 5 b CM73 CM77f CDM76  CM76b, CM77a CHT74,  CM76a RRW74,  15  Table  1.1  (continued)  MOLEC ULES M.1  Photoabsorption  Li  of  Molecules  1s (55 eV) O SBE78 RSC76 RS74,  L i LiF LiCl 2  B  0  1s  (535 eV) NMH71, B S B 7 4 , VZA74, L75b, V A Z 7 5 , B76 NMH71 L75b, VAZ75 SCC77 VAZ75  2  RSC76  1s (190 ev)  CO C0 N0 C H OH 2  BF  F68, ZV72 FB70 ZV72  3  BC1 B H 2  C  3  6  FB70,  HB71,  2  2  F  1s (290 eV)  5  1s  CH F CH F CHF CF NF SIF  4  C H C H C He C H CH (OCH ) CH F CH F CHF CF CO 2  6  2  4  6  2  2  2  3  3  2  2  3  4  2  LBZ64, BBB78 EH76 EH7 6 EH76 EH76 LBZ64 BBB78 BBB7 8 BBB78 BBB78 NMH71  C69,  EH76,  2  3  4  3  sr  4  6  EFo  1s ( 4 0 0 eV)  N  L75b L75b L75b L75b VZA74 V Z 7 1 a , ZV72 LBK67, VZF71, 1 7 2 b , ZV72 ZV72  3  2  CH  (690 eV)  Si  2p  SiH SiF  4  (110 eV)  4  SiCl SiCl(CH ) SiCl (CH ) SiCl (CH ) 4  3  N  2  NO N 0 NF N0 2  3  2  M38, N S S 6 9 , GSM73, CMT73, VSZ74, VZA74 GSM73, MNI74 GSM 7 3 , G M S 7 5 VZ72, VZA74 SCC 7 7  V  Si  3  3  3  1s  S i C l  3  2  4  2  HBK71, VZ71a, ZV72 GMK76, FZV70 FZV70 FZV70  ( 1 8 5 0 eV) M66  HB72 HB72, FZV7 0  16  Table  P  1.1  2p  (continued)  (150 eV)  PH P0C1  Ge  HB72 GMK76  3  3  2p, 2s  GeCl Ge  S  2p  1s  GeCl VZ71a, VZ71a, KGM77 VZ71a, KGM76, KGM77 BZF67, NMH71, BHK7 2 , GKM77  2  2  so  2  COS  S  1s  CF SF SF 0 S F 0 3  5  2  2  2p  C l HC1 BC1  (205  ZV72, MBS72  3  C C I 4  Se Se  eV)  Cl HC1 CH C1 CHC1 CC1 C H C1 C H C1 CF C1 3  3  4  3  2  5  2  2  (2830  eV) SKN51, SMB70 SBB68, HG76 SBB6 8 SBB68 HG76 HG76 HG76  SBB68, SMB70  keV) KE75  4d  (40  eV) HRS73  2  4d  Xe XEF XEF XEF  (55  eV) CNS73  I2  Cs  (13.5  2  Te  I  eV) CM77c  1s  Br  Te  (60  2  4d 2  4  6  4d  CsCl 1s  2  keV) KE75  4  3d  Br ZF67, ZV72, VZ72,  GKM77 HB72 FB7 0 P34, N71  2  Cl  (11.1  ZV72  LD66, M71, L75a BM62, LD66 , BK73 LD72 LD7 2 LD72  2  Cl  HB72, ZV72,  (2470 eV)  H S  2  M66  4  (180 eV)  H S  cs  (1250,  (65 eV) CHN73 CHN73 NHS 7 4 185 e V ) SS76  1410)  17  Table  M.2 C  1.1  ISEELS  (continued)  of  Molecules  1s ( 2 9 0 eV) 0  CH  4  CD C H 4  2  c a C H 2  6  2  2  4  C H (CH ) CF CO 6  6  3  CO  2  4  C0 COS CS CH OH 2  2  3  CH3OCH3  CH N H CH F 3  2  3  C H 3 C I  C H 3Br CH I C H F C H C1 C H Br C H I CH Cl2 3  6  5  6  5  6  5  6  5  2  C H C I 3  CC1  4  WB7 4 b , B WD 7 6 , TKB76, HPB77, TKR78 HPB77 HB77 HB77, TKR78 HB77, TKR78 HB77 WB74f W874d, TKR78 W S 8 7 0 , WBW73, TKB76, KLW77a, TKB78 WB74a, TKR78 W B 7 4 e , T KR 7 8 WB74e WB74b WB7 4 b WB74b HB78a HB7 8 a HB78a HB78a HPB78 HPB 7 8 HPB78 HPB 7 8 HB78b HB78b HB78b  0  1s  CO C0 NO COS CH 0H 2  3  C H 3 O C H 3  N 0 2  F  1s  6 4  S 2p  (180  CS COS SF 6  2p  (205  5  6  eV)  5  2  HB78c  eV) HB78a HPB78 HB78b HB78b HB7 8 b HB7 8 b  C H 3 C I  C H C1 C H C1 CH C1 2  eV)  WB74e WB74e HBW78,  2  Cl  WBW73  HB7 8 a HB78c WB74d  3  2  C H C I 3 4  1s (400 eV) Br  N  (690  CH F SF CF  eV) WB74c WB74b WSB70, WB74a WB74c WB74e WB74b WB74b WB74a  2  H 2 O  CC1 N  (535  2  NO N 2O NH 3 CH3N H 2  W S B 7 0 , WBW73, KLW77a , KRT77 WB74c, TKR78 WB74a, TKR78 WB7 4 b WB74t  3d  (90  CH Br C H Br 3  6  5  I 4 d ,3 d C H 3 I  C H I 6  5  eV) HB78a HPB78  ( 5 5 , 6 5 0 eV) HB7 8 a HPB7 8  18  engaged shell  i n I S E E L S studies. spectra  larger  than  reflecting studies  obtained the  the  i n this  that  provide  discussed  state  processes  i n sections  relationship  by  photoabsorption photoabsorption  region.  are often  However,  K-  i s considerably  i n performing  and almost  occur,  a comprehensive survey  spectra.  o f carbon  iapact  obtained  difficulties  spectra  similar  nuaber  solid  so t h e number  by e l e c t r o n  spectral  Although excitation  Even  soae  gas  phase  identical,  no a t t e m p t  of  solid  features  of  inner-shell indicating  h a s been  state such  made t o  inner-shell studies  are  1.4.1 and 1.4.2 w i t h e m p h a s i s on t h e i r  t o gas p h a s e  Electron  studies.  Impact  Synchrotron  20 J  Bremstrahlung  65  70  75  Y e a r of P u b l i c a t i o n s  Fig.  1.3  Tine d i s t r i b u t i o n o f t h e gas phase inner-shell e x c i t a t i o n s t u d i e s l i s t e d i n t a b l e 1.1.  19  1.3  Related  The  Gas  by  which  figure  loss  techniques  X-ray  energy  of  i n a  that  levels  obtained  techniques.  the  this  inner-shell chapter  one-electron  'monochromatic'  energy  of  binding  the  spectroscopy the  are  model)  i n  +  X  (XPS)  energy  i n  the  energy  measures  ejected  the  i n  the  1  • X i *  photon  (XPS)  electron  *  e  source  photoelectron  photoelectron  recoil  Spectroscopy  process: hv  i s used  i s  so  directly  o r b i t a l i s  (1.3.1)  from  which  ( n e g l e c t i n g the  that  the  kinetic  related  to  i t was very  i t s  removed.  small  ion  energy) : E  most  (1253. 6  p  =  E  f r e q u e n t l y used eV)  although  that  a l l of  (within  Photoelectrqn  photoionization  being  to  photoabsorption  discussed  photoelectron  kinetic  The  four  involve inner-shell  underlying  diagramatically  X-ray  The  describe  1. 4.  1.3.1  A  b r i e f l y  which  and/or  processes  spectroscopic  Studies  i n f o r m a t i o n complementary  energy  physical  presented  sections  techniques  provide  electron  The  Inner-shell  following  spectroscopic and  Phase  and  some  XPS  performed has  Excellent  been reviews  Al  K  a  studies (WAD77). applied are  hv  -  XPS  BE ( I ) light  (1486.6 using XPS to  (1. sources  eV)  well  solids, (SNF67,  the  Mg  characteristic  synchrotron i s a  available  are  liquids SNJ69,  Ka lines  radiation  developed  3.2)  are  technique  and Si74 ,  gases. Si76).  20  (a)CORE-EXCITATION E =E -E I #  hv=E  +  A  I x x  I#  e) -xx x  - X — X -  X  X  x  X  X  X  ion fragments  OR  1. -L  Autoionization  Excitation (PA or ISEELS)  (b)CORE-  E =E -E *  I  A  P  i  X  X  X  - X — X -  X  X  1+  hv=E *-E*  2  T  - X — X -  ion fragments  OR  Q  (e,e*ion)  IONIZATION E e=hv-E *  X  X-ray Emission  4 - X Ionization (XPS) (PA or ISEELS)  X -  Auger  -6—xX-ray E mission  (e.e.ion)  -time  g.  1.4  Orbital diagram of core e x c i t a t i o n , i o n i z a t i o n and core-hole decay ( a u t o i o n i z a t i o n , Auger, X-ray emission)  21  Orbital useful  for  spectra  the  very  (see  excited  between  derived  from  spectra,  the  sufficient widths  accuracy  s h e l l  and  only  a few  are  spectrum  (chapter  spectra  reported  10),  measurements.  halobenzene and  performed  by  UBC  gas  In  analysis observed based  M.S.  phase  on  XPS to  in  a  methyl  halide  B.  in  not  spectral identify line  usually  i n  inner-  from  XPS  derived  from  sulphur  6  2p  analysing from  gas  (chapter  the phase  7)  and  available i n  from  Wallbank  De  the  measurements  (HPB78,  BB76)  using  apparatus. providing the  series  excitation such  and  can  natural  SF  obtained  obtained  can  and  those  the  were  IP's,  excitation  derived  were  IP's  the  orbitals  resolved  used  were  Banna  spectra, of  core  therefore  addition  individual  8)  the  from  resolution  IP's than  EEL)  correct  IP's  thesis of  core  except  core  in  large  being  accurate  a l l  this  (chapter  l i t e r a t u r e  Thus,  the  Some  lines  or  limits  resolve  The  very  upper  on  spectral  Rydberg  more  o r b i t a l  series  to  are  derived  of  depends  series.  For  i n  Rydberg  limited  often  analyses.  the  a  with  Rydberg  XPS  of  and  types  ability  excitation spectra.  measurements  values,  XPS (PA  ionization  c r i t i c a l l y  the  members  certain  of  from  excitation  term  Although  analyses  combined in  state  of  4.1).  assignments  obtained  e x c i t a t i o n energies  characteristic  section  result  energies  i n t e r p r e t a t i o n of  since  difference be  binding  core  chemical of  IP's shifts  compounds  spectra.  comparisons  was  useful  can A  often  for  assigning  derived be  compared  correlation found  from  to  be  to  XPS those  technique helpful  i n  22  analysing 9).  the present  XPS  than  chemical  chemical  features. XPS  reflects  s h i f t s  shifts  This  ISEELS  spectra  (seechapters  are normally  i n the energies  i s because,  chemical  within  shifts  i n  Koopman's  t h e  whereas  excitation  energies  energies  of both  the i n i t i a l  and f i n a l  discrete Gas  spectra  excitation  a valence  events  XPS  are  energies  shell  observed  than  that  (SNJ69,BB75).  can  rise  s h e l l  t o weak  continuum  and  electron  spectrum give  can  at  as of  orbitals  only  one  by the  involved  i n  In  involve  inner-shell  These  typss  at higher  line  i n  spectra  of  binding  the such  XPS events  continuum  onsets  i n t h e direct  inner-  energies  above  the  to the  ISEELS  comparison  with  XPS s p e c t r a  WB7<4a) ,  N 0  (HB77,  main  which  of an  peaks  excitation  i n  2  a i di n identifying  ionization  the  continua  6  excitation  of  events  s a t e l l i t e  o f t h e XPS s a t e l l i t e  6  interpret  a r e determined  (shake-up) .  separation  C H  and  approximation,  energy  also  due t o m u l t i p l e e x c i t a t i o n  simultaneous plus  8  transition. phase  structure  to  o f discrete  o r b i t a l  a  simpler  7,  spectra  (0 1s-WB74a),  chapter 5 ) .  and  i n  main  have CO CS  IP  lines.  been  Shake-up  identified  (C 1 s - W W B 7 3 ) , 2  equal  by  C O 2 (0 1 s -  (C 1 s , S 2p-WB74e)  and  23  1.3.2  Auger  There decay  a r e two c o m p e t i n g  of  the  ionization  of  (X-ray  (Auger,  core  highly  interest  (SNF67,  of  a  • X*  Xi*  • X**  energy  (doubly) Auger  depend  )  E *  I  +  the  core-excited  involving  core  hole  and  of energy Auger  X*(x that  occupied  energy.  For  £  A  =  E * 1  =  2 +  )  mechanism  1.4)  figure  ejected.  E±* -  an The  and t h e Auger  symbolized  -  and  as:  E+ E  2  (1.3.3) (1.3.4)  +  (ionized)  represents  r e s u l t s from  the  ejection  state singly of  an  A  decay  rates the  which  the electron by  A  of  E .  between  electron  E  decay  Auger  states  c a n be  are  (i.e. those  i s  the core-excited  i o n state  dominated  those  energy  e  )  the overlap  containing i s  +  For the  both i n  either  non-radiative  non-radiative In  species  by  These  and  1 keV  (depicted  *• e  (E  1  general on  the  KRK74) .  represents  charged  containing  decay  I +  electron In  that  the  immediate  created  1.3.3)  than  c h a r a c t e r i s t i c of  1  of  S72,  X *  (X  less  study),  of the core-ionized  1  the  electron.  see  processes  autoionization  X *  core  -  energies  this"  autoionization  where  states  a  emission  with  t o  dominates  decay  excited  for  autoionization, Coster-Kronig).  holes  electron  mechanisms  or excitation of  radiative modes  Spectroscopy  which  the  some  core  hole,  'drops  into  i s  fastest  crbitals  and s i g n a l  the  orbital  the hole',  ejected. processes  closest core  intensities  The  and Auger  and thus  i n energy  excitations  to  by the  t h e non-  2a  radiative  decay  principle  process  shell  i n i t i a l l y  (e.g.  f i l l e d  by  called  Coster-Kronig  rapidly  and thus  give  competition  Auger  spectra  photons. arising  from  ionization  electron  c a n be e x c i t e d  hole  (when  integrated  much  larger  states,  Auger  processes  the  main  from  lines  to  be  great  relevance  decay  of the states  the  autoionization There  the  autoionization spectator).  details  Coster-Kronig  and  either  of  electrons show  both  or  structure  neutral  and  the p r o b a b i l i t y f o r core  f o re x c i t a t i o n t o d i s c r e t e  processes  whole  2  (1.3.4)  +  Auger  yielding  These work  continuum)  give  rise  spectra  while  (1.3.3)  X+  latter  since  they  which  reported  often  example  was p r e s e n t e d  lines  of  dominate these  a r eof the  i s  ejected)  rise ISEELS  types  of  i n SCH69.  of autoionization  the core-excited  notation  are  represent  s a t e l l i t e s ,  as Ie-V ( f o r a u t o i o n i z a t i o n  electron  i s  i n the t r a n s i t i o n s giving  structures  i n which [This  inner-shell  that  a r e two c a t e g o r i e s  core-excited  very  t h e  produced  c a n be d e n o t e d  occur  For futher  i n electron-excited  s a t e l l i t e s  are  over  s a t e l l i t e s .  The f i r s t  i n  spectra  Since  t o t h e present  discrete  spectra.  which  by  r e s u l t i n g i n X  autoionization  considered  to  than  are  KRK74.  decay  states.  same  processes  peaks  Auger,  s e e B 7 2 , S72 and  the  2s h o l e s  usually  spectra.  between  always  lines  broad  the non-radiative  core  Such They  .Electron-impact-excited  ionized  to  t o  i n  row elements,  electrons).  rise  of  decay  3rd  electrons  transitions.  and ejected  fluorescence  f o r  2p  excitation the  involves  and  i n  which  Ie-VVe  ( f o r  electron  i s a modification  remains  of that  a  used  25  by a  Moddeman vacancy  after at  state  higher  than  10  20  eV  to  to  of  shake-up  those  core-excited comparing discrete,  core-excited  (unless  resonant  Ie-VVe  lines  Moddeman  et  identify  discrete,  and  d i f f e r  and  usually  X * 2  cannot  by  from  less differ  always  considerations  arise  the  decay  be  distinguished  can  cannot  frcm  are  energy  used  used)  and  processes this  i n  a  of core  neutral-  spectra. by  thus  by The  X-rays Ie-V  and  photon-excited s t i l l  comparison  s a t e l l i t e s  states  of  produced  (non-resonant)  IVe-VV  have  be  similtaneous  Auger  be  because  decay  states  l i e lines  The  the  core-excited  Auger  excitation).  absent  high  +  ion  from  energies  a l . ( M C K 7 1) the  X  core-  the  usually  processes  which  states  whereas  T +  e and  typically  normal  electron-excited  photon  are  describe  the  resulting  shake-up  photon-  right  energetic  lines  valence  and  spectra  these  ( i . e .those  and  X  orbital  describe  lines  indicate  shell),  hyphen  the  and  1  from  IVe-VV  states  than  energies of  However  with  the  (V)  unoccupied  Autoionization  X *  letters  valence  the  energies  the  capital  usually  tc  energies of  eV.  ionization  to  l e f t  identified  overlap  Auger  the  whereas  30  or  a  kinetic  positively of  (I)  o c c u p a t i o n of  while  the  i n which  inner  core-hole decay].  because  by  the  symbols  excited  a l . (MCK71)  ( i n the  indicates a l l  et  technique  arising number  occur.  from of  the  simple  molecules. An  additional,  the  autoionization  to  use  Auger  resonant  spectrum  and of  discrete  photon  w i l l  highly  only  specific, inner-shell  excitation show  (WK72).  lines  way  of  excited In  arising  examining states  this from  case  i s the  Ie-VVe  26  processes. reported Ie-V  An  investigation  f o r K r (3d) a n d  processes  ejected the  (those i n which  arising  ionization detected  from  of the valence  by  measuring  the  as  a  function  of  required  t o  line  would  excite  then  photoline. excited  Experiments  Auger  measurements  electron  energy  required  No  such  Although complement much  and  possible  impact  gas  processes  lines  arising  more  complicated  discrete  from  states.  investigations Moddeman sensitive obtain Auger  et  that  t h e decay than Few  have  shown  i s  even  be  of  The  However, more  thus  to  they  are  the  many Auger  are  the  even  decay  resolution  Auger  and  used  states  have that  state.  normal  from  high  environments  information. shifts  because  molecules  to molecular  chemical  detailed,  of  can  the  reported.  investigations,  arising  lost  discrete  of core-ionized  those  (e,2e) ejected  have  y e t been  the  photon-  the  which  energy  of  between  contribute.  be  process  o u t by  have  interpret  can  Ie-V  resonant  spectra  excitation  a l . (MCK71)  chemical  Auger  the  carried  electrons  experiments  could  enhancement  be  f o r  photoelectron  The  to these  i s t o  process  through  the core-excited  to  contribute  the  state.  coincidences  phase  d i f f i c u l t  of  The  electron  processes  energy  could  recently  (EKK77).  only  .Such  resonant  incident  inner-shell  more  photon  to produce  electron  V.  analogous  involving  states  will  intensity  a  was  photoelectron  level,  experiments  Auger  event) the  as  type  the core-excited  the discrete  appear  this  Xe(4d)" e x c i t e d  i n the autoionization  l i n e  of  of  Auger  been  made.  spectra c a n be  are  used  to  the interpretation  of  complicated  than  the  27  interpretation to  the  fact  involved have  been  J  2  6  1.3.3  6  the  Auger  2  4  at  there  CH4  (K73, and  SiF ](K73)  and  4  soft  have  and  X  1  been  been  the  CO 2 J  N  [CF  4  ,  to has  studying  spectra to  of  gas  resolve  (WGN73,  2  (WNA73,  and  group  of  resolution  of  than  incentive  Siegbahn's  emission  high  resulting  interpret  capable  x-ray  because  WNA75),  WNA75),  [ NH 3 ,  C H ,  CHF ,  6  6  3  reported.  emission ionized  processes  involving  the  decay  i n  Fig.  species  are  depicted  hv  hv» =  E  of 1.4  as:  •X •X*  to  study  some  Recently  Studies  (NAN77)  2  easier  has  [CO,  to  However,  sufficiently  symbolized  Xi*  studies  2  and  4  (HNA75)  (WNA75) 0  X-ray  be  are  [0 ,N0,C0  d i f f i c u l t  considerably  thus  NO  core-excited can  levels  S A K 7 5) ,  (ST75),  yields.  structure.  (HNA73)  The  and  i s very  impact-excited)  species  C H 0]  SiH  apparatus  (NAW76),  2  (MCK71,  2  investigations.  (NWA75) ,  N 0]  H 0  (x=0-4),  emission  and  an  vibrational 2  due  ( X - 0 - 4 ) ] (SBM70) .  x  often  these  developed  phase  4  ( o r more)  spectra  Detailed molecular  HF  X  excitation  three  MCK71),  fluorescence  spectra  (electron  4  in  Emission  are  pursue  H 0  X  X-ray  lew  spectra  for  [CH F _ x  of  processes.  CH Br _  >  shifts  energies  (SCH69,  2  X-ray  Soft of  the  performed N  C H  6  chemical  Auger  (MCK71),  [C H , 2  that  i n  S B H 7 0) , C0  of  + +  hv  hv  =  ET+-E+  (1.3.5) (1.3.6)  28  where  the  symbols  section.  As  arising  in  decay  of  states. i n  of  to  energy  features  the  studies to  main  decay  identified  a  core-excited  such,  the  , CO  states are  essentially the  valence  ray  emission  The equal  orbital  to  of  of  thus  f i r s t ,  of  X-ray  the  can  emission  be  the  considered  i n  high  resonant (WGN73). sufficient emission  corresponding have  NH 3  [ NAW76 ] .  of  the  to  lines  i n  i s  most  levels.  As  photoelectron  the  a  been  relation  have  major  to  discrete,  emission  valence  as  i s  these  resonant  d i f f e r e n c e between Thus  so,  have  interest  supplementary  Auger  line  observe  X-ray  occupied  the  determined  states  decay  studies,  i n  efficient,  not  lines  lcwer  neutral  state  did  greatest  the  Even  an  the  core-excited of  as  spectrum.  the  the  energies.  spectrum  energy  and  the  emission  ( C i s ) [ W NA75 ] and  i s  main  X-ray  emission  excitation  technique  spectroscopy.  the  from  of  i s e a s i e r than  core-excited  investigations  the  decay  discrete-state,  X-ray  2  because  the  ME68, L72b)  neutral, i n N  arising  core-excited  observations  inner-shell for  (e.g.  of  Although  of  lines  core-excited  neutral,  required to  neutral  lines.  lines  preceding  emission  neutral,  excitation  weak  was  separate  only  of  the  X-ray  the  photoabsorption  apparatus  Previous  useful  i n i t i a l  extremely  resolution  forming  energy  are  i n  s p e c i e s {1. 3. 6)  spectrum  or  from  to  than  identification  the  emission  the  weaker  loss  resolution  the  of  emission  because  defined  decay  i n i t i a l l y  the  identical  from  much  However,  spectrum  an  the  are  been  spectroscopy,  core-ionized  probability  state  Auger  from  states(1.3.5)  have  energies  core  part  of  IP the  and X-  photoelectron  29  spectrum  displaced  by  Since the emission electric used  dipole  process  to  In  strictly  rules,  this  PES,  level ionization  i s fairly  the p a r t i c u l a r  transition.  complementary  core  selection  to identify  given  the  governed  peak i n t e n s i t i e s  valence regard,  which  energy.  does  by  c a n be  levels  involved  in a  X-ray  emission  is  n o t have a n y  selection  rules. In  addition  identification structure aid  of  of  energy  offers  curve  of the core  structure  in  X-rays  ray  spectroscopy  reviews  Ionic The  energetic - l s  in hole  ordering, the v i b r a t i o n a l  ionized  with  state.  reported  recent  X PS  (G74,  the  peaks GSS74).  are  given  for  N  attempts through  This  IWNA75),  2  to  resolve  the  use  Further details in  a  type  of  o f X-  number  of  Fragmentation  inner-shell n e u t r a l or  to 1 0  the  - 1 6  two  energy  photon,  the  (071 , WNA75)  1.3.4  (10  been to  monochromated emission  aiding  t o g i v e i n f o r m a t i o n on t h e geometry and  alternative  vibrational  in  l i n e s c a n be a n a l y s e d  which h a s o n l y  an  potential  orbital  emission  data,  analysis,  i t s  of v a l e n c e  i n X-ray PES  potential  to  excitation ionized  sections.  i s removed i>y  Mechanistically,  states  s e c ) by A u g e r o r X-ray  preceding  some  process  of this  i t  the  is  occurs  which  dissipated through  highly  decay  rapidly  emission  Although  Auger  creates  as d e s c r i b e d  most  electron in  o f the c o r e or  bond  dissociative  emitted breaking. excited  30  states  of  from  the  the  to  singly  of  time  order  singly  core or  doubly  a  neutral of  fluorescence  a l l possible factors,  excited  or  of  probe  single  The  the  a  very  the  ionized)  the  -  1  wide  range  being  *  to  the  10-  .  occur  to via  states.  Thus  core  hole  probability  states and  of  subsequent  minor  low  of  (relative  to  the  because  the  low  of  technique, has  performed electron  the an  To  characteristic  ionized  following by  using  knowledge  no  f i r s t  technique  have  developed  can  be  species.  excitation  photon-excited  my  of  inner-shall  pattern)  and  through  inner-shell  following  impact  example  distribution  the  the  excited  specific  depend,  of  fragmentation  fragmentation  been  curve  a the  both  fragmentation  be  and  Thus  inner-shell  with  state  potential  ionic  by  within  states  states.  techniques.  11,  be  population  ionic  or  studies  latter  chapter  on  energy.can  coincidence  (10  decay  possibly  ionization),  dissociative  the  of  spectrometry  shell  of  ionic  (i.e.  Studies a  time  result  states a  core-excited  core-excited  ionized  distribution  to  on  fragments  only  because  (valence  overlap  used  neutral  to  core  decay  periods  expected  vibrational  excitation  fragments  neutral  which  yields.  dissociative among  i s  species  dissociative  minimum  can  of  path  probability  The  the  solely  production  the  ionic  vibrational  decay  de-excitation  ionized  These  charged  excitation  fluorescence  producing  decay.  into  inner-shell  doubly  with  few  Dissociation  neutral  hole  scales  of  and  at mass  electron-ion  detailed been  innerreported.  which  i s  presented  i n  at  FOM  Institute  for  the  31  A t o m i c and  Molecular  co-workers. discussed  Physics  Experimental  details  in  section  3.5  fragmentation  expected  from  in  chapter  excitation by  this  11. of  3d  KLW77b) and  1  either  reflection sensitive it  is  excited  SF  species  and  loss  0(1s)  to  are  given  investigated Ar  2p  (WW71, ionic  (WSB70,  chapter  WS72,  11).  silicon  high  can  be  the  surface  this  regard  studies  of  have  of  absorbed  inner-shell  electron  on  oxides  using to  In  scattering  structure  silicon  related  studied  very  resolution  been p e r f o r m e d and  be In  electron  the  experiments  more c l o s e l y  s o l i d s can  used.  sensitive  l e v e l s of  in this thesis.  are  inelastic  have a l s o  are  reported  note that  studies  energies  by  studies  energies  Surface  Transmission  ionic  inner-shell  the  CO  are  Solids  investigate  CSS77).  the  r e f l e c t i o n techniques.  loss  e x c i t a t i o n by  (F77).  (HBW78, see  6  or  energy  been used  and  2  scattering  transmission  to  on  (WW75, WW77) l e v e l s and N  and  apparatus  been  of  Wiel  Loss  electron  interesting  recently  ad  Excitation in  impact  der  following  studies  S 2p  i f low  vibrational  energy  including  excited  mode  this  m o l e c u l e s has  K-shell  Inelastic with  atoms and  Energy  van  comments  production  of  Electron  by  inner-shell excitation  Xe  Inner-shell  of  while  (WS75) and  fragmentation  1.4.  both  technique  WWT76) , Kr  1.4  Ion  (Amsterdam)  the  the  (KL75, MR77,  high gas  S i (2p)  incident  phase  Such e x p e r i m e n t s must be  studies  performed  32  o on  thin  films  microscopy, the  to  energy  s h e l l was  2,000  ensure  loss  oxygen Recent  collodian  of  acid  carbon  (CJ72).  transfer  dependencies l e v e l s of  have  performed.  energies  dependence One  of of  s o l i d s  the the  by  quantitative present  ray  Severly  most  to  of  the  light  by  x-ray  L i  (RSG74b) , Be These  to  active  in  this  X-ray  1  keV  elements  analysis  because  of i s  a  of survey  solid the  and  very  the  light momentum of  Mg  the  (SGS76)  high  incident  the  angular  inner-shell excitation the  has  been  can  low  of  microscopy. by  w i l l  be  techniques  impact  examine  which  development  reviewed  analysis  electron  of  films  (SC68),  reported  examine  technique  (Z<20)  thin  Be  of  use  electron  microprobe  thus  and  electrons.  excitation  in  This  and  films  signal.  impact  since  of  (MSP78)  and  areas  field  incident  the  impact  keV)  loss  carbon  have  studies  300  the  studies  electron  inner-  allotropes  of  of  electron  fluorescence, up  losses  of thin  the  Jouffrey  dominate  through  (RSG74a) ,  and  and  energy  (JS76).  to  losses  Al(2p)  microanalysis  status  complement  (200  keV  electron  report  of  8  for  events  excitation  Sophisticated  inner-shell  electron  using  (172)  energy  elements  been  on  Colliex  inner-shell  (R48)  inner-shell  bases  (EW74) .  earliest  Butheman  investigations  used  transmission  K-edges studies  those  scattering  The  electron  of  as  single  by  nucleic  and  that  such  observation  include  of  A),  spectrum.  e x c i t a t i o n by  the  of  ( <  can  K-shell  cannot  be  fluorescence  The  Jouffrey a  useful  using  study  X-  energy  excitation  e a s i l y yields.  studied  33  1.4.2  Photoabsorption  Inner-shell been  an  Early  studies  and  of  active  used  Few  excitation field  studies  were  detectors  techniques rays  have  and  Since  region  of by  studies,  most  extended  X-ray  notably  a  see  section  and  chapter  of  synchrotron are  studies  discussed  fine  9).  The  hard  the  X-  the  i n the  t o hard  soft X-ray  development  techniques  of  (EXAFS)  (Sn74 , L S S 7 5 ,  reviews  more  performed.  impact  inner-shell of  many  structure  tool The  number  using  been  applied  enabling  on  i n a  have  been  structural  1.2.  radiation,  the largest  absorption  because  (P59) .  had  i n  keV)  monochromators  investigations  also  E>2  excitation.  i n section  synchrotron  i t has  A,  has  X-rays.  region  sources,  discussed  of  line  X-ray  solids  as  solids  with  (\<6  X-rays  of  investigations 4.6  hard  Parratt  of  has  although  photoabsorption  the discovery  i n the soft  early  studies  radiation  by  characteristic  been  advent  photoabsorption  X-ray  have  reviewed  the  Synchrotron  or  results  been  since  d i f f i c u l t i e s  which  solids  involved  performed  the technical  and  ever  typically  Bremstrahlung  of  and  BNS77  results  excitation  (G69,  -  Ha72,  of  C73,  B74) . One solids  aspect which  comparison their  of  of i s  gas  localized  very phase  and  nature, not  photcabsorption  studies  relevant to the present  atomic-like  and  s o l i d  environments.  state  do  inner-shell  solid  state  inner-shell  differ  much  Thus  any  work  spectra. orbitals  i n atomic,  of  i s the Due  are  molecular  d i f f e r e n c e s i n gas  to very or phase  34  and  solid  character  state  of  the  transition. in  or  these  more  to  diffuse  those  with  solid  to  orbitals  in  very  often  remain  state.  Thus,  upper  solid  the  molecular  most,  state  gas  rise  photoabsorption  gas  phase  features  the  smallest linewidth.  phase have  and  solid  Eu  of  (MC76) ] a n d  CsCl  state  c o n t r i b u t e d to  structure  the  atoms molecules SF  icularly  useful  in  potential  barrier  effects  10),  6  spectra  are  based  understanding [Kr,  and  and  (RS76)  transitions  [ I  2  Xe  This  identifying (see  to  broad  the  Mn  which and  gas ideas  (CMM76)  technique  4.4  of  electronic  x = 2,4  x  the  spectral  simple  the  XeF ,  species  section  structure  whereas  these of  the types  Comparisons on  as  i n  those  usually  (HKS69) ,  (CNS73),  (BHK72) ].  to  are  such  overlap  spectra  corresponding with  will  i n  Conversely,  orbitals,  Excitation give  result which  phase.'  character,  only  allowed  will  spectrum  virtual  structure.  at  dipole  orbitals  state  in  l a r g e Rydberg  w i l l ,  solid  will  or  band  specific  species  atomic  a  a  extent  cf  have  in  the  radial  observed  form  involved  in  small  types the  changes  a  those  a  reflect  which  solid  structures i n  similar  of  orbitals  the to  will  orbital  molecular  in  transitions sharp  upper  Upper  atomic  localized  spectra  and  (CH N 7 3 ) i s  ,  partexhibit  chapters  7,  9  35  CHAPTER  2  THEORY OF FAST ELECTRON  IMPACT  "Let us work without theorizing; i t i s the only way t o make l i f e e n d u r a b l e " Voltaire  2.1  Electron  In  Energy  electron  Loss  Spectroscopy  energy  loss  spectroscopy  * monoener get i c '  electrons  molecular  (fordetails of electron  on  target  solids  see  Electronic, detected in  vibrational  scattered  used  1. 4  section  as s t r u c t u r e  the  is  to excite  and  and  of  an atomic o r experiments  references  therein) .  rotational  beam.  beam  impact  excitations  i n the d i s t r i b u t i o n of electron  a  The  energy process  are  losses may  be  represented as: e(E )  +X  0  where  X  state,  E  beam,  X*  internal is  is  »-X*(E ) n  the  target  is energy  an  scattered  E  n  state  gas  phase  oriented electron  has  no  cf  angle  fl  i n space, energy  the  target  which  which  the  which  state  and  respect  target  i s usually  loss experiments,  azimuthal  electron has E^  i s i nelastically  (0,<£) ( w i t h If  electronic  incident  to t h e ground  beam) i n t h e c o l l i s i o n .  randomly  the  of t h e e l e c t r o n  the  (2.1.0)  i n i t s ground  of  with respect  through  are  intensity  species  excited  [ 0,0])  1  i s the k i n e t i c energy  Q  t h e k i n e t i c energy  incident  • e(E ;  (<f>) a n g u l a r  to the  molecules the case i n  the scattering dependence.  36  Application  of  the  E  where  E  i s the  t  law  =  Q  E  i s  transferred  during  the  c o l l i s i o n .  E  «  t  i t can  (2raE /K)[1  m  and  target  molecule  disparity near the  M  E ~10  -  angle  eV  3  t  (E ~400 study  (E =2.5  energy  loss,  of  loss  the.  scattering section:  Q  1  of  -  Q  n  i s very  angle,6  of  inside  i s being a  experimental - 2  rad).  be  energy  Experimentally,  the  current  at  bracket,  example,  K-shell  electron  used the  to the the  this  electron  energy  ( i . e .the  energy  f o r  energy,  E  n  loss  electron spectrum'  magnitude  to the  of  neglected  •absorption  an  mass  For  Therefore  gives  and  because  square  may  of  (2.1.2)  and  conditions  electrons  i s proportional  the  nitrogen  scattered  measured  momentum  large  examined.  A measurement  the  target  electron  the  and  i s e s s e n t i a l l y equal  the  of  the target  small  of  the  c o s 0]  1 / 2  0  Because  energy  promotion  of  of the incident  and  electron  that:  {1-(E /E ) (  the masses  spectrum)  electron  projected  consideration  the terms  E -E ,  target.  scattered  (K68)  to the target.  distribution energy  shown  keV, 0 = 2 x 1 O  0  transferred  a  n  the  the  From  scattering  with  (2.1.1)  t r a n s l a t i o n a l energy  of  f o r the  eV)  n  to  y i e l d s :  t  of  the electron  r e c o i l  small  conservation  + E  respectively.  cancellation  when  Ei  (E /2E )  are  between  target  +  n  be  -  0  where  energy  k i n e t i c energy  which  conservation,  of  of  loss,E  d i f f e r e n t i a l  the n  and cross  37 d o* / d f t ( E , 6) n  f o r excitation  0  d c r /dftdE(£ ,0) o  for  impact  small  visualized  impact the  electron  sharply the  Fourier be  range  w i l l  the  an  transform  extend  The  over  a  this  f o r  spectrum  properties electron target  the  i s  of  the  scattering with  emphasized  a  that  of  other  'white  c a n be  virtual  photon  to  large  passage  f i e l d by f i e l d  of  collisions The  quantum  from  photoabsorption angle  inelastic  as the interaction field  This  target.  'light'  small  of  obtained  glancing  the  absorption  energy.  with  the v e l o c i t y  f o r the  of a  Thus  viewed  no r e s o n a n c e  from  electric  when  be  results  of frequencies.  words,  l i g h t '  proportional  the e l e c t r o n impact  range  absorption  target.  can  field  the  spectrum  frequencies  In  and  photon  ( i . e . those  uniform  and  n  scattering  S-function-like pulsed  large  t o larger  continuum  probability  a  to E  quantitative  scattering  experiences  a  states  relationship  frequency  of such  electron i s higher.  generate  angle  target  a  the v i r t u a l  essentially  i n time.  constant  This  collisions  The  as  pulsed  w i l l  to  glancing)  i s  electron  through  Small  parameters).  there  sections.  W74).  (or  are large compared  i n e l a s t i c  semiclassically  (C71,  distant  cross  which  angles,  between  photoabsorption  model  energies  scattering  relationship  states.  f o r excitation of continuum i n t h e e n e r g y r a n g e dE.  z  For  of discrete  although occurs  of  i t must  with  the be  regard  38  2.2  Bethe-Bcrn  For  a  Theory  quantitative  scattering  of  fast  scattering-theory derived  by  reviewed theory  underlying  standard  been  general  The the  detail  principles  and  the  Bethe  theory  Born  therefore  wave)  i s  this  for  the  the  assumption,  the  exciting  a  atom  /dS2  hydrogen atomic  (6)  theory  and  (W74)  the  number  of for  atom,  atoms  =  units  electron  with  molecules,  .  Only  the  Bethe  theory  will  by  an  the  to  the  {1i=m=e=1)  t  0  0  n  n  t n  based  assumes  target  (approximated  the  electron  i s  which  and  wave  ( »7r)-2{k /k ) | / U 1  A71)  an  weak  a  plane  by  angle  discrete  by  that  Within  cross-section  into  (W74)  state  on  i s  interaction.  differential  of  n  a  Bethe  scattering  (M58,  incident  scattering  dcr  electron  negligibly distorted  Hartree  of  been  scattering  i n  hydrogen  results  has  The  found  Wight  i n i t i a l l y  and  178).  complex  approximation  i n e l a s t i c  in  mechanical  was  (F54)  The  by  inelastic  here.  i n t e r a c t i o n between  and  of  in  f i r s t  the  cases  This  be  the  discussed  discussed  (171, can  angle  quantum  Fano  A71). by  the  a  by  derivation M58,  small  required.  Inokuti  scattering to  i s  extended  by  (e.g.  generalizations  be  ,  the  texts  electron  has  (B30)  detail  of  electrons  treatment  Bethe in  description  for  6  while  i s  given  :  ( r ) e x p [ i ( k - k ) . r , l  0  1  ]dr,|2 ( 2 . 2. 1)  w here U  and  ^  0  ( r  2  )  o n  (£i)  i s  the  =  2 < * ( r ) | 1/r n  ground  2  state  ] 2  -1/r,  l *  0  ( r  wavefunction,  2  (2.  ) >  ^  n  ( r  2  )  i s  2.2)  the  39  excited the  state  wavefunction,  incident  transfer  K  in  =  2  where  | K|  and  the  =  2  k n ^ )  target  c o l l i s i o n  I  K -lt, ! the  _r  k  and  the -&K  coordinates i s  2  the  of  momentum  by:  -  2 0  are  2  electrons given  =  2  0  i s  .r., a n d  k,z  wavenumber  2k k  -  of  0  c o s 6»  ]  the  ( 2 . 2. 3)  incident  (scattered)  electron. This  i s  interaction  generalized with  a l l of  to  complex  the  target  atoms  by  including  electrons  so  the  that:  N  D  =  o n  2<*  |Z /r  n  -  m  E(r-r )-»|* 5  >  0  (2.2.4)  5=1  where  r  i s  the  position vector  respect  to  the  nucleus  carried  out  (whose  coordinates  expression showing  the  positions  are  resulting  r ) .  incident electron  Z^)  and  of  a l l  Bethe  s  from  exp ( i K . r ) / | r - r | s  the  differential  inelastic  scattering  combining term  charge  the  the  substituting  integration i s  atomic  (B30)  with  has  electrons  simplified  2.2.4  into  2.2.1  the by  that:  J[  Thus  over  (of  of  2.2.1,  which  2.2.4  i s  ]dr  =  exp (iK»r )  from  complex  2.2.5  i f  for  small  atoms  i s  (neglecting  the  (2.2.5)  s  cross-section  and  zero  (HT/K?)  atomic  the  angle  given  by  nuclear  wa v e f u n c t i o n s  are  o r t h o g o n a 1) : N  dc /dft(0)  =  n  (Jfk^kolK-^K^I  Eexp(iK.r ) s  | t  Q  > | 2  (2.2.6)  S=1  or dcr /df2(0) n  =  4 ( k , / k ) • K-». 0  ie  o n  (K) I  2  (2.2.7)  no  where €  0 n  (K)  This  this  <^ |ex n  i s  scattering In  =  P  ( i K . r ) W>  further  (2.2.8)  Q  s  generalized  by u s e o f t h e a p p r o p r i a t e  case  one n o r m a l l y  assumes  Oppenheimer  approximation  wavefunctions  as  the  electron-molecule  molecular  wavefunction.  the validity  and  product  to  of the  expresses  of  the  electronic  Born-  molecular  and  nuclear  term s: *  e v r  (£/0J  where ^ e v r designates electronic r is  the  average  accompanying  Franck-Condon  involving  i n  factors) Born  (2.2.9)  )  describing  (v) a n d r o t a t i o n a l  (r)  the  (nucleii)  intensities  an e l e c t r o n i c (overlaps  of  n  n  n  I^  exp(iK«r ) |*e >-<* s  i t  has  i n valence  agreement even  when  by 2.2.7  been  shell  with  found  electron  optical  the scattering  approximation  0  V h  that  the  scattering  (e v r ) 0  0  rJ*v r 0  0  >  that  t o the  0  (2.2.10)  vibrational loss  spectra  ( i . e . Franck-Condon  conditions are  no l o n g e r  f i n a l  with:  energy  values  0  state.  and  so  state  J2  are given  i n i t i a l  (171)  the ground  i s given  h  and  vibrational  transition  of  the  motions,  c o n f i g u r a t i o n of t h e ground  from  (e v r )  <*e  Experimentally intensities  l  wavefunction  wavefunctions)  excitation  =  f  r  c r o s s - s e c t i o n f c relectron-molecule  state  Gondi)  the  factors  vibrational  d i f f e r e n t i a l  are  nuclear  ( v  o f the electrons  approximation  excitation  excited  e  (e) , v i b r a t i o n a l  this  state  * (i;0,o)**  the total  (OJ a r e t h e c o o r d i n a t e s  Within  by  =  applies.  This  such  that  situation  41  has  been  rationalized  From i t  the  can  be  i n e l a s t i c  while  involves the  of  Bethe also  be  of  a  within  case  f i r s t  of  Born  transitions the  K  =  2.2.1  the  of  the  matrix  s  expression  and  solely  solely the  f o r  target  exp(iK«r )  i . e . factors loss  2.2.6)  expression  a l l the  and  dependent  experimental  Strengths  that the  (K-2)  (E /2) n  generalized  of  entirely the  e l e c t r o n impact f i r s t  be  by  energy  loss  approximation (SL7C,  are  n( )  l  K  0  the  SL71) at  most  df^/dE  from  commonly  given  and  Born  Q  n  incident  approximation:  (2.3.2)  by  d o2  /dfidE  for  of  the  Breakdowns found of  for  specific  variations  energies,  observed  can  parameters  /dfi  n  do" /dn  been  by:  fp(K,E )  experimental f i r s t  i n  (2.3.1)  observations  different  (GOS),  z  continuum). have  excitation  approximation  strength,  n  replaced  an  strength  o s c i l l a t o r  of  Born  (E /2) (ko/k! ) (K2)dcr  =  Q  | G  from  validity  (K,E )  dependence  deviations  -  generalized o s c i l l a t o r  calculated  the  i n  of  energy  described  be  n  factors  shown  effective  (f ' should  included  remainder  (LSD68).  Bethe-Born  cross-sections,  has  An  n  (equations  the  Oscillator  (B30)  n  f '  a l .  conditions.  f (K)  regardless  i n  the  Generalized  terms  summary  are  the  value  Lassettre et  that  kinematic  scattering  can  seen  factors  element  2.3  preceding  d i f f e r e n t i a l  dependent  on  by  when  E. 0  there  i n  These are  42  identical  term  symbols  f o rt h ei n i t i a l  and f i n a l  states  of a  transition. The  GOS  strength,  f  i sa g e n e r a l i z a t i o n o f t h eo p t i c a l which  n  i sd e f i n e d a s :  f  Gi  where  I  transition  from  (En/2)G  =  n  i s the  on  oscillator  matrix  l o ( )  2  ( 2 . 3.3)  element  t h eg r o u n d  (o)  f o rthe electric-dipole u  t o  t h e excited  state  (n) ,  i.e. :  6  = K*  2 l o n  f  i s proportional  n  for  of  [ t f , p t («b) = 1 . 0 9 7 5 f 0  The  in in  3  4  n"*  n  optical  becomes apparent  element  cross  section  discrete  state  (2.2.6)  and when  i sexpanded  generalized  t h e exponential  i n a power  series  (iK»r) / l  (2.3.5)  K:  exp(iK»r)  so  2  ].  between  strengths  t h ematrix  the  (eV-i)  n  relationship  oscillator  < - ' >  2  s  t o the photoabsorption  excitation n  £ l*o>l  s=l  u  and  t  I  n  that  1 + i(K«r)  =  (assuming  £on  ( K )  =  € i t  ^  i  )  K  (iK*r)2/2  *  and  n  e  +  2  l  t i  K  . . .  n  n  are orthogonal):  Q  )  +  2  €  +  3  (  i  K  )  3  +  • • •  (2.3.6)  and f (K)  =  n  (E /2)[£ n  2 1  •  ( £ 2 - e e ) Kz* . . . 2  2  i  3  0(K«)3  (2.3.7)  where  G = A  d/JUXM'nl E  Is *o ,  (2.3.8)  >  s and  £  A  i sthus  the  order  multipole  matrix  element  (A=1  43  is  electric  electric  dipole,  equation  lim f K-»0 thus  momentum  and  ( K )  n  =  the  dipole  and  decrease  loss  electron  impact  energy  section energy  i s loss  =  factors.  by  cE E -3f n  n  (171)  impact  Lassettre  ~  3  At  The  strength  properties  be  observed, should  photoabsorption  a r i s i n g  3  0=0 i s  and  the  f o r E >>E , Q  to  o p t i c a l  t o t h e OOS,  spectra  are  causes  a large  energy shown  n  the  of  the  behaviour  of  the  impact  been  cross  electron related  decrease i n  losses.  validity  frequently  the  simply  the  electron  the  (2.3.10)  Since  which  limiting  from  related  have  has  transfer,  spectra  (LSD69)  of  from  small  :  i n t e n s i t i e s at large  regardless  approximation.  factor  et a l .  (00S) a t  (optical)  and photoabsorption n  -  section  proportional  E  (GOS)  momentum  to the  l o s s )  directly  electron  optical  (energy  cross  0  strength  transitions w i l l  constant.  the  o s c i l l a t o r  (2.3.9)  strength  of zero  numerical  through  applies  (optical)  (relative  strength  n  i s a  t o  loss  o s c i l l a t o r  c  i s  i n r e l a t i v e i n t e n s i t i e s throughout  kinematic  dcr /dfi  where  n  photoabsorption  spectrum  proportional  electron  f  o s c i l l a t o r  induced  loss  by a  energy  optical  jl= 3  that:  oscillator  In the limit  spectrum)  the  =  2  n  optical  energy  only  (E /2)€,  generalized  transfer.  the  the  guadrupole,  o n  electric  differ  electric  2.3.6 i t c a n be s e e n  the  approaches  only  i s  octupole etc.)  From  and  X-2  that  used  (2.3.9)  f i r s t  Eorn  generalized t o  experiments  derive either  44  by  extrapolating  momentum HR69)  by  using  scattering  GS68,  GS69,  electron  can  impact  absolute  values  strengths  such  data.  This  f o r the S F  reported  Thomas-Reiche-Kuhn  K->-0  t o  6  GS65,  conditions,  approach  11.  GT66, optical  experimental  was used and  HE68,  energies and  (GW65,  absorption  series of  HSL71,  normalize  i n chapter sum r u l e  a  impact  the latter  used  a t  LS71,  high  that  Under be  made  ( e . g . SL71 ,  sufficiently  angles  W70) .  cross-sections  measurements  t o K= 0  transfers  o r  small  GOS  t o obtain  i o n  o s c i l l a t o r  Alternatively, the  (FC68):  (2.3.11)  (where  Z  normalize  i s t h e number  N  small  corrections and  momentum  transfer  for the experimental  electron  impact  (WWB77).  A  o s c i l l a t o r  strengths,  (and  o f target  kinemtic  s i m i l a r  constant)  sum  electrons) energy range  also  i . e .f o r electron  momentum  transfers  of  these  under  (WB72, Bo73, sum r u l e s  conditions  momentum  scattering  angles  spectra  t o obtain  of constant  constant  shell  Bo75)  and f i n i t e  are discussed  after  o f scattering  angles  have holds  been f o r  applied  generalized  scattering  a t f i n i t e  (2.  N  has d i s c u s s e d absolute  scattering  transfer.  spectra  (B30) :  Z  Bonham  loss  factors  rule  c a n b e used t o  The  momentum  the application  oscillator angle effects transfers  i n the following  3.12)  strengths  rather cf  than  non-zero  on  section.  inner-  45  2.4  Applications  2.4.1  Energy  to Inner-shell  Loss  and  Excitation  Angular  Dependence  o f t h e Momentum  Transfer  The  difference  scattering be  very  2.1  large  shows  eV  The  than  i s  n  by  percent  electron.  energy  losses  2  energy  2  (9/2)  n  +  momentum A)  at  zero  0  i s i n contrast a t 2.5  f o r  a r e marked  by  For  Q  transfers  kinetic  energy  (2.4.1)  degree  (energy  has  i n  i s  0.7  S i sthe energy  used  at t y p i c a l  scattering 2  loss),  been  large  the  (L74) :  i s the incident  transfer  (i.e. K  c o l l i s i o n  2  and E  A) a n d  the hatched  energy  accurate  the  inner-shell  n  i s f a i r l y  much.  (curve  (E /4E) ]  relationship  (curve  very  losses  angles  t o  Figure of  (K) i n a n i n e l a s t i c  a u a t 0 = 0° f o r 2 5 0 e V e n e r g y This  o f 250 eV  i s sufficiently  0  The  the  of the incident  E=E -E /2  This  operating K  square  (2.2.3).  degree  i s not expected  of  the t r a n s i t i o n energy  constant,  decrease  transfer  zero  energy.  losses  thesis  and  electron  scattering  this  as ( 4 E / R ) [ s i n  2  2.1.  0.5  i n  i s given  ten  figure  but  dependence  approximation  K  E  keV i n c i d e n t  f o renergy  momentum  an e l e c t r o n  following  the  2.5  Typical  region.  Rydberg  losses  B) .  reported  where  i n n e r - s h e l l energy  transfer  (curve  less  angle  angular  spectra  of  small  with  the  momentum 25  at  between  angle a t  plot  inner-shell  o u c  au  to  of  experiment would 6 = 1°  not and  loss).  to the s i t u a t i o n f o r valence-shell  keV i n c i d e n t  energy  where  small  changes  46  0 (rod)  0  00 8  004  O  1  2  3  4  5  0(de F i g . 2.1  Angular dependence of the square of the momentum transfer for 2.5 keV incident electrons at energy losses of 250 eV (curve A) and 25 eV (curve B). The range of scattering angles used in the ISEELS studies is shown by the hatched area. Note the logarithmic scale for K . 2  47  in  scattering angle  changes values  in of  K  the 2  processes incident  dominate energies  of  energy  losses.  to  thus  present  identified  i n the  inner-shell optically shell  only  Kr  very  3d,  Xe  are 3d  i n  (KTR77)  are  transfer  much  at  identified observed  (KTR77) ] and  obtained  Higher  spectra.  10 at  electron  studying  of  i s one  larger the  inner-shell would  the  advantage incident  required  be  a  spectra of  the  energies for  i s appreciable  non-dipole  spectra  chapter  Much  scattering angle  of 2. 5  the  smaller  impact  are  similar  i t seems  that  contributions found  i n  the  momentum  in  gas  S  rare  2p-^4p thesis. (present  are  spectra  transition Argon  i n  2p  apparatus)  compared  to  been the from  transfers.  transitions  the  the  valence-  non-dipole  this keV  i n  t r a n s i t i o n s have  Indeed,  t r a n s i t i o n s than  those  dipole  Transitions  have  loss  with  photoabsorption.  few  ISEELS  the  c l o s e l y approach  when  transfers  with  that  NSS69).  more  chosen.  of  Even  large  comparisons  insensitivity  momentum  positively  spectra keV  the  forbidden  spectra  discussed  1.5  momentum  spectra  energy  ISEEL  loss  the  The  energy  experiment  tc  cause  indicate  (W74,  scattering angle  simulation  though  spectra  case  B) .  experiment,  transfer  O p t i c a l l y Forbidden  Even  2p,  in  (curve  spectra  parameter.  stnaller  2.4.2  our  required  that  electron  quantitative  The  In  changes  incident and  in  our  are  direction  transfer  zero-momenturn  c r i t i c a l  small  occur  forward  photoabscrpticn  limit  more  the  momentum  which  corresponding  from  the  i n [Ar SF  6  energy and photo-  48  absorption  spectrum  transition impact  at  246  spectra  and  absorption  guadrupole the  in  eV  observed  i s  i s  for  figure  completely  spectrum.  rationalization  of  (NSS60)  King  the  et  and  guadrupole  K  the  momentum  The  to  in  matrix  photo-  presented  this  a  electric  authors  elements  »-4p  electron  the  have of  these  2p  i n both  absent  intensity  According  dipole  weakly  a l . (KTR77)  relative  transition.  2.2.  the  i s given  ratio by:  6  where average mean  is radius  radius  units) This  and  for the of  that  crude  expected  However of  the  gas  of to  electric  inner-shell  Rydberg  initial  and of  roughly  agree  with  orbitals  of  spectra.  i n  be  appropriate between  (~E  (a f e w  atomic  details  final  states  smaller  radial  apparently lower inner-shell  the  i s  at  thus best.  intensities  in  i t  atomic  of  result  transitions  the  units) .  and  observed  Also  in  _ l n  a l l  the  (KTR 77) . the  will  magnitude  ( AJI = 0)  f o r the  forbidden transitions  valence-shell  orbital  order  i n terms  i s an  Q  orbital  an  spectra  r  which  neglects  quadrupole  inner-shell  and  inner-shell  the give  i t does  rationalization  dipole  of t h e  transition  estimate  w a v e f u net i o n s only  the  transfer  the  rare  presents extent intensity  spectra  than  a of of in  49  •a  E =1500eV K =1.5au o  2  IK**' '  l\  f w h m =0.07eV  o 252  248  244  9=0°  E =2500eV 9=2 K =10au f w h m = 0-20eV  a it  o  2  © 2^4  T  248 E N E R G Y L O S S (eV)  252  O  Ar  2p-**4p  quadrupole transition  PHOTOABSORPTION K*-0 f w h m =0.15eV « J  —t— Ml  Fig.  2.2  -t 2i0  1  (il  1  212 loVI  A comparison of electron impact (King et. al.(KTR77), present work) and photoabsorption (Nakamura et. al.(NSS68) spectra of Argon in the region of 2p e x c i t a t i o n .  50  3  CHAPTER  EXPERIMENTAL  "He had been e i g h t y e a r s upon a project for extracting sunbeams out of cucumbers, which were to be put i n phials hermetically sealed, and l e t out t o warm t h e a i r i n raw, inclement summers" Jonathan Swift  3.1  The  The energy an  Spectrometer  apparatus loss  spectra  improved  pioneering feature  of  version  this  of  second  of  the  work,  instrument  was  and  number  of  modifications  include  the  use  electron  double  deflection  improvements were  directly  source,  to  installed  a  The  been  In  was  result  heated  the  the  a  this  optics  and  before  the  and  the  made.  a  These  filament input  c o l l i s i o n  had  stages  evaluation,  were  lens.  was  second  i n i t i a l  analyser  spectrometer  i t  completed of  new  monochromate  tungsten  mor.cchromator e x i t  after  the  the  major  of  to  as  in  as  constructed  improvements  before  developed  The  electron  studies.  a  .  used  electron  used  presence  three-element  system  the  (W74)  the  beam.  As  was  instrument,  construction  a  thesis  analyser  had  inner-shell  spectrometer  was  evaluated.  of  this  Right  present  the  the  generation  analysers  commencement  the  the G.R.  electron  hemispherical  obtain i n  electrostatic  incident  this  of  constructed,  hemispherical  of  to  reported  studies  i n i t i a l l y  the  used  lens,  chamber These  been  as a and  features  operated  for  51  some  time  and thus  identical are a  at  apparatus  presented  noticeable  thesis  both  1  plate  -  schematic  this  method  for  and  less i s  energy  the  the  accuracy  analyser  control  described  of the study.  discuss  of the  briefly  and  weeks  Molecular  i n chapter  11.  located  1977  The  aspects a t  of  these  sections made  sections of  details,  the  loss  s c a l e s and  last  section i n  of the  electron-  FOM  Institute  the  (Amsterdam) to  and t h e  apparatus  energy  The  interaction  Subsequent  purity.  Physics  i n September,  the  i n  components  Each  operational  d i s c u s s e s some  spectrometer  3.1.  (and d e t e c t o r )  to  the course  handling  shown  i n the following  improvements  seme  the  circuitry.  i n turn  i s  of f i v e  monochromator,  loss  on the  coincidence  reported  throughout  i n figure  t o consist  and  three  results  there i s  s t a t i s t i c a l  given  of sample  Atomic  the  therefore  spectrometer  the inner-shell  chapter  and  spectra  of calibrating  details this  source,  i s  chapter  the  considered  electronic  throughout  for  a  c a n be  emphasis  order  under  resolution.  while  the  recorded  In general,  of resolution  energy  components with  i n  electron  associated  ion  improvement  the electron  region,  not a l l  configurations.  i n terms  spectrometer  were  i n chronological  equivalent The  the spectra  obtain  which the  was  used  results  P l a t e 1:  The ISEELS Spectrometer.  Fig. 3.1  Schematic of the Inner-Shell Electron Energy Loss  Spectrometer.  54  3.1.1  The  A beam  Electron  thermionic  forming  electron  used  alkaline  f o relectron  energy  loss  metallic  t h e spectra  tungsten being  cathode.  The o x i d e  P h i l l i p s  6AW59  heating  cathodes  element  designed  to provide  current  at  found  20  keV  t o provide  below  2  extended  gases.  Even  simple  found  r e l a t i v e l y In directly  to  short  order  television  energy  gun  cathode,  i n a beams the  attack time  the  LaB , 6  e t c . ) and present  cathodes used,  and  with  robust  most  tungsten a  which  consists  of  a  a grid,  an anode  and  a  beam vacuum  even  a t  oxide  these of  clean  they  cathodes will  guns a r e  several have  kinetic  juA been  energies are  only  quite operate  (>24 h r s ) i n u n r e a c t i v e  at pressures  oxide  The  o f  Although  periods  the  part  and thus  hydrocarbons  harm  been  of  include  the  integral  (G)  electron  emitting  of  10~  surface  5  torr i n  a  time.  t o overcome  heated  gun  In  oxide  an  a narrow  t o chemical  f o r  are  as  heated I r  t h e more  lens).  However,  stably  with  (einzel  suitable  keV.  susceptible  were  obtained  filament, the oxide  focussing  heated  f i l a m e n t s have  television  (W,  filaments.  indirectly  used  systems  directly  filaments  type  spectroscopy.  cathode  (BaSrO),  metallic  both  heated  emitting  oxides  heated  directly  b y some  i s usually  electron  spectrometer  followed  system  heated  directly  emitter  optical  earth  indirectly  of  electron  electron  source  commonly  Source  tungsten as  a  the problems f i l a m e n t was  replacement  of chemical mounted  f o r  i n  attack, a the  the oxide  6AW59  cathode.  55  I n i t i a l l y  the filament  hairpin.  However,  electron  gun  (.0005"  .03")  filaments  were  presence  pressures  of  arrangement than  those  these  was  found  of  _  by  factors  One  minor  filament stable  was  of  changed  the  resistance  filament  when  the  constant  voltage  mode.  filament  heating  could  emission  against  such  directly  heated  t o  Lambda  LH118  voltage  stabilized  across  oxide  with  and  thus  used  new  the  heating  operable  necessarily (typically  2-3  This  deposits  was  current the be  was  which of  operated  potential.  the I R  the filament  of  achieve  the i n a  mode f o r electron  done  with  e l e c t r o n energy  However  modes)  of  tungsten  to  sample.  not  of  supply  this  electron  temperature  potential 2  by  heated  surface  could  since  the cathode  a  the  power  the  stabilize  this  operating  neither  hours  constant  to  i n  region.  c i r c u i t  a  even  the characteristics  the  heating  effects,  to  of  ribbon  monochromatic  but  because  the  tungsten  f o r m e d  less  several  Although be  beams  cathode  introducing  of  typical  and  sharp  with  emitters  the directly  took  filament  keep^  constant.  drop  broader  determined  filament  surface  electron  a  tungsten  types  (at the  the formation  i s referenced  creased  interaction  after  because  essential  The  i t often  probably  scale  stable  species  problem  operation  a  c r i t i c a l  i n the  that  thus  into  to align  electron  essentially beam  d i f f i c u l t  be  the  was  formed  Both  somewhat  produced  electron  to  wire  instead.  torr).  s  0.003"  and  oxidizing  5x10  a  proved  used  were  monochromator the  this  apertures  x  the  was  Thus  the a c t i v e  a  loss  i t  i s  emitting  (supplied  by  a  i n either current  or  involves volts)  a and  voltage thus  any  56  changes  in  scale  this  and  can  resolution. filament passed  voltage  through  (An  to  The  A  this  electron  the 2.5  decelerated  to  (M)  Fig.  .  the  used The  diameter  a  high  voltage  voltage  desired  to  voltage the  gas  mode  for  sample  was  emission  tungsten  had  filament  would  i s  i n i t i a l l y  those  used  the  are  each  identical, of  2.5  electrostatic  be  or  a  possible  energy.  hemispherical  The  (P38,  der  mean  The  Wiel  and  S64,  been  gap  lens  energy  radius  of  KS67,  (see  consists lens  (0.16d)  of with  and  parameters  used loss  10  of  investigated  SK66,  the  a are  .  analysers  properties  have  (L1)  (W70)  at  beam  c y l i n d r i c a l  1.21d) , a  then  electrostatic  electron  tube  to  i s  focussed  two  beam a  beam  lens  electrostatic  having  analysers  the  0.64d).  van  and  by  source  entrance  (length  by  The  the  cm)  formed  electron  energy  electron  cm.  authors  the  pass  (length  hemispherical  of  instrumental  source  monochromate  element  monochromating  number  of  (d=4.75  element  essentially  of  monochromator  equal  gap  heated  kinetic  s l i t  an  The  the  electron  beam  output keV  entrance  analyser  low  and  the  electron  to  energy  Monochrcinator  (typically)  3.1)  u n t i l  spectral  problem).  narrow  mm  the  constant  used  indirectly  pumped  accelerating  1  the  always  system  s h i f t  contribute  reason,  was  the  d i f f e r e n t i a l l y  3. 1. 2  this  heating  solutions  w i l l  significantly  For  stabilized.  drop  S70,  cm  for  both  analysis and  a  pole  hemispherical by  a  large  RCI74 ,  IAK76,  57  P76).  Their  anaysers St73,  relative  have  been  WGS74) . t o  fields  more  electric  fringe  f i e l d s  analysers.  have  hemispherical  i s  f i e l d  produced  hemispherical the  velocity  velocities aperture between mean is  given  V  where  the  1  energy, by  2  exit  V  0  by  plane  easily  a  2  range s l i t  deflect  the entrance  and  thus  dispersing electrostatic the  two  depends  on  of e l e c t r o n cr  of the analyser. to  coupled  spectroscopy.  of deflection a  magnetic  (HSK68) , t h e  energy  thus  of  electrostatic  i n an r ~  placing  required  from  of  d i f f e r e n c e between  amount  be  circular  The  voltage  electrons  to the exit  of the  aperture  (W74) :  =  r , , r  respect  selected  the hemispheres  pass  The  magnetic  problems  symmetry  loss  as  electrons  t h e e l e c t r o n and  c a n be i n  a c t  by t h e p o t e n t i a l  of  of axial  are  more  thus  i s more  f  can  fields  properties  energy  S70  than  mirror  analyser  of  control  i n t h e case  analysers  surfaces.  and  severe  systems  deflecting  uniform  and  superior  lens  ( e . g . S67,  fields  f o r electron  Hemispherical by  produce  c y l i n d r i c a l  electrostatic  preferred  elements  more  somewhat  electron optical t o be  magnetic  Although  analysers  t o  types  analysers  because  electrostatic  a r e much  to other  extensively  analysers  Also  than  respect  electrostatic  d i f f i c u l t  fields.  shielded  to  general  magnetic  easily  with  discussed  In  preferable are  merits  V(r,)-V(r ) 2  2  to  respectively.  [V(r ), 1  V ) 0  =  V [ (r /r, ) - i r , / r ) ] 0  2  V ( r )] a r e 2  of  the  (3.1.1)  2  the  inner  For t h e hemispherical  radii and  (voltages  outer  electrostatic  with  hemispheres analyser  58  used  in  voltage  the  present  between  the  a  energy  incident by  of  )  /  2  transmitted  is  the  pencil The  =  i s  the  taking  beam,  R  diameter  angle)  absence  at  of  a  of  resolution  of the  to  detailed  been  given used  Those through  linear  by  the  electrons  as  the  distribution,  can  be  =  of  in the  to  the  of  approximated  i n  a  the  for a  of  exit  the  (3.  1.3)  of  the  hemisphere,  apertures  and  ( i . e . the  hemispherical  analyser.  the  f i r s t  hemispherical terra,  mm,  the  R =5.0 o  order  analysers. theoretical  cm)  i s :  (3.  0  theory  and  (as an  a  beam  indicates  of  0.010Y  maximum  electron  the  (S=1.0  a  comparison  energy  hemispherical  loss  1. 4)  with  the  analyser)  analyser  identical  present spectrometer. which  monochromator  acceleration  diameter  of  performance (W74)  half  divergence  analyser  electrons  the  of  properties  treatment  at  e n t r a n c e and  angular  operating  those  of  )V2  (a  mean  entrance  A E  has  angle)  width  angle  focussing  +  0  the  term  the  actual  transmission  and  (S/2R )  i s the  0  the  Neglecting  A  cm)  2  ( 3.1.2)  i n t o account  space  f u l l  divergence  angular  r =6.35  St73) :  A E  i s the  cm,  0  ( i . e .the  over  A E ^ / V Q  S  1 . 0 7 V  =  2  energy  electrons  (KS67,  where  L  resolution  function  (r,=3.81  hemispheres i s :  V  The  apparatus  have  the  exit  (typically)  correct  s l i t  2.5  keV  are  energy  formed  kinetic  to  into  energy  pass a  beam using  59  a  second  two element  i n i t i a l l y  constructed  entrance an  lens  the acceleration electron  divergent.  This  voltage  section  4 . 0 5 cm  interaction allowing  the (AE  spectra made  12  stages  following  this  has greatly arrangement  resolution  observations spectrum  2  moderate  the  c o l l i s i o n  pass  between  energy  i s  was  very  the  low  this  length i n  the  alteration  resolution inner-shell modification  work.  Only  structure  only  i n chapters  one  1s  9 and  Although  acceptable  produced  was  the carbon  the apparatus,  the  the original results  of  the  i n the carbon  a t  f i r s t  K-shell  5) . conditions  i n n e r - s h e l l  monochromated  chamber  by  d i d produce  operating  resolution  increased  This  even  the  t o t h e present  modification.  (see chapter  typical  inonochrpmator energy)  4  lens  available  improved  that,  (100:1),  the  and t h e spectra  of vibrational  of C H  Dnder  and  used  showed  currents  o f this  run  cm  was  However  lengthening  high  meV) .  7  experimental  spread  o f  i n chapter  alteration  modest  greatly  shown  were  1.1  beam  achievement  (Fig. 3.1).  by by  lens  monochromator  properties  formed  by  This  the  typically  corrected  The were  i n the latter  spectra  beam  (FWHM) < 1 0 0  1 / 2  to  optical  ratios  of the lens  region  (L2).  i n the schematic  was  (0.85d).  lens  identical  of i t s electron  high-energy  of  t o be  a s shown  analysis  with  c y l i n d r i c a l  of  2 5 eV  beam  between  0.2 a n d 0.3 e v .  used  t o  obtain  spectra a n d 2.5 k e V  current  1 and 5x10  (i.e. a incident  entering - 7  A  with  an  the energy  60  3.1.3  The  The 1.5  mm  interaction  x  energy  Interaction  1.0  loss  introduced is  cm  through  a variable leak  experimental  i n  base  when  the  i n  chamber  target  c o l l i s i o n  electron gas  Although  10 a n d  times  R G - 7 5K)  of  i s  the  i s allowed  4x10  of  the  on  torr  - 7  gas i s present.  chamber  not  c o l l i s i o n  100  pressure  i s  - 5 100) a n d  the  (Veeco  pressure  the  951  with  to to  Thus t h e  the  order  of  before  the  torr. A  double  c o l l i s i o n on  to  small  as  With  sets  this  the f i r s t  polarity  beam  intercepted  generate passes by  plate  This  plates  opposing  the second  by a  single  set  from  the centre  the angular  selection  twice  both  magnitude  so  but  source.  that  of the gas c e l l plate  the  chamber.  voltage  deflections  through  examine  consists  of the c o l l i s i o n of equal  beam  system,  (BWT75),  equidistant  fields  applied  t o  deflection  et a l .  with  and placed  the electron  (P3) i n o r d e r  double  by B a c k x  e l e c t r i c  c a n be  (DD) , l o c a t e d  to deflect  and the centre  arrangement  fields  incident  selection  of deflecting  as  system used  described  set of plates  opposite These  c a n be  scattering.  t o that  long  f i r s t  chamber,  angle  two  deflection  the angular  similar  is  The  an  sample  system.  between  c e l l  When  the  pressure  t o be  gas  (Varian  the  t h e i o n gauge  a  torr  - 5  pressure  of  the  by  recorded  through  chamber.  from  4x10  10-3  flowed  long  s l i t s .  i s being  recorded  increase  1 cm  and e x i t  (CC) i s e s t i m a t e d  pressure  i s a  spectrum  measured,  chamber  ca.  region  entrance  continuously  directly  Region  (P3).  the but This  61  permits  examination  of  small-angle  scattering  without  r allowing  t h e main  The  incident  the  energy  analyser.  beam  beam  to enter  i s deflected  dispersing Small  angle  f o r the reasons  this  purpose  the double  e a r l i e r  plates  the  cone  viewing  incident rather  than  leading  t o loss  3.1.4  The  i n  target  into  aperture and  entrance analyser.  the The  deflected  by  geometry  analyser  i n section i s an a  analyser the the  and  inner-  3.2.  For  improvement  s i n g l e  set  of  arrangement,  intersected the  deflecting  maximum  gas  the analyser  plates density,  which  t o the pass the exit  electron  cm  x  tube  lens  have  kinetic  energy  about  the  aperture  and (CEfl  (L3) on  identical slot  was  to  mm  t o the  energies  detected  Mullard  loss  after will by  B419AL) .  hemispherical  that  milled  1  electrostatic  be -  gas  decelerated  of the analyser  of the energy  1 cm  the  hemispherical  multiplier  essentially  by  and a r e then  three-element  electrons  A 4  scattered  (1Q-* s r . ) c e n t e r e d  and operation  monochromator.  o f  o f t h e second  through  are  f o r  to  Analyser  ccne  a  equal  channeltron  required  are i n e l a s t i c a l l y  i n P3, enter  Those  perpendicular  In the e a r l i e r  between  analyser.  monochromator  only  loss  region  Loss  which  aperture  loss  signal.  a small  deceleration be  of  focussed  used.  i n  the  Energy  Electrons  i n which  were  beam  i s  discussed  of t h e energy  electron  the  d e f l e c t i o n scheme  arrangements  deflecting  of  scattering  studies  energy  i n the plane  planes  s h e l l  over  the  i n  used  f o rthe  the  outer  62  hemisphere reduce of  and  electrons  The  identical exit.  one  a  studied  conditions energy,  70:1.  to  enable  ( 2 5 eV  Thus  by  voltage  versus and  potentials voltage that  analyser  the element  .the  plus  voltage  which  t o the closest  on  analyser  i s scanned  the  pass  was  range on  25  focussing  eV  (these  I t  The  ( 2 . 5 keV)  closest to  of  chamber i s  energy  i s set  of the  potential).  element  energy.  100:1  energy  to t h e c o l l i s i o n electron  energy  installed  voltage  of  only  incident  f o r a  incident  cathode  obtain  of  t h e optimum  energy  at  between  lens  the  an  entrance  keV  varies  element  analyser  to  two-tube  resolution  a n d 2.5  ratio  f o r  pass  electrostatic  the  moderate  plots  incident  voltage  hemispherical loss  loss  not  properties  of the transmission  t h e energy  establishing the  while  three  3.2  was  a  f o r the range  energy)  deceleration  are referenced  on  optimum  eV) ,  pass  Figure  the  dump.  i n i t i a l l y  empirically adjusting  an  beam  loss  into  analyser  of this  to  scattering  a t t h e monochromator  1,000  analyser  to  analyser  the  However,  t o  due  i n order  valence energy  the  was  have  the present  element.  keV  w i l l  and  of  lens  was a d d e d  spectra  of  used  optimization  losses  (BD)  the presence  ratio. (0  centre  2.5  lens  the required  and  energy  by  entrance  deceleration  losses  surface  t o those  Such  cage.  performance  impaired  analyser  long  elastic-scattered  o f f t h e back  noticeably The  cm  i n inner-shell  beam,  channeltron.  and  5  backgrounds  t h e main  lens  a  to  the  the  energy  i s the  l a t t e r  energy  loss  electron  spectra. The  3-element  lens  was  found  to  be  a  significant  63  improvement count a  over the  rates  f a c t o r of  shell  to  the  analyser.  increase  resolution quite  Fig.  the  3.2  Hhen  the  to  the  three-eleaent  to optimize by  i n the  however, i t was  sensitive  different  3 i n the  the  lens  in  The  increased  effective  solid  found  that  focussing  lens  elastic  the  entrance  voltage  focussing  operated  peak  voltage  spectral function scattered  peak) .  i s  by  innerprobably angle at  shapes  of t h i s  the  larger  signal is  s p e c t r o m e t e r was  instrumental  shape of the  that  most commonly i n v e s t i g a t e d  l o s s regions.  due  2-element  m o d e r a t e r e s o l u t i o n were t y p i c a l l y  2 or  energy an  at  original  of  high were  lens.  &  required  (as i n d i c a t e d The  probable  Optimum f o c u s s i n g v o l t a g e f o r maximum t r a n s m i s s i o n through the analyser entrance lens for 2.5 keV i n c i d e n t e n e r g y and 25 eV a n a l y s e r p a s s e n e r g y .  64  reason  for  this  transmission scattered  has  that  These  the  analyser At  largely  observed  energy  symmetric A  the  position range  of  3.1.5  shown  schematic figure  supplies.  The  constructed  at  Two used, volts)  types  both of  of the  be the  and  to the  the This  (IAK76) high  energy  when  found  voltage t a i l  such  as  to  the  a  be  high four-  able  to  the  beam  of  transmission  be  the  be  divergence  to  and  on  control  the  transmission.  were  to  who  divergences.  shapes  lens,  angular  of  focussing  throughout  a  ratios.  Ccntrol  of  The low  and  Circuitry  the  spectrometer  required  DC  impedance,  electron  which  small  required  optimize  3.3.  of  shapes  complicated  a  maximum  a  diagram  UBC  for  only  to  commercial,  peak  with  deceleration  in  peak  entrance  order  the  tuned  a l .  angular  focussing  optimize  Spectro iieter  A  by  i n  large  i n  et  and  the  would  analyser  are  analyser  analyser.  Imhof  of  more  system,  simultaneously at  i s  r e s o l u t i o n the  side.  element  there  lens  the  by  the  divergence  occurs  changes  independent  reasonably  entering  discussed  when  of  angular  broadening  entrance  moderate  dependence  the  beam  peak  appears  the  on  been  shoulder are  i s  function  electron  dependence showed  effect  a  schematic  energy were  gun  voltages  were  control for  scanning  analyser  this  (ramp) by  the (MCA).  power  c i r c u i t r y i s shown  i s  supplied  voltage-regulated  controlled  multichannel  e l e c t r o n i c s  was  in  W74.  arrangements  were  ramp For  output energy  (0-4 loss  ELECTRON  ENERGY  GAS  GUN  SELECTOR  CELL Dellection  Plate  Controls  ANALYSER  Current  C hanneltron  M onitor  H.V. Supply  GUN  MONOCHROMATOR  I M P A C T ENERGY  ANALYSER  CONTROLS  CONTROLS  H.V. SUPPLY  CONTROLS  — c z =  ENERGY  LOSS  POWER SUPPLY  PROGRAM CONTROL  Count  A mph fier/  Input  Discriminator  Channel Advance Reset  MULTICHANNEL  ANALYSER / R A T E METER  SIGNAL  OSCILLOSCOPE  AVERAGER  X-Y RECORDER  F i g . 3.3  TELETYPE  Schematic of the ISEELS spectrometer electronics and data handling system.  66  scans to  of  less  voltage  series  of  a  voltage  was  readout  of  (energy  than  a  voltage  divider  required  beginning  of  Pulses amplification  by  and  also  device  for  c i r c u i t  f o r the  spectra Nicolet operated address  the  were 1070 i n a  For  the scans  t h e MCA  ramp  mechanical of  a  the Fluke  voltage  by  means  voltage.  system rate  412B  range  (when  time  of The  a  was The  voltage  response  coupled  t o <0.5  resulted  of  to  the  sec/channel  and  delay  from  electrons  (of 8  high  voltage  electronics. both acted  The  to prevent as of  a  recorded Fabritek  multichannel  the  were  sec) , at  and  synchronously  loss  voltage  with  signal mode with  processed  through  Energy the  a i d  averager whereby the  a  protection  electronics.  i n W74.  d i g i t a l l y  scaling  then  unit-amplification  the counting  1064)  channeltron capacitatively  signal  high  p r e a m p l i f i e r i s shown  i s stepped  to offset  shaft  program  i n  scan.  remainder  (or  placed  the  the  used  of the potentiometer.  synchronized  the detector  served  to  ramp  the scan  used  voltmeter,  varied  readout  single  counting  preamplifier cable  each  of  from  standard  long  a  which  be  supply  volts)  large  choice  t h e MCA  limited  350  resistance  could  mechanical  of  (up t o  The  was  was  cf interest.  Digitec  supply.  on  t h e use  decoupled  to  range  potentiometer)  region  voltage  power  which  connected  suitable  c i r c u i t  Digitec  was  power  by  a  rarap  PCX-100  volts by  used  MCA  supply  loss  100  which  the  Kepco  412B  monitored  loss)  achieved  the  a  Fluke  potentiometer  the  volts  to t h e energy  greater  actual  100  program  with  analyser  than  the  analyser  A loss  of  a  (MCA) channel scan  67  voltage.  The  continuously program reset step  size  number  typically and  moderate 5-10  hours,  hours)  with  Spectra oscilloscope, printed  manipulation backgound be  was  means o f  as  subtraction,  performed  analysis data  such  plotted  i n  transferred paper  tape.  both  the  only  the  collection channel  s t a t i s t i c a l slow  counting  recording  d r i f t s  times  f o r  spectra  are  times  (up t o  spectra. memory with  could an  A  and  For  squares  to f i l e s  any  longer  be  X-Y  viewed  on  recorder  limited addition  i n t e g r a t i o n and  (e.g. the least  and  per  inner-shell  shifting  MCA.  advance  data  FWHM)  a Teletype.  the  4610  of  time  be  Ortec  t o improve  Typical  resolution  on  both  could  to record  out the effects of  i n t h e MCA  numerically  i n order  used  ( 0 . 3 5 eV  point  t h e channel  i n t h e minimum  significantly  stored  an  optimization  parameters.  f o r higher  spectrum  using  where the counting  to average  resolution  1000  allowed  s e c , were  the apparatus  i n a  to determine  interest  scans,  0.1  1 and  of channels  of  Multiple  channels  between  This  region  accuracy  48  and  of  unit  o f t h e MCA.  time.  in  varied  control  spectral  was  number  amount of  and/or of  f i t t i n g  i n t h e OBC  data  spectra,  differentiation  more  could  sophisticated procedures) IBM/370  an  system  data the by  68  3.1.6  Spectrometer Magnetic  The brass  Construction,  entrance  for  plates  deflection located  components  the  current  which  plates  and  are  and  e l e c t r i c a l l y  sapphire  balls  undersize  holes.  The  uniform  were  surface  emission. surface beam, the  coated  found  spectrometer The The  vacuum  jar  arrangement  The  groove  top  of  containing head. ceramic  the  base  charged  be  a  tube in  the  (not  as  This the  or  8  elements,  mm  Nidau) of  each  i n  order  are  diameter  located  i n  hemispherical to  secondary  cleaned  whenever  deflected  produce  a  electron insulating  the  electron  procedure  arrangement  visible a  aluminum i s  (EIMAC  in  19" a  plate  viton  by  restores  the  are  made  soldered  chamber  an  allows can  25"  be  plate  a  bell  high,  ionization via  a 1).  plate gauge  high  voltage  or  single  flanges  mounted  access  easily  in  plate  aluminium  rapid  1/2"  located  CA8000) in  i n  i s  (see  and  (Varian)  arrangement  2)  0-ring  plate  closed  valve  i s shown  diameter,  base  connections  vacuum  lens  apertures  5  This  from  analyser  reduce  and  r e s t i n g on  (Ceramaseal) ,  plate.  and  performance.  chamber  plugs  soot  problem.  a i r admittance  octal  spectrometer  was  c o n s i s t i n g of  A l l electrical  feedthroughs  to  experimental  the  an  benzene  optimum  chamber  aluminium  machined  t c  to  complete  2.  thick  which  AG  surfaces  spectrometer  deposits, were  (Saphirwerk inner  The  by  machined and  monitoring  insulated  with  a l l  molybdenum.  p o t e n t i a l and  The  were  monitoring  current  precision  analyser  System  Shielding  spectrometer except  Vacuum  on  to  the  removed  (no  P l a t e 2:  Complete ISEELS experimental  arrangement.  70  bolts  are  used) .  diffusion working  liquid  chamber.  vacuum  nitrogen  located  between  These  reduce  nitrogen  trap  was n e v e r  torr)  - 7  could  because  f i l l e d  be  also  the  spectrometer surfaces  by  a  or  by  was to  outside  f i e l d  either  judicious  that  the c o i l  the  region  current large  placement  and  A  of a  of  the  i n  5010)  a n y pump o i l The  base  liquid  pressure pumping  contamination  magnetic  f i e l d  chamber.  t h e bottom  magnet.  shield.  monochromator  the  of  i s screened  energy  A  rau-metal residual  o f t h e mu-metal c a n of Helmholtz  This  end  o f t h e I t  was  by showing with  coils  correction moncchromator demonstrated  the residual  was i n d e p e n d e n t  pass  water  encountered.  was n u l l i f y i n g  position  to  t h e vacuum  without cryogenic  of the proximity  o r magnet  o r magnet  analyser.  i s used  speed.  with  N.RC  as the  (Airco  t o trap  the use o f a p a i r  o f t h e mu-metal  changes  pump  t h e vacuum  near  by  necessary because t h e bottom  4"  pump.  a s an a d e q u a t e  problems  were  a  18" wide ,hexagonal,hydrogen-annealed  magnetic  nullified  pump  valve  t h e pumping  o f the ambient  (W56) p l a c e d  static was  majority  30" high,  shield  no s e r i o u s  gate  surfaces  obtained  and  The  1402 r o t a r y  diffusion  provide  greatly  by  10 p o l y p h e n y l e t h e r  a n d 4"  items  but  pumped  f o rt h e d i f f u s i o n  trap the  vapours  (4x10  i s  Convalex  A Sargent-Welch  the backing  baffle,  chamber  using  fluid.  provide  are  pump  The  that  f i e l d i n the  coil  respect  to  o f the monochrcmator  or  71  3.2  Spectrometer  Prior applied DU),  monochroraator  gun e i n z e l  adjusted  to  through  beam  current  was  analyser  by u s i n g  Faraday  cup.  incident  electron  energies  moderate  the  main  loss pulse  counting  mode,  L3  voltage  f o r an  non-spectral onset  i n order  up  of  the  2.5  P3.  at  then beam  energy  keV)  inner-shell  and  main  as  a  desired  the  (typically  pass 25  eV  spectra), energy  operating  i n the  optimized.  This  the ratio feature  DD  and the  of the count  to that  the  energy  while  of the  at the  inner-shell  by  current  (CEM)  deflection using  (as estimated  beam  The  inner-shell  further  loss  interest.  the exit  beam  The  were  ( P 2 , o r P3)  and analyser FWHM)  the  main  plate.  t h e main  onto  of  channeltron  to maximize  inner-shell  through  the  by t h e c h a n n e l t r o n  t h e main  background  plate  maximized  ( 0 . 3 5 eV  was  (D1  maximizing  preceding  (usually  as measured  adjusting  the  setting  deflected  voltages  of L3,  signal  directing  of the  energy  involved  rate  the  t h e cone  was  element  loss  monitoring  on  the  hemispheres,  by s i m u l t a n e o u s l y  resolution  beam  signal,  focus  energy  of t h e monochromator  for  analyser  eventually  After  spectrum  and t h e center  current  the current  and  involved  apparatus  'downstream'  loss  deflection plates  the  procedure  the  minimizing  lens  maximize  tuning  a  an energy  to the electrostatic  electron  on  t o recording  t h e  The  Operation  f o rthe  signal  loss  region  below of  interest) . This inelastic  apparatus  could  scattering  most  be  used  to  effectively  examine  zero-angle  i n the valence-shell  72  region  ( i . e . a t energy  spectral small  region,  high  decreasing  energies. high  a t similar  for  CO  (LSD68) , w h i l e  be  compared  Inner-shell conditions  zero-angle  than  the  cculd used  easily  by  and  analyser  pass  o f t h eapparatus energy  as a loss  Energy  previously  o f CH3I  2.3)  several  degraded times.  loss  reported 3.5)  (figure  may  photoabsorption  i n  crders  order  zero-angle because inner  beam  at zero  angles,  surfaces  were  two reasons  f o r i n e l a s t i c  scattering loss  inner-shell  o f magnitude reason t o  high  loss  smaller  than  t h e resolution  have  acceptable  from  could  with  this  exit  t h e improved modification,  n o t be o b t a i n e d .  generates  lens  inner-shell  s c a t t e r i n g o f t h e main  o f t h eanalyser  data  performance  raonochromator  Even  (faster  energy  resolution  a n d 12) .  spectra  under t h e  resolution,  t h e increased  resulting  inner-shell  There  of the  o f 7  high  increasing energy  I t was o n l y  (see chapters  be o b t a i n e d  record  F o rt h i s  l e d t o t h er e c o r d i n g  electron  t o  and thus  by t h e m o d i f i c a t i o n  spectra  n o t  section  rapidly with  a r eusually  produced  incident  relatively  a n d 3.5.  spectra.  t h ec r o s s  E-3 - seesection  acquisition  the  as those  First  usually  that  a s  corresponding  valence-shell signal.  was  is  t h e  spectra  o f f very  signals  widths  been  t h espectrum  valence-shell  this.  f a l l s  r e s o l u t i o n s have  this  peak  electron 3.4  I n  (HTW75) .  spectrum  for  with  monochrcmator  a r e shown i n f i g u r e s  t o  50 e V ) .  be o b t a i n e d  valence-shell  spectra  same  than  o f t h ep e r f o r m a n c e  resolution  spectrometer  could t h e  Examples  less  resolution spectra  a s 2 5 meV FWHM  suitably  losses  a  This  beam o f f background  73  1.0-4  0-5H  0-^  1-0H  05-J  12  13  E N E R G Y LOSS (eV) F i g . 3.4  Valence-shell energy loss spectrum of CO (1.5 keV impact energy, AE = 0.03 eV).  -3/  2  «=-1/2  CO  c  ZJ  >> o 15 v_  •1  I  o  >-  l i ;«  i  CO  !  i  I.  •  j \  I .1 -  LU  1f  -|  1  6  F i g . 3.5  1  7  1  1  8  1  1  1  1  1  9 10 ENERGY LOSS (eV)  Valence-shell energy loss spectrum of methyl iodide. (2.5 keV impact energy, AE, = 0.08 eV) -3  1  11  1  r  12  75  which, and  although  n e g l i g i b l e f c r vale nee-shell  3.5),i s relatively  spectra. applied  This  occurs  t o t h e beam  large even  dump  the  slow  secondary  main  beam  on t h e back  (see  i n the inner-shell  i fa  large  i n order  electrons  positive  t o more  generated  surfaces  F i g . 3. 4  energy  loss  potential i s  e f f e c t i v e l y  by the impact  o f t h e analyser  trap  o f the  and t h e  beam  dump. Inner-shell obtained  at -zero-degree  experimental coincidence i s  i s  apparatus i n  t h e results that  spectra  a t  optical  beam,  e l a s t i c are  analyser.  Even  inner-shell enter  because much  more  electrons  s c  the analyser, i t  reduces  numerous inside  a  angles  are  used,  expected  t o be v e r y  the  incident  the electron very  i n e l a s t i c  l i t t l e  most  s t i l l  Although  t o zero  beam  angle  does  of the  energy  non-zero  inner-shell  a t  b e n e f i c i a l  due t o s c a t t e r i n g  valence-shell  present  of the  scattering  o f t h e main i s  main  scattered  dump a t t h e b a c k  dump  and  s i m i l a r  system  Zero-degree  have  small-angle  t h e background  the  which  other  and because  beam  where  the analyser.  electron-ion  e s s e n t i a l l y a l l of the  beam  e l a s t i c  other  i n connection  The  entrance  studying losses  thesis  because  valence-shell  when  been  two  i s t h e  1 1 .  cases  a  with  KTR77, KRT77).  that  into  have  I n s t i t u t e , Amsterdam  collimated  directed  energy  angles  i n chapter  at the analyser  spectra  these  (TKR76,  well  and  loss  3.5 o f t h i s  i n these  aberration  electrons  not  reported  i s  systems  of  a t t h e FOM  Manchester  beam  chromatic  One  section  a r e achieved  electron  energy  scattering  systems.  described  with  electron  scattering  spectra  spectra  loss  are  obtained  76  at  t h e same  this  incident  statement  momentum average have  on  decomposition  products  Energy  loss  spectra  Data of  some the  cases  used C 2 H 4  of  a  carbon scales  3.6  scales  was  of  of  the  2.3.  The  arrangement rad, both  by  measured  a t  by  geometrical  electron  beam  f o r a l l inner-shell  energy  o f P3.  d i d  of  t h e as  was  f o r carbon  f o r  excitation  being  performed thus  shifts  and  of  standard  1s e x c i t a t i o n regions  A  the  5'/2-digit accuracy  energies. standard  In  so  overlap  calibrated. by  contact  any  I na l l the  problems  potentials.  techniques and  that the  recording  avoiding  CO  to  stated  significantly  of gases  CO  a  relative  the calibration  t o this  o f CO.  a secondary  not  of a mixture  eV  feature  the sample  energy  calibration  voltmeter with  used  mixture  1s spectrum  0.05  and a l s o  by  loss  t o measure  i l l u s t r a t e s  relative  scales  d i g i t a l  calibration  gas-dependent  Figure  voltage  established  peak  features  spectrum  than  was  t h e  2  of the current  on t h e surface  1s e n e r g y  3500  calibration  spectral  with  carbon  cases,  1 a n d 3x1 0 ~  observations  energy  were  Precision  0.008%  present  of  Calibration  absolute  prominent  on  i n section  the  between  deflection  based  The  i n  j u s t i f i c a t i o n  dependence  presented  o f t h e dependence  the double  The  angular  used  t o be  measurements  3.3  been  angles  estimated  energy.  of the  has  scattering  investigation P3  i n terms  transfer  been  electron  with  the  Energy  C 2 H 4 .  are accurate t o  better  regions.  energy  widely  The  separated  from  the  77  carbon for  1s r e g i o n a r e somewhat l e s s  the  fluorine  estimated The the  t o be a c c u r a t e  carbon  Fluke  reported et  in this  ev FHHfl)  energy  thus  depend on  calibrator  thesis  to  the  are referenced t o t h i s  have  obtained  spectrum  of  accuracy  this  a  be 2 8 7 . 4 0 ± 0 . 0 2 eV.  high  peak  of  peak was  (WBH73, W7 <4)  power s u p p l y .  o f t h e d o m i n a n t v=0 t r a n s i t i o n  reported  even  s c a l e s are  The maximum o f t h i s  t o be 2 8 7 . 2 8 ± 0 . 0 5 e ? by Wight  a l . (TKB76)  (0.07  (700 eV) t h e e n e r g y  1s f e a t u r e o f CO.  343A v o l t a g e  although  t o w i t h i n 0.2 e v .  absolute energies  determined a  1s r e g i o n  accurate  using  A l l energies value.  Tronc  resolution  i n CO i n w h i c h t h e  (see  F i g . 12.2)  S i n c e t h e v=1 peak i s l e s s  CO  2 4 n  2-60  -s  286  284 Fig.  3.6  Calibration  cf C H 2  4  was  288  eV  (C 1s) by CO (AE=0.5 eV).  78  20%  than  of the  envelope  v=0  (which  peak, t h e  will  centroid  correspond  to t h e  maximum i n a low  resolution  spectrum)  higher  maximum o f  the  v=0  0.5  eV  Wight  than  the  (W74) , o b t a i n e d  directly  comparable  significant. energy  of  calibration peak  at  good The  the  clarify  this  with  r e s p e c t to the  eV  and  a  carbon  1s  (SDL67)  with  t h a t two  the  performed a t  lower  value.  in  energy  energies  3.4  the The CH F 3  factor  source  samples  and used  bottle  some o f by  the  i f this  of  eV  would t h e n  be  is  absolute by loss  Precision  3500  0.15  This  peak  eV. maximum,  by  were  Wight used  support  value  devise  be  been d e t e r m i n e d  gives strong  an  in  (W74). in  the  for  the  i s found energy  to  be  scale  a p p l i c a b l e t o a l l the  thesis.  s t a t e d minimum  were used  lecture  removed  0.12  of  Purity  chemicals  For  which  value  should  of  determined  matter t o  reported i n this  Sample The  CO.  However,  error i t i s a simple  correction  UBC  peak  slightly  Thus t h e  Data  voltmeters  determinations  only  the  v a l e n c e - s h e l l energy  f o r the  value  of  resolution,  resolution  different  be  peak.  the  o f 2 8 7 . 3 1 ± 0 . 0 5 eV  agreement  will  f e a t u r e has CO  vibrational  position  discrepancy  using  spectral  the  discrepancy  CO  a value  fact  and  the  8. 390  voltmeter yielded  To  with  of  the  pumping  in this  study  without was  on  (where quoted)  listed  i n table  sample  1s  spectra  at l i q u i d  The  percent  the  CO  nitrogen  of 3.1.  purification.  to c o n t a i n a few  carbon a  are  further  found  C H 3 F  purity  of was  temp-  79  Table  3. 1 :  Sample  Compound  CH  and  Purity Manufacturer's Stated P u r i t y (%)  Source  Mat h e s o n  4  CD  Source  Merck,  4  C H 2  6  C  >99  Sharpe  Bohme  >99.9  Mat h e s o n  >99  Matheson  >99  C H 2  4  Phillips  C H  6  Matheson,  6  and  66  Hydrocarbons  Coleman  and  Bell  >99 >99  CH F  Matheson  CH C1 3  Mat h e s o n  >99  CH 3 B r  Mat h e s o n  >99  CD Er  Merck,  C H 3 I  Fischer  C H F  Eastman  C H C1  Mallinckrodt  C H Br  Mallinckrodt  C H I  Eastman  3  3  (>99) *  Sharpe  and  Dohme  >99  Mat h e s o n Mat h e s o n  >99  CO  Mat h e s o n  >99  N  Canadian  5  6  5  6  5  6  5  CH C1 2  2  Fischer  Kodak  Kodak Spectroa nalysed  C H C I 3  Matheson,  CC1  4  Eastman  C  5  2  SF  *  H  C 1  6  2  found  to contain  Coleman  and  Bell  Kodak  Liquid A i r  a  few p e r cent  isotopic  >99. 5  Spectrca nalysed  -  6  isotopic  >99  o f CO  80  eratures the  CO  (HD78a). was  For the C  retained  samples,  several  remove  dissolved  energy  loss  purity (see  were 3.4  7.5),  a  recorded  t o establish  detected  ( < 0 . 5%) . problem  carefully in  the  sample  severe  halobenzenes  and  the inner  several even  though  large. one  A  system  while  of  the vapour second could  the other  spectrum  be was  of  system.  liquid  i n use.  to  sanple  3  sample  was  No  CH 8r  was  the  system  to  f o r  effects were the  form  films  I t took  samples  be  as  up  to  these  films  was  quite  was c o n s t r u c t e d  prepare  to  effects  such  seemed  system.  had  memory  These  which  3  which  samples  study  3  to c o m p l e t e l y remove  pressure of  pumped  check  the CD Br  of  to  valence-shell  to  handling  i n l e t  inlet  liquid  performed  purity.  of t h e sample  sample  For  3  possibility  pumping  F i g . 7.3  For the CH Br/CD Br  chloromethanes  surfaces  days  3.5).  the  with  were  recorded  sample  i n  resolution  the i s o t o p i c  c o n s i d e r e d was brass,  cycles  often  mass  shown  the spectrum.  High  and  with  particularly  on  to calibrate  gases.  (e.g. Figs.  One  spectrum  freeze-pump-thaw  spectra  section  1s  later  so  that  studies  8 1  3.5  The E l e c t r o n - I o n The  has  electron-ion  been  detail  This  described  (W71,  diagram  Apparatus  coincidence  in  a p p a r a t u s and  the l i t e r a t u r e  i n  HW71, BKW73, BW74, BTB75, BWT75).  o f t h e c o m p l e t e a p p a r a t u s i s shown  apparatus  energy  is  loss  absorption)  (WSB70,  measurements  threshold  very  and  in  technique  considerable A  schematic  figure  h a s been  (simulating  3.7.  used f o r photo-  BWT75, KLH77) , e l e c t r o n - i o n c o i n c i d e n c e photo i o n i z a t i o n )  coincidence  photoelectron  electron-photon-ion  versatile  measurements  (simulating  electron-electron  Fig.  Coincidence  (8W71,  measurements  s p e c t r cscopy)  coincidences  3.7 T h e e l e c t r o n - i o n c o i n c i d e n c e  (simulating  (BWT75,  iW77)  (simulating  apparatus  WWB77),  and  photo-  (Amsterdam).  82  fluorescence)  (DKW73).  fragmentation four  types  singles  of  2p  of  ionized  i n chapter  of experiments  counting  electron-ion coincidence each  S  For the i n v e s t i g a t i o n SF  were  energy  6  described  performed.  loss  measurements  measurement.  The operation  of these  four  modes  i s  These  measurements,  coincidence  the  11,  involved  two  and  ionic  types  an  of  ion-ion  of the apparatus i n  described  i n  the  following  sections.  3.5.1  Electron  The from  electron  analysis  electrons. portion  Loss  energy  less  of zero-angle In  i n  d i f f e r e n t i a l l y optimum  pumped energy  0.5  eV.  For the SF  the  hemispherical  an  overall  the TV  study  because  of  einzel lens  system  angular  because  (BTW75)  lenses  beam,  of  1.0  with  was eV  consists  two-element a l l electrons  plate  (see  of  F i g . 3.7)  this  by  a  thus  i s l i m i t e d to  100  energy eV  FWHM.  of  yielding  Zero-angle main  beam  incident  electron  analyser  entrance  two  deceleration which  keV  ISEELS  and  negligible  collimated  8  energy,  the pass  of the sophisticated  a  transmits  selection  the well  which  and  of  produced  11)  resolution  obtained  t h e UBC  (chapter  background  system  from  resolution  are obtained  lens  impact  spectral  spectra  and a l s o  differs  incident  inner-shell  beam  scattering  e l e c t r o s t a t i c analyser  spectral  was  6  gun, i s n o t monochromated  loss  6  of SF  t c the larger  spectrometer that  spectrum  inelastic  addition  o f t h e FOM  spectrometer  the  Energy  pass to  three-element lens.  This  through  the  the  analyser  83  entrance  lens.  I t also  and  allows  efficient  thus  beam  dump  placed  Because the  converted  gas  known  Bethe-Born  high  impact  relatively  may  s t i l l  energy First  be  order  where  and  experimentally  Although  was  as  large  as  for S  momentum  because (K) .  f o r He  the f< >  order of  imply the  by  l  are negligible,  will  strength.  This  2p  excitation  [=  correction, the  small  2 2  -  and  of equating  the  value  CH 3  at  f<*><»K  2  o f  (180 eV au.  2G,G )  ] term  but  i s c a . 0.3  strength  (BTW75) [={£  the  and, to the extent  transfer  oscillator  20% of t h e f<o>  the first  the  f o r valence-shell excitation  accurate  determined  eV.  transfer  terms  angle  dominated  2.3.7)  using  Therefore  o s c i l l a t o r  valid  optical  60  0.3%  non-dipole  the  to  than  equation  are  I n addition,  transfers.  and  c a n be  strengths  scattering  be  the  angle  intensities  2.3).  will  i n  kinematics  corrections to the approximation  generalized  losses,  loss  degree  strength  reasonably  beam  hemisphere.  scattering  (see section  optical  i s most  loss)  the  t h e energy  (see  the  approximation  i n the outer  momentum  o s c i l l a t o r  to  slot  and zero  the higher-order, equal  well collimated  generalized oscillator  theory  term  beam  characterized scattering  thus  small  zeroth-order  be  and  energy  generalized  a  target,  to relative  the  that  behind  t h e main  t r a p p i n g o f t h e main  of the well  localized  accurately  leaves  have 4  been  (BWT75)  out  ] terra  f o r He  some  energy  was a l w a y s the  less  momentum  84  3.5.2  Electron-Ion  Positive 8  keV  Coincidence  ions  electron  produced  impact  (TAC  i n  the  are extracted  electron  beam  into  the  tube.  electric  field  (3G0  V/cm)  chamber  and  complete  collection  kinetic  energy  (ca.  30  such  cm)  and  that  obtained fixed  a  energy  a  spectra  with  a  time-of-flight  losses  are  converter from  an  energy  from  ion signal.  with  loss The  i s  electron circuit  c o i n c i d e n c e measurements  section  figure  of  coincidence generates the  time  modes  an  for  a  the this  output  times  TAC  start  and  f o r the  i o n  to  a  aass  by  6  stop  i o n and  mass  tube  (4 keV)  are  of  of  20  50  can  spectra  eV  be at  started  a  and  by  stopped the  by  TAC  i s outlined, of  a  pulse of  i n the  top  a l l three The  TAC  i s proportional  pulses. will  This  be the  time  to i s  characteristic distribution  of  (PHA)  of  ( s e e F i g . 11.3).  In  the  peak  producing  a target  pulse  mode  experiment.  spectrum  probability  i n the fragmentation of  d r i f t  height analysis  spectrum,  ensure  time-to-  Thus,  pulse  c o l l i s i o n  the a i d of a  amplitude  fragment.  yields  the  SF  d r i f t  the  i s a schematic  the whose  time-of-f light  species  i n  (as measured  output)  proportional  which  pulse  t o Vm/e'  specific  flight  used  between  proportioned  3.8  the  than  Mass  f o r  electron-ion  by  less  power  analysis.  which  to  system  energy  resolving  obtained  (TAC)  of  kinetic  the  lens  having  length  i o n  angles  across  accelerating  The  chamber  ion time-of-flight  a l l ions  the f i n a l  arising the  of  (BWT75) .  mass  from  amplitude  four-element  collision  at right  incident An  Mode)  a  molecule  areas given  are ionic  following  85  target  (a)  Electron-ion coincidence: TAC mode  target  ('time-of-flight')  ^ del  gun ions  CN  >»l  ft  det  Oi  T3  u  I-c  n.  gate  u  1 3  c o u o  gate' del.1  (b)  true. 2 (random) (.ni*n ) random ("0  7" | delay  u  del.2  2  Electron-ion coincidence ( ' f a s t coincidence' mode)  target S*  det  ,— >  10  ai •o  TAC  PHA  (c)  Ion-ion coincidence (ion autocorrelation)  Fig.  3.8  Configurations for coincidence  experiments.  86  excitation of  by  measurements  ion  fraction  oscillator loss  given  a range  spectrum  strengths,  this  o f energy  which  mode  obtain  Coincidence  coincidence  characteristic  i o n o s c i l l a t o r  directly  strength  by sweeping  electron-ion the fast  coincidence  rate.  the  electron-ion  arises  from  both  true  circuit  corrections  obtain  (n,)  (relative)  obtained  true ion  by  energy  strengths. to  SF  6  are  the specific  time  ionic  loss  while  F i g . 3.8b  shows  Since  schematic  of  interest  coincidences,  are easily  rate  i s  TAC  (after  Ionization fraction  mode  the  and  thus  The  (n,+n )  t o  directly  subtracted 2  second relative  obtained  (n -n,)  strength  a  the  made).  the  coincidence  correlation  spectrum  i o n  a  the  (Inthe  the  Thus  recording  and randoms.  factors).  species.  f o r one i o n i s obtained  are automatically  combining  only  determine  o s c i l l a t o r  Mode)  t o examine  to  coincidence  kinematic  have  single  random  correlation  signals  which  time  included  f o r t h e randoms  the  electron  i s  and  of trues  time  an  absorption  Coincidence  a r e used  circuitry.  at  complete  with  method  (Fast  spectrum  t h e energy  coincidence  contributions  generates  oscillator  TAC  gates  cf a  signal  delay  losses  A series  non-coincident  i o n  o f the  loss.  combined  from  electron-ion coincidences  correlation  and  i s  derived t o  Electron-Ion  In  t c t h e energy  11.  i n chapter  those  egual  of the application  3.5.3  of  over  measurements,  Details  the  an energy  and  2  thus  the  corrections f o r  e f f i c i e n c i e s (from  TAC  are mode  87  measurements) fast  and t h e r e l a t i v e  coincidence  with  the  measurements)  t o t a l  measurements) .  i c n o s c i l l a t o r strength  absorption Thus  required  to obtain  spectral  regions  both  f o r a  (from  fast  absolute where  single  i o n  the  ionic  non-coincident  coincidence  o s c i l l a t o r  species  energy  a n d TAC  ionization  (from  loss  modes  are  strengths  i n  efficiency  i s not  unity.  3.5.4  Ion  In  Autocorrelation  certain  dissociative is  produced  can  be  the two  i c n i c  ionization from  studied  11.4).  involves inputs Since  t h i s  sensitive  the  i n i t i a l  with  i s integrated  arising  from  events  would  were i s  keV be  at s p e c i f i c  event. over  required energy  events  correlations  between i s  i n  signals  equal  fliqht  from  to  the  times. on  SF  Ion (see  6  outlined  i n F i g . 3.8c  t o  start  both delay  only  Thus  i n one  involves  the ion  possible  impact.  t o measure  lcsses.  fragment  Such  and input ions,  cr the scattering  a l l  electron  ionic  event.  performed  suitable  loss  one  event  measurement  excitation  spectrum  experiment  a  t o the energy  8  the time  the i o n signal  coincidence  not  loss  characteristic  technique  t h e TAC  than  [e.g. double  f o r time  single  measurements  applying of  energy  since a  their  The  more  by l o o k i n g  from  i n  autocorrelation Fig.  single  signal  arising  difference  (DDI)],  d i r e c t l y  ion detector ions  a  fragmentations  A  and stop  line. i t i s  angle  of  autocorrelation  excitation  events  triple-coincidence  the frequency  of  DDI  88  All are  modes o f o p e r a t i o n  controlled  electron-ion  by a  accuracy the The the the  peak  maximum  minicomputer data,  prints  energy  flight  were  and proceeds I n  the  recording.  In data  instrument.  t o  minicomputer  this and thus  way  i ti s  Teletype,  plotting  an  a  extremely  on  new  time-ofthe  data  f o r further  data  graphs)  apparatus  loss).  increments  controlling  c a n be used  the  energy  on  calculations  t o accumulate  a  s t a t i s t i c a l  a t each  on a  the  1000 c o u n t s  any d e s i r e d  addition  ( e . g .c a l c u l a t i o n s ,  2p s t u d y ,  of  accumulates  specified  obtained  performs  mode  the system a  S  6  out the r e s u l t s  spectrum.  processing  obtaining  then  loss  acquisition,  until  (for the 5F  spectrometer  I n t h e TAC  experiment  spectrum  i s reached  largest  minicomputer.  coincidence  time-of-flight  of t h e electron-ion  i s  even  while  continuously time-efficient  89  CHAPTER 4 THE  INTERPRETATION  OF  INNER-SHELL  EXCITATION  SPECTRA  "It i s certainly not the l e a s t charm o f a theory that i t i srefutable." F.W. Nietzsche  4.1  M.O.  A  Models  one-electron,  frozen  sufficient  to  inner-shell  excitation  review  the o r b i t a l  of  transition  energies  differences such  interpret  i n  a  E  n  orbital  the  spectra  gross  features  ( s e e WM77  concept) . are  model  In this  assumed  homogenecus  to  f o r  i s of  cften  molecular  an  excellent  model,  electronic  be  equal  set of o r b i t a l  to  energies  the 6 j ,  that:  (4.1.1) In  non-relati vistic  energies  are derived  Hartree-Fock  theory  these  from:  (4 . 1. 2)  £; = 6 ° * E ( 2 J i j . - K j - ) where  €; i s the  electron field  'pseudo-eigenvalue'  orbital  (SCF)  solution  orbital  and  associated  i s obtained  o f t h e Fock  from  equation  a  with  t h e one-  self-consistent  (fi=m=e=1):  (4.  1.3)  where =  [ ( - V V 2  -£z /r ) k  k  •  E(2Jj-Kj)]  (4. 1.4)  90  The  f i r s t  term  an  electron  i n 4.1.4 plus  electron-electron Coulomb  M  accurate  <</>i(M) K * j ( " ) I r  =  <4>J(M) I <<*>j(0  treatment  making  rough  r e l a t i v i s t i c o r b i t a l  inner-shell  often  approximation electron  the Even  where  o r b i t a l ,  interaction though  electron,  t h e inner-shell  o r b i t a l  features model,  i nt h e  relaxation Also,  with  this  theorem  spectroscopy. Hartree-Fock effects and f o r  discrete t o  a  t o describe  thecore  a r eneglected  i t c a ns t i l l  the  and  i spromoted  a r erequired  electron  method  0.3 eV.  Koopman's  electron  o f  F o r t h e carbon  n  WM77).  terms  of the excited  important  frozen  hole  a  of  €. =0,  theorem  (Sh73,  additional  hasgiven  i sc a .  t h e  more  treatment  i nphotoelectron  core  terms  F o r a  r e l a t i v i s t i c  energies.  t c  Koopman's  neglects  correlation  excitations v i r t u a l  that  applied  (4.1.6)  t h e magnitude  i o n i z a t i o n ,  approximation  known  o f  correction  i s equivalent  i swell  f o r a  (Sh73)  t o o r b i t a l  approximation  I t  ( 4 . 1.5)  interactions,  Shirley  (~ 3 0 0 e V ) t h i s  For  o r  o f  given by:  coordinates.  levels  estimates  correction  elements  o f  The  terms  ( 0 > l * j (M)>  spin-spin  a r e required.  i n  " i |«PJ ( „ ) > l *j (AO >  electron  o f core  o r  corrections  1s  label  M  energy  a l l nuclei.  expressed  (K- ) matrix  =  i>  with  a r e  < * i < M ) U j I4>;<M)>  spin-orbit  for  interactions  =  and  f o r the kinetic  i t si n t e r a c t i o n  (Jjj ) andexchange  J ij  where  accounts  hole.  i nt h e  be useful  one-  f o r a  91  semiquantitative  description  particular,  i t  should  description  of  inner-shell  (E <50  eV)  n  the  excitation  excited  smaller  electron  than  A  that  scheme  with  f o r  required  within  the one-electron  conveniently  from  MO's,  overlap  interpret  usually  orbitals  are strongly  i t i s f o rthese o r b i t a l  2.  A single  be  considered a  radial  extent,  quantum  transitions, transitions  that  studies  virtual  MO's  (non-bonding)  energies  of  of  are  (n,£). energies  o r b i t a l s  (i.e. the  of constant  £  the  These molecules  one-electron,  adequate. Rydberg  states ion. the  o r b i t a l s which  o f an  electron  Because i o n  core  orbital.  characteristic analogy  of a  can  derived  principal shell).  a Rydberg  By  of  character,  atomic  i s the least  the d e t a i l s  the  earlier  of o r b i t a l s that  p o s i t i v e l y charged  numbers  many  structure  classes:  occupied  types  to t h e energy  transition  o r b i t a l s  discrete  of antibonding  as the stationary  of  (S74).  characteristic o f i n d i v i d u a l  model  s e t of  f i e l d  irrelevant  two  of the valence-shell  of the outermcst  frozen  From  considerably  molecular  the  f c ra  i n t e r a c t i o n of  i s  hole  i t i s known  into  orbitals  and  hole  virtual  model.  be d i v i d e d  Valence  core  In  valence-shell  t h e exchange  the  excitation  accurate  than  a valence-shell  t c  features.  more  rather  describing  i s  valence-shell  considerably  because  with  (MO's)  1.  be  of the spectral  series  and i n c r e a s i n g  t o  of  i n the  of t h e i r a r e  can  large  somewhat  Thus  Rydberg  the  orbital  atomic  of molecular n are given  Rydberg Rydberg by:  92  where  IP  i s  the  converges,  T  (R=13.605  eV) ,  obtaining  by  number  with  of  (n)  the  the thus  the  to  the  up  to  i s  same  a  description  of  of  used a  survey  for  <5s,  to  <  4.5  The  d  eV,  lowest  because valence R75)  2.2  of  s  type  from  that  the  body  give  row  and  series  should  be  i n  Rydberg  terra  virtual values  promotions  and  of  (SL) .  to  to  molecule.  the  of  0.7  1.6  <  nature  and  frequent  and  values to  for  2.6  T(3d) large  1.3 5d.  of <  <  s,  p  T (3s)  1.8  eV.  variation  mixing  with  Robin  (R74,  to  Rydberg or  unified  on  ranges:  valence  apply  leading  members  According  and  excitation).  the  to  limit  +0.2  a  of  absorption  l i m i t s  lowest  this  nature  convincing,  such  either  the  a  has  apply  In  expected  value  o r b i t a l s .  should  characteristic  of  -0.2 the  eV  i s  elements)  of  2.6  quantum  valence  empirical  values  <  principle  electronic  term  T(3p)  a  involving  Sp  number  transitions  limits  cf  ( f o r second for  be  Rydberg  to  constant  ionization  might  series  quantum  transitions,  values  idea  Rydberg  Rydberg  number  determines  i t s penetrating  these  arising  <  Rydberg  places  0.7 the  • Rydberg  (s^)  quantum  (chiefly  defects  i s the  designated  defect  this  the  effective  ionization  Robin  which R  the the  vast  quantum  Alternatively,  value,  i s  term  the  (4.1.7)  2  to  corresponding  of  and  limit  term  only  2  A  momentum  spectra  0.5  F/ tn - 6 )  quantum  of has  this  -  Rydberg  (R74)  From  IP  n*  orbital,  loss  =  molecular  each  energy  R/(n*)  correcting  energies  Robin  -  the  and  of  i n i t i a l  IP  ionization  angular  treatment  =  core  transitions electrons.  93  The  assumed  valence  to  W47a-f)  of  regions  Wang  et  of  The  more by  taking ion  core.  atomic  energies  of  the  inner-shell  analogy  the species  core  absorption applied soft et  to  X-ray  a l .  and  F  which  can  and  approach nuclear  of  (Z+1) with  equivalent Thus  the  H 0.  by  More  2  the  innerscope  of  can  be  species  be  are  determined  spectra  or  from  known  from  conversion  studies.  region  a  authors,  of  et  a l .  of  the  be  inner-  done  atom core  by  which  of  one  atoms  v i r t u a l  valence-excited  Wight  of  analogy  the  excitation  MNI74),  procedure  energies  core  inner-shell  (NSS69,  as  easily  i s well  number  spectra.  expand.  molecular by  (W74,  molecular  Rydberg  excited  valence-shell  analogy  spectrum  atom  etc).  and  Wight  reintepretation  most  the  ground  a  some d e t a i l s  can  (e.g.  N,  of  0  of  excited  are  experimental This  number  from  Analogy  equivalent  0  those  core  the  this  expected  to  account This  inner-shell  and  be  (Z«-1)  into  replaces larger  to  description  of  the  are  Core  application  by  support  values  ISEELS  reversed  studies continues  accurate  shell-excited  ,N  to  by  of  application  spectra  Equivalent  obtained  C  have  values  this  term  f r e q u e n t l y used  (WFM77)  term  examples  excitation  A  Rydberg  interpretations  a l .  excitation  4.2  of  valence-shell photoabsorption  frequent s h e l l  was  support  inner-shell  the  core  core t c  Recently using  t r a n s f e r a b i l i t y  of  o r b i t a l  approximated states of either  the from  calculations. early  X-ray  I t  has  bean  spectra  i n  the  including (WBW73,  Nakamura  WB74a,c,g),  9U  Gluskin  et  RSC76,  SCC77).  found  to  a l .  be  in  in  a  recent,  and  Xe  4d  The s h e l l  (1) of  Core  high  core  In  extra  the  i n  these  Geometry  S75,  energies  SB76,  were  experimental study  of  the  case  in  orbitals  as  well  corrections  geometric  Z+1  Ar  as  must  of  o r b i t a l ,  between  also values  2p,  Kr  3d  of  inner-  to  Rydberg  usually  be  the  of  the the  Schwarz carbon  I s . cr*) and  *  exchange  core  analogy  species  are  properties  of  in  the  a  of  usually  the  analogy  Buenker  spectrum  of  states  presence  large which  ionic  description  corrections  LiF  have C0  2  excitations.  negligible  for  radius  the  of  are  largely  core.  approach  of  (SB76)  (linear)  valence-shell  2  corrections  inaccurate  the  and  and  1s  N0  d e t a i l s of core  to  species.  (bent)  the  (due  species)  t r a n s i t i o n s because  unacceptably (Li  interactions  the  the  exchange  Recently  *  applied  excited  modeled  and  independent  i n  corrections,  Rydberg  Rydberg  and  with  ISEELS  however,  exchange  inner-shell  calculations  pure  be  valence  differences  successfully by  agreement  can  case  electron  geometry  With  (S74,  for:  an  and  a l .  (KTR77) .  to  this  et  predicted  resolution  analogy  excitation  Schwarz  analogy  excellent  differences  (2)  and  excitations  orbitals. made  (KGM76)  was of  (RSC76)  were  found the  to  (Li  even  applied  be  1s,a*) though  to  both  This notation for excited states i s used throughout this thesis. The underlined orbital refers to the l o c a t i o n of the hole while the o r b i t a l c o n t a i n i n g the e x c i t e d e l e c t r o n i s not underlined.  95  calculated residual core  and  experimental  d i s c r e p a n c i e s were  approximation  fractional  atoms  virtual  orbital  The  and  impossible  to  also  chapter  4.3  Ab  A core  Initio  AsCF  which  correlation  and  be  where the  The  of  the  the  large  inner-shell effects  inverted to  may  been  S74),  [ArH,  and  be  because  has  (WB74C,  of  ab  i n i t i o  have  some  of  However,  on  of  applied H 0  ClH ,  SH ,  2  reactivity  or  to  of  PH  3  ionization or  studies  {WB74g,  3  obtain  d i f f i c u l t  the  which  there  are  4  S75, J  Sc76),  (S75)  (see  effects  but  does  between  very  for  of  This not the  of  (e.g.  molecular BS72,  by  Koopman's  calculations  state  energies.  calculations difference  the  total  technique  treat  Sh73,  few  such  the  values  states.  Theorem  ignored  excited  evaluates  ground  energy  reported  factors  procedure  minimized  Koopmans  calculations  been  inner-shell  accepted  variationally  relaxation  B,  energies  which  directly  energies  for  method  and  can  excitation  species  S75)  treat  nature  excited  the  OF  number  binding  generally  breakdown  observable  C a l c u l a t i o n s beyond  approximation. this  has  energies.  5) .  large  CGS74)  ,  (WB74g,  2  a  between  approach  study  S74)  H F]  atcm  to  possibly  size  This .technique  (WBK73, 4  analogy  radical  i n s t a b i l i t y .  [NH ,  Z+1  i n f o r m a t i o n on of  and  core  the  state  attributed  L i , Be  i n  valence  energies.  core  potentials  CF  i n  change  excited  useful  BeF  any  ground  of and  i s  A the  between  energy  of  corrects the  of  changes  the for i n  core-excited  96  states.  One  d i f f i c u l t y  excited  state  calculation  lowest  state  must  introduced  be  hole  any  throughout  energy  a  the  there basis  agreement  symmetry.  rather  a single  center  a  flexible  differences  i n ground  should  performed.  be  workers the  0  using  (ASW75)  1s I S E E L S a  very  treatment in  what  type  ground in  set  s e t  large  state  the  basis  the  s e t ,  CH  H 0  accuracy  s e t and  However  the most  reported  DC76)  and  using  an e v a l u a t i o n o f t h e  than  double  inner-shell  energies  experimental  f o r the inner-shell  which  values.  and  t o w i t h i n 0.2  ab  zeta  a  i n i t i o  CI  that  2  1.4  when  f o r  N , eV  by  AO both  resulted larger  t h e AO  changed  MO  even  69-function  states of  However,  by  SCF-CI  found  uniformly  eV  co-workers,  quality)  was  co-  limited  and  t h e same  excited state  energies  of a l l features of  (BBP77),  excited  were  Agren  Butscher  using  1s  DK75,  terms  including  extensive  better  i s used.  regard,  (WB74b)  2  are  carbon  4  (BKL73,  the energies  of  core-  i s considerably  basis  this  calculations,  and  there  the  devices  concerning  the relaxation  basis  yet  (of b e t t e r  excitation  than  spectrum  i s probably  CI  when  and e x c i t e d s t a t e c o r r e l a t i o n  f o r a l l states.  extensive  Even  ( D K 7 3)  In  core  energy,  multicentre  calculated  calculation  basis  a  the  lowest  and e x p e r i m e n t a l  addition t o treating  sufficiently  maintain  these  the  measures  the  Thus  when  A r t i f i c i a l  t o determine  s e t used.  energies  to  also  guestions  calculated  i n any  collapse  and  but  than  excitation  In  to create  calculation other  be s u r m o u n t e d  symmetry.  are always  between  than  must  variational  given  s t a t e o f each  employed,  i s  not only  o f any s t a t e  excited  of  of  which  basis  using  a  97  smaller  scale  orbital,  the  (although et  factor  calculated  s t i l l  a l . (BBP77)  effective  although  rationalized  was  by  to treat  are  very  4  only  therefore  ignore  excitation  which  flexible  SCF-CT  H 0,  3  only  state  to describe.  Thus,  excitation  similar  such been  those  calculations  and N ) .  4  to  performed  on  Also,  2  excitation  geometry rise  inner-shell  inner-shell  SiH  vertical  possible can give  have  of the  ground  techniques  HF,  2  calculate  upon  excitation,  to date,  Butscher  i n terms  their  1s  agreement  eV).  charge which  nitrogen  i n better  ~0.7  to calculate  ( C H , NH ,  treatments  these  energies  changes  on  to vibrational  a  and  inner-shell  structure  (see  4.7).  Potential  This  Barrier  section  developed  inner-shell  redistributions complete  are  elimination  transitions  as  i n an  distributions  molecular  number  Effects  describes  ( N 7 0 , D72)  intensity  much  and  the  observation  core  valence-shell  molecules  4.4  this  analogy)  i n i t i o  complex  were  by  insufficiently  ab  used  section  i n  i t i s possible  energies  few  large  ( c f . t h e Z+1  s e t  shrink  energies  too  increase  excitation basis  to effectively  of  15 e V  attempt  of  which  Rydberg by  Model  of  the  to understand are  often  spectra.  characterized  localized  above  an e x t e n s i o n  excitation  accompanied  sharply  a n d t h e M.O.  and  the inner-shell  model  the  unusual  observed  These  i n  spectral  by a  reduction  or  near  threshold  continuum  a dramatic features  MO  enhancement which  c a n be  ionization  almost  of a  small  located  threshold  as as  98  well  as  i n  ionization  the  normal  limit.  These  spectra  of  molecules  BF  and  SiF  (F68)  3  of  a  central  ligands.  including which  those  of  not  have  do  From  the  i n t u i t i v e l y  excited  above  to  expected  to  to  understand  Calculations of  the  exchange  existence the  a of  the  by  even  and  2  a  CO,  number  which  were  not  of  two  would  but or  types  electron  i t  to  excited  was  This  normally  forces  led  largely  The  to  the  barrier  i n  (N70,  D72) .  the  origin  that  either  provided  the  implied  the  barrier -  be  virtual  continuum.  potential  states  electron  such  speculated  centrifugal  of  not  ligands  of  ionization  substantiate  was  force.  inner-shell  effects a  observed  promoted  ionization  invoked  seams  assignments  between  unusual  performed  to  the  the  features  i t  features  above  interactions  which  the  electronegative  repulsive  excited  from  these  model  (Coulomb)  of  N  structure  involves  surrounding direct  barrier  necessary  similar  spectra  as  transitions  states  strong  need  region  that  surrounded  this  excitation  the  of  consist  electronegative  such  localized  to  o r b i t a l s  and  development  of  the  LBK67)  which  excitation  attribute  IP  excited  Such  owing  i n  ZF67,  recognized  atcm  the  to  the  levels  the  of  However,  f o r the  originates.  been  central  intensity  states.  thresholds  number  diatomic molecules, a  (LD66,  the  atoms.  and  transitions  a  below  noticed  molecules  inner-shell  reasonable  below  by  region  f i r s t  SF^  i.e. i n  has  many  were  as  surrounded  i n  electronegative  both  (VZ71b),  4  atom  occur  effects such  Recently, i t  effects  discrete-state  those  localized  i n inside  which the  99  barrier  (inner-well  electron  was  excluded  (outer-well highly  be  highly  rules)  On  the  considered orbitals diffuse  by  basis  to  Rydberg  of  a  be  in  experimental This  chapter  the  10.  It  interpreting  the  s h e n  of  spectra Although  simple  model  chemically firm MO  of a  When  convincing  [cf.  MO  SF  model  F  is  in  present  well  barrier  a  large of  (chapter concept  appeal  in  obvious  basis  spectra  .  In found  with BF  SF  some tc the  (CFT72)].  3  in  the  presented  6  framework the  for C fre-  9) . on that  which i t  electronegativity, the  more  qualitative  were  of  are  the  i n t e n s i t i e s i n  Furthermore, any  states  (D72)  useful  spectral  barrier.  i l l u s t r a t e d  spectra a  states  minimum  (GGL72) ,  6  spectral  excitation  manner  to  valence-type  with  energies,  ISEELS  notions  basis.  of  agreement  chloromethanes  has  expected  these  coupled  are  molecular  typically  inner-shell  potential  intuitive  does.not  were  provided  trends  based  theoretical  model  has  the  the i s  and  be  v i r t u a l  are  states.  values  S  the  inner-well  of  quantitative  barrier,  of  r a d i i ,  v i r t u a l - o r b i t a l  term  potential  explanation in  number  reasonable  would  of  states  MO  state  in  limitations  occupation  concepts  ground  the  orbital  in  atoms  states  core  excitations  potential  barrier  cases,  inner-shell  excited  molecular  the  the  interpreted  the  presence  potential  be  of  the  outer-well  continuum  could  which  to  outer-well  large  in  transitions  or  schemes  region  specific  the  involve  whereas  the  (within  whereas  inhibited  those  inner-well  probable  selection be  to  and  Since  around  transitions  would  from  states).  localized  core,  states)  Coulomb  explanation  this  involves i t has  no  barrier, for  the  100  unusual  spectral  inner-shell (e.g. this  intensity  spectra  of  [ N , C 0 ] (WBW73)  and  2  thesis).  shell  Recently  excitation  discussed with  Coulcmb  experiment  reported  The  Shape  The  Resonance  1s—•7r^  transitions) ,  a  a very  broad (HBW73).  and  unusual  the  [f=0.19 simple  MO  Dehmer  and  Dill  calculations molecular about  the  atomic  low  on  individual  symmetry  of  10  at  eV  of  a  coincidence  (assigned  the  ionization  the  form  obvious been  a  rationalized  by  the  molecular  (MSM-X°*)  expresses  a  wave  partial  process  there  atomic  of of  i s a  centres  solution.  peak  within  treatment  solutions  that  maximum  discrete  multiple scattering  In  to  Rydberg s t r u c t u r e  first  have  of  nitrogen  the continuum  the  This  i t i s found  the f u l l  to provide  eV  weak  of  features  i n terms  around  401  immediately  basis  to  inner-  comparison  molecular  above  of  not  atoms.  waves  of  This i s  a  order  of  relatively  DD76a,b).  wavefunction  Jl-components  components  the  {DD75,  partial  molecular  a  These  with  8  11.  peak  intensity  picture.  f o r these  electron-ion  Explanations  are  i n  spectrum  intense  (KLW77a) ]  and  Model  maximum  potential  the  5  presented.  along  i n the  molecules  i n chapters  been  model,  K-shell  of  ir-bonded  section,  i n chapter  consists  and  has  interpreting  nitrogen  observed  a l t e r n a t e model  barrier  f o r  t  an  features  framework  4.5  many  the spectra  i n the following  the  distributions  the  expansion  matching  the  the correct ^coupling to  A more  high  of x-  physical  10 1  picture s h e l l  of  this  excitation  dipole  process  I s — • n p  followed p-wave  by  conversion  into  higher for  On  basis  the  (DD76a)  in  the  N  TTg  channel,  of  interpret  and  as  the  terminology  kinetic an  due  energy  atom  or  electron  a  is  electron  being  as  Very resonances,  temporary  detected Both  the  in  N  (and  2  and  N  temporarily  occupy  the  although  process  of  1s  the  at  the  The  an a  discrete  virtual  shape  to  i n  low  energy  inner-shell  way  process  excited of  or  'discrete'  the  i n  inner-shell electron,  in  these  inner-shell  shape  excitation have  co-workers are  the  state.  core-excited  and  =3  level  out  electron  orbital  X  i t s  on  incident King  the  when  the  the  in  describe  visualizes  of  eV  The  to  for  ionization  401  an  electron  i t s  and  cross-sections  analogy  trapped  as  used  direct  excited  eV  channel.  of  one  by  peak  resonance  418  u  of  energy  i f  TT *  occurs,  atom-centered,  scattering  trapping  CO),  f i r s t  molecule-centred  shape  &  excitation  of  a  at  simultaneous  trapping  which  discrete  negative-ion,  involving  incident  the  electron  direct  recently,  K-  Dehmer  commonly  fairly  following  the  calculations  the  more  i s  atom  the  maximum  (S73).  a  of  Xa  in  to  in  intermediate,  (d-wave)  temporarily  in  autoionization  and  close  imagining  process  nitrogen  S.=2  resonant  by  electron.  ionization  either  step  intense  i s  scattering and  system  an  molecule  excitation  given  the  low-energy to  a  MS  resonance  in  at  continuum  resonance structures  two  the  their  shape  are  of  a  ejected  (f-wave)  which  as  be  A-components  the  spectrum  2  can  transition  wavefunction  D i l l  approach  been  (KME77) .  thought  events. excitation  to  Thus, and  102  negative  i o n , core-excited  different  (and care  arising  from  resonance'), shell  According  the high  a  specific  angular  Coulomb of  high  i s when  t o Dehmer  and  D i l l  angular  outgoing  potential  angular  momentum  rapid  responsible  such  as  maxima from  t h e  barrier  (MC68,  f o r a number  delayed  to  the  penetration  of  region  of t h e Kr 3d a t o m i c  radial  distribution  ef  continuum  electron  FC68,  wavefunction,  energy  shape  at  of 6 Rydbergs  core.  I t  momentum  wave  barrier  that  known  atomic  where  they  4.1  the f  wavefunction  features continuum  Figure  the  into  The l a c k  the  calculated  along  and  (taken  centrifugal  waves  I t shows  (80 eV) .  i n  spectral  of  threshold  i n the  attractive  prominent  low-energy  high  t o penetration  D74, FTD76)  effects  the  resonances.  are well  continua.  o f t h e K r 3d  term  the  angular  and  orbital.  n*  wave i n  This  the molecular  of prominent  thresholds  i l l u s t r a t e s  with  centrifugal  effects  of  p a r t i a l  barrier  o f these  i n 3 d a n d 4d i o n i z a t i o n  MC68),  barrier  into  the  intensity  ionization  are  waves  inner-  attributable  energies.  coupled  potential  overcomes  t h e large  inner-shell  a  intensity  centrifugal  penetration o f a high  energy  Centrifugal  a t these  when  'shape  by, t h e v i r t u a l  i s directly  repulsive  which,  generates  i t s  explains  implies a  term  f o r both  of the dominant  channel  confusion  mechanism.  the  features  momentum  the  capture  are quite  avoid  probability  similar  term,  this  high  to of  t o a  momentum  molecular  uses  t o , and e l e c t r o n  resonance  formation  taken  attributed  shape  to  be  the r e l a t i v e l y  c a n be  excitation  should  conflicting  excitation  orbital  resonance  with  the  a  free  of an  ef/3d  f o r  103  overlap  at  energies  the  f  barrier  and  penetrate  orbital. be  threshold  These  unaffected  attributed spectra  the each do  exhibit  4.1  seen  region  centrifugal  barrier  formation.  been  observed  halides  the  At  centrifugal  of  the  effects  3d  the  Br  (chapter  core  appear  Spectral in  higher  features  3d a n d  7)  to  I  and  4d the  8).  molecular  channel  any  overcome  centrifugal  the  demonstrated.  the  methyl  of  to  into  have  molecular  excitation  not  Fig.  them  (chapter  anisotropy  clearly  molecular  the  halobenzenes  is  atomic  by  to  of  The  wave  is  (e.g.  potential  barrier field.  in  N , 2  barrier  has  It the  its  is Tr  u  R a d i a l w a v e f u n c t i o n s f o r t h e Kr £ f c o n t i n u u m w a v e s (£=0 a n d 6=6  specific  and  resonance  origins  cJ'g  to  channels  effects)  3d o r b i t a l Rydbergs).  in  .  and  It  the  104  has  been  postulated  centrifugal  SF  by (VKK74,  6  shape >  HS-Xa  H i 76)  resonance  containing necessary  ligands.  model  to  substantiate the  method.  that  calculations  Xa  resonance  continuum In  of  N  view  multiple  the in  I t  i t  was  this  sulphur  2p  demonstrated  also  applicable Further  shape  view  spectrum  of  that  the  to  species  picture  of  the  are  and  revealed A n  an  to  multiple  i t i s i n t e r e s t i n g to  valence-shell  i s  examples  resonance  have  to  general  note  analogous  photoionization  2  out  important  that  interest to  measurement  nitrogen  1s  ISEELS  (DD76a) Much  were  by  et  the  spectrum found  better  further  f i r s t  of  2  Dehmer  only  i n  to  be  results  (KLW77a)  and  (RL77)  who  has  employ  with been a  continua of  involved  intensities  agreement  experimental  and  absolute N .  be  experimentally  experiment  a l . (KLW77a)  the  calculations  investigate  The  of  resonanee - type  i n inner-shell i o n i z a t i o n  Kay  of  application  c a l c u l a t i o n s of  molecular systems.  Langhoff  for  associated  have  regard  (D76)  structure  carried  agreement.  this  method  of  careful  results  t o be  applicability  possible  i s  i s also  s u i t a b l e  the  the  the  scattering  resonance  type  i n  the  localized  .  2  of  phenomenon, done.  In  of  of  phenomenologica1  assumed  Support  types  the  a  ligands.  .general  scattering  shape  i s  electronegative  demonstrate  MS  which  for  by  barrier  calculatons  SPK74,  these  responsible  explained  potential  electronegative  given  are  previously  e l e c t r o s t a t i c  that  f  barriers  structures  with  (DD76a b)  and  of  this a the  D i l l ' s  semiquantitative the  achieved  quantitative by  Rescigno  Stieltjes-Tchebycheff  105  imaging  technique  electron  orbital  wavefunctions  edge  while  effective  continuum expected second and  reproduces an  MO a p p r o a c h ,  description molecules.  potential which  ionization model  unusual  i s  described 3cr  N  of  seem  these  u  due t o  i n  the  t o note  i n the I t i s  1lTg  the  3d a n d 4f A O ' s i n t h e u n i t e d  spectrum  i sa c l o s e  leads  i n section  correspondence  4.4,  can give  excitation  differences  t o differ  accurately  one t o s u s p e c t  interesting  resonance  structures  than t h e  composed o f  that  calculation  Taking  relatively  i s  i n molecules  MO-type  localized  of  valence  o u t (M74).  descriptions.  the  terms  other  orbital  u  pointed  there  both  below  a p p a r e n t l y doas not  orbitals  3c*  one-  peak  antibonding  u  which  2  of  ( 1 s ) — t r a n s i t i o n s  a n d MO  and shape  thresholds.  treats  1 t f  inner-shell  be  c l a r i f y  models  descriptions  o f  the  with  as outlined  barrier  these  an  K-shell  2  I t would  experimentally  the intense  phenomenon  resonance  of  strength  valence  and thus  that  t h eN  oscillator  I t i sinteresting  (RL77)  fact  LCAC-ttO  previously  correlate  t h e shape  The  i n  that  t o be a g e n e r a l  limit  betwen  been  orbitals  u  Hartree-Fock  The  bound  The fact  row atoms.  3&  atom  potential  has  c f  i n t h e continuum  any unoccupied  1 TTg o r b i t a l .  pseudospectrum  work,  structure  i s located  support  latter  transitions.  u  a  continuum  i s d e s c r i b e d i n terms  1c5g(1s)—»-3<5  weak  a  I n this  t h e continuum  orbital,  convert  energies  into  distribution. the  t o  between  substantially  structures a somewhat  above naive  as quasi-discrete  a  valid  f e a t u r e si n  and  models.  that  useful  t o  the  MO-  One a s p e c t i n i si n  their  inner-shell view, states  t h e MO which  106  presumably that  of  will in  have  their  the  core  influence  potential  ionized  subsequent  photons)  unstructured the  shape  may  regions  decay  i n  electron  caused  molecular  field  processes  by  and  when  (chapter  11)  i s  given  i n that  the  MO  and  was  shape  (ions,  DD76a) .  regions  Auger  electrons  the structured In  some  of  this the  i n this  might  decay  regions  simple  structure  electron-ion  commenced. chapter  A  along  resonance  be  species  was  coincidence  more  r e a l i s t i c  with  further  decay  expected  products  which  of the  model,  s t i l l  as  outgoing  i n  o f the continuum  picture  and  contrast,  the  the inner-shell ionized of  curve  differences  t h e continuum  Thus,  from  this  the electron-optical properties  unstructured  visualized  of  and thus  function'  d i s t r i b u t i o n  I t was  different  shape  between  treats  'escape  (FTD76,  identical.  will  and the be  i n i t i a l l y experiment  interpretation discussion  of  models.  EXAFS  Along structures  with  extending inner-shell known  the  i n the near  superimposed  well  model  c h a r a c t e r i s t i c of  structured  4.6  expected  the  the  events  products  i n the structured  therefore  The  of the continuum.  resonance  modulations  be  be  curve,  state.  t h e d i s t r i b u t i o n of decay  or  to  own  on  several  the  freguent  continuum, direct  hundred  excitation  eV  spectra.  i n the K-shell  occurrence weak  of  l o c a l i z e d  oscillatory  structure  ionization above This  continuum  threshold type  photoabsorption  of  and  can occur structure  spectra  of  i n i s  solids.  •>  107  Early of  theories  long-range,  However,  the  molecules  [e.g.  to  attempted  Dr  coherent wave  i s  developed  applied  to  specific  atom  to  in  of  of  geometry  K-shell  area  at  have  provide  sites. been  the  a b i l i t y  to  e a s i l y  heavy  elements.  X-ray  photoabsorption  observed  hard  relatively  reported of  Also,  in  an  region. X-ray  heavy  the  studies  The  and  i s  can  be  around  any  measurements  metal  scatter EXAFS  the  of  atoms  been  of  of  the in  i s  structure  section out  EXAFS K-shell  solid  this  electrons  targets  carried  of  usually in  i s  containing  d i f f i c u l t i e s in  i s  determinations  atom  to  I t  non-crystalline  BNS77) .  outlined  (Z>20)  structure)  investigations  majority  studies  elements  the  spectra  have  the  (SSH76,  of  This  under  which  or  from  density,  because  investigations  spectral  involve  sites of  atoms.  structure  application  active  the  ejected-electron  tool  local  due  from  investigations.  c r y s t a l l i n e  i t s electron  most  X-ray  the  Preliminary  already  proportional  EXAFS  of  gaseous  i t i s  arising  fine  unique  ionization continua  such  Since  few  a  .  correctly  attention  absorption  terms A63)  i n  that  surrounding  much  i n  {K31,  more  outgoing off  promising enzyme  i t i s  structural  molecular, One  present  for  effects  pattern  the  X-ray  examinations  environments.  the  thus,  received  (extended  expected  the  between  structure  indicates  interference  recently  EXAFS  and  backscattered  has  being  widely  an  that  phenomenon acronym  as  t h i s  i d e n t i c a l structure  clearly  interactions  scattering  and  of  (KE75)]  2  explain  d i f f r a c t i o n  observation  short-range  interpreted  crystal  to  with  soft  1.2, i n  the  very soft  observations continua  environments.  of A  108  number HS77)  of  L-shell  including  studies  studies  of  region  (RSG74a,  PK75) .  reasons  why  should  EXAFS  although  i t  surrounding of  the  energy  close loss  ISEELS  are  (chapter  spectra.  have  been  the  Al  reported  of  in  by  to  Stern  o s c i l l a t i o n  i n  surrounded  by  of  and  Si  in  are  no  obvious  in  soft  relatively  atomic  number.  and  AIO3  phase  studies this  on  a  series  Nj  atoms  a  (Sn74,  loss  i n  mechanism  spectra  of  However,  no  spectra  had  been  chloromethanes  of  an  co-ordination r a d i a l  for  LSS75) ,  continuum  cf at  electron  expected  EXAFS  the  because  thesis.  co-workers  inner-shell  and  (LC76).  ISEELS  spectra  whenever a l l  are  energy  theoretical  Also,  the  M66, X-ray  X-ray  weak  features  (e.g. soft  photoabsorption  electron Al  the  s i n g l e s c a t t e r i n g theory  and  the  by  characterized  the  be  reported  a t t r i b u t e d to  the 9  been  appear  similar  gas  to  A l  between  the  i n  chapter  According  low  solid  prior  described  derived  i n  of  EXAFS  reported  2)  to  Features  K-edge  examples  not  of  analogy  Na,  There  i s expected atoms  have  distance  molecules the  atom  EXAFS  which  i s  shells  (each  Rj ) ,  given  i s  by:  X(k)  =  <Uirk)-  1  £ N J  R j - 2 f j ( 7 r , k ) e x p [ - 2 k z <J*  • s i n [ 2 k R j -2  where is Rj,  the 8j  outgoing the  k)  fj(7r,  i s  root i s  mean  the and  outgoing  the  5j (k) J  (4.  b a c k s c a t t er i n g square  electron  given  amplitude  fluctuation  energy-dependent  backscattered  ]  waves  of  phase and  ( i n A* ) -1  k  the shift  i s the  by:  of  atom  j ,  j t h atom  <r j  about  between wave  6.1)  vector  the of  109  k  where (in  (E-IP)  eV) .  = [ 0 . 265 (E-IP)  i s the The  kinetic  behaviour  the  damping  due  i s  temperature  dependent).  and  R j ~  the  In  govern  2  the  to  while  most  simple  a  wave  pattern  the  terms  a l l  of  information simpler  derivable  treatment  spacings. maxima  This  and  k-space)  the  order  pattern,  the  numerous  phase  given  pair  another  shfts of  have  atoms  based  (CEK76).  reason  EXAFS  fj(7r,k),  Nj  only  one  i s  of  GeCl )  analyses  based  4.6.1  to  the  pattern  the  pattern,  obtain  on  4  maximize  e x p e r i m e n t a l EXAFS  EXAFS  the  reflects  excitation  eguation  i s  interatomic locations  which  a  are  of  given  (in  (4.  6.3)  of;  2kR  -  2 5(k)  interatomic <5(k) EXAFS  been and  there  Although  used  for  pattern.  K-shell  be  the  (for this  where  can  s h i f t , of  the  an  obtain  phase  studies  these  to  to  of  electron  term  remaining terms  from  solutions  outgoing  responsible  motion  occurs.  i n the  the  exponential  The  i n  (n + 1/2)7r =  In  the  f o r Ge  treatment  minima  by  i s  case  (eg.  on  term  intensity  shell  sine  of  vibrational  coordination single  energy  sinusoidal  oscillatory  (4.6.2)  ]i/2  must  be  patterns  found  thus  spacings from  to  be  of  a  known  from  From  structures,  characteristic  linear  EXAFS  evaluated.  transferr able  Further,  the  one  of  a  system  approximation  to  (4.  6.4)  6 (k) , i . e . :  6(k)  =  ak  +0  110  has of  been  found  maxima  and  to  ba  reasonable  minima  backscattering  off  radial  i s  distance  in a  group  a  plot  arbitrary  of  set  the of  Previous  analyses  generally  small  EXAFS  of  =  k  of  integers (LSS75,  compared  -  atoms  at  a  from  constant ;  (4.6.5)  a  and  arising  by:  maxima  CEK76) R  locations  2/3  has  to  the  pattern  given  2k(R-a)  values  Thus  identical  approximately  (n+1/2)7r  and  the  (LSS75) .  and  minima  slope have  no  of  an  "/[2(F-a)].  shown  example  versus  that of  a  a  i s  larger  o  than (in  0.5  A  cases  i s  where  interference the plot  known.  actual  chloromethane  EXAFS  EXAFS  i s  calculated  (LB77)  identical  to  derived patterns EXAFS,  It  with  ionized  i s  an  (HB78b, as  more  phase claimed  multiple  LB77).  electron  For  of  the has  This  a  they  from  more  i s  small  A  k  vs.  the been  tool  used  of n to  i n  the  the  are  to  kinetic  derive  sometimes  aire a s s u m e d systems  to  of  spacings  be  known  can  analysis  accurate must  to  of  be EXAFS  description be  taken  especially important close  0.5  observed  s h i f t s  similar  effects  pattern a  A  the  9).  phase  in  of  has  features  interatomic  0.02  scattering  (RSn76).  analysis  shifts  of  slope  analysis  freguently  identified  within  s t r u c t u r a l the  be  dominates  spacing the  of  a  can  wave  chapter  that  accuracy  (LSS75,  consideration correct  the  simple  spacings,  but  a  from  origin  used  interatomic  structure.  This  spectra  features  deriving  spacing  above.  the  EXAFS  backscattered  by  interatomic  demonstrate  unknown  single  pattern),  indicated  When  a  Thus  threshold energy.  of  into  for  the  where  the  The  f u l l  111  molecular states  wavefunction must  amplitude since  by  note  used  4.7  yet  transitions, accompany whenever core ground  with  state  state.  neglected,  (KE75,  and  reported data  thus  i n  atomic  level  the  chemical This  monochroraated  X-rays  changed and  the  MS-Xa  method  on  a  electronic expected  of  the  in  Auger  in  terms decay the  of  the  from  the  effect  of  lifetimes  observation  of of  of  (SNJ69).  lines  advent  core-  because  electrons XPS  the  vibrational  linewidths  of  of  molecular  i n s i g n i f i c a n t XPS  to  processes  level  recently,  widths  first  be  that  core  with  Transitions  may  from  of  on  can  Theoretical  vibrational  be  discussed  MS-Xa  features  ionization  u n t i l  the  same  molecular  and  determining  enviroment situation  of  different  in  the  too  interesting  the  Inner-Shell  to  is  in  available.  lowest  character  were  i s  excitation  the  It  usually  resonance  from  excitation cf  are  { D D 7 6 a , b) .  types  thought  differences  same  in  other  i s  was and  effects  i n t e n s i t i e s  approximation  suggest  shape  scattering  EXAFS  RSM78).  D i l l  However,  non-bonding  ST72).  are  Structure  geometry  excitation  Observed  frozen-orbital  vibrational  the  ionization  a  be  inner-shell  hole  i n  two  the  core-ionized the  reproduce  experimental  occurs  and  to  EXAFS  to  ground calculated  calculate  treat  Vibrational  As  the  to  have where  of  the to  effects  Dehmer  accurately  system  order  factor  that  results  used  calculated  a  technique also  in  relaxation  large to  (fj)  those  which  be  for  (FHP72,  XPS  using  partially  112  resolved CH  vibrational  (GSS74,  4  structure  G74)  could  reorganization creation  of  recently  cf  from  carbon  1s  (JS75,  upper  DC75,  levels  have  state  geometry  because  of  i s  expected  similar  to  analogy  transitions UPS  in  levels  antibonding  to  Until  resolve  adequate been  show  and  in  the  electron  excess  optical  vibrationally reported.  extended  for  of  long  structured  However  the  spectra  of to  no  the  The 'excited Thus  transitions  XPS  line.  [A  Rydberg  comparisons  the  quite  lowest  in  with lying  frequently  energy  have  transitions seme  cases  be  progressions.  was  i n  both  photo-  insufficient  transitions  below (see  detailed  inner-shell  structure  by  in  Even  the  extent.  available  resolution time,  on  i d e n t i f y  experiments  eV.  have  ionization)  the  might  structure  the  Several  Rydberg  lower  resolution  energy a  levels  vibrational  200  by  structure  radial  that  the  considered.  However,  impact  vibrational  induced  influence  used  ].  thus  vibrational  attainable  to  valence  and  be  excitation  excitation  recently,  absorption  energies  the  character  inner-shell  expected  to  and  also  of  DC77a).  core  inner-shell  valence-shell (R74)  to  large  frequently  bands  C1PI77,  l i t t l e  similar  i s  vibrational  Rydberg  in  be  electrons  GP77,  must  in  line  accompanying  vibrational  their  structure  that  changes  opposed  orbital  1s  (i.e. relaxation).  XPS  (as  carbon  recognized  hole  Rydberg  vibrational  the  geometry  pure  the  then  of  excitation  the  in  valence-shell  treatments  core  of  It-was  the  appeared  For nature  . arise  the  theoretical  structure  200  section  where  1.2)  analysis  transition  tentatively  eV  with  has cf  a  has  been  assigned  to  113  vibrational  excitation  excitation  of  excitation  of  The a  SiH SC  ( KG M76)  2  clear  transition  above  CO  studies  CH  (TKB76) .  structure ISEELS  4  was  also  spectrum  (EH76) of  of  Manchester,  the  observations including  in has  2  vibrational structure  in  the  been  and  In  the  1s  (0.2  the  eV  described latter  ISEELS of  0.1  important  spectrum  cr  the  better  consideration  (KRT77) .  (see  of  vibrational  structure  excitation  the  influence  the  the  core  much  hole.  longer  consider stationary should  is  be  When t h e than  the  a  l i f e t i m e of  possible  In  the  these  (instrumental  carbon  chapters  5,  and with  observation  excited  state  i t i s reasonable as  and  inner-shell  autoionization  those  infrequent)  resolution  7  12).  in  wavefunctions (probably  the  obtained  rapid  v i b r a t i o n a l period  vibrational  state.  of  of  relatively  work c a r b o n  the  interpretation  extensive Vibrational  using  chapter  for  resolution  species  been  (see  yield  number of  present  have  the  enabled  the  in this thesis  stages cf  in  has  eV), i n s e v e r a l  sectra  eV  FWHM)  of  state  0.25  time  high  in a  of  vibrational  synchrotron electron the  by  excitation  same  o b s e r v e d , even -  the  i n Manchester  resolved  (0.07  ( I s , TTg)  2  the  in  K-shell  More r e c e n t l y  4  N  and  obtained  about  resolved  also  spectra  An  2p  carbon  and  in  (KGM77) .  2  of  apparatus  the  K-shall  resolutions  S  Partially  C H .  moderate r e s o l u t i o n  nitrogen  the  2p  S75)  was  reported  well  progression  9) .  of  Si  of v i b r a t i o n a l s t r u c t u r e  a  structure  CS  eV  (HB77)  spectrum  and  200  observed  HB72,  observation  impact  and  been  (HBK71,  4  first  electron  has  of  of is to a  cases, i t  permitting)  to  11 a  observe  vibrational  treated when  with the  hole  period,  in  the  representing  no  state  of  with  autoionization  electron)  On  i s  be  accurately  the  much  other  shorter  vibrational  and  of the  can  analysis.  quantized  overlap  curve*  which  lifetime  excited  the  •potential exact,  Franck-Condon  core  vibrational exist  a  structure  only  the  a  ground  'core-excited wavepacket  in  the  than  level  smooth state  of  w i l l  envelope  (to  the  Franck-Condon  a  with  state'  the  hand,  the  be  more  outgoing  region  will  occur. The  most  situation spacings  complicated,  arises are  similar.  frequently  f o r  soft  region  X-ray  elements 0.2  eV  (KRK74) range  vibrational  situations  be et  the  on  states  the  decay  have  the  of  small  to  l i f e t i m e s of  1.1)  vibrational  those  while 0.3  observed,  of  a  of  width  stationary  in  of  suggested  that  separation  the row  0.05  to  frequencies s i t u a t i o n ,  the  vibrational and  thus  of  the  negative ion  a  Similar  analysis  negative  HBi71,  of  used.  internuclear  (H68,  in  this  short-lived, case  quite  second  state  be the  occur  range  but  s t r i c t l y  with  account  the  In  be  should  the  eV.  vibrational  molecules  in  to  internuclear  and  interesting,  linewidths  may  For  very  expected  K-shell  encountered  into  (KRT77)  dependent  not  (S73).  taken a l .  be  structure  resonances in  might  0.02  analysis  are  vibrational  This  Fig.  from  are  time-dependent  widths  to  structure  wavefunctions  decay  since  (see  alsc  the  core-excited  correspond  typically  changes  when  but  ion  resonances,  separation  must  DC77b) .  King  T  may  be  somewhat  in  the  case  of  less  inner-  115  s h e l l  excitation  s t i l l  be  terms  of:  (1)  and  reasonable.  the  dominant  They  a  time  involving  opposed  the  the  orbital  independent  rationalize  contribution  processes to  thus  this  to  r  occupied  containing  of  may  suggestion  i n  autoionization  valence  the  treatment  orbitals  (as  core-excited  electron)  occupied valence  orbitals,  and (2)  the  expectation  that,  the  properties  which  (e.g.  the  of  degree  functions  of  the  The  of  King  a  work  standard,  this  i s the  only  detailed  theoretical  recently  i n  papers  appeared  w i l l  not  rate  be  strong  on  N  2  successfully  employed  Franck-Condon  experimental study inner-shell  treatment  which  autoionization  geometry.  a l . (KRT77)  structure  photoabsorption, have  et  the  correlation)  molecular  a time-dependent  Several  govern  time-independent  vibrational for  for the  on  adopt  has  yet  yet  to  be  structure  KMG77).  the  of need  demonstrated.  time-independent  (GMN75, GMK77,  As  reported  excitation,  vibrational a  analysis.  i n  X-ray  approach,  116  CHAPTER CARBON  K-SHELL  EXCITATION  OF  5  C H , 2  C H ,  2  2  C H  4  2  AND  6  C H 6  6  "The human mind i s c a p a b l e of being excited without the application of gross and violent stimulants . . . and one being i s elevated above another i n proportion as he possesses this capability" Wordsworth  This loss  spectra As  C 5 H 5 .  of  chapter  in  compounds,  excitation  and  chromophore The  investigated  and  using  source.  obtained  electron  gaseous  radiation. placed  C H 4 ,  In  inside  monochromated  localized the  i s and  yield C2H6»  soft  nature  of  and  C 2 H 6  large  classes  studies  of  i s e s p e c i a l l y  of  for  i n  inner-shell developing  optical  of  C 2 H 4  loss  the and  a  C 5 H 5  phctons.  The  the and  the these  reported  (EH76)  K-edge  have region  synchrotron  gaseous  sample  bombarded  spectrum  weak  in  between  using  been CG67)  very  carbon  a l .  carbon  chamber  i s  spectra et  experiment  ionization  from  have  (CHM65,  spectra  agreement  Eberhardt  C 2 H 2 /  X-ray  these  energy  spectra  C6H6  continuum  l i t t l e the  and  C 2 H 2  presumably  Recently  an  f o r  This  potential  spectra  emission,  this  C 2 H 4 ,  2  spectroscopic  interests  structure  spectra  thesis.  2  prototypes  Bremstrahlung  There  this  in  a  by  C H ,  energy  interpretation.  absorption  Bremstrahlung in  the  of  the  great  absorption  complicated  X-ray  cf  K-shell electron  hydrocarbons  are  thus  type  X-ray  the  of  carbon  fundamental  are  light  the  simple  species  molecules  true  but  the  these  organic  these  of  reports  i s  i s with  recorded  117  (after  gas amplification)  arising  from  the  ionized/excited absorption have  reproduce the  formation  states  techniques.  equal  by c o l l e c t i o n o f c h a r g e d  decay  and/or  rather  Auger  than  I f a l l carbon p r o b a b i l i t i e s  the o p t i c a l absorption  K-edge  decay  processes  w i l l  of  by  spectrum at least  K-shell  conventional  K-shell this  p a r t i c l e s  hole  states  technique  should  except double  that the  above electron  yield. Qualitatively spectra the  K-edge  within are the  are quite  t h e  synchrotron  s i m i l a r  t o the energy  and t h e energy  spectra  below  structures  agree  uncertainties.  quantitative  differences  i n the r e l a t i v e i n t e n s i t i e sof  discrete  structures continua  and t h e shapes  are  are too large  differences  between  absorption  (171)  experiment  (impact  angle ~2x10~ losses  .  electron  momentum  not  that  i s approximately  s t r i c t l y  one  features  t o be v e r y  optical  absorption  probable  that  impact  can  close  to  t o those  spectra  (NSS69,  scattering  data  conditions  t h e o p t i c a l larger  the  VSZ74,  differences  present  a.u. f o r energy  t h e energy i n  photo-  the  average  (W74) a t e v e n expect  and SEY  and i n  0.7  These i n t r i n s i c  the experimental  s i m i l a r  the large work  keV;  Q  inner-shell spectra  indicate  impact  transfer  E =2.5  Although  t o t h e  limit,  values  loss  of  spectral  corresponding  MNI71).  between  a r e mainly  there  K-shell  different.  t o be a t t r i b u t e d  energy,  300 eV.  therefore  electron  The  However  of t h e carbon  completely  fast  radians)  2  around  previous  is  f o r most  (SEY)  measurement  differences  K  values  loss  yield  t h e mutual  ionization  are  electron  Thus i t  the  present  due t o  problems  118  associated detailed in  with  comparison  section  5.1  the electron  ethylene,  Energy  Loss  carbon  K-shell  benzene  and acetylene  2 8 0 eV t o 3 4 0 e V a t 0.6  0.4  eV  C H5  2  FWHM) s p e c t r u m i n  resolution  spectra  intense  resolution. as  carbon  term  with  (DS74,  suggested  PJ74)  o f the term  literature  values  calculated  using  shell  Rydberg  assignments features  i n  In  f o r term  (WB74)  t h e molecules  energy  loss  values  depend  core  I P ' s .  cases.  are also  shown  higher of  the  a t 0.21 e V as  - 5.4  noted  well  along  that  the  of the  Excitation  energies  corresponding  valence-  t o  listed  several  i s  ionization  5.1  support  energies  energy  s o f a rs t u d i e d ,  peak  XPS  be  given  The  shows  on the accuracy  from  a r e  (0.3 t o  K-edge  features  i n tables  I t should  region  i s given.  a spectrum  a r e listed  inner-shell have  including  5.1-  loss  the  5.3  using  transitions some  Figure  values  figures  (FWHM)  below  derived  i n t h e SEY s p e c t r a  Previous molecules  given  ethane,  resolution  o f the labelled  assignments.  magnitudes  higher  region  K-shell  values  potentials  resolution  inserts.  The e n e r g i e s  i n  o f  o f t h e energy  a somewhat  of ethylene  spectra  a r e shown  eV  cf the  the  loss  a spectrum  a n d C5II5  2  presented  most  molecule  energy  from 2  i s  A  Spectra  F o r each  C H /  of detection.  o f t h e EEL a n d t h e SEY s p e c t r a  5.5.  For  method  5.2.  Electron  The  yield  of  equivalent  f o r comparison.  loss  spectra  distinctive  the spectra  the  of  of  features.  those  with  I N T E N S I T Y ( a r b i t r a r y units) p  cn  o to  O  ro oo o  o  OJ  no  -s cr O 3  CD  O  as  l  cn  CD -s  o  to to to  •a n> o c+ -S C  fD  s > m  2=  CL la  a>  C5  OJ  r ?  0  PI  o  CD -<  _  O CO CO  ro co  OJ  o  ro coco  <  O  OJ OJ  o  OJ  o 6TT  ro—  ro ro  ro  CDCD  CDCD  a  if)  1.0C2H4  O  15 y  >  k-edge  C -SHELL k  0.5-  CO UJ  i  111 i i 1 2-456 7 8  ;z CH  T  280 Fig.  y  290 5.2  300 310 320 ENERGY LOSS (eV)  330  340  The carbon Is energy loss spectrum of ethylene (AE = 0.5 eV FWHM). O  121  F i g . 5.3  The carbon Is energy loss spectrum of ethylene ( A E = 0.35 eV (main) and 0.21 eV (insert) FWHM).  i.cH  CH 6  6  C -SHELL k  CO  c k-edge  >% \_  O  IT  15 0.5fi  >-  2 3  #  I  t co LU h-  i »  0280  i Vi  1  285  IN  4 T"  -1  r  290  i  1 2 456 7  290  1 300  ENERGY Fig. 5.4  1  1 310  1  \  320  LOSS(eV)  The carbon Is energy loss spectrum of benzene (AE = 0.6 eV (main) and 0.36 eV (insert) FWHM).  330  340  CO -+—  C2H2  1.0-  C -SHELL k  c  13 >^ v_  O  I  fc  lo  >t  'A  1 —  0.5  1  — i —  284  *v v v ^ ^ ^ - ^ ' ^ v ^ w , k-edge  I  1  I  2 1  — i —  3  n  288  — 1 — ' — r  292  •.V?ftr  Ii ill I It H&3456  CO UJ  I 7  a s m  4  (  I 8  : /  0  T  280  T  290  1  '  1  1  1—  300 310 320 ENERGY L O S S (eV)  T  330  1  340 h-  1  CO  Fig.  5.5  The carbon Is energy loss spectrum of acetylene (A E = 0.6 eV (main) and 0.4 eV (insert) FWHM).  124  TT-bonds which  are usually  has  been  dominated  associated  electron  to  the  containing  only  cr-bonds  edge  been  has  only,  orbitals  apparently  The  spectra  features.  The  a l l  have  the  K—•rr*  an  energies In  on  Eydberg  ordering members  However, to  a  number  nature  since  resolve  Rydberg  these  s p l i t t ings.  values  and  Rydberg valence  various has  which  these  acetylene  i s assigned  of peaks to  same  a t  Rydberg  higher states.  the s t r u c t u r e can  be  to  does  explained  are  assigned  and t h e expected  energy  3s  <  nd  t h e np  and  3d ~ 4 s  nd  This  of  the  performed  are  a  K-  due  to the  can  result  Rydberg  resolution  higher  non-spherical  o f symmetry (S71).  <  orbitals  Promotion  components, been  3p <  i n the  environment.  hole  spectra  Rydberg  components  the experimental  transitions  and  i n a lowering  of  and  i n these  of the K-shell  s p l i t t i n g  to  K-  transitions.  np  molecular  benzene  hand,  K-edge  orbitals:  of  show  series  the other  term  The  the  unoccupied  to transitions  the  Rydberg  below  chapter  peak,  weaker  transitions  electron results  further  a  on  typical  of the  localized a  and  Rydberg  ( R 7 4 , R75) .  symmetry  in  of  of  into  s h e l l  of  i n this  energy  correspond  i n terms  K-shell  observed.  lowest  spectrum  peak  molecules  transitions to  of ethylene,  as f a r below  the basis  s p l i t  spectra  which  The  transitions  a  In  structure  of  loss  of  TT* o r b i t a l .  i n terms  being  transition  extend  solely  no  energy  promotion  the discrete  reported  intense  t h e ethane  not  with  the f i r s t  with  unoccupied  explained  orbitals  by  i s not  orbitals. adequate  assignment ignoring  of these  125  Electric the  dipole  electron  conditions small  energy  of fast  atom  f o r the  because  combinations  t h e  molecular  these  o r b i t a l  w i l l  small (e.g.  t h epresence  U  be a l l o w e d . i n  t h e same  t h e (a-| , e g  between  than  t h eexpected  5.2  Comparison  The  most  synchrotron  u  line  with  occur  f a c i l i t a t e  the  synchrotron  electron  and 5.7.  them 2  a r e no  width  1  u  any  making  i na  unoccupied carbon  molecule a r e  there  should  be  s p l i t t i n g s ab  separation  (Mg69,  another  of a l l  1 s MO*s.  o f ~ 0 . 1 eV  carbon  one o r  F o r benzene,  ) C  symmetry  orbitals  energies  maximum  that  a r eseveral  due t o molecular  2  and b  g  confirms  there  virtually  o f C H ).  2  symmetry  one  theoretically  i n i t i o  o f 5 0 meV  This  i s less  KRK74).  t h eSEY S p e c t r a  significant  electron  spectra  , e  that  environment  predict a 1  of  T r a n s i t i o n s from  although  (BWP68)  loss) and  than  1s a t o m i c  to  dominate  energy  There  o f more means  t h e same  g  (~9 x  transitions  The binding  a n d 1o* l e v e l s  calculations between  molecules  t o  due t o t h e e x p e r i m e n t a l  allowed.  orbitals  differences 1C  expected  analysis  assigned  K-shell.  orbitals  essentially  5.6  An  o f t h ec a r b o n  molecular  K-shell  loss  angles.  i n a l l o f these  linear  of  spectra  a r ea l l e l e c t r i c - d i p o l e  restrictions  up  loss  a r e  incident electrons  scattering  considerations they  transitions  yield i n  between  (SEY) a n d t h e e l e c t r o n  t h e relative  comparison yield  differences  o f  energy  intensities.  To  t h eSEY and E E L s p e c t r a t h e  spectra  I n t h e SEY s p e c t r a  the  are reproduced  o f C2H2 ,  i n figures  C2H4 a n d C H 6  6  the  126  11  i  280  i  i  i  I  i  285  i  i  I LTJ^J  290  i  i  i  I i  295  i  i  i  I  300  PHOTON ENERGY (eV)  Fig.  5.6  The synchrotron electron y i e l d spectra of CH, and C H 9  127  ~i—i—i—i—i—i—i—i  r  i—i—i—i—|  i  i  i  r  C H ETHYLENE 2  CD •VI  4  C6 6 H  co  BENZENE  CO  t= 2  PHOTON ENERGY  Fig.  5.7  (eV)  The synchrotron electron y i e l d of C H , C H and C ^ . 2  4  6  6  °=»  spectra  128  ratio  of  the  K—•TT*  the  ratio  transition  in  relative  the  i s  K-edge  s h e l l  to  IP  the the  spectrum.  near  threshold  support the  the  K-edge  interaction The  i n  the  MK*  the is  the  and the  much  for  K-shell  larger  at off  ionization  SEY  the  low  spectra  at  above  l e a s t of  a  the  two  the  K-edge  are  extra,  by  unassigned Above  less  10  eV  larger  above  cross  EEL  to  to  Kthe  observed  spectra  section  i s due  the  compared  the  the  intensity  intensity  i n  same  spectrum  the  with  as  molecule  the  is  just  may above  post-collision  of  the  over  this  the  being  ionization region  the  energy  Auger be  how  K-shell  far  above  Since  the  i n i t i a l  distorting  for  the  the  with  the  decay  of  ionization the  K-edge  extent  the the  of  electron  kinetic  detected, chamber  other  from  region.  decay  detected  the  d i r e c t  related  r e s u l t  autoionizing  examined. on  be  finally  However  to  also  this  should  frcm  according  depends  may  from  K-edge,  being  particle  in  from  produced  varies  yield  state  electrons  below  K-edge  electrons  and  charged  the  HWT76).  MK+  the  than  285.2 eV.  relative  arises  amplification  vary  start  electrons  gas  w i l l  spectrum  that  the  photoelectron  efficiency  an  spectra  The  produced  electron  furthermore  i s  that  i t s energy  below  intensity  (EH76,  states  structure  SEY  t r a n s i t i o n s to  C2H5  the  relative  in  efficiency  For  lower  but  photoexcitation  i n i t i a l l y  •Rydberg  structure  the  same  the  suggestion  these  K  discrete  the  of  the  and  SEY  to  One  of  discrepancies fact,  the  spectra.  different  a l l of  r e l a t i v e  EEL  EEL  observed  of  i s considerably  intensities  radically peak  intensities  energy  of of  detection photoelectron  shape  of  the  129  continuum. for  Even  i f  the photoelectron  the  spectrum  signal  would  charge C75) .  differing  above  may  and  above  result  van  decay  yield  t h e  der K i e l  results  of the synchrotron  too  t o be  Below the  EEL  may  postulate yields  the  f o r  t o t a l  even  i f  entirely  by  contains  only  strength of  high  the  decay  of  a  single  small  fraction  region,  X-ray where  i s observed  emission t h e decay  {see section  unlikely  are available  any  no  f i n a l and  i n the seems  t h e SEY  the  the  spectra  could  states. could  state of  decayed states  o s c i l l a t o r  investigation  i n t h e high K-shell  could 2  energy excited  eliminate  a n d CO,  exceptional  A  s t i l l  these  total  of these  I n N  One  fluorescence  KHK74)  detailed  and  assumptions  states.  one  1.3.3),  possibility. (WNA73)  of  excited  A  ionized  spectra  and i o n i z e d  of  by  2  of the  rise  different  K-shell  N  below  between  (Mg69,  since  and  steep  excited  yield  and  effects.  K-excited  fluorescent  fluorescence a  the  WW71,  d i f f e r e n t  yield  inadequacy  of radically  various  resolution  seemingly spectra  electron  the  multiple  some  quantum)  the  f o r a l lthe transitions.  s a t e l l i t e states  to  the  a  the differences  the existence  negligible result  K-edge  be due  concerning  absorbed  e n t i r e l y due t o t h e s e  the  o f CO  excited  predict  twice  (CK66,  indicate  K-shell  Nevertheless  continuum large  studies  same  electron  Higher  cascade  (SW72)  would  (per i n i t i a l l y  K-edge..  vacancy  the  Auger  at least  t h e K-edge.  from  f o r  energy  i n that  coincidence  paths  These  electron  distorted  electron-ion  El-Sherbini  states.  be  e f f i c i e n c y was  f o r the high  detected  states The  as  would be  the detection  where  features  this such  i n the  130  fluorescence note  spectra  however  carbon been  that  differences  determination contamination carbon  a l .  (EH76)  of  the  incident  of  the  in  SEY  the  grating  contamination  Eberhardt  their  et  above  dominated  under  to total have  (EH76)  was  problems of  the  also  of  give the  the a  more  relative  factor  only  The  d i f i c u l t i e s  a  used  have  loss  accurate spectra  conditions  at  studies 10  - s  torr  particularly SEY  experiment  expected  dipcle-  spectra  obtained  loss  and  these  small  spectra  representation of  recent  the  energies  energy  with  monochromato r  i n  the  a  photon  more  been  the  energy  impact  of  be  differences  incident  maintained  of  may  the  the  by very  to  though  present  absorption  the  u l t r a - h i g h vacuum  because  large  mirrors i n  this  the  continuous  i n  i n  limitations  of  angles,  to  cause  must  conditions  to  due  with  and  Errors  monochromator  electron  intensities  the  to  absorption  even  of  considered  i n  molecules  due  structured  nature  scattering  35%  grating  encountered  the  a l .  and  a  occured  Since  flux  spectra.  and  operated  Because  outlined  under  This  contamination  severe.  of  also  and  t o r r ) .  - 9  to  d i f f i c u l t i e s  studied. spectra  sets  were  (BBB78).  (<10 of  two  stored  interesting  different  photon  contributing  between  study  i s  up  mention  cause  being  the  significant  continuum  of  monochrcmator which  regicn  intensities  of  yield  et  deposits  wavelength  It  (HTH72).  Eberhardt  was  observed.  K-shell fluorescent  reported  very  were  of  molecules.  are the  131  5.3  Details  Specific discussed. of  ethane  that  the  the  Rydberg  (see  electric  is  intense  most  spectrum and  of  i s of  spectrum  one  of  both  the  by  ethane  should  lead  the  series.  series of  the  Hp  those defect  On be  5p  (6 =0.8) p  the 3  of  rise,  the  U, are  from derived  3p  f i r s t  associated  Rydberg  from  the  term  energy  because  core  of the  levels than  the  np  spectrum on  the  transitions  energies  value  loss  reasonable  shoulders  formula  their  intense  i n  SEY  intense  and  more  with  the  i n  more  from  to  orbital,  In  The  structure  the  transition  less  member  as  methane  assigned  much  agree  and  i n  vibronic  Rydberg  the  being  than  i n  this  spectrum  Their  transitions  structure  be  observed  orbitals.  to  through  excitation  series  except  that,  transition. to  spectrum  methane  spectrum.  the  intense  and  EEL  methane  basis,  most  Rydberg  predicted  the  Rydberg  this  Features  continuum and  np  to  appear  character  the  should  ethane.  K-shell  to  the  be  photo-  peak,  i s relatively  K—*-3s  to  to  i n the  would  comparison  atomic-like  ns  the  fact  second  loss  i n ethane  f o r ethane  electron  peak  the  now  the  assigned  accessible  The  intensity  assigned to  by  w i l l  to  of  stronger  whereas,  this  comparable  spectrum  i s much  feature  energy  spectra  i s only  6)  spectra  similar  structure  explained  K-shell  ethane  i s  allowed.  of  electron  (WB74b)  loss  chapter  promotions the  EEL  be  dipole  individual  K-shell  orbital  a  the  orbital  may  Rydberg  coupling is  and  Assignments  5.1)  energy  This  3s  in  (figure  f i r s t  3s  Spectral  carbon  (C69)  methane. the  the  features  The  absorption  to  of  the  f o r  to  with  quantum peak  2.  132-  Table 5.1'.Absolute  Energies (eV), Term Values and Tentative  of Peaks Observed in the Carbon k-shell  Energy '10.leV  Peak  Term Value  3  Assignment*  Assignments  Spectrum of Ethane.  3  Estimated Energy  0  286.9  3.7  3s  287.0  286.8  2  287.9  2.7  3p  287.9  288.0  3  289.3  1.3  4s 3d 4p  288.9 289.1 289.3  289.7  0.9  5p  289.8  290.6  0  oo  K-edge  e  a.  Defined as the difference e x c i t a t i o n energy.  between the i o n i z a t i o n potential  b.  Only the f i n a l o r b i t a l i s  listed.  c.  e.  d  1  4  d.  SEY energy  289.6  and the  Estimated using the Rydberg formula En = A-R/(n-6) where En is the e x c i t a t i o n energy for the Rydberg level having quantum number n and " quantum defect 6, A is the carbon K-shell i o n i z a t i o n potential and R is the Rydberg constantThe quantum defects were derived from the valence shell spectrum(KS71, R74);6(ns) = 1.1; S(np) = 0.8 and 6 (nd) was assumed to be 0. EH76. From  XPS (PJ74).  133  Table  5.2:Abso1ute Energies (eV), Term Values and Tentative Assignments of Peaks Observed in the Carbon K-shell Spectrum of Ethylene.  Peak  Energy +0.1eV  Term Value  1  284.68  6.3  V  Assignment  a  Estimated' Energy  5  SEY energy C  lb  (TT*)  284.4  285.04  lb  (rr*)  284.8  1"  285.50 (?)  lb  (rr*)  V"  285.90 (?)  lb  (TT*)  2  287.4  3.2  3s  3  287.8  2.8  3p  4  288.3 (sh)  2.3  3d  288.4  5  289.3  1.4  4s  289.0  4p  289.3 289.9  6 K-edge  d  290.1  0.5  5p  290.6  0  oo  7  292.6  8  295.2  287.6  286.8 287.4  289.0  ]shakeup  a.  Only the f i n a l  orbital is  b.  Estimated using the Rydberg formula and quantum defects from the valence s h e l l spectrum of ethylene(Wi56): 6 (ns) = 1.09; 6 (nd) = 0.5. The values" for the 4p and 5p Rydberg o r b i t a l were calculated from the quantum defect of 0.8 derived from-the energy of the t h i r d peak.  c . . EH76. d.  From XPS (DS74).  listed.  134  Table 5.3: Absolute Energies (eV), Term Values and Tentative of  Peaks Observed in the Carbon K-shell spectrum of Benzene.  Energy ±0.1eV  Peak  Term Value  Assignment  Estimated Energy  3  *  1  285.2  5.1  2  287.2  3.1  3s  287.5  3  288.0  2.3  3p  288.2  4  288.6 (sh) 288.9  1.7 1.4  3d 4s 4p  288.7 289.0 289.2  0  00  K-edge  d  Assignments  290.3  5  290.4  (  6  291.3  )shakeup  7  293.5  b  SEY energy C  285.2 287.1  289.0  i  293.7  a.  Only the f i n a l o r b i t a l is shown.  b.  Estimated from the Rydberg formula and quantum defects from the valence shell spectrum of benzene — 6 (ns) = 0.77; 6 (np) = 0.47 and 6 (nd) = 0 . 1 2 (PW47, LSD68, JL69, K072).  c.  EH76.  d.  From XPS (DS74).  135  Table 5.4:Abso1ute Energies  (eV), Term Values and Tentative  of Peaks Observed in the Carbon K-shell Spectrum of  Energy +0.1eV  Term Value  1  285.9  5.2  2  288.1  3.0  3s  3  289.0  2.1  3p  4  290.0  1.1  4p  291.1  0  Peak  v  K-edge  d  5  291.4  6  292.4  7  295.6  8  300.6  Assignment  3  Assignments  Acetylene.  Estimated* Energy  5  SEY energy C  285.6 287.9 288.7 290.0  \shakeup & < shake o f f  J  295.6  1  a.  Only the f i n a l o r b i t a l is  b.  Estimated from theRydberg formula using the quantum defect derived from the valence shell spectrum of acetylene (P35)*- <5 (ns) = 0.95. The value for the 4p Rydberg o r b i t a l was calculated from the quantum defect of 0.45 derived from the energy of peak 3.  c.  EH76.  d.  From XPS (DS74).  shown.  136  Transitions in  this  t o 3d a n d 4 s Rydberg  energy  For  a r e  structures  intense  peak,  highest  the  energies  and  t o  c a n only  excited  so  the  K—MT*  c f 2 further  vibrational  c o r r e l a t e with  i n  this  a  K - s h e l l electron i n theantibonding  should  chiefly  result of  i n a twist  ethylene  shoulder  from  being  observed  peak),  associated asymmetric in  with  on t h ehigh  terras  Alternatively,  of this  also  o f  be  energy  could  be  and p o s s i b l y  I n t h e SEY  spectrum  structure with  (0.36eV that  This  to  FWHM  t h ef i r s t  a  i s  of  peak,  somewhat  may b e i n t e r p r e t e d  vibrational due  orbital  2  transition,  unresolved  be  P l a c i n g a non-  length  benzene  side.  should  t h e maximum.  observed  K—*-TT*  stretching  TT* 1 b g  shows  0.4 eV a b o v e  t can the  bond  geometry.  peak  spectrum  i  C-C  planar  ( F i g . 5.7) t h i s  In. t h e i n s e r t elastic  the  the energy  mode  nonding  affect  structure  C-H  transition.  above  a t higher  this  progression  such  In the  0 . 3 5 eV  peaks  t h esymmetric  t c s e e why  i s  experimental  peak  I f  f i r s t  5.3, where t h e  identical  i s a second  than  The  structure.  SEY  ofa l l  transition  i nfigure  o f ~ 0 . 4 eV.  a single  strongly  spectrum.  under  a suggestion  I t i sd i f f i c u l t  SEY  given  peak  spacings  theenergies  vibrational  spectrum  elastic  with  corresponds spacing  t c  i t shows  that  and  a r e 0.3 t o 0.4 e V h i g h e r  the  was 0.21 e V , t h e r e  maximum  expected  5 . 3 ) , t h e EEL  except  assigned  resolution  of  mode.  similar  i n that  conditions the  very  structures i n  interesting  FWHM  ( F i g . 5.2 a n d F i g .  i n t h e EEL spectrum  coresponding  a r ealso  region.  ethylene  spectra  orbitals  structure.  transitions  to  two  137  different. rr*  electronic  orbitals  (§2g' 2u)  ' 2u  e  the  in  A  K-shell  separation than  2  eV  Tr*  SEY  by  electric  of  the  at  to  sign  TT*  of  a  -  t  e  not  s  a  r  cf  i s  benzene  Another  the  that  an  EEL  spectrum.  to  the  3p  although assigned  to  8. shows  between weak  This  Rydberg  i t seems  upper  peak  additional  the  f i r s t  the  TT*  difference  larger  the  chapter  K—•  the  assigning  to  assigning in  from  i s  with  states  given  the  However  orbitals  agree  of  only  accessible  e  TT *  electronic  C5H5 i s  peak  t  antibonding  symmetry  virtual  orbital  i n  value  Ds^,  two  transitions.  favour  transitions  SEY  i s  and  an  EEL  It  may  present,  the  K-*-3p  be  peak  assignments  of  spectra values  and  spectra  extra  This  defects  two  observed  spectrum.  term  2  spectrum  the  s  are  peak  can  be  on  the  o r b i t a l  anomalously  transitions  the  to  weak the  3s  orbital.  The  four  b g  asymmetry.  i s  to  Rydberg  there  2  A  does  i n  b g  i t s term  compared  and  u  ' 2u  dipcle  which  spectra  to  of  2  There  Within  '^2g)  these  the  of  eV  assigned  e  SEY  EEL  288.0  basis  as  the  and  (-1u  d  argument  orbital  l i t t l e  n  (BWP60)  An  In  benzene. a  transitions peak.  states.  peak  peak  in  acetylene  at  288.1  i s assigned but  the  to  unresolved  SEY  the  higher  are  given  energy, i n  from  on  energies  differ  (peak  the  low  Further  5.1  2)  K—*-3s  Rydberg  tables  the  eV the  spectrum.  transition  derived  of  -  i n i n  the  energy  side  details  along  predicted  from  corresponding  EEL  transition.  of  transitions 5.4  that  of the  i n a l l  with  the  quantum  vale nee-shell  transitions. An  interesting  feature  of  these  spectra  i s  the  presence  1J8  of  structure  not  i n  peaks  above  I n t h e SEY  C 2 H 6 .  i n the continuum  prominent  observed  EEL  apparent  existent  i n solely  labelled  7 and 8  be  associated  a  that  electrons  K-edge  above  transitions  and  two  major  EEL  occur  than  6  (-300 eV) ,  has  been  spectra  this  w i l l  and  the  from  K—**-TT* suggests  shake-up o f  transition. i n structure  (see  above  e x c i t a t i o n  than  These shake-up  as onsets  be d e t e c t e d  section  (OFK75,  (Fig.  5.4).  L S M 78)  maximum  continuum  (~308 eV)  a r e marked There  of as  1.3.3).  and r e l a t i v e i n t e n s i t i e s spectrum  and  electron.  also  o f benzene  the broad  2  of a K-shell  spectra  results  non-  structures,  that  these  or  may  energies  They  weak  species,  i n t h e spectra  i n this  t h e broad 2  fact  i n XPS s p e c t r a  benzene  C H  and  (W74) . i t  These  resulting  appear  peaks.  observed  Alternatively, 6  structure  simultaneous  spectrum  some c o r r e l a t i o n w i t h  C H  the  loss  with  a t higher  The e n e r g i e s  of  i n  and v a l e n c e - s h e l l  should  s a t e l l i t e  spectrum  7)  o f t h e Tf-bonded  i n  or  K-shell  s a t e l l i t e s  peaks  most  molecules.  process  should  reported.  the  molecules  i n conjunction  transitions  been  as  (feature  t h e K-edge  a  t h e  are  energies  energy  intense  of  Only  there  The  ionization  energy  C 5 H 5  2  and  2  . electron.  shake-off  high  but  excitations  possible  rather  2  TT-bcnded  i s  ionization  C 5 H 5  simultaneous  i s t h e most  Another the  electron  i n the spectra  with  of C H  same  and  2  Similar  of-bonded  t h e structure  valence  spectra  , C H  4  structure  i n  valence-shell  transition  2  spectra.  i n previous  most  in C H  a t t h e  continuum  corresponding  i s  t h e K-edge  has  of the on  appears  the t o be  a t 3 0 0 eV. maxima  and t o a  observed  lesser  extent  i n i n  139  C2H4  (~300 e V ) , may b e a s s i g n e d  section  4.5)  guasibound between  o r , i n  1.1s,C*) the  C  •isoelectronic  carried  5.4  states.  N2  1  out f o r  Related  2  resonance  (see  transitions to  degree  o f  similarity  and t h e N I s spectrum  2  supports  and Dill  resonances  description,  of C H  (WBW73)  shape  b y Dehmer  MO  shape  The l a r g e  1s spectrum  Unfortunately, performed  the  as  this  interpretation.  calculations  (DD76a,b)  of  have  of  t h e type  n o t  y e t  been  hydrocarbons.  Experimental  Studies  of the  K-shell  Excited  Sta tes  Further K-edge  i n f o r m a t i o n cn t h es t a t e s a t e n e r g i e s  c a n be o b t a i n e d  radiative  decay  spectroscopy. occur  (which  decay  be  observable C R4  Unless  very  anomalous  suggested  between  intensely  t o  A high  decay  i n t h eX - r a y  has  been  published  were  reported  emission  peak  at  t h e  and  Auger  electron  fluorescence  t h e relative  and  high  energy  these  states  and Auger  yields  intensity  SEY s p e c t r a ) (K,1T*)  non-  only the  states  will  satellites should  spectra  be  o f C H2# 2  n o t i n C2H5.  X-ray  emission  IKNA73)  but  and t h ereproduction  n o to f s u f f i c i e n t a  o f  radiative  and  populated Thus,  t h e  resolution  by  t h e EEL  a n d C5H5 b u t p r o b a b l y  2  of  emission  observed.  corresponding  is  by X-ray  o f t h e most  l i k e l y  their  modes  may b e  discrepancies  by e x a m i n i n g  telow t h e  quality  no h i g h  of  energy  energy  o r deny of  benzene  s a t e l l i t e s  of thephotographic  t o confirm  expected  spectrum  plate  t h e presence  285. 2 e V .  High  140  resolution have  been  show 275  carbon  K-shell  reported  any  high  (SBM70) .  energy  energy  i s  9.3 e V  between  t h e (K,TT*)  Transitions  account  f o r t h e Auger  are  expected  5.5  from  the  states of  energy  shell  respect levels  lowest  energy  the  core  analogy  C H  2  2  H3CNH3  4  r  and  C H6 2  radicals  using  other  very  limited.  the  radical to  be  of  with  t h e  higher  molecule. a n d C6H6  energy  of  Auger  s t a t e may structures  of Radicals  with  formed  t h e  term  will  presented. respect  about  evidence C67) HCNH  excited spacings  value  equal core  species of  UCNH,  values  these  f o r  t h eI Po f  t h ep r e d i c t e d  of their  Information  has been  the  radicals  estimates  (DGV66,  K-shell  b y r e p l a c i n g t h e K-  The  5.5 g i v e s  radical  (see section  one r e f l e c t  The equivalent  a r e  Table  with  model  excited state  Experimental  unstable  ionized  Potentials  t h e Z+1 a t o m .  K-shell  techniques.  (JH67)  energy  Similar  core  t o t h elowest  along  pyridinyl  I P  o f C2II2 a n d C2H4.  theIonization  C5H5NH.  these  spectra  not  t o t h e d i f f e r e n c ei n  2 6 8 eV.  i n t h e molecule  the  The f i r s t  and t h e higher  t o t h eequivalent  e x c i t e d atom  C H ,  a t  does  a r e two peaks a t  o f C6H5.  similar  a n d C5H5  6  Analogy  positions  with  2  o f C2H5  an e x c i t e d s i n g l y  peak  o f  t h e Z +1  According 4.2)  to  i s state  i n t h eAuger  Predictions  o f C H  s t r u c t u r e butthere  which  peak.  spectra  The spectrum  eV a n d 2 6 8 e V i n t h e s p e c t r u m  benzene  2  Auger  H2CNH2, I P ' s of obtained  species  i s  f o r theexistence o f and  t h e  has been  t o i t s tautoraer  CH NH 2  2  calculated  H CN 2  (LC74).  141  Table 5.5•• Predicted Ionization Potentials of Core Equivalent Radicals (Energies in eV).  HCNH H CNH 2  5.2 .  6.05 ,  3  5.1  CH,NH  3 . 7  5  3  7.9  0 3  From extended Hu'ckel c a l c u l a t i o n s (LC74).  b.  From appearance potential measurements of the ChLNH the mass spectrum of CH NH (CF66). 6  3  Derived from enthalpies  of formation for CH NH 2  +  2  2  f  + ?  fragment in  L  2  (CH NH ) = &H (CH NH ) - A-H (CH NH ).  I.P.  1  -  a.  c.  a  6.03  b  6  2  C H NH 5  Other Estimates  Predicted I.P.  Species  2  2  f  2  2  2  CH NH2 where +  and  2  f(CH NH ) = 7.89 eV +  2  2  (JH67) and &H (CH NH ) = 1.86 eV (SF73) were obtained from ionf  2  2  molecule reactions of CH NH 3  of  C H5NH 2  2  respectively.  2  and appearance potential  measurements  142  Only  estimates  calculations data  of t h e I P ' so f (LC74)  (CF66, JH67,  There  i s  predicted  IP  HCCH the  of  2  2  data.  2  2  and  f o r  [from  there  HCNH.  the differences i n the stable  o r ,  more  extended  likely,  Huckel  extended  mass i n  between that  However, IP  (from  be found  agreement  H CNH  t h e calculated  reflect  H CNH  SF73) ] c o u l d  reasonable,  spectrometric with  and  HCNH  spectrcmetrie  t h e t h e  derived i s very This  Hu'ckel  literature. core  analogy  from poor  agreement  discrepancy  geometries  mass  may  o f HCNH a n d  i t may b e d u e t o t h e l i m i t a t i o n s o f  calculation.  143  CHAPTER ISOTOPE  EFFECTS  ON  THE  INTENSITIES  SPECTRUM  6.1  OF  IN  THE  K-SHELL  EXCITATION  of  has  METHANE  Introd uction  The  K-shell  investigated electron  been  a  by  loss  several  including detailed  excitation  both  energy  spectrum,  been  relatively  the  transition  Rydberg  peak  i s  transition  calculations Bagus  value,  et  a l . (BKL73)  transition  i s  therefore spectrum coupling  (C69) or  a  adaptation  Herzberg-Teller estimated  the  transition  and  strong of  absorption  edge  this  peak  has  recently  much  weaker  peak  at  of  and  a  values to  T=3.2  the  the  eV;  1a, ( 1 s ) — • 2 t  to  have  pointed  the  out  in  l  on that  the  5 =0.78). p  (1s)—•3a Ab  (3s)  1  i n i t i o  assignment.  that  the  K-rKJs  photoabsorption  et the  Rydberg  the  Pople's  Bagus  has  forbidden  quadrupole  and  lower  peak  ( 3p)  this  [the  dipole  occurrence  predicted  1a  support  electric  eV  defect,  s  DC76)  effect  2  eV,8 =0.95).  DK75,  the  intense  quantum  attributed  coupling,  have  this  288.0  term  Murrel  In  at  e l e c t r i c  isotope  techniques.  and  peak  observation implies  EH76)  intense  formally  i t s  (C69,  been  the  (T=3.2  (BKL73,  4  below  (TKB76) ] of  CH  occur  (C69,wB74b)  (terra  weaker  TKB76)  structure  basis  assigned  The  (WB74b,  vibrational  On  spectrum  photoabsorption  structures  investigated  energy.  an  6  of  either  vibronic  transition. treatment  Using (MP56)  a l . (BKL73)  intensity  of  oscillator  and  the  of have  K—^3s  strength  144  for in  the CH  lower  i f  4  this  energy  (3s)  transition  peak  in  CD  should  occurs  as  a  the  carbon  4  be  result  twice  of  that  vibronic  coupling. The energy the  H/D loss  isotope spectrum  intent  mechanism  of  for  theoretical usefulness molecular  6.2  isotopic  inner  due  features  in  the  composed  partly  and  partly  primary  of  typical  smaller  vibrational  out  band  of  the  are  a  the  back  background energy  the  discrete  determination  second  peak  (3 p)  of  The  background s h e l l  due  of  were  portion  and  4  of  CD  4  experimental  energy  surfaces  this  the  CH  spacings  valence  off  valence  lower  the  on  s h e l l  the  of  structure.  located  underlying  the  of  the  and  of  the  assignment  resolution  beam  region  of  the  identical  the  spectra  for  coupling  examine  of  lower  extrapolating  In  spectra  background  Corrections  to  with  spectra.  structureless  scattered  both  light  the  apparently  smooth  a  the  in  electron  vibronic  generally,  essentially  to  to  more  excitation  shows  The  tend  and,  studied  proposed in  K-shell  Results  under  i s  the  been  substitution  s h e l l  6.1  conditions.  have  transition  prediction  Figure  which  methane  K—^3s  Experimental  spectrum  of  on  investigating  the  of  obtained  effects  tc  the  CD  4  in  CD  4  discrete which  i s  continuum  unsuppressed  loss  electrons  the  analyser.  made the  by  smoothly  spectrum  into  features. of  was  the used  isotope to  ratio  the  intensity  normalize  the  intensity  145  1-OH  0-5CO  c K-edge O  v-  15 t_  >-  0  3s  3p  1-oH  if)  UJ  0-5H K-edae  o-  3s T  3p  m.  288  292  ENERGY LOSS(eV) F i g . 6.1  The carbon Is energy loss spectra of CH^ and CD (AE = 0.35 eV FWHM).  146  of  the  each  f i r s t  spectrum  since,  K-*-3p)  were  of  an  since  only  obtained.  e l e c t r i c  depends  only  essentially The  relative  This  at  to determine  peak  heights In  and  3p  truncating second  the  the  f i r s t  weighing.  i n each  The  This  One  required  for the  3p  f o r any  areas  that  The  second  used  peak  to  methods  were  measurement  measuring  of  the  peak  or  determination  before  and  then  the  peak  method  squares  to  f o r the  3s  peak  f o r the  TKB76).  This  resolution  after  by the by  overlaps  are  curve  eV  the  determined  of  286  account  (HB74b,  isotope  of  were  assumes  was  s p l i t t i n g  Three  namely  the minima  from  peaks.  peak  a r b i t r a r i l y defined  spectrum  gaussian  Jahn-Teller  the  by  were  least  of  which  spectrum  of  portion  -  .  4  complicated  methods  as  area  peak  consisted  (such  peak  at  method  CD  total  of  independent.  determination  account  method  the spectra  transition  employed.  different  the  wavefunctions  were  i n t e n s i t i e s ,  two  peak.  isotope  determinations  and  peaks  and  4  i n  procedure  approximation,  allowed  f o r CH  intensities  i s a reasonable  the electronic  the resolution  used  areas.  on  dipole  identical  intensity  overlapping  3s  (3s)  w i t h i n the Born-Oppenheimer  intensity  are  peak  peak  area  f i t t i n g  289  eV  while  to  were  due  procedure of  three  two  asymmetry  dependence  the  to  should the  peak  overlaps. A each for  number method  CH  4  and  the  r a t i o  The  results  of  separately  to  determine  CD . 4  of  The  these  a r e shown  run the  isotope averages i n table  spectra average  effect  3s/3p  has  f o r each 6.1.  were  of  been  evaluated intensity determined  the three  by ratio as  methods.  147  More  confidence  determinations that  t h e band  two  species  are  very  as  table  three  i s  since shapes  t h e peak  6.1  methods  on  height  and a l s o  to small  shows,  changes  the isotope  agrees  within  the  area assumes  transitions  because  i n  t h e peak  i n resolution.  effect  t h e  peak  determination  f o r corresponding  are identical  sensitive  placed  the  heights However,  determined  from a l l  reproducibility  of  the  measurements,. The the  isotope  error the  errors  associated  effect  resulting  various  from  intensity  between  t h e  indicates  that  Table  were  each  calculated  method  as  the  of  determining  most  probable  t h e u n c e r t a i n t y due t o t h e s c a t t e r ratio  results there  with  f o r  a r e no  measurements. the  three  The  agreement  different  significant  of  methods  systematic  errors  6 . 1 : I s o t o p e e f f e c t o n t h e i n t e n s i t y o f t h e K—*~3s t r a n s i t i o n i n methane. [Intensity ratio, R = (3s/3p)x100] Method peak  height  1  area (weight)  1  area (curve f i t )  R(CH )  10.7±0.7 (10) 2  6.86±0.7(10)  6.63±0.5(6)  R(CD )  8.1 + 0 . 3 ( 5 )  5.56±0.7(5)  5.54 + 0 . 2 ( 5 )  4  4  R ( C D )/R ( C H ) 0.79±0 .06 4  4  0 . 8 1 ± 0 . 10  0.84±0.C7  1)  The valu the and  l a r g e d i f f e r e n c e between peak height and area R es f o r a given molecule i s t o be e x p e c t e d owing t o d i f f e r e n c e s i n band shapes and w i d t h s f o r the 3s 3p p e a k s .  2)  The figure i n parenthesis indicates the independendently r u n , time-averaged spectra obtain that particular R-value.  number o f used t o  148  and  that  taken  background  into  f i n a l  account.  and  peak  overlaps  Averaging  the  three  6.3  values  adequately  leads  to  the  I  3  s  (CD )/I  I  3  s  (CH )/I  4  (CD )  3  4  4  3  0.8110.08  (CH )  p  4  Vibronic Coupling Interpretation  The effect  2.5  fact  has  methane  been  observed  that  a  found  indicates that  by  keV  electrons  (vibronic)  coupling  quadrupole This  suggests  t h e same  been  point  momentum  Bagus weaker  et  the isotope  (K =0.7 2  i n  au)  CD  experimentally  4  see  have effect  quadrupole  ratio  vibronic cf  isotope  effect.  here This  should i s  transitions a t  an have  values  of  experimental  2.4.2.  K-*-3s twice  dipole electric  to the present  with  than  of  an  spectra  section  i n  scattering  observed  the experimental  the  transition  process.  loss  isotope  e l e c t r i c  an  direction  observed  the source  to  opposite  rather  Herzberg-Teller  paragraphs  -  that  a l . (BKL73) in  electric  K-*-3s  alternative,  photoabsorption  corresponding  the  the  due  the other not  significant  i n e l a s t i c  mostly  i n e l e c t r o n energy  i s apparent i s  angle  would  since  transfer  conditions  effect  since  i n the  observed  It  i s  that  as  s t a t i s t i c a l l y  small  transition,  important  a  been  result:  =  be  have  isotope  to that  intensity  predicted  by  transition  being  20%  as  However  the  strong.  i s within  the  treatment.  the erroneous  expectations In  the  prediction  of  following by  Bagus  149  et  a l . (BKL73)  estimate  of  i s identified.  the isotope  Herzberg-Teller reasonable  coupling  agreement  with  Ilerzberg-Teller transition distances. Taylor's  series  moment i n t e r m s eguilibrium expression dipole  effect  mechanism  i s shown  the experimental arises  with  Within  addition,  intensity  coupling  moment  In  as t h e f i r s t  Q=Q  about  yields  0  approximation  a  symmetric  dipole-allowed  first  term  second  term,  involves  s  0  0  n  which  two  accounts  integrals.  simplify  the f i r s t of thefirst  dipole  .  n  a  .  n  a  .  and  symmetry  .  Q  to  forbidden  incorrect  To d i s c u s s  o f Murrel  and i s an  a  create  a  t r a n s i t i o n the reasons.  f o r the vibronic  from an i n v a l i d  (4.3.1)  coupling.  f o r symmetry  The  integral. part  and e v :  antisymmetric  respectively  vanishes  i n BKL73 a r o s e  following  0  Sn  indicate,,  the correct  electric  [R o( ) 1  nuclear  0  modes  predicted  summary  e v  t r a n s i t i o n through the v i b r o n i c  a formally  the  the  *-*=u  and  mode o f  transition  • < v,v | Q |v v >  0  s  vibrational  antisymmetric  For  a  a  t o the i n t e n s i t y o f a  e  subscripts  be i n  internuclear  the electronic  Rno(Q) = Rno(O) + E L {<^ n /dQ I M l e >(  where  a  approximation,  t r a n s i t i o n between t h e v i b r o n i c s t a t e s  a  on  to  in the  of t h e normal c o o r d i n a t e s  configuration  based  result.  t h e Born-Oppenheimer of  simple  from v a r i a t i o n s i n t h e  changes  expansion  a  coupling,  isotope  assumption this  and P o p l e ' s  The  error  effect used  to  a brief  treatment i s  required. The  first  i n t e g r a l i n the second  term i s e v a l u a r e d  by a  150  perturbation electronic  expansion  wavefunction  electronic  n  n  perturbation  a  •  0  i n  terms  m  m n  =  (  are  E  m -  E  n > -  l  <  6  m l  H  ' l  e  state  of a l l other  can  be  Hamiltonian  evaluated  expansion  given  (4.3.2)  m  i n  f i r s t  n >  order  as  (4.3.3)  H', i s g i v e n  t h eelectron-nuclear interaction  series  excited  by:  t h e perturbation  This  t h e  dA /dQa>L _ e  3  coefficients  theory  X  in  n  = |(de /aQ )}  a  expansion  and  (c^e /^Qa)  i n  states:  be /hQ The  o f t h e change  with  t h e  motion  second  term  of theelectron-nuclear  H' = -Q (d/dQa) £ a  z  <r/r  by t h e c h a n g e along  i na  Q. a  Taylor's  interaction:  j<r  icr  = £  Z^cX^/dCa) ( r  |  V  /r 3)Q | V  (4. 3.4)  a  icr  where  r  f  f  i s the position  displacement are  error can  t o  i n  BKL73.  be seen  At t h i s  t o involve of  normal  they  the  coordinate  a  isotope  stage sum,  (Dr  a  i s  the  further  manipulations  intensity  effects  a r es u f f i c i e n t  displacement [  cr a n d  o f nucleus  Although  determine  4.3.2-4.3.4,  derivative the  co-ordinate.  required  equations  vector  t o point  t h etransition over  £ (c-rcr/SQa) ] .  out the  moment  a l l nuclei,  coordinate I n  with BKL73  from  R  of  n 0  /  the  respect t o this  was  cr  then  incorrectly  motion the  o f  basis  the  simplified hydrogen  o f t h e much  by n e g l e c t i n g  c r deuterium  larger  2  value  thee f f e c t s  atoms  o ft h e  - presumably  f o r carbon  on  (which  151  becomes  a  Z  intensities). since,  when  effect  of  even  to  much  t h e  though  If  deuterium  larger  t h ee l e c t r o n i c  integral  related  t o  i sa l a r g e  motion  (with than  isotope  effect  i sc a n c e l l e d  carbon  i nZ, i s  mass-dependent  becomes will  carbon  atom  displacement  normal  term  be c o n t a i n e d  (4.3.1)  moment  i n a  of t h e  equivalent  a l lisotope  i n t h es e c o n d  v  < v  s ' s v  n  > 0  excitation  of  accompany  t h e  probability  transition  |v > a  o—•n  b e made  t h e  integral:  (4.3.5)  Sn  Franck-Condon  symmetric  factor  vibrational  excitation  vibrational  and  modes  | <1 „l <3aI ° a > I  2  a  o f a single mode  f o rthe  that  quantum makes  which -is  the  of the  the  o—•n  allowed.  estimate by using  and assuming  frequencies  a  t h ee x c i t a t i o n  dipole  A crude then  gives  2  totally  for  antisymmetric  l  n  0  t o  intensity  v  v  o  (q) ,  (Q) , t h e f i r s t  equation  and  i s expanded  coordinates  coordinates  mass-independent  n  l  due  t o thecentre o f  < V s I S a l a s > = <1a lg l Oa><v i s> where  The  and  disparity  respect  by t h e  motions.  hydrogen  t h e  transition nuclear  i nt h e second  effects  o r  atoms  spectral  i n t h esum a r e c o n s i d e r e d , t h e  hydrogen  there  f o r  vibration.  than  4.3.1  an incorrect  atom  mass-independent  rather  expression  o f t h ecarbon  o f t h ehydrogen  molecular  t h e  introduces  o f t h eterms  motions, t h e  i n  a l l o f t h et e r m s  cancellation  in  This  o f t h emotion  effects  mass)  term  2  that  occurs  c f t h eisotope harmonic no change  between  intensity  o s c i l l a t o r  wavefunctions  i ngeometry  ground  effect  and excited  or  can for  vibrational  states.  With  152  these  approximations  effect  can  frequencies  be  an estimate  made  since  solely  o f  from  the isotope ground  s t a t e  intensity vibrational  (WDC55):  <1aJ<3al°a >  ~  <1a lg l°a >  =  0  <1a lgal<>a > 0  0  and 0  a  0  M- 2<1a IQal0a > ,/  o  M-' V-^  0 4  where  M  i s t h e  frequency force M  constants  -i/2  i  s  a r e  (4.3.6)  /2  reduced  andt h e force  mass  relating  [v=  constant independent  proportional toV  o  t h e  (2TT)-  vibrational  ^ k / M' j .  of isotopic  Since  substitution,  and thus:  <1a lqal0 > o  V'  a  (4.3.7)  /2  Therefore l 3 s (D) _ i3s< ) " H  where  V  normal K—*-3s  a  i s t h eground mode  i n  both  R  state i n  V>a(P> Va  (4.3.8)  l H )  vibrational the  methane  3s< ) / 3s ( >  o f thet  vibronic  D  2  H  I  vibronic  this  coupling  4  frequency  of the  coupling.  For  treatment  7  predicts  the an  (4.3.9)  5  modes  3  agreement with  additional  ° -  [v (H)=3020  4  reasonable  =  vibrational  V (H) = 1306 c m - i , V (D)=996  An  2  effect o f :  I  for  ^ ~  2  involved  transition  isotope  I B3«; (D) I l 3s(°) I  which c r  cm-» (H45)].  1  ,  of  rise  t o  V (D)=2258 cm-*; 3  This  t h e experimental  mechanism  cangive  estimate  i s i n  ratio.  vibrational-electronic  153  interaction is  exists  associated  with  approximation.  (OS72). the  I t i s treated  e l e c t r o n i c wavefunction  term  of the f u l l  this  mechanism  is  similar  molecular i s called  symmetric  mode  vibronic  coupling.  On  intensity for with  the  Teller  and  same  i s  coupling the  momentum  K—*-3s  considerably  seems  unlikely.  transition  dipole  dominated  Herzberg-Teller  kinetic  except  i n  the  should  used  L  momentum  electron  larger  /V [Cll )  4  a  ]  3  nuclear  i n  loss  =  0.42  t h e Herzberg-  isotope  this,  observed  coupling.  4  intensity momentum  i t can be concluded  energy  and  be c o n s i d e r a b l y  the experimental  Therefore  momentum  isotope  to estimate  than  there  the  ( lV ( CD ) a  I t i s  o f t h e non-  nuclear  c a n be d i s t i n g u i s h e d by  smaller  reason  that  nuclear  on  energy  this  t o t h e energy  basis,  i n methane  vibronic  operating  (For  coupling  coupling  Since  by  momentum c o u p l i n g ) .  active  this  coupling  Born-Oppenheimer  the nuclear  nuclear  assumptions  coupling).  effect  since  the  Hamiltonian.  this  coupling  effect  nuclear  with  proportional  totally  Herzberg-Teller  of  of vibronic  mathematically  to Herzberg-Teller  an a d d i t i o n a l term  type  breakdown  the  very  This  that  photoabsorption  spectra  i s due t o  154  CHAPTER THE  This  chapter  excitation  only  energy  below  performed  by  o f  LaVilla  spectrum  the  of  any  had been  <UB78a)  was  Recently,  reported  taken  into  found  t o  When  this  t h e  CH I. 3  i n this  work  was  Bremstrahlung obtained  photoabsorption  a t 0.4 eV r e s o l u t i o n h a s  thedifferent  agreement  and  absorption  t h ephotoabsorption  be i n good  ISEELS  halides  t h esynchrotron  1s r e g i o n  (BBB78).  account,  1s  t h e 3  t h e methyl  o f F  inner-shell  CH Br  C 1 ,  before  (L73).  i n t h eC  3  a l l  with  reported  i n t h e region  been  C H  of  C H 3 F  3  of  observable  published  o f CH F  study  3  that  and  HALIDES  7 0 0 eV i n C H F ,  spectrum  region  spectrum  reports  structures  spectrometer The  METHYL  7  with  resolutions are  spectra  o f CH F  a r e  energy  loss  3  the present  spectra. The 2840  photoabsorption  eV,  corresponding  reported  and  assigned  interpretation in  C H  the  C 1  3  given  C l 1s  7.4.3) . useful  spectrum  of  i n this  (HG76)  related  photoabsorption  1 2  and  C H 2  6  (chapter A  energy  excitation, t h e  inner-shell  has  been  less  been  of  the  (see  which  halide  o f t h e  regions  assignment  proposed  spectra  has  excitation  results  spectra  2815 and  basis  an a l t e r n a t e  of the methyl  synchrotron  t h e  On  experimental  i n t h eanalysis  (CNS73)  C l 1s  chapter,  between  3  (HG76) .  t h e other  spectrum  Other  t o  of CH Cl  I 4d  of CH  4  se c t i o n  have  spectra  of  been  a r e the  region  of  (WB74b) a n d  5) .  d e t a i l e d study  o f c o r r e l a t i o n s between  Rydberg  state  155  energies  and  (valence)  shell  halides  has  latter  work  aid  in  from  the  the  been  presented  suggested  use have  ionization  photoabsorption  assignment  the  features  f i r s t  of  the  of  spectra  Hochmann  et  correlation  the  the  been  by  potential i n  carbon  largely  methyl  (HTW75) .  procedure  This  used  as  spectra.  technique on  outer  the  a l .  K-shell  correlation  assigned  of  the  the  an  Aside  the  observed  basis  of  term  values.  7.1  Long  Range  Figure excitation A  7.1 of  similar  carbon  in  these  above in  spectra  400  the  eV  scans  function spectra  no of  except  relative only  the  very  be  studied  i s  of  not  CII F  made  to  the  include signal  largely cross  due  to  section.  been  made  those  small ratio  in  are  changes occur  spectrum.  the  long for  only  the  energy  losses  7.1  analyser the  be  i s  made  off for  energy  transmission i n  a l l of  the  7.2,  the  and  quite  accurate input  transmission small  weak  f a l l  range  the  in  the  eV.  energy  claim  to  over  350  this  rapid  However,  figures  thus  since  i n  expected  and  constant  lens.  the  and  higher  No  c o r r e c t i o n has input  shown  inner-shell  becomes extremely  the  analyser  the 50  occurs  3  over  for  each  CH F  of  between  3  intensities  essentially in  CH I  3  loss  intensities  deceleration will  was  impact  relative  as  of  Features  spectra  and  3  since  energy  electron  accurate  survey  excitation  attempt  Continuum  CH Br  3  spectrum  No  and  shows  CH C1,  K-shell  region.  Scans  energy  as lens  function regions  156  C l 2p  Cl 2 s C1s  i  in  1  r  300  200  x16  I 4d C 1s I4p  \  14s  K/  X 6 4  100  i  |  i  200  ENERGY Fig.  7.1  i  i  |  i  300  LOSS(eV)  Long range scans of CH^Cl, CH^Br and CHgl between 50 and 350 eV.  r  157  Aside loss  from  i l l u s t r a t i n g  technigues  regions  t o  study  the ability  several  simultaneously, figure  inner-shell  7.1  shows  hydrogenic  character  o f t h e Br 3d and I  which  a delayed  onset  have  above  the  effects  ionization  i n terms  wavefunction  of a  i n  channels  of  centrifugal  the  has been  barrier  of CH I  where  to  f-wave  continuum  the  given  continuum  i s  resonance  -  i . e . ,as  a  discrete  state  (FC68).  Very  in  Ud  the  atoms  CH I  (~85  3  eV)  However,  spectrum i s mostly  similar (CNS73)  i s an  of due  i n t h e energy  loss  photoabsorption  gaseous  shifts  loss than  i s  a  t o  factor  i n CH I 3  i n the of  a  observed  spectra  (FC68,  of  AGL69,  phenomenon. spectrum  i n the  solid  I  2  impact  t h e maxima  spectrum  the position  spectrum.  or  barrier  terms  atomic  to the electron  by  i n the I 4d  semi-stationary  table  i n the energy  of the resonance  agreement with  i n  structure  lower  effect  t h e maximum  essentially  the intensities  The  a n d i n t h e Ud  eV  momentum  of the  to a  i n the periodic  which  t h e maximum  better  2  2)  of  that  described  i s approximately 8  this  Correction puts  to iodine  (see chapter  features  such  transition  o f t h e maximum  absorption  factor  of I  This behaviour  position  and l o c a t i o n  these  continuum  angular  prominent  of  well  of  the  (MC68, FC68) .  accurately  spectrum  adjacent  HKS69). The  more  i s  maximum  to  higher  non-  both  explanation  barrier  i s most  the size  excitation  the extremely  peak-like  dominant,  energy  Ud c o n t i n u a ,  An  centrifugal  spectrum  3  a  threshold.  the  outgoing  and  of electron  (energy  a t ~ 9 5 eV  o f t h e maximum  photo-  (CNS73) .  kinematic  of very  lower  of  broad  energies. l o s s ) i n  -  3  ,  much  i n the I  2  158  It  is  absence  also  interesting  (within  scatter  of  the  the  data  points)  excitation  of  Br  Us  electrons  in  CH I.  Discrete  structure  10  eV  below  section  for  Excitation absorption  3s  The  SMB76) would  be  marked  the  excitation  energy  is  in  positions  of  expected if  weak  or  to  these not  spectra  the  by  associated  CH Br  or  3  IP's  on  I  in  the with  tp  for  the  occur  any  7.1  indicated  the  indicated  of  figure  structure  electrons  edges  loss  in  accuracy  any  are  the  structure or  of  3p o r 3  (BB67,  note  statistical  the  subshells  to  or  these  figure. the  region  appreciable  cross  subshells  existed.  observed  in  of  corresponding  the  the  photo-  CH I 3  I  t o  'c  M  "SHELL  "4,5  Z3 >^  o Maedge  lo >-  "1 |M edge s  CO LU  620  Fig.  7.2  700  660  E N E R G Y L O S S (eV)  The energy loss excitation region.  spectrum  of  CH I 3  in  the  I  3d  159  subshells  i n  Calculations cross 3d  f o r Kr  sections  and  Ud  between  and  positions  edges  were  Within  the  and  Xe  eV  the  from  i s observed  below  continuum  shows  maxima  ionization  thresholds.  comparable  to  11.6  eV  onsets  (BW76). (FC68)  observed 7 . 1) . has  spectrum  15  below  4d  reported of CH I 3  above t h e 3d  analogous  and  (D68) shown  i n  maxima  Br  and  the ionization ionization  3d  to  similar  7.2.  spectrum  with  thresholds.  thresholds  absorption BW76). discrete  the a  The  relative separation  splitting  of  with  delayed  delayed  onsets  regions  ( F i g .  i n the 3d  region  to the iodine  Two  delayed  maxima  or  3d  onsets  peaking  Discrete  i s weak  3  thresholds.  have  Xe  )  no  excitation  i s very  CH I  (HMS72,  the  of  of  excitation.  5 / 2  associated  spectrum  i n figure  t h e Xe  5  (XPS)  are presumably  are  M (3d  above  spin-orbit  photoabsorption  observed eV  and  3d  the ionization  These  3d  They  i n the I The  been  are  the  I  obtained,  eV  the  (KM72) .  measurements  ~21  than  spectrum  of and  2  accuracy  structure  smaller  loss  M (3d3/ )  HKS69) .  photoionization  species  region  XPS  s t a t i s t i c a l  that  energy  4  A G L 6 9,  a r e much  i n t h e same  i n the  two  (CNS73,  indicate  of the iodine taken  Xe  subshells  shows 700  and  2  sections  7.2  600  I  f o r these  cross  Figure  The  Kr,  about  structure  nonexistent.  160  7.2  Carbon  K-shell  Figure the  carbon  were  K-edge  lens  presented are  and  into  exception be  in  the  each  shown The  i n figure  taken to  0.15  between  CH 3r from  ±0.1  (T70,  3  a  in  may  features.  For  considered  to  a  weaker  eV  due  data  IP's  the  two  (T70,  The  HB78a.  The  small  C  1s  IP  CH I 3  are  the taken  s l i g h t l y  v e r t i c a l  scale  amount  of  continua  of  loss  region  negligible  slope.  CH Cl 3  and i s  An thought  are  the  F,  3  reported of  taking  i s  7.1  energy  have  PJ74)  HB78a  during  ionization  there  values  shift  thus  f o r CH  i n 7.3  which  3  and  the  [although  CH I  i n table  the  those  resolution.  indicates  to  spectra  than  shown  i n figure  energy  backgrounds  K-shell  XPS  i n  7.3  over  these  PJ74) ].  graph  As  i s mainly  carbon  accurate eV  in figure  7.3  from  spectra  reported  shells.  indicated  are  those  of  below  monochromator  resolved  spectra  reported  These  the  spectral  undetected  resolution  which  energy  an  to  shown  spectrum  energies  spectrum  background lower  t o  from  those  observed  halides.  better  different  due  higher  different  with  earlier  The  methyl  general the  the  error  structure  modification  In  the  i s  discrete  somewhat  agreement  recording. from  the  are  account  the  in a l l four  i n HB78a.  i n good  for  shows  obtained after  exit  to  7.3  Excitation  are a  and  CH Br 3  stated  to  difference  f o r the was  C  be of  1s I P  of  interpolated  AJA73.  be  expected,  a l l except consist  second  band  cf  the  spectra  methyl  fluoride  four  which  regions -  i s s p l i t  a  into  share the  similar  spectra  broad two  many  f i r s t  peaks  or  may  be  band, shows  CH F  CH Br  3  3  (CO)  'i  i  I I  i i  i  111  1  4  6  7 8  2  5  05-  9  T  r CH CI  1 I" I I I  I  H  2 3  7  K  4  r  5 6  1  -1  1  r  10-  3  CH3I  \  \ i I  \ \  /  \  A. .  1/  1 286  05H  II  I I I II  2 3  4  5  6  r 288  290  7  I  '•',V.'  ^  ||  1  8  —I 292  r  1  284  2 3  1  286  1  I I I II I 4 5 6 7 8 9  1—  288  —1  1  290  ENERGY LOSS (eV)  7.3  Structure below the carbon Is IP in the methyl halides  (A E = 0.25  eV FWHM).  r292  162  signs  of  a high energy  which  has  weaker  intensity  the  two  high energy  spectrum  band.  shoulder,  just  spectra  (see f i g u r e  energy  shoulder  7.4  labelled  in  i n the CH F 3  CO  which  Since  a l l  was  other  intensities (WBW73) no be  less other  For each  than  spectrum  5%  Rydberg  orbital  excited,  are based  throughout A  Robin  the  of (R72,  3  by  1s—*--jr*  to  CO  C  for  various the  high  that  this  peak  transitions  CH F  sample.  3  1s s p e c t r u m  the  at  287.3  have  eV  peak  spectrum  are expected  statistical  accuracy  of the  to on  the  structures  T a b l e 7.1 with  tc  spectrum  which  carbon  the expected  regularities  and  term  values.  i n d i c a t i n g the unoccupied  halides  intermolecular R74)  observed  applied  in  g i v e s t h e e n e r g i e s of  their  K-shell  observed  in  The  valence  electrons  Rydberg term  values the  or are (R75)  spectra  series.  a i d t o the assignment  valence-shell CH I  sharp  second  CO  along  the m e t h y l  useful  method  that  a r e numbered.  as  suggest  [The  the  of d i s c u s s i o n  assignments,  well  the  impurity i n the  of  the  7.3].  structures  suggested  and  i s due  f e a t u r e s of the  purposes  these  the  spectrum  observable with the  shown i n f i g u r e  as  peak.  of  r e g i o n of  d i s c u s s i o n ) and  first  .features  to l a c k  7.3  band  inspection,  between  2 in figure  p r e s e n t as an  first  appears  ensuing  third  a fourth  On  correlation and  band o v e r l a p s t h e b r o a d 287. 3 eV  fluoride  the  intense  s h o u l d e r s , and  b e f o r e the I P .  of methyl  However, b o t h  the  of  these  spectra  i s the  correlations  developed  t o the  transitions in  Rydberg  photoabsorption spectra  Hochmann e t a l . (HTW75).  of  CU C1, 3  This procedure,  by  CH Br 3  which  Table 7.1: A b s o l u t e e n e r g i e s ( e V ) , Term v a l u e s , C o r r e l a t i o n Slopes and T e n t a t i v e Assignments f o r the Features observed 1n the Carbon Is energy l o s s s p e c t r a o f the Methyl H a l i d e s .  TR3TEnergy +0.08  1  288.94  2  289.55  TR3TT Energy +0.08  (eV) 4.65 4.05  d  TR3T  TR3W T  Corr.D  (eV)  **  Energy +0.08  (eV)  **  Energy +0.08  t (eV)  +0.01  Assignment  1  287.29  5.00  1  286.48  5.30  1  285 62  5.70  0.65  2  288.36  3.95  2  288.09  3.70  2  287 65  3.65  1.45  3  288.65  3.65  3  288.39  3.40  e nsa 1  3  287 96  3.35  1.45  nsaj + V  1  4  290.34  3.25  4  289.39  2.90  4  289.16  2.65  4  288 68  2.60  1.33  npe  5  290.75  2.85  5  289.81  2.50  5  289.50  2.30  5  288 96  2.35  1.33  npe + U j  6  289 25  2.05  6  291.33  2.25  6  290.21  2.10  6  289.79  2.00  7  289 68  1.60  1.20  7  291.98  1.60  8  292.28  1.30  7  290.97  1.35  7  290.62  1.20  8  290 04  1.25  1.05  9  292.68  0.90  8  291.41  0.90  9  290 42  0.90  1.00  IP?  293.6  IP  292.3  IP  291 3  -  npe + 2Vj npa •4s  -  IP  291.8  -  294.9  (n+l)p, ( n - l ) d  -  293 4  303.5  297.3  295.5  double  295.6  exci tation  313.0 (a)  T = IP - E . n  (b) From f i g u r e 7.4.  This s l o p e 1s analogous t o A  n a  o f HTW75.  ( c ) Only the f i n a l o r b i t a l  i s listed.  (d) From a l e a s t - s q u a r e s f i t o f two l o r e n t z l a n Hneshapes t o the 288 - 290 eV r e g i o n o f the CH F spectrum. 3  (e)  0  n • 3 f o r CH^F, n = 4 f o r CH^Cl, n = 5 f o r CH^Br and n = 6 f o r CH^I. See the comments on Rydberg nomenclature i n the f o o t n o t e .  ( f ) Except f o r CHjF where 3d i s the lowest p o s s i b l e d-type Rydberg (g) From XPS (T70, PJ74).  orbital.  f  164  relates  the  series  of  the  group  and  (2)  ranks  term  molecules, of  that  the  a  molecules  this  of  i s  molecules  independent In  values  being  within  as  in  the  the  figure  features versus  in  the  the  linear  7.4,  C  C 1s  correlation  each  spectrum  correlation In  a  i s  dependent  of  ranking  assumes to  of  each  the  observed.  The  7.4  o r b i t a l  are  picture,  the  and  o r b i t a l energies.  may  since  be  the  extents  large  of  the  negligible excited  expected  inner  electron  shifts  of  indicates energy shell  of  and  the that a  orbital.  between  a  the  transition  of  the  for  the  as  of  table  of  in  of  the  s h i f t s the  of  s h i f t s  excitation spatial  result hole  i n  and  the  approximation the  chemical to  energy.  A  shift  originates  in  in  the  slope  the slope the  i n i t i a l means  of  o r b i t a l  different  orbitals  A  7.1.  frozen  r e l a t i v e  unit  peaks  inner-shell  chemical  a  molecule.  inner-shell  measure  plotted  (AIP/AE) i n  and  various  are  the  A  this  K-shell  Eguivalently,  used  related  sum  s h e l l  Within  energies  carbon a l l of  valid  outer  are  orbital  by  separation  (S74).  slopes  unoccupied  be  energy  interaction  correlation the  to  of  study.  the  chemical  are  model  given  of  listed  energies final  which  role  i s  of  slopes  excitation i n i t i a l  IP  molecule  energies  frozen  exists the  energies  between  figure  that  related  correlative  the  potential  in  (1)  a  parameter.  excitation  spectrum  the  HTW75,  -  i n  suitably  parameter  and  respect  transitions  assumptions  ionization  i s  lines  two  examined  study  the  1s  on  group  with  molecule-dependent In  based  molecule  variable  case,  corresponding  the  shift  of  chenical of  unity  excitation carbon that  Kthe  Fig. 7.4  Correlations between the carbon Is excitation ionization potentials in the methyl halides.  energies and  166  binding  energy  transition same  expected average  the  rest  large  the the  differ  i n the  two  with  groups  qualitatively of  penetrating to  5.7  transitions than  the  upper the  to  term  transition  this  symmetric  upper  shape  transition geometry  halides  to  from  a  of  the  orbital  charge. orbitals be  For with  a  expected  as  most  state  state.  into  molecule  being  term  are  lowest  likely  energy  the  large  the  highly (4.6  somewhat  The  by  a  corresponds  which a  or  that  values  molecular  peak  correlation  candidate  orbital.  with  f a l l  indicates  peak  i s supported f i r s t  the  The  the  they  f o r the  diagram,  orbital  f i r s t  <r*(C-X)  the  sees  i n each  unoccupied  orbital  where  essentially  halides  type  However this  the  i s  from  may  rest.  valence  The  ground  methyl  transition  lowest  the  distant  correlation  f i r s t  dissociative  the  the  the  expected  -  slope  the  behaviour  i s  f o r  from  B75).  i s the  or  i s  o r b i t a l  positive  transition  that  valence  (R74,  methyl of  a  i n  i s a  of  unity.  orbital.  values  o r b i t a l  nature  for the  suggest  electron  orbitals  from  f i r s t  involved  Rydberg  unit  spectra of  Rydberg  eV)  a  This  electron  the  orbital  transition)  molecules.  thus as  f i n a l  the  character the  different  orbital  the  for  Rydberg  slopes  the  0.65  cf  Rydberg  the  transitions  slope  and  valence  on  value  the  s i grif icantly  Based  upper  of  molecule  of  i n  non-penetrating  penetrating amount  term  centre  the  electron  series  position  of  highly  an  for a  molecular  the  to  (i.e.,  throughout  that the  of  to  larger Rydberg for  orbital  the of  antibonding broad indicates change  and a i n  167  Figure CH F  C  3  1s  strongly  spectrum  electronic by  7.4  this  peak  function peak and  does  12.2),  this  have  This  a  energy  the  shoulder  lorentzians  t a i l  shoulder was  t o t h e 288  this  shoulder  to the  the (Js,cr*)  strongly states  of  leading  that  v a l ence/Ry dberg the case,  a  character  there  i s no  large  to  be  f i t  to  Schwarz  straightforward  interact o f t h e two  (SM78)  state  However,  of  explanation  reason,  two e l e c t r o n i c  have  tentatively  assigned  i n this  region"  as s u g g e s t e d  calculations help  and  to determine The  ( r r e , a*)  higher  the correct  excitation  A state  -  resolution  CH F 3  Accurate  spectra  may  assignment.  t r a n s i t i o n t o t h e a* spectrum  i s also  that  states  the  the c o r r e l a t i o n diagram.  (possibly)  corresponding  valence-shell the  by  mixed  f o rt h e  For this  of  has  i f  shoulder.  spectrum  of  two a j -  observed been  two  overlap  these  of mixing  of  spectrum.  an  expected  region.  of  assignment  implies  one e l e c t r o n i c  ,in this  7.3  The energy  suggests  assignment  the  figures  3  and  of  by  o f t h e CH F  repulsion.  i s only  2.  squares  l a r g e > amount  mutual  there  7.4)  this  would  3  side  response  sufficiently  least  state  With  CH F t c  and possibly  suggested  is  state.  states  a  energy  (compare  one  supported  as i n d i c a t e d  as f e a t u r e  (figure  (Js,3s)  i s further  i n CO  i n the  than  the instrumental  seem  from  peak  more  t h e high  - 2 9 0 eV r e g i o n  c o r r e l a t i o n diagram  symmetry  not  obtained  t o  t a i l ,  peak  marked  The  with  eV  does  due  on  Although  high  the f i r s t  suggestion  7.3).  f o r t h e 287.3 this  that  actually  of a shoulder  (figure  shape  produce  i s  t r a n s i t i o n .  the observation  suggests  -  from  observed  orbital  the ground  as a  broad  i n the  state  peak.  to The  168  energy  f o r  correlation the  methyl  this  valence-shell  with  the f i r s t  halide  correlation  slope  ( A I P / A E = 0 . 6 5) . for  CH F  to  the  state  correlation shoulder  energy  shifts.  peaks  the term  have  values  t h e Rydberg  term  reasonable  orbital  C  3  7.4)  indicate  thus  slopes  8  w i l l  2  lines  between  f o r the term  than  one  Rydberg  series.  have  be  an  regarding  since  the of the  t o t h e cr* a n d  2  t o examine  guantum  to 8  although  the  unity.  This  The  lower valence  to  chenical  the assignment the  defects  of  magnitude  as  derived  4.1.7).  i n the spectra 3.7  present  appreciable  susceptible  (eguation 3  the  for features  approach  associated  and  supported  energy.  which  often  although  i s  by  transitions  i t i s useful  formula  values  i n  state  transition  spectrum  t h e same  information  and  number  value  have  A  and t h e o b s e r v a t i o n  that  the  spectrum  the  suggestion  1s  1s  the  approximation)  CH F  (figure  This  to  i d e n t i f i e d  i t underlies  eV.  series  through  Features  10  expected  For further 2  that  that  a  throughout  similar  the carbon  t o note  are a l l greater  (R74) a n d  features  i n  i s  experimentally  approximately  of Rydberg  character  1  exhibits  potential  slope  of the correlation  t h e behaviour  from  2)  1s s p e c t r a  members  of  have  slopes  the C  at  the  diagram  orbitals  higher  of  (feature  The  is  peak  been  frozen  interpretation  in  f o r  never  (7re,3s)  (within  3s  whose  (R74) h a s s u g g e s t e d  the  ionization  I t i s interesting  has  3  Robin  series  transition  and  value  4.0  of eV.  of t h e lowest  figure This  7.3 i s  Rydberg  a  169  o r b i t a l  (n =  and  6  n  =  3  for CH F,  f o r CH I)*. 2  and  progression  i n a  in  the  for  3 as  peaks  2  than  the  slope  of  This  may  reflect  C-H  upper  i s to  the  peaks  supporting two  valence  assigned to  may  The C  are  a  ns  1s—*-3s  i s  nature  line larger  transition. of  the  indicate  the  of  presented  correlation  Possible  either  3  vibrational  Rydberg  also  CH Br  assignment  of  the  f o r  i s considerably  for a  orbital.  orbitals.  of  penetrating i t  5  transition  which  expected  -  the  members  slope  i s 1.45,  highly  n  3  The  although a  f o r CH C1,  electronic  valence-type orbital  antibonding  because  3  unity  o r b i t a l  transition an  and  4  f i r s t  section.  both  Rydberg  the  single  following  =  Evidence  3  features  n  3  lowest  that  the  candidates f o r aj o r  assignment transitions  e  i s are  symmetry preferred observed  * Different choices exist for the nomenclature of molecular Rydberg o r b i t a l s . The n values used i n this chapter treat the Rydberg orbitals as e x t e n s i o n s of the halogen atomic orbitals. This i s the traditional nomenclature used i n discussions of the methyl halide valence-shell spectra. One c o u l d e q u a l l y w e l l c o n s i d e r the Rydberg o r b i t a l s as e x t e n s i o n s of the carbon atomic orbitals i n w h i c h c a s e n w o u l d be 3 f o r t h e l o w e s t s , p a n d c R y d b e r g orbitals. C o r r e l a t i o n w i t h the u n i t e d atom ( A r , F e , Ru and Sm) Rydberg o r b i t a l s would r e s u l t i n a d i f f e r e n t set cf n values. The most a c c u r a t e and s y s t e m a t i c n o m e n c l a t u r e would be a s e q u e n t i a l n u m b e r i n g on an e n e r g y b a s i s o f a l l o r b i t a l s with the same i r r e d u c i b l e r e p r e s e n t a t i o n i n the m o l e c u l a r point group. However t h i s would require calculations to determine the energy ordering of valence and Rydberg orbitals. Hochmann et a l . (HTW75) have suggested a s i m p l i f i e d nomenclature where m o l e c u l a r Rydberg o r b i t a l s are sequentially numbered starting with n=1 for the lowest member o f e a c h s e r i e s . This nomenclature emphasizes the fact that the effectve guantum number ( n * = n - 5^) f o r c o r r e s p o n d i n g R y d b e r g t r a n s i t i o n s i s e s s e n t i a l l y t h e same i n a r e l a t e d s e r i e s of m o l e c u l e s such as the methyl halides. Although this seems t h e most s e n s i b l e n o m e n c l a t u r e i t has not been u s e d i n t h i s work b e c a u s e of the possibility of confusion with the atomic nomenclature used f o r the inner orbitals.  170  in  both  5), C  CH  the 1s—*-3p  (peaks  C2H5.  and  4  intensity  and  transition  i s  2  and  3)  methyl  halide  3s/3p  intensity  greater from  than  the  5,  4  which  ns  as  peaks  a  4  feature  though  in  5  6  and  (1.9  to  i s  to  the  between 5)  and  methyl  chapter dominant  the  second  regions  to  note  of  the  that  the  halides  i s  evidently  might  be  expected  as  between  the  the  eV)  to  for  (7  i n  (see  (1.20)  suggests  consistent p  the  with  Rydberg  the  a,  component  assignment  of  the  the  np  of  the  that  for  assignment than  of  as  peak  I t s  that  o r b i t a l of  lowest  between 5.  and  are  correlation  rather  separation 4  a  5  and  from  structure  between  4  the  has  i s  following  assignment  3  transition  energy  the  of  the  Feature  energy,  peaks  CH I)  slope  Ihat  lowest  to  as  eV.  higher  component  6  that  3.1  values  vibrational  i s  the  eV  term  values  the  and  structure  separate  similar  assigned  n  2.6  ~0.4  different  cases  to  of  (1.33) .  of  2.3  4  6)  at  Feature  a  most is  the  symmetry  (with  as  transitions 6  e  5  continuation  that  (peaks  (chapter  values  s l i g h t l y  and 6  in  basis  the  o r b i t a l  with  relative  i s interesting  vibrational  transition).  line  I t  shoulder  the  to  Rydberg  term a  On  assigned  third  to  (HI377,  spectrum  symmetry.  i s  section).  and  methane  has  interpreted  l a t t e r  similar  ratio  in  the  separation  spectra.  lower  Peak  In  4  a  even  features term  value  expected  and  of  thus  lowest  p  for  feature Rydberg  t r a n s i t i o n. Further tentative  due  intensities  to  that  the  large  occur  i n  spectra  amount the  of  higher  peak  becomes overlap  Rydberg  much and  series  more weaker  members.  171  Use  of  guantum  assignments CH I  transitions. are  also  the  very  weak  especially  methyl  in  the  carbon  table  7.1.  weak  K-shell These  Rydberg  levels  the  i n  -  excitation  (W74,  chapter  observed  are  to  relatively  electron  (see  K-  molecules  where  structure continua  carbon  contrast  observed  structures  Vibrational Structure  7.3.1  Isotope  In structure spectra  order in  spectra figure  Studies  to  methyl  CH Br 3  and  conditions of  CH33r  7.5.  immediately  significant  of  in  and  The  the  Methyl  substantiate  the  of  operating  is  of  been  Rydberg  other  multiple  have  in  4p  in  i s  many  (8  figure  in  the  7.1)  are  probably  due  to  electron excitations.  7.3  in  attributed to  energies  This  np  region.  i s observed  systems  and 7  with  nd  energy  of  ns  feature  and  molecules.  ir-bonding  the  associated  this  spectra  from that  (n+1)s  i n  shake-off),  halide  l i s t e d  to  structure  these  with  and  l i k e l y  occur  K-shell ones  (shake-up  two  of  structures,  The  most  to  carbon  5).  i s  derived suggests  Transitions  continua  large  2 - 6  expected  Only s h e l l  peaks  CH3F)  and  3  of  defects  C  3  (0.25 CD Br 3  eV  the  assignment spectra,  were  FWHM).  between  284  differences  in  However the  and of  of  vibrational carbon  under  The  there  spacings  of the  recorded  essential similarity  apparent.  Spectra  Bromide  halide CD Br  1s  identical  energy 292  eV  the  two  are  Is  loss  are  shown spectra  small  features  2  and  but 3  172  CH Br 3  •s. • - . . .  c  2  i  L  2 3  4 5 6  >CO  CDoBr  ./  ) I I V:  1  23  ENERGY  7.5  |  292  288  284  Fig.  4 5 6  • • •  L O S S (eV)  The carbon Is energy loss spectra of CH Br and CDgBr 3  (AE = 0.25 eV FWHM).  173  i  r  rH  j j—i—j—i—j— —|—i—|—f r  |—i—i—i—i—|—i—i—i—i—p 288  Fig'.  7.6  289  290  Least squares simulation of the C Is energy loss spectra of CH Br and CD Br in the region of features 2 to 6. 3  3  17a  and  also  figure along the  between  7.6  which  with  the  spectra.  widths and  of  3  width  along  and  presents  computed  the  the  peak  to  4  and  5  forced  or  were f o r  expected  as  f o r a  pairs  measured  by  separations, computed along  a  results  The  widths  addition,  the  the  assignment  4-6  of  6  i n  7.6  cf  the  i n CD Br 3  drawn  given  widths  of  with  the  2,3  significance  test.  The  measured  20%  and  uncertainty.  embodied  the  pattern i s  spectra  i n  i n the  peak  from  the  table  7.2  a  the  methyl  from  the  isotopic  4-5  terms  of  section. i s the  This  supports  3  as  a  4 and  halide  the  separate  5.  From  spectra,  studies  In same  continuation of  i n peaks  among  and  CH Br  bromide  than  2-3  i n  i n the preceding  progression  peaks  peaks  interpretation  vibrational  this  ratios.  ca.  methyl  2  allowed  these  listed  s h i f t  rather  conclusions  the  s t a t i s t i c a l  are  transition  relationship  the  of  while  This  of  intensities  electronic  close  widths  the  peaks  were  6 of  7.6,  Similarly,  chi-sguared  separation  peak  origin  2 to  the value  heights  egual  lower  given  experimental of  while  freeing  decrease  structure  i n figure represent  simulate  isotope  strongly supports  vibrational  by  and  the derived  to  seen i n  'deconvolution'  unrestrained.  to  i n figure  observed  spacings  have  normalized  f i t shown  with  within  gave  used  easily  features  the residuals.  were  or  cf  squares  equal  vibrational  shapes  more  views  p o s i t i o n s and  Attempts  peak  be  to 6  are  f i t shown  peaks  minimize  peak  widths.  4,5  least  restrained to  i n order  lorentzian  a  gaussian  vary  equal  expanded  For  to  that  These  of  with  parameters  5.  results  t h e two  were  4  on  the the the  methyl  175  Table  7.2: P e a k  Separations,  Shifts  derived  Features  Widths,  from  Intensities  and I s o t o p e  theleast-squares  2-6 i n t h e CHLBr  analysis  a n d CD B r C i s s p e c t r a .  CH^Br Energy  a  CD^Br  FWHM (eV)  (eV)  of  I  b  Energy  FWHM  (eV)  (eV)  I  2  288.092(5)  0.24(1)  1.0  288.097(6)  0.24(1)  1.0  3  288.40  (1)  0.24(1)  0.42  288.35  (1)  0.24(1)  0.52  4  289.16  (-)  0.29(1)  1.0  289.16  (-)  0.28(1)  1.0  5  289.49  (1)  0.29(1)  0.35  289.43  (1)  0.28(1)  0.42  6  289.88  (2)  0.40(8)  -  289.85  (2)  0.50(8)  0.31  (1)  0.25  (1)  0.33  (1)  0.27  (1)  ^ 2,3 E  * 4,5 E  0.72(3)  * 4,6 E  Isotope  a.  -  0.69(3)  Shifts:  ^  2  >  3  k  4  )  5  &  4 ) 6  (D)/A  ( D ) / A  2  )  4  ( D ) / Z\  The a b s o l u t e  3  5  (H)  = 0.81(5)  ( H ) = 0.82(6)  4 j 6  (H)  = 0.96(6)  energies  were  obtained  from  thecalibration of  p e a k A i n CH^Br. b.  The i n t e n s i t i e s  o f peaks  3 and 5 a r e e x p r e s s e d  as a f r a c t i o n of  the  intensities  o f peaks  2 and 4 r e s p e c t i v e l y .  The i n c r e a s e i n  the  intensity  states more  of thev=l t r a n s i t i o n  on i s o t o p i c  favourable  spacing.  substitution  overlap  i n CD^Br  i n both  the (ls,ns)  c a n be i n t e r p r e t e d  and  (Is,npe)  i n terms o f a  due t o t h e d e c r e a s e d  vibrational  176  bromide the  would  also  following  (i)  the  ns  i n the  atoms  suggests  does  in  observed  not  the  (e.g.  approximate  a  heavier  of  V , ( a , ) (C-H)  ground  state  i s 0.37  with  which state  i n  the i s  V, of  a,  at modes  least (e.g.  The  The  i n V,  s  Rydberg  some  mixing  the  3  i s  ( 1 s ,ns) i n  the  eV  for  thus  an  orbital.  that  V (a,) (CH -Br) 3  and  This of  been The  ~0.06  methyl  ].  have  the  of  lowest  (H45)  halogen  spacing  bond  than  the  this  frequency  C-H  higher  a l l three  below).  decrease  i n  very  i n  would  the  [0.73  as  vibrational  vibrational  spacing  the  of  see  stretch.  distinctly  in  the  halides  mode  the  2-3  in  -  i s  mode  motion  active  of  to  mode  much  state  (H45).  weakening  character  shift  other  eV  eV  active  decrease  the  the  antibonding  the  (Is,npe)  as  occurrence  (C-  different  state,  (~0.30  3  methyl  constancy  (J_s,ns)  CH I  significant  state  ground  a*  the  Modes  very  assigning the  0.82(5)  with  section.  the  that  with  isotope  with  considerably  i s somewhat  3  and  involve  the  indicates a  CH I  i n  consistent  \)\  spectra  have  i t s overlap  Vibrational  CH3Br  CH3Cl,  otherwise  spacing  of  in  This  -  to  following  spacing  transition  other  w i l l  3  in  vibrational  cases).  the  CH F  due  transition  Assignment  similar  to  transition  npe  The  i n  character  discussed  7.3.2  apply  transition  F) ( a , ) the  to  exceptions:  different  (ii)  seem  bromide found  in  implies V]  The  (C-H)  stretch  i s the the  sretch which  177  has  an  the  energy  ground The  in  active  f o r  mode  and  spacing  table  to  5 and  For  result i n  ground  atom. state  Halogen  The shell  This modes  correlation other  the  assignment  most  spectrum thus  of  spectra  available.  additional zone  are  vibrational -  state.  that  peak  The  considerable  as  decrease  throughout  the active  mixing  4 and  interpreted  transition  motion  mode i n of  the  o f t h e V] a n d v  3  state.  observed  amenable  spectra.  t h i s  regard  a l l the  due t o halogen  to  the  comparison  i n t h e same  t h e C l 1s r e g i o n from  vibrational  this  However,  these i n  the decreased  Spectra  not  inner-shells  interesting  (seeF i g .  a large  structure  of  halides  indicates  suggests  technique.  from  gets  spectrum  f o r  series  i s  t h e 4-5 s e p a r a t i o n  i n t h e (Is,npe)  Inner-Shell  excitation  I  i n t h e (.Is,npe)  discrete  from  methyl  an  1 s — • npe t r a n s i t i o n i n v o l v e s  halogen  7.4  i n  3  halide  3  spacing  different  the Franck-Condon  the vibrational spacing  the  since  CH  6 i n the CH I  structure  methyl  somewhat  i n the heavier  falling  vibrational  the  o f 0.94 i n  f o rthe vibrational  t o be  state  7.1) .  appears  shoulders  seems  (Is,ns)  smaller  transition  responsible  state  the  noticeably 7.3  shift  state).  t h e (J_s,npe)  that  in  o f 0. 0 7 6 e V a n d a n i s o t o p e  molecule Methyl as  h a s been  a  intermolec with i s  ular  excitation useful  chloride  i n  i st h e  photoabsorption  published  inner-shells  inner-  of  (HG76) a n d CH Cl 3  are  178  The  assignments  chiefly  based  spectra.  Term  orbital same  values  According  orbital  the  great  Z +1  atom. i n  (NSS69,  W74,  atom  from  i n a  any  state  involved  and  i n i t i a l  molecule.  molecule f i n a l  To  a  This  inner-shell  be  o r b i t a l s  a  large  extent  charge.  be  t o  used  observed  The  the  one  o r b i t a l s  have  a  may  on  i n the halogen  the  on  Rydberg  inner-shell  same core-  which term  the  values  o r b i t a l  f i n a l  but  atom  i n a  that  term  o r b i t a l  but  expect  atoms  i n  a  especially  true  f o r  character  and  thus  as a  unit  values  can  of the molecule  s i m i l a r i t y i n term  upper  the  o r b i t a l i s  t h e same  also  be  this  unoccupied  from  different  would  see the rest  identify  t o an  final on  with  resulting  t h e same  large  expected  used  within  unoccupied  same  atom  excitation  to identical  orbitals  This  excited  Thus,  o r b i t a l  the  following  has been  the  which  involving  similar.  which  positive  on  extent,  inner-shell w i l l  of  leads  involving  lesser  the  S74).  i n  inner-shell  of inner-shells  the inner-shell  f o r transitions  different  to  n o t on  i n any  i s promoted  number  depends  originated.  different  HNI74,  final  approximation  inner-shell  the structure  only  hole  approximation  WB74g,  of a  cores  t o replacing  analysing  one  a l l transitions  values  This  t h e same  f o r the  are  K-shall  o r b i t a l s  similar  of a  spectra  carbon  sharing  equivalent  an e l e c t r o n  molecule,  excited  electron  when  the  inner-shell t o be  be e q u i v a l e n t  approximation, o r b i t a l  i n i t i a l  to the  success  spectra  with  4.2), the effects  should  inner-shell  for. t r a n s i t i o n s  are expected  section  with  comparisons  but different  reasons.  for  on  molecule  (see  f o r the halogen  orbitals spectra.  i n  transitions  179  Also,  since  involving  of  those  portions  atom  on  of  element  the  around  orbital.  This  between  of  I  to  7.4.1  applied  ICNS73).  7.7  in  excitation. corresponding LaVilla  (L73) ,  the  table  assignments  1s  Excitation  the  the  region  This  has  of  cf  spectrum.  assignments  dipole  a  given  i t  governed i s  f i n a l  meant  molecular  be  'dipole  inner-shell  previously  assignment  been  used  the  term  i n  of  by the  choosing  values  of  CH F 3  loss  spectrum  of  fluorine  K-shell  i s  similar  very  f i r s t The  for the  the  well.  energy  the  to  being  i n i t i a l  only  the  of  must  i n the  photoabsorption spectrum that  the  the  f o r which  spectrum  except  Thus  this  of  probe  close  enunciated  idea  f i te q u a l l y  shows  present  suggested  This  are  atom  of  and  Fluorine  fluoride  symmetry  (S74)  structures  Figure  excited  been  2  should  of as  By  has  alternate  observed  the  thought  component  core  localized,  intensity  rules.  transition  highly  which  the  concept  Schwarz spectrum  the  i n a  i s located.  be  selection  the  (AA=1)  orbital  can  of  i s  inner-shells  determines  symmetry  matched'  upper  transition  the  orbital  from  inner-shell  which  'pseudo-atomic'  that  in  the  orbital  excitation  electrons  which  inner-shell by  originating  inner-shell  promotions  matrix  the  of  CH3F  spectral  term  features  (F to  reported  peak, i s t e t t e r  energies,  methyl  the by  resolved  values  are  1s)  and  given i n  7.3. The  first  peak  i n  the  spectrum  has  a  term  value  of  180  5.3 e ? term first been that  and i s a s s i g n e d  value  t o F 1 s — • c r * (C-F)  i s appreciably larger  peak i n t h e c a r b o n assigned an  tightly  in  the  bound when t h e r e  i s a F 1s  vacancy i s i n the carbon The tern  second  value  sinilar peak  peak, which  to  the  orbital vacancy  value  carbon  which  has  This indicates o f C H F i s more 3  than  when  the  j o i n s onto t h e continuum, has which i s c o n s i s t e n t  t h e 3p H y d b e r g o r b i t a l .  t o the ters in  3  K-shell.  o f 2.9 eV a t i t s aaxiaum  transitions  of CH F  transitions.  cr*(OF)  This  t h a t o f 4.6 eV f o r t h e  K-shell spectrua  t o C 1 s — « » c r * (C-F)  electron  than  transitions.  T h i s term  o f 3.1 eV o b s e r v e d  K-shell  spectrum  for  and  a  with  value i s  the  third  assigned  to  CH F 3  A /,  F 'SHELL K  lo O r—  /  P-  1  680  Fig.  7.7  2  690  ENERGY LOSS(eV)  700  The energy l o s s s p e c t r u a of C H 3 F i n the r e g i o n of F 1s e x c i t a t i o n (AE=1.0 eV FHHM).  181  C  1s—>-3pe  the  transitions.  spectrum,  which  large  natural  poor  experimental  1.0  7. 3:  may  linewidths  eV t o o b t a i n  Table  No  further be  sufficient  are  due t o o v e r l a p  i n the F  resolution  peaks  1s r e g i o n  which  has  observed caused  along been  degraded  /  the t c  signal.  Absolute e n e r g i e s (eV) , term values and tentative assignments f o r features observed i n t h e F 1 s s p e c t r u m Of C H F .  Feature  Energy ±0.3eV  1 2  687. 1 689. 5  IP»  692. 4  From  by t h e  with  3  i  i n  XPS  (T70)  Term Value 5. 3 2. 9  Ass i g n m e n t (final orbital) c* a 3pe, 3pa  182  7.4.2  Chlorine Figure  the  C l 2p  potential 1.70 eV loss  excitation  between  splitting  excitation  well  from  loss  spectrum  The  XPS  2p  (PJ74).  3/i  (L )  CH Cl 3  separation  i s similar  the 2 p y ( L ) 2  to that  2  observed  C H Cl 2  (1.6 eV  5  v a l u e s and s u g g e s t e d  of  energy  limit.  This  in  of chlorine-containing  (HB72) ] and  in  ionization  3  The  The e n e r g i e s o f t h e f e a t u r e s i n d i c a t e d as the tern  of  two p e a k s i n t h e e l e c t r o n  to estieate  spectra  s u c h a s H C l [ 1 . 6 5 eV 9).  3  region.  the f i r s t  s p e c t r u m was u s e d  2p  o f CH C1  shows t h e e n e r g y  was o b t a i n e d  spin-orbit Cl  7.8  2p E x c i t a t i o n  other  oolecules -  chapter  i n figure  7.8 a s  assignments a r e given  m  'c. o JD 3  CH CI 3  >co  • v •  LU r-  ClrSHELL  .v  I II I 190  —I  12 3 4  200  1  1  210  1  [—  220  230  ENERGY LOSS (eV)  Fig.  7.8  The e n e r g y l o s s s p e c t r u n o f C H C 1 i n t h e r e g i o n o f C l 2p e x c i t a t i o n (AE=0.35 eV FHHM). 3  18 3  in  table  7.4.  The  term  are  value  assigned  similar the  C  as  f o r each spin-orbit  t o the term  value  1s s p e c t r u m 5.5  of  (see  F i g . 7.8  peaks  are attributed  of  table  two  the peaks  Schwarz  S76)  intensities  of  interactions  between  the core  variations  of the intensity  large  intensity  underlying  the second  to  with  value  of  value  CH C1.  due of  from At eV  2  most  3  with  similar  spectrum  C l 2p  least  with  t o t h e C l 2 p,/ peak  a  eV  This  3  peak. o f 3.5  o f 3.9  2  3 / 2  part  of  *-4s R y d b e r g  r e s p e c t t o t h e 2p to  (2.1 e V ) .  i s 3.5  the  term  Following  ) / 2  eV  value the  limit f o r  of  —>-  but  relative exchange upper  significant  this  peak  that  transition  which  second i s close  i n the C  occurrence  1s of  transition  to the  peak,  a  limit  transition. 3 / 2  2:1  possible  of  the  r e s p e c t t o t h e 2p  1 / 2  intensity.  i n  value  two  intensities  another  the third  term  C l 2p  t o be  I t i s also  Rydberg  tha  penetrating  f o r the second  • 4s  i n  from  result  supports  peak  spectrum  egual  arising  term  limit  and  expected  and  i s  the f i r s t  relative  to  which  which  C l 2s  basis  indicates  The 3  contributions second  anomaly  and  the variation  may  ratio.  peak.  be  orbital  this  r e s p e c t t o t h e 2p /  the term  spectrum  mates  systems  The  closer  has discussed  I n some  peak  might  spin-orbit  7.1)  the  this  eV  f i r s t  • a* ( C - C l )  3 / 2  are  orbitals.  the  On  respectively.  experimentally  f o r the  i n  peaks,  i s 5.2  and t a b l e  peak  transitions  (S75,  eV  7.4).  t o C l 2p  transitions  these  o f 5.0  f o r the f i r s t and  two  partners,  ( s e e F i g . 7.3  value  a* ( C - C l )  eV  of the f i r s t  would The  i s 1.8 peak  assignment  with  6 i n  then  term  eV  term be  value  which  i s  i n the C  1s  the  C  1s  Table 7.A: Absolute Energies (eV), Term Values and Tentative Assignments f o r Features Observed i n the. Electron Energy Loss Spectrum of CH C1 i n the C l 2p ( L 3  C l 2p Energy ±0.15eV  T  1  200.75  5.32  2  202.45  3.62  204.20  3  1.87  -  205.85  4  3/ I P  206.07  VSIP  207.77  2  a) From  b 3 / 2  ) and C l 2 s ( L ^ Regions.  C l 2s  C l Is  Energy  T (eV)  a  Tl/2  Assignment  -  L3 -*• o*aj  1  271.7  5.5  2823.1  5.6  L  2  -+• o*aj;  2  275.1  2.1  2826,7  2.0  4pe  L  3  -> 4s  L  2  •*•  3  276.1  3.1  -  -  4pai  L  3  L  2  -> 3d  L  3  •*• •  IP  277.2  L  2  5.32  3.57  1.92  C  HG76.  2 > 3  48;  Feature  ±0.15 eV  Energy  T  Assignment  3d  d  2828.7  e  OO  00  The spectrum has been reassigned as discussed i n the text.  b)  T i s the term value with respect to the appropriate i o n i z a t i o n p o t e n t i a l .  c)  Derived from the  d)  From  e)  The i o n i z a t i o n p o t e n t i a l given i n  2p^ XPS'value  (PJ74)  and the separation of peaks 1 and 2.  XPS (T70) .  and the f i r s t IP f o r CH C1. 3  HC.76 was determined from the sura of the K  Q  emission l i n e energy  185  spectrum  would  transition. then  occur  of  orbital value  on  Rydberg  Cl  2p  to  partner,  4d  f o r  are peaks  expected the  2p  would Upa.  expected  t c  3  1 / 2  and to  from  this  —**-  the  existence  Rydberg  for  7.8  C l  transitions  doubt  the  figure  levels  to  location  assignment  i n  those  transitions  K-shell  orbitals  appear  to  This  atomic  forbidden  unoccupied  p  influence symmetry  case  are  the  i n terms  to  the  4p  Rydberg  the  takes  2p  4.  The  the  4pe  1s  term  C of  assignment  operating  i n  halides.  in  a l l of  the  strong  for  weak  or  peaks  from s  Cl  4p  selection halogen  the  p  close  to and  assignments would  inner-shell  to the the  lowest the these  case  This  the  the  are  though  atomic  nature of  rules  to  relaxes  localized  I f these  to  observed.  region i s  p  Even  environment the  i n  considering  from  intense.  intensities  the  transitions  by  transitions  of  are  unobservable  explained  most  orbitals  spectrum,  vestiges  o r b i t a l  the  Rydberg  transitions  atomic  place.  pseudo-atomic  be  where  some the  essentially  where  transition  of  orbital  be  uolecular  consequences,  due  may  while  orbital of  remain  np  carbon  spectrum.  dipole  to  i n the  corresponding  methyl  around  thus  4  Rydberg  assignable  and  though  np  similar  4d  the  •Upa  3 / 2  i s favoured.  intense  nucleus  2p  spin-orbit  eV) ] l e a d s o n e  Even  to  to  Cl  labelled  the  energies  transitions  most  to  [based  4  a  shoulder  structure  (2.9  and  to  transitions  with  absence  3  The  correspond  However,  4pa  lead  may  seem be  molecular  the  chlorine  where are seem  spectra  the  correct, to  be  of  the  186  7.4.3  Chlorine  Figure the  region  figure the  7.9  shows  represents 2s  spectrum CH I  o f peak  has  curve  shapes  been  (note  from  straightening.  a  maxima  table  The  of t h e C l 2s edge  labelled The  CH C1 3  f i r s t  i s taken  region  corresponding of  L i)  below  region  (HG76)  the  the  i n each  i n t h e C l 2s spectrum  for  the  Hanus Cl  peak  and G i l b e r g  2s spectrum  o r b i t a l  to  C l 2s  IP  The  i s 5.5  This  term  the  eV  to  i s  of i n  spectra  values  and  are given  i n  by t h e  similar  to the spectrum  dominated  value  while  the  B r 3d  (indicated  being  term  maxima.  features  by t h e  f o r the  f i r s t  the  term  i s 5.6  eV  (HG76) .  peak  i n the  have a s s i g n e d t h e f i r s t  transitions  ( C l 1s—*-4p).  peak  (T70).  i n t h e C l 1s s p e c t r u m  (HG76)  sloping  photoabsorption  spectrum  case.  peak  f i r s t  XPS d a t a  i n the C l 1s  with  transition  from  since  term  i n t h e C l 2s spectrum  line  accurate  i n the  f o r features location  the  4d spectrum  assignments 7.4.  which  more  f o r  Energies,  shows  below  display  and the I  t h e peak  i n  of the  figure  and can s h i f t  7. 10)  half  curve  allows  t o  3  background  energies  used  CH C1  displacement of  of the  The e n e r g i e s r e p o r t e d taken  of  bottom  of a curved  and  (figure  7.11).  after  The  subtraction  peak  3  were  spectrum  of the spectral  shapes  CH Br  spectra  loss  the top part  This  procedure  these  3  as recorded  subtraction  distort  (figure  3  while  after  of  CH C1  1  structure.  similar  the energy  an e x t r a p o l a t i o n  backgrounds  o f  (L ) excitation.  scale)  determination  A  shows  t h e spectrum  spectrum  Cl  Excitation  of C l 2s  vertical  the  2s  lowest  v a l u e seems  value  p  too large  Rydberg f o r a  187  Fig.  7.9  The energy loss spectrum of CH C1 in the region of chlorine 3  2s excitation  ( A E = 1.0 eV FWHM).  188  Rydberg Cl  2s  assignment spectrum  transitions to  those  (5.0  eV)  first  on  (R74).  has the  f o r the  been  first  and  assignment  on  the  CH C1,  C2H5CI,  CF2CI2  valence  orbitals  might  and  molecules.  differ  values  seems  considerable  behaviour  and  i s proposed  for  C  1s the  spectrum  appeared  2  a n  be  very  Rydberg  expected  in  be v e r y that  the eV,  2  those  different the  term  various  transition  large.  i n the C l  to c l o s e l y  in  values  spaced  in  to  the  the Cl would  for transitions  of  in  intensity  splittings  to  1s c o n t i n u u m to  be  would  apparent  there of  term large  valence o r b i t a l s  Finally,  seem  (R74)  the  region,  thus l e a d i n g  spectra.  differences  This  because  the  orbital,  the v a r i a t i o n  1s e n e r g y  resolvable,  the  relative  Also,  and  T h i s i s not  term  in  values  T(HC1) = 6. 1 eV,  (HG76).  to  molecules  assignment  that  of  whereas t r a n s i t i o n s  to  ( T ( C 1 ) = 9.4  to  with  t o be  (HG76).  similar  C2H3CI,  d  their  t o t h e l o w e s t s Rydberg  much t o o  expected  RCl  eV)  transitions  linewidths  transition  value  the C l K-shell absorption  9  even  similarities  and  that  transition  between t r a n s i t i o n s be  the terra  (5.3  justified  where R i s ' o r g a n i c )  possibly  inherent  not  (HG76)  b e h a v i o u r f o r Rydberg  although  of  the  a*(C-Cl)  photoabsorption  However, i t i s c l e a r  C l K-shell  T(RC1)=5.4 eV  except  Cl  substantially  expected  1s  grounds  o f HCl  this  the s i m i l a r i t y  the  Gilberg  spectra  for  Cl 2s—•  p e a k s i n t h e C l 2p  in  peak i n  ( C - C l ) ].  Hanus  these  to  A s i m i l a r assignment  transition  3  assigned  b a s i s of  spectra.  [ C l 1s — w *  T h e r e f o r e the f i r s t  are  the  first  among C l , H C l 2  the  to v a l e n c e o r b i t a l s ,  but  expected possibly  139  not  for transitions  t o Rydberg  orbitals.  T h e r e a r e s u g g e s t i o n s o f two f u r t h e r spectrum  of  although  their  because  CH C1  (figure  3  observation  o f t h e poor of  background.  The term  C  would  Is spectrum  2.1 eV)  values  o f CH C1 3  and  tentatively  examining  suggest  thus  (which  to  i n the C l 2s  the  be s a i d  which  C l 2s  t o be  i s mostly lying  of  features  these with  peaks  have term 2  and  on  to a  the  large  (3.1  and  4 and 6 i n t h e  values  of  3 on f i g u r e  C l 2s—**4pe  edge,  definite  due  structure  correlation  features  assigned  below  cannot  statistics  difficulty  2.1 eV)  7.9)  peaks  and  2.9  and  7.9 may be Cl  2s—*»4pa  transitions.  7.4.4 Bromine Figure the  3d E x c i t a t i o n  70-80 eV  region of  the  occur.  molecule that  3d / 3  2  3  7.10 shows t h e e n e r g y  transitions  is  o f CH Br  a  where  limit  4  spectrum  features  B r 3d e l e c t r o n  was d e t e r m i n e d  t o unoccupied  (PJ74) .  from  electron  energy  loss  described  below.  The e n e r g i e s o f t h e f e a t u r e s  spectrum,  assignments, Since fitting  deconvolution of the f i r s t  along  with  (figure  their  term  to  o r b i t a l s of 3d  (M ) IP  5 / 2  the spin-orbit  from  the  3  5  The v a l u e f o r t h e  evaluated  spectrum  of CH Br i n  corresponding  The v a l u e o f t h e i n d i c a t e d  g i v e n by XPS measurements  (M )  loss  splitting  two p e a k s  i n the  7.10) i n t h e manner observed  in  v a l u e s and s u g g e s t e d  a r e g i v e n i n t a b l e 7.5.  the f i r s t  procedure  two peaks was  overlap  carried  extensively  out to o b t a i n  a  curve  more a c c u r a t e  190  t * t » t »t >l  t 1  \  V  CO  \  "E  •» » »  \  *  •AW  >  1  >% w.  »  >  O  •^^^VV-*'  v_  I  M w  >  edge  5  WW  K \ j \ 3  4 5  > •  11.0 "Z.  LU — I  0-5H  0 70 ENERGY Fig.  7.10  74 78 LOSS(eV)  The energy loss spectrum of CH Br in the region of 3  bromine 3d excitation  ( A E = 0.35 eV FWHM).  191  T a b l e 7.5: A b s o l u t e E n e r g i e s f o r Features  Feature  (eV),  Term V a l u e s and T e n t a t i v e  Observed i n the Bromine 3d (M  !  4  £  '* (eV)  )  Spectrum o f  T^ (eV)  1  70.67  5.5  2  71.69  -  5.5  M  3  74.00  2.2  -  M  4  75.03  -  2.2  M  5  75.46  -  1.7  M  3d 3d  5 / 2  3 / 2  3  M  4  1  -»- c * a  5pe  4  4  M  IP  77.2*  M 4  J  5pe  5  76.2  b  a*a  5  IP  ~120  CHjBr.  Assignment  ±0.15eV  5  Assignments  -»• 5pa  $  3d + e f maximum  (a)  From XPS ( P J 7 4 ) a n d t h e s e p a r a t i o n o f p e a k s 1 a n d 2.  (b)  From F i g . 7 . 1 .  192  energies,  peak w i d t h s  CH Br  spectrum  to  g a u s s i a n peaks  3  two  in  the  with  respect  these the  peak  69  solely  which  least  eV) ,  7.5.  The  i s 5.5  to t h e term  1s s p e c t r u m  of  5  eV  and  fitted  resulting term  v a l u e of  value  Br  of  5.3  Thus  3  2  the  f o r each  CH Br.  Er 3 d / — • o-*lC-Br)  of  squares  (1.15  shewn i n t a b l e  i s similar  in the C  derived  peak  different on  for  these  3d —*-<r*(C3/2  s u g g e s t an  Br 3d  squares  S76) .  extra  A  additional  fitting  t o 73  transition  eV  the c o r r e s p o n d i n g  is  that  the  additional  observed  in  spin-orbit  transitions  is  discussed  Schwarz  The respect  by  third to  Br 3&5/ —*-5p 2  peak  figure  by  (S75,  3  3d  Rydberg  5/2  only  7.10.  be  of  used CH C1 3  peak  2 in least  two  peaks  if  from  the 3ds  /2  expected arcund No  It i s therefore  ratio  the  exchange  Also,  excitation.  2  based  the  peak 2 r e s u l t s  for  the  exchange  such likely  3d—*-<r*  interaction  as  S76).  peak i n t h e s p e c t r u m , the  of  region.  would  3d /  intensity  modified  underlying  suggest that  energy  1.5  argument *to t h a t  results  underlying  72.8 peak  the  program  an  from  v a l u e of  which i s  neglecting  transition  excitation, eV  and  similar  However,  p r e s e n t i n the 69  posited  expected  o f peak 2 i n t h e C l 2p s p e c t r u m  spectrum. curve  the  ( 1 ( 1 ) / I (2)) i s 1.2  degeneracies  (S75,  the assignment  would  area r a t i o from  orbital  interactions  are  was  to the a p p r o p r i a t e l i m i t  peak  somewhat  the  eV  portion  transitions. The  for  t c 73  The  of equal widths  peaks a r e a s s i g n e d to Br)  area r a t i o s .  eV  energies  peaks  first  from  and  edge  of  transitions.  with a  2.2  eV,  term is  Comparison  value assigned  with the  with to term  193  value  of  2.1  eV  spectrum  of  suggests  that  Peak  figure  4  i n  respect  the  3d / 5  the  l i m i t that  to  —»-4f  expected  to  The  3d  to  be  Rydberg fact  similar carbon  a  to 1s  4  the  to and  3ds/  peak  separation  the  i n this  5pe/5pa  spectrum  the  nf  .  5 to  of  3d  peaks  4  s p l i t t i n g  (0.55  eV)  3 / 2  1.7  The  eV  with  associated Rydberg  with  series  barrier more  —»-5pa  and  to  f  reasonable  (0.5 from  supports  i s  to  the  transitions.  5  derived  by  3.  transitions  3 / 2  to  region  peak  I t seems 3d  with  leading  around be  eV  3.  spin-orbit  energy  than  may  and  2  2.2 the  centrifugal  7.1)  f o r peak  transitions  and  and  be  K-shell  transitions)  of  to  value  the  carbon  o r b i t a l  value  appears  term  to  4.5  3 and  upper  However  due  the  1s—»-5pa  intense  edge  3 / 2  orbital  that  term  more  has  (see s e c t i o n s peaks  a  indicated  5  weak  the  also i s  i n  C  be  Rydberg  4  3d  to  edge,  3 / 2  peak  Higher  are  the  with  transitions.  assign  5pe  3.  marked  respect  waves  Br  peak  sixth  could  7.10,  the  2  fact  3 / 2  5pa  peak  the  (assigned  3  of  shoulder  3d  CH Br  to  partner  for  eV)  the  this  i s CH Br 3  l a t t e r  assignment.  7.4.5  the  Iodine  Figure  7.11  region  below  expected similar have were  4d  shows  larger to  been  the made  determined  Excitation  the  the I  3d  i n a by  spectrum similar  XPS  CH I 3  energy  4d *,  spin-orbit  Br  of  5/  loss  (N )  IP.  5  s p l i t t i n g of  CH Br 3  manner.  measurements  spectrum  of  Except  this  spectrum  and  the  The  4d  (BW76).  5 / 2  CH 1 3  i n  for  the  i s  very  assignments and  The  4dy  2  energies  IP's of  194  CH I 3  IN<, -SHELL 5  O-J—T  ,  50  F i g . 7.11  ,  1  1  1  1  52 54 ENERGY LOSS(eV)  1  56  1  1—  58  The energy loss spectrum of CH^I in the region of iodine 4d excitation ( A E = 0.35 eV FWHM).  195  the  features  values  and  The  spin-orbit  s p l i t t i n g  of  This  the  larger by  f i r s t than  XPS  (BW76) .  area  ratio  the  E  but  i ti s considerably  -  factor  i s close  3  observed seems from  t o be  the  no  obvious  The  term  values  the  appropriate  to  the  term  o f 5.7  o f CH3I.  assigned  t o transitions  Peaks  3 and  5  and  6.  is  most  likely  higher with 2.4  The  members  respect eV  fourth  assigned  o f t h e 4d  values  term  value  5 / 2  similar  of of  eV  1.9  eV  f o r peaks f o r  ratio  peaks  peak  i s  There  departure  Thus  with  peaks  5 and  term  peaks  4 a n d 6 when the  3  eV  f o rthe  and  5  compared 1s  to  5 are  Similarly,  C  6  values  3 and  o f 2.6  transitions.  i n  are  corrsponding The  1s  orbital.  o f peaks  f o r peaks  value  close  peaks  mates  series.  to  i n the C  ff*(C-I)  transitions  limits  respect  reasonably  intensity  6  1.1  (BW76) .  with  spin-orbit  the  of  spectrum.  two  1s spectrum.  *- 6 p e R y d b e r g 1.9  1.55)  two  to  i s 1.7.  becomes  f o r t h e extreme  Rydberg  are  (when  basis, the f i r s t  larger  eV  1.5  peak  due t o u n d e r l y i n g  i n the C  the  2  2)  of  ratio  i s  o f 2.5  1 and  value  the  7.11,  1/peak  to the antibonding  apparently  i s  from  spectrum  which  4 are evidently  t o 4d  term  this  derived  f o r the f i r s t  to the appropriate  which peak  On  eV  eV  7.6.  peaks  (peak  from  i n t h e XPS  i s 6.1  spectrum  of  term  i n table  s p l i t t i n g  the intensity  i n t h e XPS  their  figure  t o the expected  f o r the f i r s t  limits  value  ratio  explanation  ratio  i n  widths  area  with  eV,  spin-orbit  different  peaks  the degeneracy  1.70  peaks  The  i s included  f o r  along  are given of  two  the  (FWHM) w h i l e t h e i r  eV  7.11  assignments  determined 0.9  i n figure  suggested  separation slightly  observed  are the  to the  spectrum  196  Table 7 . 6 : Absolute Energies (eV), Term Values and Tentative Assignments f o r Features Observed i n the Iodine Ad ( N i ^ )  Spectrum of CH3I.  1  50.61  6.1  -  2  52.30  -  6.0  3  54.26  2.35  -  N  5  4  54.74  1.95  -  N  5  5  55.94  -  2.45  N  4  *• 6pe  6  56.43  -  1.85  N  5  -»• 6pa  4d / IP  56.7  a  Ad / IP  58.3  s  5  3  2  2  -u66  b  *72  b  85  N  5  -»• 0 * 3 !  Ni*  N  5  a*ax •*• 6pe 6pa  +  Nj, •»• •  }  shake up  Ad -»• £f maximum  (a)  From  (b)  From F i g . 7.1.  (c)  M u l t i p l i c a t i o n of the i n t e n s i t y by a factor  (energy loss)  s h i f t s the maximum of the Ad •*• t f resonance  to 95 ± 2eV.  XPS (BW76).  197  suggests  assignment  transitions. also  be  likely of  be v e r y  weak i n a s s o c i a t i o n  I 4d  by  CH3I.  Thus,  in  transitions associated  orbitals  al.  justified  to  to  may  seem  — • -*{I-I) 0  same p a t t e r n  was  limits  which a r e  to  to  5d  5d  t o t h e 4f  and  in  4f  and 5d  Comes  et  Rydberg  4f  molecular  sight,  Comes e t  and  terms  atomic o r b i t a l s  the  by  molecular  at f i r s t  assignments  the most  2  of  local  (AO) w h i c h Rydberg  Rydberg  have  MO's o f orbitals  t h e same mechanism a r e n o t e x p e c t e d s i n c e t h e  o v e r l a p o f two i o d i n e  6p AO's i s r e q u i r e d  of s i g n i f i c a n t  AO t o t h e 4 f  broad  were  3 / 2  5d and 4f  unlikely  these  Transitions  via  5 / 2  of  energies  were a s s i g n e d  transitions  contributions  (CNS73) .  Ud  at h i g h e r  and  2  the 6p,  t o t h e 6p i o d i n e  transitions  occurrence  5  i s vary  spectrum  o f t h e 4d s p e c t r u m o f I  region  Although  CH3I  assigned  (D and E o f CNS73)  transitions  of  the  which  2  in  eV.  t h e Rydberg  Rydberg  parallel  the intense,  2  4d  al.  2  I  4d /  peaks  I  of  This  intense  large  was  nature  structure  loss  transitions.  by 1.68  have  I  with Rydberg  separated  orbitals.  of  t o t h e I 4d e n e r g y  peak  both  but would  delayed  f o r the  spectrum  spectrum  might  and F C 6 8 ) .  weaker bands  below  to  with t h e  while f o u r  observed  orbital  3  the  eV FWHM) f i r s t  Rydberg  f o r t h e C H I I 4d s p e c t r u m  photoabsorption  i n appearance  6pa  energy r e g i o n  Comes e t a l . (CNS73)  similar  to  Rydberg  7.1  (see s e c t i o n  assignments  those given  In  peaks  e x p e c t e d t o appear i n t h i s  These  (0.7  these to t h e 4f  Transitions  the f continuum  the  of  contributions  and 5d R y d b e r g  MO's.  (as i n I ) f o r the  from t h e  2  iodine  6p  198  An  interesting  occurrence Rydberg  o f  region  assigned  CH3I  peaks the I2  peak  o f t h eI  transition  C i n  Comes  although 3  weak  (peak  by  corresponding of  a  feature  e t  loss  synchrotron  transition  supports  a t t h ebeginning  of  the  a 1.  4d—»-6s  t c  i t may be h i d d e n  spectrum  the  4  i snotobserved  spectrum  i s  u  figure  and 5 due t o t h e poorer  energy  (I d) spectrum  2  o f  i nthe under  This  i s  transitions.  A  present  spectrum  t h eleading  experimental  ( 0 . 3 5 e V FWHM (CNS73).  CNS73).  edges o f  resolution i n  versus  0.02 eV i n t h e  The low i n t e n s i t y  t h econcept  o f  o f pseudo-atomic  this  selection  rules. A  f i n a l  concerns  remark  t o b e made  structures  i n  shoulders  on the, l o w - e n e r g y  maximum  centred  features,  which  figure and  may  Similar 12 et  ~ 8 5 eV  with  a l . to  a n d ~ 7 4 eV excitation  respectively, s i m i l a r i t y type  o f  theenergies  of assignment  region which  broad  by  with  promotion.  c a n b e made  5s  continuum f o r CH I. 3  i n  spectrum o f  assigned 5p  o f these  These  excitation.  valence 4d  as  66 a n d 72 e V  electron  and  3  intense  apparent  i n t h es y n c h r o t r o n were  CH I  appear  earlier) .  of approximately double  of  and  but notreadily  (CNS73) ,  i nconjunction  o f  o f t h e  (discussed  a t energies  associated  4d  continuum  side  s t r u c t u r e s , observed  at~ 6 1  similar  t h e  arediscernible  7.1, occur be  a t  on t h eI  Schwarz  electrons From  the  structures a  199  CHAPTER 8 THE  This and  chapter reports the investigation  halogen  excitation of  ( C l 2p and 2 s ,  several  shell  cf  7).  of  the spectra XPS  study  energies chloro  the  several  1s s p e c t r a  the methyl of a l l these (0FK75)  has  of the four  XPS  possibly  resolution  study  inner-shell  halides, of  CH X 3  benzene  (X=F, C l , Br and I)  t h e monohalobenzene  spectra  the  halogen  a i d i n the i n t e r p r e t a t i o n of  molecules. attempted  different  the inner-  including  o f benzene and w i t h  halides  spectra  unstudied, are i n t e r e s t i n g  In addition, t o determine  carbon  a  recent  the binding  1s o r b i t a l s  of the electron  (1.05 eV)  better  the  energy  i n fluoro,  This  orbital  identified  would from  be p o s s i b l e  the d i f f e r e n t  and i f t h e l o c a t i o n  effect  on t h e e n e r g y  loss  energy  loss  technique  spectra  i n a more  i ftransitions carbon  of the  Since  than the r e s o l u t i o n of  determine these chemical s h i f t s  manner.  little  Ud)  The i n n e r - s h e l l  hydrocarbons  eV FWHM) i s c o n s i d e r a b l y  final  I  (C 1s)  and bromobenzene by a d e c o n v o l u t i o n p r o c e d u r e .  energy  (0.35  and  o f carbon  Previous chapters report  Comparisons  the carbon  spectra  3d  hitherto  5) and t h e m e t h y l  (chapter with  reasons.  spectra  (chapter  Br  o f t h e monohalobenzeu e s .  t h e monohalobenzenes,  for  the  MONOHALOBENZENES  of the f i n a l  1s  orbital.  reliable  t o t h e same  1s o r b i t a l s carbon  could  c o u l d be hole  had  200  8.1  Excitation  Figure a l l  four  The  spectrum  and K  1  C  1s  8.1  shows  halobe nzenes  binding K  of Carbon  were  2  binding  substituted.  This  carbon  the  hydrogen-bearing  numbered  K.,  may  feature halogen  excitation  5)  peaks  seem  {number  2)  a l l other  of  electrons.  the  binding  and  spectrum  f o r peak  I t  6 i n C  features  clearly  of C H I. 6  5  through  has  6  H  5  have  i n  The  of  spectrum  the  (EH76,  spectra  are  intensities  grossly  carbon  sensitive  as  to  assigned  spectra  of Cnly  associated.  been  energy  Table  comparison  6  observed  of  assignments  Br a n d p e a k s  the  of  8.1.  been 2  Ci .  the series.  loss  o f the C  the  energy  and  r e l a t i v e  h a s an e n e r g y  2 i s resolved i s  values  halobenzene  to alter  to  values  i n table  the  o f t h e 1s e l e c t r o n  C H F,  5  given  marked  f o r purposes  2  t h e benzene  the four  substitution.  Except  Feature  term  o f  are also  although  below.  6  C  1s  the halogen i s  a r e denoted  8.1.  of the  be e x p e c t e d ,  corresponding  C H Br  1s  which  figure  assignments  similar  C-, 1 s  where  Tentative  i n  and chapter  5  to t h e C  refers  2  features  HB77  6  K  i s denoted  carbon  the l i n e s  term  previous  to  by  of  excitation.  The  (HPB78) . atom  spectra  1s  t h e e n e r g i e s and a s s o c i a t e d  with  one  XPS  carbons  on t h e m a g n i t u d e  quite  loss  of carbon  o n F i g . 8.1  atom  refers  based  As  by  energy  included.  o f the carbon  discussion.  l i s t s  i s also  determined  this  8.1  i n the region  indicated  energy  Electrons  the electron  of benzene  energies  1s  with  discussed and  7  i n  excitation  of  C H Cl  and  as a s h o u l d e r  t o peak  1 i n  loss  of  6  5  feature  2  i n  201  Ii \\//-.. .'•hi  M  I  l 34  ii , 2 1  | T  1  I I K, K  I  5  1  I  8  2  '  •i Br ii j l [ l  .^^tr  11 1 2  to 'c  I I  I  3 4  I I  5  I  6K, K  8  2  T — i — i — i — r  co i_  !5 I  W  1j  I  > 2  3 4  r  'i  CO  1  5 T  I  I  K, 1 1  K  8  2  1—  z LU  i  i  5  2-4 •I"  i  i  i  i  6K,7  K -i  i  I  i  8  2  r-  1  1  H /'"V^  I  1 285  Fig.  8.1  n-r*"**' I  1 1  V~"-  3 4 1  T  1  5 1  8  K  1 290  I  1  1  1  1  295  E N E R G Y L O S S (eV) Energy loss spectra of the monohalobenzenes and benzene in the region of C Is excitation (A E = 0.35 eV FWHM).  TABLE 8.1- A b s o l u t e Energies ( e V ) , Term Values and T e n t a t i v e Assignments f o r Features Observed 1n the Carbon Is Energy Loss S p e c t r a of the Halobenzenes.  C  6 5 H  C H C1 6  F  5  6 5  C  H  C  B r  6 5 H  C  I  6  H  6  3  Assignment Energy  Peak  ±0.1  eV  1  285.3  2  287.5  Energy ± 0 . 1 eV  T (eV) b  285.1  5.2  286.3  5.0(K ) 2  Energy ± 0 . 1 eV  T (eV)  5.4  285.1  5.4(K ) 2  286.0  T (eV)  5:4 5.3(K ) 2  Energy ± 0 . 1 eV  T (eV)  Energy 0.1 eV  T (eV)  285.1  5.3  285.2  5.1  285.8 (sh) C  C -H,*(b )  —  5.4(K ) 2  2  1  C -H,*{b ) 2  2  3  287.5  3.0  287.3  3.2  287.1  3.4  287.5  2.9  287.2  3.1  C ns  4  288.0(sh)  2.5  288.1  2.4  288.0  2.5  288.1  2.3  288.0  2.3  C^-Hip  5  289.2  1.3  288.8  1.6  289.0  1.6  288.9  1.5  288.9  1.4  C^fn-ljd ,  6  290.2  —  2.3(K ) 2  290.2  1.1(K ) 2  —  d  r  6  —  (n+l)s  C ( C H F ) - 3p 2  6  5  C (C H Brr*4d,6s 2  K 1  f  291.4  7 K *2 8  f  290.5  290.5 1.1(K ) 2  293.9  293.8  —  — 291.7  292.5  290.5  290.4  —  291.3 293.8  291.2 293.9  (a) (b) (c) (d)  From HB77 (chapter 5 ) . T-IP-E. A l l term values are w i t h r e s p e c t to K, except those marked ( K j . T h i s value Is d e r i v e d from a l e a s t squares curve f i t . The estimated u n c e r t a i n t y 1s ± 0 . 2 eV. n=3 f o r C H ; n=4 f o r CgHgCl; n=5 f o r CgHgBr and n=6 f o r C H I . See the comments on Rydberg nomenclature  (e)  Except f o r CgHgF and CgH  (f)  From XPS (HPB78).  6  g  g  g  where 3d Is  the lowest d Rydberg  5  orbital.  290.3  — —  C  l ~ 2  C  the f o o t n o t e  5  C (C H F)*3d,4s  -  6  5  2~  shake up  293.5  In  6  of  chapter  7.  203  iodobenzene gaussian between so  i s  peaks 284.5  that  peaks  as  the  occurs  unit the  K  peak  XPS  binding  2  2.  A similarly  the interpretation (see chapter  correlation  not  relating  energy  i s useful  exhibit to  approximately  between  chemical  the 5:1  the  be the  1s  interpretation r a t i o  An of  chenical 2)  and  8.2  between  f o r excitation plot  was  of the spectra  o f peak  additional peak 1  useful methyl cnly  2 and t h e  spectral  f o r peaks  and  approximately  halobenzene  t h e other  1  f o r a l l of  (peak  loss  same  binding  2  same  spectra  energy  K  peak  t h e  the  the  and  1  correlation  shifts.  intensity  i s  i n figure  and t h e energy  since  K  the  by  shown  In the  1  separation  constant  that  of the carbon 7 ) .  of  with  the  spectrum  excitation  constructed  may  maximum  excitation  i s emphasized  energy  2  associated  are e f f e c t i v e l y  the correlation  the  (due t o C  peak  energies,  loss  i ti s evident  ) . This  of  binding do  2  with  8.1.  o f  both  poor  t r a n s i t i o n  features of  two  structure  the  5  the corresponding  1  f o r  slope  halides the  ( K  energy  energies K  6  reported  the binding  of  the  C H F  uncertainties  i n every  the  i s associated  energy  the  f i t of  o f t h e f i t was  other  '2-4' i n f i g u r e  potential  ionization  true  from  monohalobenzenes  s h i f t  i n  the  separation  ionization  In  5  2 overlaps  values, and  Since  eV  curve  to  quality  C H I.  t h e combined,  1 and 2  energies.  the  thus  The  6  squares  ( 0 . 6 7 eV)  o f ±0.2  i n peak  labelled  loss  of  to  and  Within energy  2  different  structure  eV.  uncertainty  corresponding  s l i g h t l y  a least  width  287.0  o f peak  excitation)  on  of equal and  an  position  based  K  2  features observation  2  i s  the  and  2.  This  204  is  nost  clearly  observed  bromobenzene. intensities  in  the  Deteroination  i s complicated  by  spectra  of  of  the  chloro  relative  peak o v e r l a p s  in  and peak  fluoro  and  iodobenzene. According  to  energies  are simply  orbital  energies.  a  frozen  Hithin drawn  First,  orbital  final  t r a n s i t i o n s observed of  the chemical  picture,  t h e d i f f e r e n c e between  c o n c l u s i o n s c a n be the  orbital  this from  as peaks  shift  transition  initial  simplistic  and  approach  final two  the  above  considerations.  i s aost  likely  t h e same f o r t h e  1 and 2.  o f peak 2  Second,  occurs  i n the C  almost 2  1s  a l l  orbital  > >-  CD cr  UJ  2  292H  z: O CD *  CM  290  —i  1  I  285  287  E N E R G Y L O S S (eV) Fig.  8.2  (#2)  The correlation between the K binding energies and t h e e n e r g y l o s s of peak 2 i n the carbon 1s spectrum of the aonohalobenzenes. The least s q u a r e s c a l c u l a t e d s l o p e (AK /AE) i s 0.93. 2  2  20 5  e n e r g y and electrons  the energy  of the v i r t u a l  a r e promoted  substitution. correlation  Any  plot  energy. within  The  i s essentially  small  halogen  slope  are  The orbital  that  this The  term  peaks  1 and  2 i n a l l four  term  value  of  eV  transitions  Cj—• T *  f o r peak  for  1 and  C  is  a  on  (ortho, this  C 1  the  the  upper  2  will  appear  2  5.4  eV  2  for  has  been  both  t o the  peak i n t h e assigned  to  Assignments thus  of  strongly  v a l u e s f o r peaks  that the energy  With  independent on  which  the  of  the hole  this the  of the 3 C  spacing  of  1  the  and final  1s  hole  observation i n energy  the type is  1  of the  whether t h e c a r b o n  carbon.  the s e p a r a t i o n in  and  the  intense f i r s t  o f t h e term  or C - t y p e  meta o r para)  1  with respect to  f o r peak 2 a r e  — T *  d e p e n d e n c e on  be  of  the  HB77, c h a p t e r 5 ) .  i t i s apparent  little  assumption  directly  such  This i s s i m i l a r  mind i t seems r e a s o n a b l e t o assume t h a t *"* o r b i t a l  that  considerations.  From t h e s i m i l a r i t y  has  which,  with  and  molecules.  (EH76,  t h e above  8.1)  5.0  o f benzene which  1s—+-TT*  by  (measured  a r e between  5.2  1s s p e c t r u m  orbital  suggests  to  orbital  i s 0.93  i s strongly associated  values  limits)  (table  8.2  in figure  the  related  c o r r e s p o n d i n g to peaks  orbital  appropriate  2  halogen  final  to halcgen s u b s t i t u t i o n  f o r the t r a n s i t i o n s  supported  the  be  1s  small.  c a r b o n atoms.  carbon  would  on  uncertainties  insensitivity  suggests  by  the  i n the s l o p e of  unity  atom  of the l i n e  the e x p e r i m e n t a l  effects  frcm  to which  unaffected  differences  8.2)  (figure  the i n f l u e n c e o f the  orbital  of  the  o f C,  carbon  located.  With  1s  levels 3  should  C. 1s—*-TT*  206  transitions levels two  just  i sobserved  peaks  width  peak  al.  gaussian  3  peaks  separations whose  width  f i r s t  peak  component  Table  6  5  H 5  I peak  3  at half  C,-type  f o r C H F 6  5  1  1 s  i n  by  levels  loss  i sused  1  spectrum  t o derive  f i r s t  that  o f  8.2.  the The  by O h t a e t a  suitable  t h e sum c f 3  spaced result width  of C H F. 6  i n t h e  FWHM)  given  ratio),  i n OFK75,  2  lineshapes.  choosing such  the  table  1s l e v e l s  and C  n  any i n f o r m a t i o n  as t h eexperimental  i nt h eenergy  of  maximum -  i sl i s t e d  1:2:2 i n t e n s i t y  width  C  ( 0 . 6 0 e V FWHM)  i st h e same  5  a composite  at t h e i n a  peak  f o rt h e When  this  C-,1s—  Experimental and Calculated Widths o f t h e C-, 1 s — * - 7 r * Transitions i n t h e monohaloben zene spectra.  0.75 0.79 0.70 0.67*  5  6  C  (in a  Thus  t h eC  i n t h e peak  evaluated  width  1  5  6  been  Experimental W i d t h ±0.02eV  C H F C H C1 c H Br 6  the  derived  peak  8.2:  Molecule  width  of  peak  the  be c o n t a i n e d  (full  have  spectra.  of  spectrum  (OFK75)  component  will  between  i n t h eseparation  loss  i n each  separations  separation  directly  t h eseparations  monohalobenzenes The  t h e  i n t h eenergy  concerning  f i r s t  as  Calculated Width  Component Separation para ortho IT e t a  2  (0.75) 0.90 0.94  0 0 0  —  0.3 0.2 0. 2  3  0.5 -0.3 0.6  1)  From  1 i n F i g . 8.1.  2)  T h e sum o f t h r e e g a u s s i a n p e a k s o f 0.6 e V w i d t h i n a 1:2:2 r a t i o a t t h e s e p a r a t i o n s l i s t e d i n t h el a s t three columns.  3)  Prom  4)  Optimzed value of t h e width derived from a l e a s t sguares f i t o f two gaussians t o t h e s t r u c t u r e between 284 a n d 287 eV i n t h e C 1 s s p e c t r u m o f C H I (Fig. 8.1).  OFK75.  6  5  207  peak  f o r chloro  s i g n i f i c a n t l y widths of  the  since  the  -C  energy  with  that  been  from  l o s s  that  t h e peak  the  separation  halogen  of  cannot  the  widths  observed  energy of  1s  tentative  i n f o r  tested.  the  XPS  data  that  and  t h e ir*  some  2  Also  of  plot  the  of  o r b i t a l  benzene  However  the fact of  that  a  larger  the localized  density  on  explanation.  -C  o r b i t a l  by  1s the  Ohta  supported  8.2)  by  the  spectra. unaffected  s i m i l a r i t  by  ir—+~tt-* to  shift  occurs than  i n the  following  For i n n e r - s h e l l o r b i t a l s ,  t o i n  presumably has The  valence  those  i s d i f f i c u l t  1s o r o i t a l  atom.  no  concerning  been  as the  which  than  separations  2  loss  chemical  carbon  the halogen  1  i s largely  are very  K*  so,  given  figure  the halobenzenes  fixed  monohalobenzenes  have  i n the energy  (R74) .  Even  the C  (HPE-78)  and  o f t h e C-|  information of  known  estimated,  separations  been  t h e d e l o c a l i z e d ir*  larger  given  spacings  1  easily  a  the locations  Is levels  have  1  well  lineshapes.  has given  c o r r e l a t i o n  f o r  r a t i o n a l i z e  separations  of  f o r the C  s u b s t i t u t i o n i s not unexpected  observed  loss  observed  i s not  be  to derive  C^-type  peaks  fact  excitations  energy  c r i t i c a l  of the carbon  from  The  the  the  (through  made  spectrum  a l . (0FK75)  derived  energy  monohalobenzenes  lineshape  more  separation)  2  spacings  much  of t h e  component  i s much  has  components  the  suggests  are  transitions.  the  (which  attempt  et  Is levels  widths  experimental  the u n c e r t a i n t i e s i n the approximation  level  in  the calculated  the  This  are not consistent  Since  the  than  8.2).  C ^ t y p e  C-, 1 s — * - T T *  for  bromobenzene  larger  (see table  the  OFK75  and  a  i s a  chemical  20 8  shifts  result  from  distribution. f e l t  by  hand  This  the inner  electrons  are localized.  chemical charge  determines  electrons  the o r b i t a l  f  polarization  f e l t  from  change  appreciably  binding  energy  essentially  feature  ir* o r b i t a l .  I n benzene  of  2  three  orbitals  separation  of these  -  o r b i t a l  a  frozen  transitions separations in 7r*  the  to  seem  oxygen  and carbon  somewhat  5  intense  In f i r s t  N  2  on  the other  redistributed  effective the  (total)  molecule value  by  nuclear may  (which  not  i st h e remains  a  and  2  yields  b  a separation  f o rthis  whose  with  the  may  1s s p e c t r a  structures  these  i n  the  apparent.  by invoking  are essentially  weaker  and  expected  or  spectra  are  large  one o f  i s not readily  spectra  The  (BWP68) be  only  i s suggested  to t h e carbon  there are  o f >2 e V f o r  benzene  inner-shell  (WBW73)  a l l cases  t o i n  the  t o be  i n benzene  o f magnitude  either  of  symmetries.  2  i s expected  orbitals  explanation  similar  i nthe  7r* orbitals  i n the halobenzenes  orbitals  order  occur  1s)  transitions  a r e two unoccupied  . Transitions  a n d CO  band,  ,  t w o w*  The r e a s o n  possible  n  approach  t o  with  6  these  be d i s c u s s e d i s t h e nature  v i r t u a l  the  analogy  C H X.  be  1s—>-w*  while a  o f t h e same  halobenzenes.  also  where  i n a v i r t u a l orbital)  there  of  halobenzenes.  orbitals  One  charge  atom  the term  the  should  a n d b .g s y m m e t r y n*  may  electron  nuclear  electrons,  i n  thus  of  which  u  the  o f an e l e c t r o n  halobenzenes  2  density  atoms  and  outer  constant.  Another  e  on t h e s i n g l e  but  a l l the  the  the effective  For outer  electron  substitution  of  an  (nitrogen,  identical  and  of  and  C_ H_ 6 6  dominated occuring  by the below  209  the  inner-shell  appearing (The  above  second  higher  the  and  continuum in  onset  (~300  D i l l maximum  terms  barrier  and  continuum  energies  Dehmer  edge)  edge  of  of  intense  the  resonances  (see  sections  transitions  the  d  the  potential,  centrifugal  peak  i s  pictures a-  d  that  the  cn  the  C  are  model  analogy  localized 1s—•TT*  7r*  the more  to  the  between  MO's  of  l o c a l  7r*  o r b i t a l .  rr*  o r b i t a l  peak  and in  waves.  1s—•TT*  of  o r b i t a l  in  in  with  In CO  i s  due  to  channel  arising  from  the  model,  this  HO  diatomics  i s  Thus  physical  Orbital  similar the  although  a  this  effects  centre.  giving  K-  potential  transitions.  compatible  useful  the  outgoing  In  .  second  (below  and  2  at  8.1)  the  4.5). N  are  figure  explained  the  molecular  the  explanation  p i c t o r i a l  Thus  d  terras TT *  of  of  associated  band  ionization.  to two  the  shape  explanation  i n t e n s i t i e s .  transitions  centered  to  have  (resonance)  highly  transitions  spectra. these  is  observed  By a  barrier  show  resonance the  barrier  in  descriptions  for  component  described  o r b i t a l  f i r s t  range  4.4  maxima  halobenzenes  f i r s t  shape  intense  the  the  and  the  the  beyond  large  inner-shell  in  DD76a,b)  interpretation  with  direct  maxima  eV) ,  r e l a t i v e l y  (DD75,  effects  to  two  description in  l o c a l  the  adjacent  involved  suggests in  the  like  carbon  shows  arrangements This  be  the  N  may  that of that  of a  the  this the  transitions  b  to  explain  the  upper  o r b i t a l  of  2 g  d  for  orbitals  examination w *  type 2  spectra,  halobenzene  An  b g  CO  and  set  atoms. the  and  2  help  benzene  character  should  benzene  of  o r b i t a l  than o r b i t a l  causing  peaks  has  the  e  i s 1  of  2 u  the and  2  210  in  the  halobenzene  spherical would g  harmonic  lead  to  component  a  spectra. about  Transferring this  the  description  of  the  b.  centre  of  of  transition  the  outgoing  the  orbital  benzene  channel  to  a  molecule  i n  terms  of  a  and  thus  the  expected  to  y centrifugal generate  to  resonance  losses in  are  molecular the  thus  a In  detailed most  intensity,  appears is  In there K  2  the i s  binding  a  8.1  to  there  by  a  promotions  energies.  carbon peak  the  at  energies.  be  shape  well i n  of  with  higher  the  not  be  C  1s  1  (see  These  electrons  part  from  For  C  2  the  the  benzene  differences  — • Rydberg  may  orbital  with  peak  4  peak  i n  fluorobenzene  (labelled value  and  lower  of i n  C  the  K]  CgHgCl  C H . 6  1  This  6  transitions.  2  I t s term  and  relative  separation  corresponding  of  5)  corresponding  example,  C —»~3s  identical  the  occur,  the  to  i n  these  to  from  equal  i n  of  to  given.  differences peaks  peaks  benzene.  chapter  expected  eV  at  benzene  spectrum  291.4  observed  for  underlying 1s  the  are  separation  to  within  would  assignments  least  approximately  due  be  The  are  are  than  intensity  region  contributions  which  may  transition  correlate  corresponding At  a  peaks  loss  orbitals.  stronger  probably  weaker  energy  spectra.  binding  2  the  discussion w i l l  at  transitions  Such  assignments  of  transitions,  component  DD76a,b).  figure  cases  explained  K  of  same  previous  .5=4  relative  (DD75,  Rydberg  halobenzene  and  large  assigned  i n t e n s i t i e s  be  a  in  the  this  effects.  positions  observed  to  have  picture  The  peaks  to  resonance  expected  energy  barrier  (Fig.  7)  between  the  K  with  respect  to  K  1  2  8.1) and i s  211  1.1  eV  which  of  feature  i s  close  5  (1.3  correspond  to  with  i n i t i a l  the  A  peak  be  would  simultaneous  A  8)  (labelled been  1s—>-  Tf*  second, ^300  in  benzene  of  eV  D i l l  2  and  to  CO  (DD75,  the  analogous  the  at  5.4)  .  explanation  peak  been  in  opening  eV.  of  the may  maximum  in  the  i n  this  other  1s  spectra  the  continuum peak  benzene  and  in  feature  a  wave  most  8.1,  figure  continuum  observed  has  simultaneous  corresponding  of f  the  eV)  explained  terms  but  excitation.  This  shown  This  7  involving  of  i n  not  (The  )  orbitals for  1s)  carbon  8.5  in  1  peak.  (of  maximum  continuum has  8  1  none  excitation  Although  Fig.  continuum  (C  peak  ~293.  1s  2  transition  five  broad  molecules.  which  with  a l l  C  K  5 and  o r b i t a l  explanation  since  excitations  DD76a,b)  corresponding  to  double  in  and  1  corresponding  broader  a l l 5  i s shown  and  associated An  in  appearance N  a  excitation.  C  to  peaks  final  inner-shell  maximum  with  weaker  at  in  a  the  respect  that  same  electron  strong,  i n v o l v e s TT—*• Tf *  likely  a  with  the  unlikely  the  (with  suggests  alternate  and  show  value  being  two  common  associated  with  a  spectra  i s  with  orbitals  i s  feature  term Ihis  possible  this  8.1)  (Fig.  eV) .  valence  halobenzene  the  transitions  respectively.  However,  to  in by  occurs maximum  i s  similar  the  spectra  Dehmer  shape outgoing  be  appropriate  the  halobenzene  and  resonance channel. for  the  spectra.  212  8.2  Excitation  Discrete loss 2s  of  of 6  4d  in  region  edge  1s  observed  i n the  be  spectral  6  fluorine  energy  i n  the  region  since  electron  increasing  the  1s  attributed  to  with  fact  continua  are  The figure  C l  the  size  intensity  (C H I) of  5  the  scales  chiefly  due  shells.  The  in  upper  the  and  C l  while 6  subtracting  to  2s  the  are  f o r  3d  shown  the  the  6  5  i n figure  lower  indicated  6  8.4.  For  continua  the  shown the  i n I  4d  spectrum displaced  background  i s  lower  energy  spectrum  shown  was  which  combined  3  each  of  excitation  be  CH F.  and  5  This  background,  can  valence-shell  (C H Br)  figure  observe  5  are  5  sections.  each  to  or  4  f o r  rapidly  section and  This  instrument  6  C H Cl g  could  limit  C U F  by  inner-shell of  of  5  and  5  upper  indicated  i o n i z a t i o n  portion  of  6  the  i n CF  6  C H F.  decreases  inner  C H F  previously  i n a b i l i t y  spectrum  i s  the  cross  than  of  the  structure  with  the  small  spectra Br  to  and  (WB74d)  4  of  spectrum  C H F  CF  2p  examined.  been  section  underlying  background  halogen  the  Thus  was  of  energy  and  5  spectrum  peaked  features  loss.  i n  6  has  no  the  C H Br  loss  i s close  cross  larger  of  region  impact  the  edge  1s  excitation  that  chlorine  the  excitation  However  inherently  much 2p  8.3  spectrum  the  below  spectra  loss  energy  fluorine  the  7) .  energy  i n  structure  loss  Electrons  observed  energy 1s  (*>700 e V )  of  with  3d  fluorine  observation the  The  5  chapter  detected  been  bromine  excitation  (HB78a,  3  have  of C H I . of  Inner-shell  halobenzenes  the  5  Fluorine  CH F  the  C H C1,  iodine the  Halogen  structures  spectra  edges  of  obtained  by  represents  an  200  205  210  270  2 8 0 eV  F i g . 8 . 3 The energy loss spectrum of CgHgCl in the region of Cl 2p ( A E = 0 . 3 5 eV FWHM) and Cl 2s (AE = 0 . 6 eV FWHM) e x c i t a t i o n .  214  TABLE 8.3.' A b s o l u t e E n e r g i e s ( e V ) , Term V a l u e s and T e n t a t i v e A s s i g n m e n t s f o r Features Observed i n the E l e c t r o n Energy Loss Spectrum o f C HcCl fi  Feature  i n t h e C l 2p and C l 2s R e g i o n s .  Energy +0.2 eV  Term Value (eV)  C h l o r i n e 2p  T  3/2  T  Assignment  l/2  1  201.50  5.1  —  2p  2  203.15  3.4  5.1  2p  3 / 2  3  204.9  1.7  3.3  2p  3 / 2  4  206.3  —  1.9  2p  IP  206.6(3)  a  3 / 2  2p  IP  208.2(3)  b  1 / 2  C h l o r i n e 2s  2  +4s;  2p  *3d;  2p -^4s  1/2  +TT*(b ) 2  1/2  2p  2p  1 / 2  ^3d  1 / 2  -  T (eV)  271.6  5.4  2  275.8  1.2  277.0  -ir*(b )  ^3/2"°°  1  2s I P  3 / 2  2s+TT*(b ) 2  2s-*°  a  (a)  From XPS (HPB78)  (b)  From t h e XPS v a l u e f o r t h e C l 2 p ^ 3  2  l i m i t and t h e s e p a r a t i o n o f 1.65 eV  between peaks 1 and 2 i n t h e e n e r g y l o s s s p e c t r u m .  21 5  extrapolation structure.  orbitals  those  determined  values  and  while  table  (figure  similar  based  on  hole  would  electron  assigned  In  to  i n an each  energy  excited  peaks  similar  to  carbon  =  of  a  assigned  and  second to  Cl,Br,I)  that  on  and  2s  i n table  8.3  bromine  3d  are  methyl  was  this  very  halides with  used  term  to  a i d  This  was  the  f i r s t  peak  i n each  the  halobenzenes  weaker,  spectrum peak  these  has a  i n  peaks  the have  inner-shell electrons  the carbon the  was  transitions.  f i r s t Thus  halides  while  Rydberg  i s the final  why  o f an  basis  o r b i t a l  to  of halogen  understand  energy  of the methyl  spectrum.  i n  the  2p  8.4b).  the binding  On  f o r  peaks  i n  term  the location of the inner-shell  the first  which  energies,  inner-shell spectra.  assigned  t o promotions  of the are  comparison  1s spectra  the  a n d 8.4  the  of the  halides  effect  1s  The  (figure  spectra  spectrum  were  8.3  inner-shell spectra  orbital.  halogen  halobenzenes  value  difficult (X  halogen  l i t t l e  t h e s a m e TT* o r b i t a l  f i r s t  4d s p e c t r a  i n the carbon  have  corresponding been  analysis  that  energies  are listed  t o t r a n s i t i o n s t o t h e cr*(C-X)  the  term  the  the assumption  i n  higher  8.3)  o f the halogen  from  f o r the chlorine  (figure  In the methyl  f o r peaks  binding  HPB78) .  assignments  and i o d i n e  assignment  peak  i n figures  (OFK75,  the e x c i t a t i o n  obtained  indicated  t o the corresponding  values  were The  contains  7 ) .  below  spectra.  XPS  halobenzene  (chapter  the  8.4  curve  positions  spectra  8.4a)  The  by  suggested  loss  spectral  peak,  subtracted  inner  energy  the  The  background halogen  of  o r b i t a l  f o r  1s s p e c t r a .  X—*-Tr*(b ) 2  should  have  the  I ti s  transition a  similar  O)  C H Br 6  5  Br3d  3d 3d^ V2  in c Z3 >>  i  'i  1  a  2 T  .5  3 1  i  fe  4 T  r  1  r  >-  110UJ h-  0-5H ~1—'—'— —'—I— 70 75 1  1  E N E R G Y L O S S (eV)  E N E R G Y LOSS (eV) Fig.  8.4a The energy loss spectrum of CgHgBr  Fig.  8.4b  The energy loss spectrum of CgH^I  the region of Br 3d excitation  in the region of I 4d excitation  ( A E = 0.35 eV FWHM).  ( A E = 0.35 eV FWHM).  to  (Ti  TABLE 8 . 4 : A b s o l u t e E n e r g i e s ( e V ) , Term V a l u e s and T e n t a t i v e A s s i g n m e n t s f o r F e a t u r e s O b s e r v e d i n t h e Bromine 3d S p e c t r u m o f C H,-Br and t h e I o d i n e 4d g  S p e c t r u m o f C Hr-I. fi  C H Br 6  w  5  Bromine 3d Energy  T  Feature  ± 0 . 2 eV  (3d  1  70.3  5.9  2  71.4  —  3  73.5  4  74.6  5 / 2  Iodine 4d T (3d  )  3 / 2  )  Energy  T  +0.2 eV  < 5/2> 4d  5.7  —  5.9  52.65  —  5.7  2.7  —  54.6  2.0  —  1.6  2.7  56.4  —  1.9  56.6  3/2 IP  77.3  58.3  C  C  E s t i m a t e d f r o m the mean v a l u e (76.8 e V ) o f t h e 3d b i n d i n g e n e r g y 2 i n t h e C H B r 3d e n e r g y l o s s s p e c t r u m (1.1 e V ) . g  (d)  5  From XPS (HPB78).  nd3/2+Ti*(b ) 2  ndg^-Hnp^ ndg^-Hnp  n d  (c)  5  2  d  n=3 f o r C H B r and n=4 f o r C H I . g  nd5^2a-»it*(b )  nd  d  (a)  5  3/2)  50.90  76.2 .  g  ( 4 d  —  5/2 IP  Assignment  T  5 / 2  -»  3/2^  ( b ) m=5 f o r C H B r a n d m=6 f o r C H I . g  5  (HPB78)  g  5  a n d t h e s e p a r a t i o n o f peaks 1 and  218  intensity  relative  for  X — • o'*(C-X)  the  t o higher energy transition  alternative  interpretation  and  halogen  C H X 6  5  Rydberg peaks larger and  than  thus  However  eV  those  i n CH X  expected  spectra  t h e term  both  values  that An  the  CH X 3  i n terras o f  f o rthe  f i r s t  t o 5.8 e V i n C H X ) a r e 6  assignment  2  as  halides.  solely  f o r any Rydberg  X—*~rt* ( b )  t h e  be t o a s s i g n  a n d 5.1  3  features  i n t h e methyl  inner-shell  transitions.  ( 5 . 3 t o 6.1  would  loss  5  transitions  f o rt h e f i r s t  (R7u)  peak i s  preferred. Since regions very  the details  of  similar  reader the  the halobenzene to those  i s referred  assignments  which  seemed  of  •pseudo-atomic*  the  orbitals  JL v a l u e  present halogen  inner-shell  difference the the  between  halobenzene underlying  spectra.  7 f o rt h e r a t i o n a l i z a t i o n s  of  i n tables  i n each  This  oscillator substituent.  halides  spectrum  similar  One  effects  the  those  differing  seem  o f halogen less  Rydberg involving  by  According t o occur  c f t h e halobenzenes.  a r e much  A  spectra  intense  the corresponding methyl  i s explained  by  strength  associated  with  greater  ±1  from  t o  the  i nt h e notable i s that  relative  c o n t i n u a than  the  of  was t h e o c c u r r e n c e  were  orbital.  feature  assignments  whereby  numbers  t h e two s e r i e s spectra  a n d 8.4.  rules  SL q u a n t u m  spectra  8.3  by the e a r l i e r  of the inner-shell  assignments  spectra are the  selection  with  inner-shell  Rydberg  spectra  of the methyl  observed  the  3  t o be i n d i c a t e d spectra  f o r  f o r t h e c o r r e s p o n d i n g CH X  shown  halogen  upper  halogen  t o chapter  the  transitions  of the assignments  t o  halide  valence-shell  t h e much  larger  C H 6  5  219  CHAPTER INNER-SHELL  EXCITATION  AND  9  EXAFS-TYPE  PHENOMENA  IN  THE  CHLOROMETHANES  "Prudence i s a r i c h ugly o l d maid c o u r t e d by i n c a p a c i t y " William Blake  This  chapter  reports  loss  spectra  and  chloroethane,  chlorine results  which more  model  prominent  location  CCl  With this  the  chapter  1s  spectrum  impact  Barrier  (WB74b,  the  C  1s  loss  structure spectra  4  h a s been  TKB76,  experimental  model i s intuition become  o f t h e  more  highly  o r may  n o t be  may  depending  on  the  t o the barrier. of CH C1  counterpart  2  of  , CHC1  2  CCl ,  3  are  4  to the extended  well  known  i n  K-  (see section 4.6).  been  impact  studied  HPB77  MO-potential  might  continuum  exceptions,  electron  1s,  effects  respect  (EXAFS)  carbon  simple  i n t h e C l 2p c o n t i n u a  not previously or  of CH  with  to 4  chemical  effects spectra  atoms  following  photoabsorption  on  barrier  and C l 2s  fine  have  This  1s s p e c t r a  t h e energy  photoabsorption  based  potential  as i n  s h e l l  The  energy  , x=0  x  of  4.4).  features  absorption  region  4  section  of the chlorine  X-ray  x  o f t h e empirical  i n t h e carbon  as  CH Cl _  excitation.  arguments  i n t h e C l 2p  interpreted  the  electron  i n terms  that  as well  4  2s  methanes.  addition,  methanes,  i n  5  (see  suggest  observed  and  2  i n u t i l i z i n g  chlorinated  In  C H Cl  a r e discussed  helpful  inner-shell  of the chlorinated  2p a n d c h l o r i n e  barrier  the  and  the spectra reported  techniques. i n  detail  chapter  by  6).  shown i n by  either  The  carbon  electron The  C  1s  220  spectrum The  of  CHgCl  chlorine  i s also 2p  spectrum  Bremstrahlung  radiation,  analysis  the  of  excitation also  fluorine 2p  9. 1  of  spectra the  barrier  Carbon  The to  1s  energy 4),  threshold spectrum  some  are the  are  Excitation  of  spectra  region  shown  i n  figure  suppressed  by  subtraction  extrapolated  from  the  i s mainly  f o r example).  ionization values and  term  proposed  values  previously  due  The  T70,  to  PJ74,  and which  (WB74b,  are  the  indicated are  f o r  listed  i n  assignments are HB78a,  of  S i (CH  with  but  molecules 1s  3  7.  no  inner-shell have  (BBB78)  ) C l _ x  and  the  Si  x  (FZV70,  of  possible  4  i n terms  i n  section  9.6.  Chloromethanes  the  five  the 9.1.  these  of  a  shape 2p  The the  below  from  for the  CH Cl  been  eV.  (see  the  The figure  carbon  literature  CH Cl , 2  3  to 7) , a r e  term  CHCl  3  The and  x  methane  has  286  energies,  9.1.  chapter  of  4  background  continuum  table  x  f o r the  curved  2  CH Cl ^  ionization  spectra  locations  identical  1s  Except  of  C l  molecules,  carbon  taken  OK76).  assignments  features  features,  spectral  thresholds  (SNJ69,  spectral  f o r each  The  carbon  results  the  below  (N71)  f l u o r o m e t h a n e s and  given  of  zero  9.3  the  the  true  background  presented. series  chapter  obtained  published  related  these  and  4  chlorosilanes,  effects  i n the  was  HB78a C C l ,  been  of  with  loss  i n  of  including  Comparisons  potential  (x=0  (L73)  spectra  BNZ72).  of  reported  1s  has  spectrum  spectra  been  discussed  CH4  XPS  values and  CCl  4  energies, spectral  those listed  1s  given i n  table  10! l  05H I  OH  _VI 12  III II 345 67 K  -i—i—'—i—•—r  — I — ' — i — < ~  i—r  10  ChLCI  /\ A 0  5H  II I I I I I i 23 4 5 6 7 8 K -I—'—I—"—I—i—r 1  I 1  1— —r  10-  CH2CI2  ••e  1 '"!  0 8H  I I I I I II I 1 2 1 3 41 5 6 7 8  10H  i—i—i—'—i— —i— —r  fe K  ! \  -i—i—i—r CHCI.  I I 1 2  10H  06  I 3  4  II 5  A  CCI.  4  •c '  286  1  I  T  290  T  2  i  1  1  I  1— —I 294 1  K  1  3  298  ENERGY LOSS (eV) 9.1 The energy loss spectra of the chloromethanes region of C Is excitation ( A E = 0 . 2 5 eV F W H M ) .  in the  T a b l e 9.1'.Ahsolute E n e r g i e s ( e V ) , Term Values and T e n t a t i v e A s s i q n a e n t s i n t h e C H C 1 , CHC1 and C C l E l e c t r o n Enerqy Loss S p e c t r a . 2  CH C1 2  T  1 2 3 4  288.8 289.0 289.9 290.8 291. a 292. 1 292.4 292.8  5. 1 4.9 H.O 3.1 2. 5 1.8 1. 5 1. 1  IP  C  a  f o r Carbon  1s E x c i t a t i o n  Assignment  (final  Features  4  CCI4  CHCI3  Enerqy  6 7 8  3  2  *  5  2  I  Enerqy  T  1  Enerqy  T  1 2  289. 3 290. 1  5.8 5.0  1  290.9  5.4  CH Cl 2  2  »i b, o r h j or b a, ,4s 4pb 5s 3d 5p  orbital)  CHCI3 «i e  t  4  2  7  3 4 5  291. 2 292. 7 293. 3  1.9 2.1 1.8  2  1.8  294.5  293.9  295. 1  296.3  295.* 298. 1  296.0 297.5 302  297.4  a. 4p 5s,3d  between t h e i o n i z a t i o n  potential  b. T h i s n o o e n c l a t u r e f o r the a o l e c u l a r Rydherq o r b i t a l s t r e a t s t h e a a s e x t e n s i o n s o f c h l o r i n e a t o a i c See c h a p t e r 7 f o r c o a a e n t s on p o s s i b l e a l t e r n a t e c h o i c e s o f Rydberq n o o e n c l a t u r e . F r o a TPS (SNJ69. T70, PJ74, OK76).  * see Table 9.A f o r data on t h e carbon  4p  shape r e s o n a n c e s and/or two e l e c t r o n t r a n s i t i o n s (shake-up)  303.3  a. T i s t h e t e n v a l u e , q i v e n by t h e d i f f e r e n c e and t h e e x c i t a t i o n enerqy.  C.  CC1  1s s p e c t r a o f C H C l and C H . 3  4  orbitals.  223  9.4. and  A CC1  discussion spectra  4  Since for  CC1„  the  this  complicated  of  the  assignments  observed  molecule  spectrum  of  the  electronegative  barrier model to  (D72)  carbon  1s  states )  inner-well  low  lying  the  chlorine  atoms  not  states  energy  states  are  carbon  molecular  of  3  the  atomic  orbital  1s  more  model i n  carbon  are  (D72) ,  CC1  are  4  potential  electron.  to  1s  This  electrons  inside  orbitals  potential  the  the of  which  well  Rydberg  examples  MO's  the  ( i . e . transitions  which  those  simplest  chloride  localized  occur. in  are  unoccupied from  carbon  promotions  readily  i s  electrostatic  favoured  penetrate inside  kinetic  contributions  barrier  orbitals  while  1  while  CHCl  2  then  methylene  excitations  be  and  potential  excited  that  continuum  l i t t l e  In  the  w i l l  w i l l  f i r s t  repulsive,  trap  barrier  states')  the  molecular  appreciably  well  a  predicts  'inner-well  has  can  unoccupied  potential  not  create  which  2  assignment  c h l o r o f o r m and  According t o  to  and  i s discussed  considered.  considered  CH Cl ,  follows.  spectra  four  for the  states  which  have  and  electron  outer-well from  do  ('outer-  outgoing  arising  to  states  excitation  to  appreciable  orbitals.  scheme  for  CCl.  based  on  a  4 minimum one  of  basis ai  and  the  contain  large  thus  be  may  set  there are  higher  of  contributions  expected  to  two  unoccupied  t  symmetry.  2  from  be  Within  tetrahedral  transitions  from  carbon  occur  only  to  the  t  2  1s  orbital.  (1a-|) The  by  symmetry  orbitals  of 1s  and  potential  electric  carbon  lower  orbitals  the  orbital  C C I 4  the  Doth'  atomic  localized  barrier.  the  carbon  MO's,  C C l  dipole 4  can  excitation  224  spectrum  (figure  (1.5  FWHM)  to  eV the  t  lower  are  transitions transition  to  6)  the  a  transition  below  extremely  weak  transitions  is  peak  to  the  most of  CH C1 2  Rydberg  These and  can t  2  MO be  to  2  o r b i t a l  atomic  orbitals  of  while  groups. into the  orbital change  i n  a + t  which  C  1s  potential carbon  1s  point  (CHCl  When  the  symmetry  a., s p e c i e s  )  and  remains  contributions  dramatically  3 V  to  3  throughout  The  almost  of  CHC1  been  b  CH  1  CCl  4  model.  •  these  and  3  examined.  )  4  the  ai  and  the  and  i s reduced a.,+  total  of  3  the  an  to  CH C1)  of  i s  C C I 4  expected  unchanged.  each  feature  between  ,  due  i s  4  3 v  i s  to  (CCl ,  C  the  i s attributed  have  the  (C  i n  spectra  group  to  of  spectrum  correlation  side  (HPE77,  spectrum  barrier  molecules  .  electronic-  further  peak  9.2)  forbidden  studies  A  This  i n the  the  e  to  loss  at  attributed  dipole  transition.  these  Tj  be  threshold  orbital  the the  from  the  MO's  s p l i t s  orbitals the  i n  point  2  assign  energy  observation  energy  4  eV.  Rydberg  with  obtained  corresponding (CH Cl )  294.5  low  intensity the  observed figure  due  coupling.  transitions  schemes  MO's  CH  Rydberg  accord  order the  2  4p  allowed  1s i o n i z a t i o n  at  the  peak  transitions  (see  formally  that  i n the  intense  i n complete In  dipole  Isotope  C  edge  broad  to  were  s h o u l d e r may This  vibronic  the  2s  s h o u l d e r on  demonstrated  intense,  peaks  C l  This  become  an  i s assigned  No  level.  n  by  which  the a  coupling.  observed  absence  of  peak.  Herzberg-Teller  the  to  eV  have  analogous  eV  o r b i t a l .  down  could  vibrational  be  290.9  indications 290.9  chapter  i s dominated  inner-well  2  the  to  at  energies  There of  9.1)  b  C  the  t  2 v  2  ( 2v) c  2  Of  course  molecular  series.  In  the  22 5  C  3  and C v  v  (1a  )  o r b i t a l  dipole  barrier the  previous  loss  expected  spectrum the  transitions  on t h e basis  Feature from  i n  the potential  These  a  may  limited  to be  which,  from  range  valence  Rydberg  transition  and  feature  4  i n CHC1  a r e assigned assignment  3  interpreted  shows  of  side  i n CH Cl2  transitions  t o higher i snot  i ti s offered  order  as a  (R74) .  energy  the  are  i n CHC1  t o  f o r  The l o w e s t 5  i n  3  Rydberg  value  features  Rydberg  plausible  9.1,a l l  expected  t h e term  considered  broad  t o t h e 4s  i s assigned t o feature while higher  of a  states  i s  2  excitation  sharp  1 t o 3  numbered  with  of  i n table  inner-well  broad  a t higher  a number  energy  within  of a  features  listed  to  4  consists  weaker  high  of comparison  type  rather,  states  numerous  values  have  corresponding to features  corresponding  one;  term  spectrum  3  t o t h e assignment  contributions  This  2  on  the  spectra  more since  been  t w o s h o u l d e r s a n d some  2  orbital  unoccupied  observable transitions  to  have  The CHCl  1 t o 4 i n CH2C1 .  contain  are electric  the  a r eexpected.  known  spectra  framework.  According  observed,  t o be  1s  R75).  superimposed  t h e  MO's  carbon  of the i n n e r - w e l l  characteristic  a r e  the  to  Also,  4  states  2  features  and  i n CCl . developed,  w h i l e t h e CH C1  energies  of  their  energy  with  band.  Rydberg  from  (R74,  above  peak  than  studies,  The the  are expected  i snot as f u l l y  identified  from  transitions  are the basis  model,  outer-well  values  the  which  CII2CI2  and  3  transitions  a l lof the unoccupied  Thus  MO's,  the barrier  CHC1  groups,  t o  allowed.  valence of  point  2  p-  CH C1 2  2  i n both  transitions. only  explanation  possible of the  226  observed  spectral  ordering very  and  helpful  the  features.  Calculations,  separation  of  i n determining the  though  the  details  trends  i n  the  throughout are  barrier the  as  to  Cl  2p  continuum  is  the  intensity  the  spectrum  is  found  (where  of  series the  barrier  atoms  penetration  the  localized  4  the  although  this  the  decrease  i n  the  Rydberg  barrier  o r b i t a l s  threshold as  and  not  as  intensity,  structure  as  i n  CH  4  Rydberg  throughout  the  accord  with  i n h i b i t s  the  the  region  the  carbon  through barrier  established  partly  i n  therefore  decreases  well  4  chlorine  into  by  CC1  further  Similarly,  i s expected  2p for  i n  strongest  complete of  C l  structure  interpreted  addition  due  compare  peak  Rydberg  the  4 /  i s i n  orbital.  at  i s  be  This  1s  4  i n CC1  to  unit  main  the  chiefly  one  by  the  the  compare  the  largest  basis,  of  since  continuous decrease  Rydberg  CC1 )  trend  this  potential  carbon  to  spectra  since  intensity (CH  a 4  of  1s  the  the  spectra  to  meterstick  the  Even  throughout  carbon  as  these  continuum,  increase  be  i n t e n s i t i e s  regard  a  may  CCl .  model  the  series  has  i n this  Thus  would  predictions  as  atom.  the  disputed,  of  used  weakest  spectrum  to  4  increases  continuum  the  and CH  On  3  be  therefore  underlying  intense  CH C1.  whole  from  as  could  transitions  roughy  chlorine  be  transitions)  and  of  assignment.  qualitative  be  the  w i l l  times  to  the  can  throughout  four  clear  the  The  levels,  distribution  Rydberg  series.  additional  about  correct  I t i s interesting  of  valence  assignment  are  of  ionization,  i n t e n s i t i e s  each  test  model.  chloromethane  the  series  a  intensity  of  spectral  the  useful  the  especially  because  of 1s the  model, as  the  of  the  227  d i f f i c u l t y spectral  and  In HB78c been  molecules  i s a  with  overcome  the  (delayed  i n  explained  i n the  barrier  inner-well  states.  This in  to  i s not  the  have  l i k e l y  a  observed CCl .  the  lower  maxima and  weak C  9.1  1s  f i r s t while  spectrum  presently are  labelled  features continuum  model sharp  as  as  the  above  the  maximum  3  figure  (figure  4 at  9.6)  on  and  The  (Note  in  figure  much are  are  higher  1s  not  spectra.  considered any  higher  3d  would  AG's, not  be  most  associated  with  as  weak  maxima  potential  feature  i n figure  that those  9.3.  the  as  i n and  continuum  closest The  3 9.3  to  the  extremely  energies i n  interpreted  are  do  ionization  seen  peaks  spectrum  Two  observed  9.6.  energy  carbon  thus  the  quasibound  while  4  be  to  MO's  of CC1 .  can  to  which  carbon  lying  1s  inner-  intensity  structures  based  carbon  at  have  sharp  continua  well.  discussion  and  observed  Also,  extent  i s  rise  s u f f i c i e n t  structures  maxima  under  lew  11),  arguments  according  unoccupied  i s that  (chapter  transitions  orbitals  continuum  of  has  chloromethane  potential  both  where,  continuum  spatial  effects  just  The  4  figure  IP  barrier  underlying  continuum  barrier.  relatively  larger the  i n the  inner-shell  the  such  HBW78  continuum  electron  since  are  contain  potential  in  much  inside  to  i n  unexpected  orbitals,  localized  are  present  assignments  energy w i l l  be  the  Such  the  barrier  onset)  potential  occur  of  [D72,  f i  increase  frequently  seem  SF  potential  outgoing  the  shape  negligible  an  energies  model,  as  10) ] , w h e r e  thresholds  barrier  the  background.  such  invoked, there  higher  to  estimating  instrumental  (chapter  shell at  i n  EXAFS  the and  CC1  4  are  228  discussed maxima  i n a later  (labelled  the  carbon  with  simultaneous 1s  maximum  may  DD76a,b)  that  be  transition.  This  appearance  the  features  range  of figure The  previous two  molecules  9.1)  analogous resonances,  f o r  The  observed  2  i n CC1  interpretation, required.  4  2  (DD75, a two  similar  i n CCl . 4  1s e d g e  o f t h e other a n d CH.  to  inner-shell  somewhat  the C  a  energy  i s similar  features  (beyond  molecules  c a n be seen i n  4  have  continuum  (CH Cl  and  from  the  (chapter  features  species  be  CH,C1 3  (WBW73, H B 7 8 a  transitions.  may  above  i n a l l four  i n are  associated  resonance  arising  features  occur  be  onset of  higher  explanation  t o t h e continuum  the continuum  t o those  shape  which  near-edge  electron  the  one  latter  a n d CO  features  chlorinated  similar  2  a  energy  also  publications  two-electron more  (WBW73)  Weak  studied.  of N  may  valence  to  two  the delayed  the other  of a  continuum  spectra  the  represent  a t t r i b u t e d  the  o f  Alternatively,  lower  f o r  One  while  excitation  the  excitation in  may  continuum  electron.  with  electron  3 a n d 4)  1s  carbon  section.)  and which  possibly  7)).  been  For  these  attributed t o  features CHCl ) 3  i n  are  suggests involving  the quite  that  an  shape  229  9.2  Chlorine  2p  Excitation  of  Chloroethane  and  the  Chlororaethanes  The  energy  loss  spectra  chloroethane  between  2p  excitation  and  9.2.  2s  count  edges  level.  a r e  those  these the  expected the  1 / 2  o f t h e2p  XPS edge  lines  cf t h e  was e s t i m a t e d  f i r s t to  (BDH74,  two  t h eexpected  while  t h e  peak  for  t h eother  value  separation  apparently-too-large  , L  3  2s  from  separation  andL  2  OK76).  The  expected  7,8) s i n c e  each  s p l i t t i n g ,  Although spectrum there i s  f o r CHgCl  i ssomewhat  o f thef i r s t i n  and  larger  As discussed  transitions  1  are  the  i n  2s  edges  chapters  cnly  molecules.  due t o o v e r l a p p i n g  L  and  1 / 2  (PJ74,  peaks  t h es p i n - o r b i t  three  i n figure  i n t h e XPS s t u d i e s .  with  probably  and  measurements  o f 1.6 e V  , 2p  3 / 2  chlorine  represents the  labelled 3 / 2  o f  a r e shown  spectrum  o f t h e2p  the  not reported  corresponds  agreement  C2H5CI  is  were  separation  good  by  splitting  values  roughly  by  The e n e r g i e s  o f t h e 2p  spin-orbit  each  The l o c a t i o n  determined  position  and ionization,  line-under  indicated  respectively.  t h e chloromethanes and  190 a n d 2 8 5 e V , t h e r e g i o n  The h o r i z o n t a l  zero  c f  than below  two peaks  the  second  peak. The the and  energies,  features C2H5CI  assignments previously assignments  term  observed  are  given  (scheme (HB78a,  values  i n t h es p e c t r a i n B)  chapter  follows.  a n d suggested  table 3  7).  o f CH Cl2/ 2  9.2.  f o r CH Cl  assignments  The  have  A detailed  CHC1 , 3  energies  been  for CCl  4  and  presented  discussion o f the  ~i— —i—>—i— —i— —r~ 1  200  1  1  240  280  ENERGY LOSS (eV) 9.2 The energy loss spectra of the chloromethanes and chloroethane in the region of Cl 2p and Cl 2s excitation ( A E = 0.35 eV  FWHM).  A b s o l u t e E n e r q i e s (eV) , T e r a V a l u e s a n d T n n t a t i y e A s s i q n a e n t s f o r C h l o r i n e 2p a n d 2 s E x c i t a t i o n I n t h e E l e c t r o n E n e r g y L o s s S p e c t r a o f C h l o r o e t h a n e and t h e C h l o r o e e t h a n e s . (a) C h l o r i n e  2p E i c i t a t l o n  Features  Enerqy  T  1  200.6 202.3  5.5 3.7  204.2  1.8  2 3 4 2p*jlP 2pv* I P  b  •> 6 7 8 9  (b)  T  5.7  200. 8 202.4  5.3 3.6  5.3  200. 8 202. 9  6.2 3.8  6.«  3.«  204.2  1.9  3.6  204. 8  1.9  3.5  V j  V j  V }  c  200.6 202. 4 203. 3 205.3  6.2 4.4 3.5 1.5  %  T  (/J  6.0  5.1 3.1  T  200.5 202.4 201.5 205.9  5.4 4.5 3.4  20 6. 8 208. »  206.9 208. 5  209.2  210. 1 212. 5 217. 5  211. 2  210.3 213. 4 216. U 223 236  208.0 210. 1 216.5 223 235  217.0  y/>  4s 4p Ss  6.1 5.0  CH C1 3  CHjClj  T(2s)  Enerqr  T(2s)  Enerqy  270.7  6.1  271.7 275. 1  2.1  5.5  270. 9 275.0  277.2  l p  3  2  1 8  f r o m  W*.  4p 5s  2.6  277.6  T(2s) 6.7 2.6  CHC1  CO delayed  o n s e t •ad  Enerqy 270.5 277.8  T(2s) 7.3  00  s a a k *-•p  B I I F S (see F i g .9.4. t a b l e 9.3)  CCI4  3  <i*(C-ci) <fIC-Cl) 4s 4s <P «P CO  CO  Enerqy  T|2s|  270.8  7. 2  assiqnaent f/(C-Cl| 4p  278. 0  CO  a. See the text f o r a d e s c r i p t i o n of the r e l a t i v e merits of these two assignments. b. The C l 2 p / ^ c. From XPS (T70, OK76).  4B  Features  Enerqy  276.8  assiqnaent* Scheae k Scheae B  4  Enerqy  206. 7 208.3  CjHjCl  10 11  T  206.1 207.8  236  1  Enerqy  206.0 207.6  C h l o r i n e 2s E i c l t a t l o a  2slP  T  Bnerqy  Enerqy  T  V j  CC1  CHClj  CHjClj  CRjCl  CjHjCl (  Features  OK76) . A s p i n - o r b i t s p l i t t i n g of 1.6 eV was assumed (BDH7A) to o b t a i n the 2 p  I P 1 / 2  "  232  For  a l l  structure than  spectra  i n t h e 2p  the f i r s t  and  2  Pi/  similar  CUClg  and C C 1 that i n  an  since,  these have for  Cl  from  orbital. spectra been  f i r s t .  The  great  2p  for  t h e 2p  3 / 2  Since  peak  of based  9.2)  would  since  of  2:1 2p  among  related  overlap  from  the  C l 2p  which  have  been  transitions  among  be  an  The  as  The  i n  features  except  below  the  assignment  features.  explain  (scheme the  a r e known  A  of  similar  transitions  valence  type  f o r  the  MO's,  many  1s s p e c t r a , I f  An  observed  t o be  of  orbitals  model.  same  levels  spectra  absence  (S75,  suggested  identical  i n t h e carbon  the barrier  as the  2p  transitions  t h e upper  In  the  both  spectral  transitions  observed  e x p l a i n e d by  second  expected f o r to  from  five  to the unoccupied  assigned  the  i s strongly  plausibly  (R74).  level  very  effects  levels  these  suggests  most  molecules  be  3 / 2  suggests overlapping  would  1 / 2  on R y d b e r g  Rydberg  2p  observed.  o f exchange  corresponding  solely  to  of  was  to transitions  similarity  the  naturally  2)  further  and  assignments  a l l  broader  i s approximately as intense  ratio  strongly  s i m i l a r i t y  the  broadening  i n t h e absence  continuum  assignment table  expected  considered f o r a l lo f the observed  the  second  of overlapping transitions.  spectra  intensity  the  3  of the chlorine  are  (labelled  peak  a l l four  transitions f i n a l  a shoulder  the second  transitions S76) ,  holes  CH Cl  i s considerably  t h e decay  the presence  4  f o r  region  (KRK74) , t h e a d d i t i o n a l  suggests  f i r s t  Since  inner-shell  2  that  discrete  peak.  peak  fact  except  of  c a n be barrier  233  maximum  was  chlorine  atoms,  potential orbital  to  type  the  and  the  been  be  expected  solely  These  for values  transitions  to  the  (R74,  R75)  such  term  values.  each  type  C l  2p  values this might be 7).  has  then  assignment expect  similar This  Thus  this  to  to  closer  i s also the  term  those  i s the  an  to  2  the  values  only  in  limit  for  that  and  expected  the  carbon CH C1 3  i s  that  i n  CH Cl 3  may  with  the to  of  4.5  the to B)  term  6.4  eV. f o r  eV  for  f i r s t  peak  a  valence  the  Rydberg  derived  i n  term  However, that  transitions  spectra  (see  the  a  orbital.  values.  where  (3)  expected  the  valence  there  orbitals  Rydberg  (scheme 4  A  5.3  be  2p  separated.  of  transitions  to  the  C l  problem  unsatisfactory  f o r the  from  type  assignment peaks  type  might  upper  frcm  somewhat  found  case  s  the  unlikely  second  range  than  for  2p  outer-well,  scheme  seem  i t i s possible  arises  correspond  are  larger  C l  assignment  magnitude  which  suggested  With  with  A  the  i s attractive  valence  the  lowest  spectrum  orbital.  transitions  peak  somewhat  Robin  in  i s  are  alternate  molecules.  the  barrier.model  well  an  to  the  MO's  effects  transitions  f i r s t  are  thus  inside  the  that  (A)  and  exist  to  i n  carbon  of  i s such  d i f f i c u l t y  assignment  the  valence  barrier  two  region  would  expected  assignment  One  i n these  the  transitions  height  the  localized  overlap  be  i t and  that  Rydberg  values  Rydberg  with  so  to  barrier  potential  CH2CI2  and  extend  would  considered..  significant  MO's  Only  unoccupied  the  problems  has  and  between  type  insufficient  orbitals  although are  not  occur.  location  orbital  located  valence  would  thus  transition  i f  the  well  and  Rydberg  spatially  one to  chapter  agreement  234  between  t h e term  v a l u e s f o r peaks  cr*(OCl)  the  orbital  spectra  was used  Cl  spectrum  2p  in  (chapter  values  t h e peaks  Cl  be  (see  the section  associated  Since  both  demonstrated reasonable solely  assignment  of  the  these  are  listed  term  discussed  great  that  undulations  this  the  section  C 1s s p e c t r u m At  preceding  first  the  term  methanes  9.2.  entail  6 eV  are  t h e assignment  based  altering  the  and  which  c h l o r i n e 2p  the  previous  m o l e c u l e s show  These  20 eV above  continuum  favoured  (chapter 7 ) .  features.  paragraph  be  the  of these four  first,  but  If calculations than  among  C l 2p s p e c t r u m  than  barrier  flawed  (scheme A) would  would  -  are  greater  along with r e l a t e d of  the  Rydberg  chlorinated  in table  continua  less  in  and  between  assignments  characteristic  5-8)  of  2s e x c i t a t i o n ) .  similarity  i n the f o l l o w i n g  following  valence  more  values  i n two g r o u p s  (labelled  chlorine  second assignment a l t h o u g h they  transitions  2p i o n i z a t i o n of  and  with t h e presence o f a p o t e n t i a l  o f t h e CHgCl  number  treated  the  Note  The  both  f o r Cl 2p—•Us transitions,  of  spectra.  carbon  assigned t o valence t r a n s i t i o n s i n the  of  that  on R y d b e r g  because  the  The d i f f e r e n c e s  on c h l o r i n e  both  plausible  the  7).  of  unexplained with t h i s  may  a  terms  2p and C I s s p e c t r a  remain  both  t o support the p r e v i o u s assignment  transitions of  in  a s s i g n e d t o t r a n s i t i o n s to  f e a t u r e s are  prominent  features  threshold  which a r e  second,  the  are discussed features  weak  i n the  observed  in  CCl . 4  inspection  s h o u l d e r s may  the  peak  be a t t r i b u t e d  labelled  7  t o t h e maxima  and  the  of  the  235  2p  situation, above  continua  ] / 2  spin-orbit  7,8).  A large two  this  separation maxima  considerable three  barely  visible  likely  features.  EXAFS  The  features  o f  prominent  range spectra  CC1 ,  these  spectrum  4  the  there  are  intensities  i nCC1 ,  prominent  spectral  of 4  i n C2H5CI. as  I t  double  i o n i z a t i o n  features  as well  maxima.  i n t h e C l 2p a r e  among  inner-shell  i n CC1  4  shown  a t a glancing weak  Also  such  of  i n t h e Chloromethanes  undulations  CHCI3 a n d  2  these  Features  weak  CH Cl2,  most  continuum  t o these  chapters  represent  absent  processes  than  t o explain  o r e x c i t a t i o n accompanying  contribute  t h edelayed  9.3  additional  larger  mechanisms  t h e relative most  B74) .  approximately  (BDH74,  eV  ccntinua.  are  t o the  FC68,  i s  solely  and apparently  3  (shake-up),  (shake-off),  2p  i n  (MC68,  be r e q u i r e d  features  somewhat  barrier  ionization  would  They  i n CH C1  that  excitation  as  i n the  t h e  differences  these  is  i n  energy  features  c a . 1.6  s p i n - o r b i t components  delayed  to the atomic  i s considerably  of  i f these  an  channel  which  splitting  at  centrifugal  of these  difference  the  the  ionization  spectra  i nanalogy  t o occur  to  t h e separaticn  eV i n a l l f o u r  the  due  2p—*-ed  However  which,  may b e e x p e c t e d  threshold  dominant  6  2p  and  3 / 2  features.  continua, t h e  spectra.  and can c l e a r l y i n angle  most  figure  9.3.  facilitates  An attempt  observed i n interesting  The s t r u c t u r e i s  be seen  i n  the  Examination t h e  h a s been  o f the  observation made  long  of  t o enhance  236  their  visibility  representing the  noted  that  the  estiaate The  a  data the  and  considered  are the  the  C l 2p  continua  shown i n f i g u r e 9.4  error  along  background.  intensities  This  smooth  curve  non-oscillatory portion  f o r the  However t h e  the  a suitable  subtracted  extent. in  of  curve strongly  curve.  lesser  of  results  relative  difference  background to  subtraction  chloromethanes  original  in  an  continuum.  four  by  of  the  depend  on  of  treataent  of  all  with  the  I t should  be  maxima and  minima  the  of  energies of the source  of  choice  features  error for  has  the  the vary been  following  analysis. This  Pig.  9.3  structure  most  likely  arises  from  interference  Long r a n g e s c a n o f C C 1 . The locations of o n s e t s of s u b s h e l l i o n i z a t i o n are i n d i c a t e d . 4  the  237  F i g . 9.4  Structure in the Cl 2p continua of the chloromethanes.  238  effects  associated  with  chlorine  2p  off  electron  i.e.  EXAFS.  (N.B.  in  fast  i n e l a s t i c a l l y far  the  electron  similar  to  interference  with  the  section  the  R  phase k  i s  I P ) )  i s  the  '  interatomic  between  electron  .  (E-IP)  outgoing  electron  1  loss,  2  E  and  indicates pattern should  an  of  wave i s  the  be of  molecular  f i e l d  be  EXAFS  to  to  only  pattern  atoms  w i l l  According  electron  expected  arising  wave  located follow  a  single from  and at  that  the  the  same  r e l a t i o n  the  be  k  a  spacing,  outgoing  number  by  (9. 3. 1)  • 20]  and  given  (in  kinetic the  maxima to  spaced  a  values  of  maxima  determine  energy  ( i n eV)  This  interatomic When  spacing and  this can  energy  interference  backscattering,  using  distance only  one  the  EXAFS  relationship be  minima  the  relationship  single  the  of  the  i n  k-space.  the  and  ( 0 . 2 6 5 (E-  between  IP.  the  wave  by  l  minima  analysed  interatomic  /3  A~ )  difference  in  dominates  simply  the  and  and  backscattered  ionization potential,  distance  of  - a )  the  given  evenly  may  estimate  plot  the  corresponding  interatomic pattern  the  that  be  w i l l  4.6):  s h i f t the  electron  the  interactions  a l l identical i s  molecule,  subsequent  outgoing  source  ejected  spectroscopy  considers  the  the the  loss  photcabsorption) .  I «• s i n [ 2k (H where  any  of i n  incident  the  LSS75),  from  from  that  atoms  energy  which  between  backscattered  (see  so  i n  (Sn74,  other  electron  model,  scattering  distance  away  those  simplified  the  scattering  scattered  s u f f i c i e n t l y ejected  the  derived  from  versus  n,  and a an  239  integer.  The  slope  of  simple  model.  according  to  the  are  i n  LSS75  given Since  also  the  because  and  Cl  there  combinations,  are  are  mere  better C l - C l  the  of  the  c h l o r i n a t e d species.  higher  spectral simple  EXAFS  calculated linear  9.5.  A.  model.  The  the  9.3)  give  These  are  values  listed  three  to  are  approach  sets slopes  values  only  n  these  (R-<x  of  the  data  of  s l i g h t l y  CHCl  )  continua and  3  CC1  above  features  4  the this  and  the  while  the  values  i s  clearly  shown  i n  figure  l i n e s  between  larger  C-Cl  with  9.3  and  expected  2p  analysed  and  of  be  numbered  table  k  the  Cl  CH2CI2/  of  i n  than  might  the  been  energies  squares  rise  i n  (those  have  between  lewer  least  9,4) The  wavenumbers  i n  spacing  For  features  figure  relationship  indicated  table  i n  this  electron scatterers  interference pattern  continuum  curve  of  combinations  inter-chlorine  dominate  the  7r/(2(R-a))  i s  Examples  to  more  plot  LC76.  atoms  the  this  (listed 2.9  than  i n  and  3.4  the  Cl-Cl  a l l  three  o  distance  which  molecules phase  (UTS50,  phase  t h i s  It  of  because continuum  the  of  less  than the i n  investigations  by  the  2.9  BBS55) .  similar  apparent  interpreted portion  are  EXAFS i s  of  to  structure within  s h i f t s  previous  close  MG52,  { a )  s h i f t s  explain  i s  that  simple  0.5  rapid  intensity,  energy  would EXAFS  magnitude  EXAFS  f a l l s  in off  to  be  dependent required  model. those  to  Such  found  i n  can  be  CEK76) .  observed  decrease  which  A  simple  interference pattern  the  in  Thus,  (LSS75,  the  A  s t r u c t u r e  model.  Only  a  limited  can  be  the  e l e c t r o n energy  more  observed,  rapidly  partly  than  loss i n  240  O r d e r of M a x i m a  Fig.  9.5  a n d M i n i m a (n)  EXAFS plot for the features observed in the Cl 2p continua of C h ^ C ^ . CHCl^ and CCl^ and the C Is continuum of CC1/,.  241  Table 9.3: EXAFS a n a l y s i s o f f e a t u r e s observed i n the C l 2p c o n t i n u a of CH„C1„. CHC1, and CC1, and the C Is continuum of CC1,. 2 2 3 4 H  (») Chlorine 2p restores CH C1 Order of Hax/Hin 2  eT  2  E  CHCL  3  eV 228 (1) 2.30 (6) 236 (1) 2.73 (6) 208 (2) 3.28(8) 263 (2) 3.82 (8) 0.50 (3) 3.2(2) 2.91  I-  229 (1) 2.01 (6) 236 ( 1)2.75(6) 5 200 (2) 3.13 (8) 6 262 (2) 3.80(8) 7 0.06 (6) Slope(*.-«) 3. 0(0) (R-o) (M , P. (Cl-Cl) (M 2. 90  c  «  d  e  CCl  4  E . eT  228 (1) 2.30(0) 235 (1) 2.67(0) 209 (1) 3. 33(6) 260 (2) 3.87 (8) 0.50 (0) 2.9(2) 2 .89  (B) Carbon 1s Features (CC1 ) Excerioenta 1 Predicted Order of kb k Ha x/Bin E E (n) i-» eV 2. 00 3e 1V 9 2.36(10) 317(2) 2 3.23 336 336 (2) 3.26 (10) 3 0.12 360 1.12(10) 360(2) u 5. 01 391 5 5.90 • 28 6.02(12) 133(3) 6 6.79 070 7 7.68 519 8 0. 89(0) Slope («->> 1.8(1) (P- a ) [h 1. 76 B (C-Cl) ( M a. The n rallies were chosen to «ake the intercept of the k versos n plot as close to tero as possible. b. The ootgoinq electron vavenuabers were calculated froa •quation 4.6.2. The value of 207.0 eT used for the Cl 2p IP is a weighted averaqe over the spin-orbit coaponents. c. The nunber in brackets gives the estiaated uncertainty in the last figure. d. The values of (B-a ) »«re derived froa the least squares detereined slopes and the relation given in the text. m. The interatoaic distances a r e derived froa gas phase •icro«ave and electron diffraction e x p e r i B e n t s . f . The predicted values were calculated froa the relation k«0.89n • 0.56 obtained fros a linear fit to the four c o n t i n u u B features observed in Fig. 9-6. 4  f  a  c  d  e  242  the  photoabsorption  kinematic also  factors  limited  structure. which  (171).  already may  overlap  plot  shown  known  t o have  closer  been  also  i n figure  t o  t o threshold  Since  f i t t i n g  i n t h e two C l 2p c o n t i n u a  out  t h e interference  separation  of  effects  maxima  Also  close  and minima  spin-orbit  splitting  o f 1.6 e V .  splitting  i snegligible  when  An  EXAFS  interpretation  i st h e fact  EXAFS very of  not  C2H5CI. of  present This  than I t  expected  s  i n  t h e  strongly  to  features  will  effect  that  t o wash  where  of  between  point  the  t o  maxima a n d  supporting  the  assigned  i n CHC1  intense  the  spin-orbit  t h efeatures  by t h e d e c r e a s i n g this  3  and  number structure  of either  an EXAFS-type  this  o f t h e EXAFS  be comparable  be d e t e r m i n e d  observed  structure  effects  threshold  C l 2p c o n t i n u a  supports  model i s  CH Cl o r 3  interpretation  i n t h especies  containing  one C l atom. should  explanation ascribed  i  s  effects.  may b e e x p e c t e d  relatively  As f a r a s c o u l d  t h econtinuum  more  a  2  scatterers.  is  4  i n CH Cl2  weak  t h e overlap  additional  i nCC1 ,  arestrongest  electron  EXAFS  scattering  t h espacing  grows large.  two  interference  The  minima  t o  do n o t l i e on t h e l i n e a r  due to multiple  structure  i s  threshold,  interference  the.  i snot unexpected.  structure  C l 2p  the simple  discepancy  impact  t h e C l 2s and C 1s  t h e  from  electron  EXAFS  attributed  arise  9.5.  problems  t o  with  numbered 7 and 8  t h e maxima  closest  of  The s t r u c t u r e s  transitions,  due  The observable  because  have  However  spectrum,  be  could  t o EXAFS.  noted  that  be p r o p o s e d This  would  a  possible  f o r t h e most involve  alternate  intense  assignment  of  feature feature  243  9  t o a double  which  both  removed onset  ionization a  C l 2p  i n a single occurs  required  section  4.2) t h i s  difference  potentials molecular of the  between  structure  obvious  reason  i n three  Therefore  t h e EXAFS  in  The  observation  continua  inspired  in  carbon  t h e  expected be  more  ionization  to reflect extended  analogy  i s  model ( s e e  single  ionization  Considering  that a l l  reasons.  just  9.4).  F i r s t ,  Seccnd,  thelack  of observable  ionization  a t  5  2  interpretation  i ti s  excitation  o f CH C1 and C H C1 3  this  i t does n o t  before t h e C l 2s  this  as there  continuum  this i s nc  would  be  molecules and not i n the fourth. i sc o n s i d e r e d t o  f o r t h e higher energy o f CH2CI2, o f EXAFS  CHCl  3  features  continuum. t h eshorter  i n energy.  Although  o f energetics,  a search f o r similar 1s  chloromethane  process.  on t h e b a s i s  interpretation  t h e C l 2p c o n t i n u a  energy  expectedf o r  o f these  explanation  the  9 i sa p p r o x i m a t e l y t h a t  why a d o u b l e  observed  that  the  t h e location  observed  against  i n  estimate,  i n t h e C l 2p s p e c t r a  argues  and  i n this  following  (see f i g u r e  energy  correct  double  a r eignored  i splausible  therise  core  ( 2 7 . 5 eV - FDR69) .  f o r the  structure  the  of feature  interpretation  suggesting  t h e  events  s h o u l d be a p p r o x i m a t e l y e g u a l t o  o f t h edouble  explanation  explain  energy  I n this  to  from  a valence electron a r e  a C l 2p ionized  According  effects  onset  rejected  ionize  o f argon  t h eonset  2 3 3 eV  arising  and  transition.  t o further 26 eV.  the  electron  around  around  continuum  This  features  the  observed  and C C l . 4  i n  the  chlorine  oscillatory structure  C-Cl distance  Since  be  thecarbon  structure would  and thus 1s  2p  be would  continuum  244  falls  off  continuum only  rapidly (see f i g u r e  on  CCl  up  4  to  is  9.3)  which  4  EXAFS s t r u c t u r e . CC1  and  this  is  Figure  600 eV  much  weaker  than  experiment  expected  9.6  shows  energy  loss  the  was  C l 2p  performed  t o have t h e most i n t e n s e the  C 1s  along  continuum  with  the  of  smooth  background  t h a t was s u b t r a c t e d t o o b t a i n t h e  upper  A  a t 360 eV  i n d i c a t i o n s of  maximum  two  weaker maxima  analysis  of these  is clearly  observed  a t 3 17 and 433  eV.  with  The r e s u l t  f e a t u r e s i s presented  curves.  o f an EXAFS 9.3  i n table  and t h e  o  upper c u r v e derived  of fxgure  from  The v a l u e o f 1.8(2) A f o r (R- a )  9.5.  this analysis  is  equal  to  the  C-Cl  spacing  0  [1.76  A (BBS55) ]  supports  positions  of  higher  EXAFS p a t t e r n a r e shown  observable  structure  surprising However,  an  the  energy  these  analysis  explanation  for this  reasonable  value  have o b s e r v e d  similar  photoabsorption interpreted  of  as EXAFS.  appears  The  4  of  somewhat  o f t h e 360  eV  feature.  for this  to  be  especially  CF  absence is  undulations of  The  energies  (R- a ) o b t a i n e d .  continuum  features.  seems e n e r g e t i c a l l y  structure  weak  This strongly  maxima and minima i n  9.6.  interpretation  ionization  EXAFS  these  in figure  at  alternate  estimate.  of  considering the i n t e n s i t y  terms of double thus  the error  t h e EXAFS i n t e r p r e t a t i o n  predicted the  within  feature i n  unlikely  a  and  satisfactory  considering  the  Brown e t a l . (BBB78) in  which  the have  carbon also  1s been  245  F i g . 9.6  Structure in the C Is continuum of CC1 4  246  9.4  Chlorine  2s  E x c i t a t i o n of  Chloroethane  and t h e  Chloromethanes  Weak  structure  ionization  of the C l 2s electrons  in  t h e spectra  Cl  2s  region  values in  and  the  t o  7  most  clearly  edge  are  i n t h e CH2CI2  arising  of t h e C l 2s hole.  atomic  C l 2s  agrees  which  are  level  well  i n figure At  f i r s t  2  glance, that  spectrum.  The  s i m i l a r i t y  while a l l  common  t h e term  four  expected  values  spectra (R74,  located i s some 10  and  c a n be  seen  because  of  Coster-Kronig width  of  t o b e c a . 2.5 eV  the  (KRK74) .  of feature  i n a l l o f t h e C l 2s  the assignment  as  a  eV  most  10  spectra  9.2.  ambiguous  suggests  the rapid  widths  term  2s e x c i t a t i o n  to observe  the experimental a n d 2.5  This  Coster-Kronig  i s calculated  with  between  The  i s  There  Chlorine  from  of the  The  feature  molecules.  eV  observed  9.2.  spectrum)  i n between  d i f f i c u l t  view  features  and  270  energies,  threshold.  spectrum.  t o be  The  i n table  10 i n e a c h  a l l four  above  expanded  9.4.  given  intensity  linewidths  An  f o r t h e  the ionization  f o r  e x c i t a t i o n  i s observed  i n figure  (labelled  are expected  large  shown  spectra  with  9.2.  assignments  of spectral  C l 2s  This  seen  below  the  decay  c a n be  feature eV  features  i n figure  tentative  indication  the  shown  C l 2s  prominent 6  associated  f o r  R75)  the discrete among  assignment  the based  f o r feature  t h e terra  of  value  f o r either  feature features five  on  Rydberg  10 a r g u e  i s  much  C l  10  as  i n t h e C l 2p 2s  spectra  t r a n s i t i o n s  against larger  i s  this. than  In that  t r a n s i t i o n s t o the lowest  p  247  Rydberg  orbital  transition even  for  involving  the  assignment involving  peak  and  In  10 a r e 1.5  binding  methyl  peaks  hole  halogen  0.8  eV o f e a c h  for  the  to  rule  out  the  Rydberg  C  of  argue  in  10  3  carbon  favour  (HB78a,  the  than that  1s  of  a  chapter  term  values f o r  for  the  1s s p e c t r u m .  This  v a l u e to a t t r i b u t e  of the e x c i t e d  CH C1,  electron,  first  seems too  to the  effect  of moving  the  t h e c h l o r i n e t o t h e c a r b o n atom.  In  the halobenzenes  carbon  the term  values  t o t h e same f i n a l  inner-shell  spectra  for  orbital in  were  within  other. the  shift  a  magnitude  of  t h e term  v a l u e s seems t o o  valence  or  Rydberg  assignment,  i n the e x c i t a t i o n  one  spectra  were used  (HB78a,  (T70, 0K76)  consistent  orbital.  v a l u e s f o r t h e C l 2s  for feature  to t r a n s i t i o n s  either  following  2s IP  Rydberg  peak i n t h e  energy  to support a v a l e n c e assignment.  halide Cl  i n term  from  and  Although  used  used  t o 2 eV l a r g e r  h a l i d e s and  the  chemical  f o r the f i r s t  was  energy  assigned  large  to  s  - or  obvious support f o r assignments  t h e . corresponding  inner-shell the  lowest  seem  Rydberg  a C l 2s e l e c t r o n  the other three chloromethanes  in  the  of  intense  e x c e p t i n the spectrum  (C-Cl) assignment  large a difference on  most  between t h e term  that  (5.0 eV)  2s—»• cr*  peak  values  similarity  (5.5 eV)  feature  the  valence o r b i t a l s  the  7).  to  t h e y do n o t o f f e r  spectrum Cl  term  s h o u l d be t h e excitation  transitions  Although  where  - which  increase  10 c a n  be  Arguments s i m i l a r  to  i n the assignment  chapter 7).  (see  of f e a t u r e  table  towards  The  9.2)  the  XPS show  of the  methyl  v a l u e s f o r the a  t h e more c h l o r i n a t e d  small  but  methanes.  248  This  i s the chemical  shift  electron-withdrawing molecule. for  However  excitation  increasing  i s  given  the  of  i n  chlorination  the shifts  the  must  upper be  i n t h e C l 2p. o r b i t a l  s h i f t  i n  energy  excitation  shift of  molecules, with shift  should  resulting  increasing i s  chlorine  chlorination.  10  transitions  t o  which This t o  a  molecules.  This  corresponds  given  the  C l 2s  for  disagreement the  C l 2s  explained can shell  between and  by  C  hole  localized  Is  when  values to  inside  (C  of  f o r  the  1s) w h i l e  of  observed  a  strongly  of f o r  feature a l l  four  7).  The  transitions level  barrier  of moving levels  the other  upon  previously  (chapter  potential  inner  increases  antibonding  t h e a * (C-Cl)  the effect  orbital  the  assignment 3  not the  i n a l l four  assignment  of CH C1  the  observed  which  orbital  10,  than  the  However  less  lower  further  the  same  energy  the  spectrum  t o amplify one  give  the  a* (C-Cl)  levels  upon  behaviour  to  and  f o r feature  o r b i t a l ,  about  suggests  feature  i s definitely  becomes  t h e term  upper  with  orbital  magnitude  to  Rydberg  the influence of the  be c o n s i d e r e d  i n  This  the  observed  frozen  Thus  substitution.  with  orbital  further  energy  be  i s  the  i n energy  energy  i n an e x c i t a t i o n  consistent  ant i b o n d i n g  the  larger  f o r a  a  of  f o ran e x c i t a t i o n i n  energy.  expected  which  In  o r b i t a l  even  shift  decreases  i n the transition.  change  chemical  shift  increasingly  remainder  chemical  which  chemical  involved  change  10  the  the  substitution.  the t h e sum  from  of  the opposite  chlorine  by  orbitals  nature  feature  approximation  expected  an  from may  be  which inner-  involved  i s  ( C l 2s) i s o u t s i d e  249  the  barrier.  the  barrier  The is  fact  that  expected  to  the  discrepancy  be  the  i s  largest  largest  where  supports  this  explanation. A shift Cl  2p  s i m i l a r ,  although  of  excitation  the  region.  assignment (scheme  B  in in  the  the  2p  feature  and  10  is  to  to  a  This  maximum  which  i s  of  electrons.  and  i s  1s  300  eV 1s  ionization  measurements The  excitation  in  (0K76) spectral  are  10  loss figure  Cl  to  i s  l i s t e d  the p  Cl  2s  of  in  onset  of  threshold  less  region. a  valence for  in  9.2.  table  edge  i s  then  orbital.  the  Cl  these Cl  the  preferred  Rydberg  maximum the  2s  the  o r b i t a l s i s  argument  position  2s  2s  I t edge  spectra. ionization  for  ionization  Chloroethane  spectrum 9.7.  indicated  to  i s  and  the  close  of  the  shift  lowest  to  features  expected  in  in of  argument  assignment  potentials  are  the  than  weak  peak  energy  shown  valence  the  that  Excitation  electron i s  to  to  feature  note  peak  promotions  p o s s i b i l i t y  to  f i r s t  chemical  favour  Rydberg  t h i s  the  i n  chemical  attributed  The  K2.  a  further  expected  Carbon  carbon  and  to  to  the  in  argue  region  transitions  corresponds  9.5  than  occurs  of  although  this  between  interesting  s  of  only  structure  assigned  Cl  basis  rather  used  involving 9.2)  trend  energy  be  table  assignment  The  can  scheme  convincing On  This  weaker  The as by  a r i s i n g overlap  C2H5CI  of  between  location  of  determined the from  lines  the  284 twc  by  XPS  labelled  Ki  C2H5CI  considerably  carbon  1s  because  250  transitions aethyl will  inner  which  have  level  unoccupied  will  large  on  (C ) t o t h e sane  the  occur  same  only  Because  to  expansion atom.  transitions  unoccupied  C2H C1  spectrua  of C H Cl 2  that the similar,  c a n be e x p e c t e d t c  5  and CH3CI  4  spectra.  o f t h e f e a t u r e s o f t h e C H C l C 1s s p e c t r u m 2  a  f o r atomic  are  5  from  orbitals  Thus, t o t h e e x t e n t 3  excitation  orbital  inner-shell  coefficients  i n C B 4 , C H C 1 and  by t h e s u a o f t h e C H  All  1.0 eV.  (C^) and t h e  final  2  only  LCAO  orbitals  carbon given  by  carbon  i s s p a t i a l l y l o c a l i z e d , strong  given  orbitals  the nethane-like  carbon  separated  excitation  be  both  chloride-like be  the  from  5  (figure  10H C  2  H  5  C  •s c >. o i  0-8H  w K,  o  g  0-6-  I  1  284  9.7  2 H  UJ  Fig.  K  I  2  —I 288  I  4  1  I  I  5  "  T  T  292 296 E N E R G Y L O S S (eV)  300  The e n e r g y l o s s s p e c t r u a o f C H C 1 i n t h e r e g i o n of C 1s e x c i t a t i o n (AE=0.5 eV FHHM). Ki a n d K i n d i c a t e t h e t h r e s h o l d s f o r 1s i o n i z a t i o n of t h e • e t h y l ( C ^ and a e t h y l c h l o r i d e ( C ) c a r b o n s . 2  5  2  2  251  9.7)  occur  at energies  features C2H5CI Full the  i n  spectrum  given  i n  chloride chloride  withdrawing apparent  of  from  C  t h e  A second  f i r s t from  1s—»-3a peak  t h e  of  C2H5CI  spectral  from  either  or C  and  CH C1 3  spectra  2  t h e  group.  o f  the  due t oan  the  by  ethyl  and methyl  may b e p a r t l y of  a  spectrum  the electron  This  shift  i s  of thecorresponding  features  agrees  with  I P  of  causing observable differences  i n  the  5  t h e symmetry  has been  o f t h eCH  4  features excitation cn  C  on  the  corresponding t o the removed.  intense  than  Although  spectral  the  restriction  i n C2H5CI  i s more  based  and  t h e difference 1s  2  t h e C2H5CI  the  allows  which a r e  principle.  o f an a d d i t i o n  are  t h e methane  I P c f C H C1  1  that  C2H5CI  features,  two peaks  shift  transition  additivity  explanation terms  i n  with  simulate  i s caused  transition  (3s)  comparison  7)  portion  3  factor  Rydberg  C  which  This  spectra.  u n s u c c e s s f u l i n terms  o f t h eCH Cl  t h eK  C —»-3s 4  of  This  t h eenergy  i st h efact  CH  )  t o  strong  these  comparison  energies of thef i r s t  spectrum 1  n  spectrum.  0.4 eV b e t w e e n 4  this  sum  appearance.  0.3 eV a b o v e  CH .  t h e  t o  chapter  of  and therefore the  including  an attempt  was r e l a t i v e l y  character  4  analogy  o f the. m e t h a n e - l i k e  i n  theCH  by  energies  soectra  Although  as  spectral  (transitions  about  9.4.  assignment,  shift  the  CH-Cl  (HB7 8 a ,  3  spectra  t o  t h eassignment,  spectrum  resulting  and  a n d CH C1  table  satisfactory  energy  of  (KB74b)  4  CH.  i sa s s i g n e d  details CH  in  t h e  close  shape  and CH Cl 3  Thus,  may b e a  b e made i n  spectral  c a n be i d e n t i f i e d  energetic  expected  guantitative  cannot  by a c o m p a r i s o n  the  as  with  shapes, arising t h eC H  4  considerations.  Table  9.4: A b s o l u t e  E n e r g i e s ( e V ) , Term V a l u e s  Features  C F C1 T(C,) Enerqy 2  #  1 2 3 4  *,  5  291. 4  r d  292.1 T h e CH^  b.  T(C ) 4.8 3.9 2.8 1.5  energies to  The C H ^ C l  C Is excitation  in  9.1.  similar  CH 4 En erqy  a n d CH_C1  2R7.0 288.0 289.4  IP  290.76  Features  a r e from  excitation  WB74b.  corresponding  to  HB78a  Excitation  are listed  The term  values  d.  F r o m XPS  (OK76).  are with  respect  comparison.  CO 8  291. 3  6p  IP  292. 3  CO  T h e CH^  spectrum  (chapter  excitation  7).  i s shown  to occur  i n figure  at similar  The CH^Cl  spectrum  i n C2H,.C1 a r e e x p e c t e d  t o t h e IP o f t h e i n d i c a t e d  carbon  2  c**(C- C l ) 4s 4p 5p  4s 4p 5p  287.3 288. 4 289. 4 290. 9  energies.  c.  for  Ass iqntsent f ron c f r o a C,  CH C1b Enerqy  i n C2H,.C1 a r e e x p e c t e d  e n e r g i e s a r e from  for C Is  C Is spectra  3  #  1 2,3 4-6 7  1,2 3-5 6  0.7  corresponding  figure  *  C  2  C Is excitation  Features  o f t h e CH.  a  3.8 2.9 1.8  291. 1  Analyses  5  287.3 288.2 289.3 290.6  d  a.  of CLH-Cl.  and T e n t a t i v e Assignments  Is electron.  9.1.  energies. i s shown  to occur at  253  Comparisons C2H6  (HB77,  discrete  between chapter  the  C  may  also  5)  structure  seems  superposition  o f t h eCH C1  the  relative  to  continuum that  9.6  observed  made.  Although  t h e  accurately  described  as a  and C H  spectra,  4  to t h ediscrete  i nt h eC  o f  1s spectrum  the intensity of  structure  i s  similar  o f ethane.  Discussion  From  section  explanation can  and  spectra be  more  3  C2H5CI  1s  be  Thus  i  o f t h ecarbon  given  t h e  9.1,  i n terms  u t i l i t y  o f  this  regard,  i t i s  interesting  carbon  Is  spectra  (WB74d,  i s  with  and with  barrier  i na l l three  valence  strength  type  potential  The  from  transitions  barrier  t o the  (FZV70).  o s c i l l a t o r  model  supported  chlorosilanes model  of  o f t h eCoulomb  tool  BBB78)  apparent  1s s p e c t r a  interpretative  spectra  t i s  with  the  by t h i s  Rydberg  i s  study.  t h e  2p  of  addition  In  this  chloromethane  spectra  trend a  (D72).  fluorome thane  expected  of the by t h e  redistribution  transitions  because  model  gualitative,  corresponding t h eS i  reasonable  chloromethanes  a  compare  series  a  barrier a s  dominant  t h e  that  t o  the  of  inner-well,  growth  of  a  o f  electronegative  a similar  redistribution  substituents. In to  thefluoromethanes  that  intensity with CF  4  seen  i nfigure  becoming  increasing (WB74d,  BBB78)  (BBB78)  9.1 i s o b s e r v e d ,  concentrated  i n the  fluorination.  The  i ssimilar  t o that  with  the spectral  valence carbon of  transitions 1s s p e c t r u m o f  CC1  4  i n  that  a  254  single  broad  peak,  dominates  the  observed  superimposed  widely has  CF  assignable  spaced  been  to  is  than  CC1 .  orbitals  expected  to  be  absence  C  show  any  Aside  features  from  barrier  the  predictions strength appear  i s  dominated  spectrum  attributable  to  structure  trends  in  of  in  terms the  somewhat with  the  seem of  a the  the  the  to  by  CC1  CF  is  complete ionization  the a  F  single  which  4  due  to  i s  dees  barrier  spectral  i n not  effects.  spectrum,  4  1s  strong  This  satisfactory  Si  the  qualitative  intensities  2p  contradict  the  spectra  the  intensity those  of  barrier  redistribution  experimental different  to  fluoro-  chloromethanes.  and  barrier  the  by  for  be  the  state.  the  This  might  presumably  of  i t  of  fluoromethanes.  inspection, (FZV70)  the  potential  in  the  spectra  edge,  thus  outer-well  by  inner-well  give  since  comparison  2p  That  also  too  larger  region  at  1s  i s  the  intensity  to  f i r s t  chlorosilanes  Cl  of  and  i s  (WB74d).  barrier  both  F  and  i s  electronegativity  indicated  seems of  inner-shell On  the  the  4  (F 1 s . t g )  fine  model  understanding the  to  effects  since  CF .  i s  4  structure  structure  inner-well  i n  the  the  contrast  the  which  to  This  penetration  BBB78)  close to  that  transitions  weak  transitions  surprising  CF  173)  peak.  Rydberg  continuum  (WB74d,  transitions marked  1s  in  (w'B74d,  transition  vibrational  smaller  larger,  threshold  to  into  considerably of  this  the  1s—*-t2  However,  suggest  Thus  4  C  on  to  would  Rydberg  spectrum  due  somewhat  considerations 4  be  assigned  observation  CF  spectrum.  4  to  of  the model  oscillator  distributions  expected  from  Thus,  a the  255  Si  2p  spectrum  easily  identified  weaker peak  features, with  However, spectra for  of S i C l  transitions  to  of  C  •7a  1s(1a ) 1  weakly  2p  ( t  that  at  levels  highest  which  potential  i t  i s dipole energy,  decreases,  the  Si  3d  overlap  other  chlorosilane  pretation and  of  the effects  given  of  (BNZ72).  the a  satisfactorly  f i r s t  two  features  the chlorosilane  present  forbidden  whereas  the  level  third  from  strong  to excitations are localized chlorine  very  more weak.  Rydberg  a  more  spectra  the  peak,  t o S i 3d  inside  the  substituents  diffuse This  and the process,  t r a n s i t i o n s i n the  the observed  with  electronegative  2  only  becomes  A  the  t  a t most  The  explains  strong and  1  except  of  i s observed  of  and  to  inner-well  1  and thus  substituents.  of  Thus,  the  allowed.  valence  spectra  model.  that  symmetry  orbital  of spectral  electronegative  spectrum  t r a n s i t i o n s become  with  number  Is  As t h e n u m b e r  S i 3d  along  the  analogous  4  side.  contributions  i s  i n CC1  broad  these  be  The  i s assigned  are low-lying  barrier.  2 p — • S i  to  can  of  that  t r a n s i t i o n s to the a  C  4  i s  transition  ) level  2  CCl  the barrier  the  number  low energy  suggests  states.  This  a  i s a single  4  dominant  t o S i 2p  transition  because  corresponding Si  1  with  (neglecting and  the  (QNZ72)  of  inner-well  the  on  spectrum  4  terms  levels.  assignment  3  structure  S i C l  are attributed  inner-well  o f S i(CH )  i n accord  the  i n  that  peaks  splitting)  analysis  are i n fact  interpreted  peaks  fine  detailed  example,  3 strong  spin-orbit  whereas  seme  a  shows  4  decrease i n  decreasing  number  detailed based  on  substituents  MO  of  interconcepts has  been  256  Thus three  series  barrier three the  show  series  i t  they  related The 1s  the  of  EXAFS  twice A  (B54)  s h i f t  eV  of  multiple  gases.  most  carbon  most  1s  simple  potential of  the  spectra  of  to  informative  as  interpret  examples  through  a  of  series  this  in  9.3).  observation  CF  EXAFS,  of  terms  would  regularity  not of  are  large  terms of  to  of  shake-up  seem these  scattering technigue  to  be  Dehmer  the  A  CF  of  EXAFS  CF  to  phase F  4  be  explain  Alternatively, D i l l  may  i s 1.9  model.  could  4  are  which  dependent  and  the  features  processes able  of  these  simple  that i n  distance  energy  features. of  observed  3.8(2)  explain  the  electron  note  spectrum  i s  from  results  by  to  these  ( R - a)  actual  derived  EXAFS  i n t e r fl u o r i n e  4  reguired  i n  of  and  largely  These  interesting  when  2p  the  (R- a )  photoabsorption  value  be  between  table  to  C l  convincing,  (see  unreasonably  features  very  However,  the  to  high-lying  of  It i s  X-ray  an  the  values  due  derived  seem  interpretation  apparent  the  by  in a l l  comparison  the  f i r s t  (L73) .  Thus  would  although  the  seems  and  the  the  large  .  continuum  explained  correspondence  possibly  the  as  be  c e n t r a l atom  potential barrier  analysis  on  continuum  analysed  a  close  spacings  studies  50  of  the  structure  the  undulations, f i r s t  that  perhaps  of  the  foregoing  i n t e r p r e t a t i o n of  constitute  impact  1s  one  growth  EXAFS  simple  thus  are  can  the  appparent  of  molecules.  interatomic  F  i s  continuum  because  which  From  are  apparent  spectra  trends  concepts.  thus  the  C  inner-shell  chloromethanes  and  of  the  1s An  given the the be  257  useful. and  This  near-edge  manifestations f i e l d s  on  therefore continuum  approach 'potential of  the  escaping i t  treats  extended  barrier  electron  effects*  optical  photoelectrons  be  uniguely  suited  features  in  the  spectrum  1s  effects  (DD75,  may  F  continuum  to  as  related  of  molecular  DD76a,b)  explain of  features  CF . 4  the  and  unusual  258  CHAPTER ISEELS  The been  STUDIES  e x c i t a t i o n of  previously  photoabsorption (S  2p,  (F  1s  2s -  these  -  the  spectra.  A  to  quasibound  barrier  simple  seemingly  ZV71,  s a t i s f a c t o r y  photoabsorption  spectra.  been  i n t e r p r e t i n g  useful  spectra they of  i n  of  other  a r e composed  molecules of  a  electronegative x  4  Recently inner  s h e l l  a  more  features  resonances. consistent to  the  and  the  This f i e l d  1s S  (HB78b,  2p  X«)  are  been  explained  technique  SF  6  i n  of  to SF  with  i n  a  and  terms  N  and  SPK74,  has  that  number CPT72) ,  to  the  without i n  of  which shape  scattering  f a r only  (VKK74,  by  6  presented  CO  SF$  etc.].  so 2  a  e x c i t a t i o n  approach  (multiple has  the  HB71,  9)  a  given  explanation  (F68,  of  inside  has  s h e l l  molecules  has  MS-SCF-X^  of  3  i n  terms  of  surrounded  chapter  of  excitation spectra spectrum  of  t h e o r e t i c a l  substituents  S7U)  intense  l i m i t s  i n  similar  [ e . g . BF  general  D72,  are  GK M 77} ,  considerable  localized  type  BK73) ,  unusual,  inner  atom  excitation spectra  electronegative prominent  x  same  which  ligands  been  explanation  the  central  ZV72) , C U C l 4 -  SiF (ZV71,  The  X-ray  LD66,  description states  has  0  by  i o n i z a t i o n  ZV72,  SF  BHK72,  the  the  excited  (N70,  has  of  below  BM62,  VZ72,  There  of  d e t a i l  -  NMH71,  q u a l i t a t i v e  potential yet  1s  i n t e r p r e t a t i o n and  levels  some  [ (S  L72b)].  above  HE X A F L U O R I DE  s h e l l  i n  BZF67,  r  VZF71,  observed  transitions  a l l inner  studied  ZF67  i n  features  SULPHUR  spectroscopy  LBK67,  interest  OF  10  self  been  applied  (DD75,  DD76a,b)  Mi76) .  I t  may  259  be  considered  because  i t  energies with  gives  and  the  on  useful  discussions shape for  ionic  giving based  a on  and  the decay  simple  of S  the  basis  2p  A  o f these  highly  approaches excited  q u a l i t a t i v e discussion  energy  Although  SF  photoabsorption differences excitation attempt  F  1s  D  among spectra,  11)  levels  been  the  are  the  relatively  there  6  well  are small  various  but  reported  p a r t i c u l a r l y i n t h e S 2p these  discrepancies  the inner-shell  Although apparatus  has  the electron-ion  has been  SF  11)  shape scale  considered. S  2s  and  i s used f o r inner-shell  spectra.  techniques,  to resolve  complement chapter  loss  the  the  f o r  model  the  chapter  i s  reported  of  of  the time  species  the  calculations  of  when  excitation, the MO-potential barrier  electron  not yet been  f o r use i n  contrast,  similarity  F  ensuing  remains  (HBW78,  calculations  the  schemes,  measurement 0  the  which i s  By  Since 1s  have  SF  agreement  model,  complex  recent  ionized  state  spectral  picture  necessitates  essential  excited  MO  intuition.  model  However,  barrier  physical  molecule.  fragmentation  resonance  minimum  chemical  particular  (KLW77a).  potential  treatment  emphasized  for  state  of  are i n reasonable  results  derived  resonance  each  has  excited  q u a l i t a t i v e  predictions  i n t e n s i t i e s which  easily i n  to the e a r l i e r ,  quantitative  experimental  qualitative based  preferable  coincidence excitation  studied  s i g n i f i c a n t inner-shell  region.  and a l s o  I n  an  i n order  measurements of the S  by  2p, S  to  (H BW 7 8 , 2s  and  studied. ISEELS  expected  spectra  obtained  to te dipole-dominated,  with  this  differences  260  between arise  the photcabsorption from  kinematic higher  two  cause  losses  approximately Second,  factors.  factors  energy  energy  First,  loss  of s p e c t r a l  with  r e l a t i v e  proportional  the t c  E~  momentum  process, can occur  i n  the  supporting  the assignment  S 2p energy  loss  spectrum  of a  o f f being  from  2.3) .  non-dipole  spectrum.  are  at  i n t h e i n e l a s t i c  non-dipole  o f SF6  i n t e n s i t y  section  transfer  ISEELS  can  scattering  f a l l  (see  3  contributions  transitions  spectra  the electron  a decrease  due t o t h e f i n i t e  scattering  and  Arguments  t r a n s i t i o n i nthe  presented  i n  section  10.3.  10.1  The S  2s  The S  2p  Potential and S  sharply  energy  Following these  loss  referenced  s h e l l  scale  to the location  of  spectra As  2p s p e c t r u m .  indicate  determined series  potentials. was u s e d  from  XPS  (GKM77). are those has been  the  obtained  a r e shown  the  F  1s,  S  L72b,  limits  D72)  inner-  average  of the  the r e l a t i v e  energy  these  on  components  of the S  f o rthe F  t y XPS m e a s u r e m e n t s (D72),  and  energy  respective  two v e r t i c a l l i n e s of  2s  r e l a t i v e  weighted  and a n a l y s i s  e a r l i e r  F 1s,  i n figure 10.1.  ZV71,  a common  t o locate  The  The i o n i z a t i o n  noted  A  position  (S HCl 6 9)  of t h e  (VZF71, on  components  o f the S  spectrum  been  0  placed  ionization  spin-orbit  of SF  presentations  have  of t h e  Features  regions  spectra  previous  Interpretation  Excitation  structured  spectra  scale  2p  Barrier  2p 1s  this as  Rydberg and S 2 s  (SNJ69).  the prominent  features  261  0  •10  1  1-0Sh. n IJ  + 20  •10  —r  +30 eV —I  r  F is  1  \i \  0-5H / 1g'"  t  a  •2fl  1 u  (A CL  6  0-  o o  1  680  ]  700  a  30-  LU h<  —  r  t2g  r  1  eV  720  e  -1u  20-  —i  r  S2s  g  cr  10H  r -  z  D  o o  o120H  r  1  230  250  1  t 1u /  40-  0-  \(R; .) d  a  1  170 Fig.  10.1  S2p  /1 /  eV  270  ft  80H  i  1  1  \  -2g  r  190  1  The energy loss spectra of SFg in the F Is, e x c i t a t i o n regions ( A E = 0.4 eV FWHM).  r  1  210 eV S 2s and S 2p  r  Table 10.1: Energies(eV) and Assignments of Features in the S 2p, S 2s and F Is Energy Loss Spectra of SF--. Absolute energy  Relative energy  Absolute energy  2 3/2  Pi  Relative energy  Assignment (final  +0.2eV  ±0.1eV  +0.1eV 2p  Absolute energy  Relative energy  orbital)  / 2  -8.4  173.2  237.4(5)  1  -7.3  1  688.0  -6.6  6 a  -4.3  2  692.6  -2.0  6 t  1,2  172.0  3,4  (175.8)  5,7  177.29  178.51  lu 4s (Rydberg)  6,8  177.98  179.20  4p (Rydberg)  b  (177.0)  b  -4.6  240.4  2  3 IP  C  9,10 11  180.4  181.6  183.1  184.3 196.1  IP  0  d  244.7  0  IP  d  694.6  0  694.6  0  +2.7  3  246.8(3)  +2.1  4  699.1  +4.5  15.3  4  258.9(5)  14.2  5  712.2  17.6  721.2 743.5  12  204.6  6  13  216  7  6t  lg  lu  2 t  2g  4 e  9  j two-electron j transitions  a. The r e l a t i v e energies are differences from the respective IP's. For the S 2p level the s p i n - o r b i t components of the a, , t, and t~ peaks gave the same r e l a t i v e energies (within +0.1 eV). b  The energies of the (S_2p_,6t ) components are estimated from a least-squares f i t of 2 gaussian peaks to the broad structure underlying the Rydberg peaks. See F i g . 10.4 f o r a clearer view. lu  c. The S 2p IP's are from XPS (SNJ69) and analysis of the S 2p Rydberg structure (GKM77). d.  The S 2s and F Is IP's are from XPS (SNJ69).  26 3  in  a l l of  same  the  SF  inner-shell  6  position  observation  i s  cn  manifold  largely  independent to  orbitals in  the  number  are  overlap  in  thought  i s of  the  to  be  these  o r b i t a l s  by  the  inner-well  upper  intense  transitions  from  level  2p  spectrum.  i s  indicated  transition S  2s  and  from  s  where  1s  a l l  four  of  The in  the  l i s t e d  6  by the  the 3a  spectra.  )  F  the  1s  SF  in  table of  the  inner-shell  qualitative,  a  (S  1 g  In  2s)  MO's  and  i s  (S  U  the  case  can  virtual  10.1. potential spectra.  two-dimensional  (S  g  1s) F  orbitals of  the  large  in  of  3  the  3  one  strong  levels 1s  i n  loss  , 1e )  g  and  g  to  observed. observed  spectra  10.2  gives  barrier  interpretation figure  the  excitation,  transitions are  i n  inner-wall  Figure  potential  parity  by  a l l features  energy  This  inner-  observed  only  strong  assignments electron  change  gerade(2ai  occur,  each  the  ungerade,  of  both  by  in  existence  of  1a-|  upper  The  l e v e l  single  hcle.  potential.  indicated  2p)  and  from  inner-shell  0  2t-|  a  are  atom  with  the  observation  inner-well  energies  presentation SF  u  Thus  Similarly  promotions  ungerade( 1 t i  the  of  a  sulphur  manner  orbitals  o r b i t a l s  which  transitions  requirement  transitions.  gerade  S  virtual  to  these  the  well  simple  This  inner-shell  around  double  a  of  model,  intense  in  l o c a l i z e d and  the  the  scale..  transitions  the  barrier  the  explained  e l e c t r i c dipole  the  of  about  energies  of  localized  region of  to  the  location  potential  identity  spectrum  levels,  at  energy  attributed  upper of  the  inner-well and  shell  of  occur  relative  logically  common  According  the  spectra  a  are visual  of  combines  surface  with  the a the  264  V a l e n c e , Inner-well  Ryd b e r g . O u t e r - w e l l MO's  ' MO's  S4s  F2 ~ >  -20.  |  -30.  S 3p  1x  -lOJ  /(5t *3e ) v >1t ^ 1u  2 u  4tiu  a  ^  g  S3s  9  UJ  z  UJ  •1  F2s  2e  -40-1  c  CD  ex  O  -100J  S2p  2t •200 J 3a  -500.  F1s  S2s  ift.  (2a ,1t .1e ) 1g  1u  g  -1500J  Fluorine AO's  Fig.  S1s  1aie  -2500J  10.2  SF  6  MO's  The molecular orbital  Sulphur AO's  scheme for SFg.  265  minimum  basis  diagram  the  sulphur  molecular  MO's  are  atomic  contributions  considerations. obtained UPS  from  (G74,  v i r t u a l  Green's  of  3e  v i r t u a l  the  shown  on  w i l l  to have  i n figure  of  the  to  quasidiscrete  continuum  of  the  from  a  and  where  (SNJ69),  by  the  four,  unique  be  that  the toe  curve.  emphasize  virtual  of  inner-well  orbitals  which  electron  o r b i t a l  of  promotion  i n  of  a  position  potential  to  an  by  taken  embedded  from  The  given  noted  created  inner-shell  orbital  photoionization  state  states  the  assignments  cannot  chosen  and  of  f o r the  10.2  was  were  frozen  I t s h o u l d be  i t s own  symmetry  spectra.  the  of  large  MO's  i s that  except  highest energy  rise  and  energies  excitation  one  10.2  fluorine provide  XPS  experimental  excited  this  L70)  the  orbitals  used.  electron  to  (L72b) ,  (NCD75)  i n figure  each  orbitals  localization  shell  In  0  occupied  deduced  orbitals  been  (M52,  while  SF .  those  the  inner-shell  based  have  shown  of  calculation  since  curve  energy  were  valence  to  of  expected  emission  MO's  (G78) ,  inner-shell  give  energies  1t2u  curve  l i t e r a l l y  The  The  the  sections,  potential  an  of  and  g  of  are  measurements  function  Gustaffson cross  basis  inner-well  ordering  the  the  scheme  only  which  X-ray  KMJ76)  interpretation  of  connected  orbitals  on  orbital  the  the which  ionization i s  being  excited. This  type  previously  j u s t i f i e d  corresponding orbitals  frozen  to  approximately  to  by  promotions  the  same  the  same  approach  the  claim  from  different  inner-well, position  virtual on  the  has  that  been  features inner-shell  orbital relative  occur  at  energy  266  scale. table  However, 1 0 . 1)  relative the  r e l a t i v e  energy  on  model.  t h e Z+1 been  o r b i t a l  increased  binding  been  effective unit  core  o r b i t a l s interact  the  outermost tightly  resulting  bound i n  as  higher  the  of  well,  most  an  inner-  i t s core  charge  inner-well  charge  leads  i n  a  fluorine  F  1s  The  as  effect with  6  C1F  1s  6  t o an  energy  of  electron  core fact  potential that  SF Ne 5  within the  the S atom.  S-inner-shell  the  has increased  because  excited  r e l a t i v e energies  a  inner-well-localized,  t h e system  i n a  electron  of  by t h e S F  strongly  potential  state  the ligands  has l i t t l e  electron  a  potential.  6  one c o n s i d e r s  well  as  of  spectral  (S7U, S75 ,  the upper,  when  be  rationalized i n  of  core  1s  absolute  of the  r e l a t i v e t o the binding  o f one  approach)  could  concepts  i n the ground  and  2 s , 2p a n d  inner-shell  o f  determined  C1F  charge  ( i . e .  analogy  a  the  ISEELS  double  sulphur  i n  between  treatment  analogy  energy  t h e energy  remains by  a  However,  0  promoted  than  energy  and  i n terms  increase  i n SF .  orbital  rather  core  the  unit  orbital  upper  when  i s s i m i l a r t o that The  the  to core  and  features  S  c a n be  analogy  i s equivalent Thus,  XPS  scale  with  10.1  difference  i n the positions  4.2)  promoted,  species.  one  atom.  1s s p e c t r a l  the  of t h e core  According atom  i s observed  of this  i n  shift  section  excited  that  half  the r e l a t i v e energy  see  shell  has  This  F  (see F i g .  of the corresponding  only  of a coupling  barrier  has  most,  scales.  SB76,  c a . 2 eV  t o " inaccuracies  features terms  of  inspection  of the intense  energies  At  ascribed  closer  difference  energies  features.  to  a  on  state  w i l l  excited  f o r peaks  by the  innerThus n o t be state,  associated  267  with  F  1s  promotions.  corresponding the  same  treats  S  within a l l  essentially  10.2  S  energy  2s  excited  additional  weak  shown S  2p  the parity 2p  peaks S  i s  errors  and  with  this  been  underlying  S  subtracted. features shoulder  above on  the S  occur  by a  as  of  the  at the  same  with  peak of the  spectra.  eV  and  F i g u r e -10.3c a  valence the  2s  IP there side  clear  spectra  i n the S  and  i n  184 eV  weak  shows  10.3b) a  2  has not  of  view the  has  been  of  two  observation  o f t h e 240 eV  (2t g)  further  estimate  an  the  structure i n  continua  i s also  2s  to the positions  figure  s h e l l  with  t h e low energy  The  visual  spectra,  structure  (6a.] g )  of  barrier  three  occur  close  10.3.  10.1  which  of these  features  The  concept  potential  i n a l l  energies  t h e 173  and t h e  features  such  (see f i g u r e  Along  rule  transitions.  and  atom  most  l o s s a n d XPS  localized  Four  i n  i t  same  associated  a r e observed  reported.  2p  the  since  Features  i n section  structure  t o be  the determination  selection  i n between  2s spectrum  previously of  the  at relative  discussed  are expected  transitions  f o r t h e major  forbidden  spectrum  2p  states  10.1.  spectra  on  of the energy  features  i n figure  f o r  approximation  levels  S  the parity  accounts  the  and  scales  transitions  energies  Experimentally,  within  reasonably  S  analogy  Additional Spectral  quasibound  of  core  determination  Although  and  2p  equivalent.  energies  position absolute  the  relative  and S  inner-shell  corresponding r e l a t i v e  2s  The  indication peak.  of a These  268  (a) F i s 'ij! j  i  F1s  1 2 3  4  r i  S  2  P  240  260  280  240  260  280  N  ll  910  180  200  220  ENERGY L O S S CeV)  Fig.  10.3  Extended energy range spectra of SFg in the F Is, S 2p and S 2s regions.  26 9  three  features  transitions Such  to  {1,3,4  the gerade  transitions  may  become  may  Comparison  be  due  with  a  have  levels  formally e l e c t r i c  weak  S  due  been  (6a-|  to  electric  2s  NMH71,  ,  assigned 2t g,  S  BHK72)  g  forbidden  but  coupling.  2s  energy  quadrupole  those  to  4e ) .  2  vibronic  photoabsorption than  g  dipole  structures i n the  to  accuracy  (ZF67,  virtual  allowed  these  s t a t i s t i c a l reported  are  dipole  Alternatively spectrum  i n F i g . 10.3c)  loss  transitions.  spectrum  which  of  better  have  should  been  c l a r i f y  this  assignmen t . In  addition  forbidden S  2p  and  F  1s  i s  readily  1s  this  of  peak  eV  the  were  qaussian 704  i n the F  1  g  region  and  only gerade any  e  on F of  F  g  1s  the 1s  seems  this MO's.  peak  F  of  the  peaks  shoulder This  i n t h e 685 One  that  shoulder  However  a  large only  a  i n  f o r such  a  level  up  four to  possible between  i s  transitions  ungerade  molecular  make  observed  The  i s  to  The  f i t of  splitting  peaks  shoulder  squares  i s the  the s i n g l e  the  published  assumed  spectrum.  to  on  L72b) .  shoulder fact  parity  features i n the  VZF71,  10.1)  a least  1s  the  previously  (LBK67,  (table  other  The  to  ( F i g . 10.1).  corresponding to  weak  a low-energy  three  the  unreasonably level.  by  the  of  levels the  spectra  features  to  for  interpretation.  l i k e  i n any  assigned  further  spectrum  determined  peaks  explanation a  1s  apparent  two  are  including  photoabsorption  energies  transitions  there  spectra  peak  F  the  levels,  second not  to  keeping  observed  from  and  the  the  not  with  2 on  this  splitting  of  tightly  bound,  atomic-  molecular  field  experimental  ca.  2  eV  270  s p l i t t i n g s are in a  1  those XeF2  g  of of  an  <0. 1 e V  and  XeF  levels  in  alternate  which  single  peak  Weak continua  direct  2p  the  peaks  10.3  and  table  S  energy  (see eV  F i g .  i n the  et  can  be  in  as  well  figure  fragmentation  as  10.4 study  10.1).  and  also  (HBW78,  of  2p  that  peak of  a  continuum.  S  2p  and  to  The  F  the  1s 4eg  shoulder  at  ( F i g . 10.3b)  most  previous  reported  by  shoulder  appear  to  (Fig. to  2p  10.3b). the  convincing directly since can  the  chapter  This  onset  ionization  states from  this  spectrum  12  seem  order  overlap  i n  surprising  Rydberg  the  observed  spectrum  appears  i s not to  not  the  assigned  s  An  as  fact  i n the  this  resonant)  and  g  observed  ionization  attributed  intensity (which  S  feature  been  to  1s  of  the  reported  does  to  to  loss  the  e x p l a n a t i o n does  l i m i t  continuum seen  (BHK72)  intensity  opposed  to  i n  F  e  smaller.  be  the  observed  than  Only  a l .  continuum  ionic  weaker  previously  this  2p  the  F1s  However  widths  due  above  has  ionization  be  be  levels  transitions.  explain  energies  (as  However,  simply  may  also  similar  shoulder  IP  the  4d  involve  to  Finally  are  studies.  a  1s  with  the  reported  would  expected  structures  Blechschmidt have  then  the  considerably  optical  shoulder  FWHM). F  of  this  be  been  of  certainly  of  at  205  separation  onset  transitions about  the  with  components  features  eV  have  almost of  would  would  the  which  unresolved Rydberg  (0.4  straddles  level  The  will  6  sharper  resolution  shape,  S  SF  transitions  peak  i s  (CHN73) .  4  from  considerably the  between  interpretation  contributions such  inner-shell  (D72) .  as  above  some the  tunnelling  occur) .  results 11).  of  of The  This the MO,  271  Coulomb able  barrier  model  to account One  about  f o r this  plausible  structure  (feature  217  eV  electron ionization  of a  processes  have  excitation  spectra  s a t e l l i t e s  i n XPS  peak  i n the F  also  be  one  could  which  the  C l 2p  been  referred  this which 2.4  A  i s  phase  shift  form  part  particular higher  shell  and  a  loss  EXAFS  bond  2p  a  S  i n  are  eV  maximum i s  a t  two-  e x c i t a t i o n and  2p  well  205  spectrum  electron.  previous  Such  inner-shell  known  as  simple  shake-up  an  of  an  the  and  of  larger large  thus  EXAFS  the observation i n the F  be  of  than  value  c f more  The  LSS75) i n pattern  have  the Cl-Cl reader  i s  When  are analysed  using  A  i s  F-F  of the  of  energy-dependent  Further oscillatory would  obtained  spacing  f o r these  1s c o n t i n u u m ,  i n  analysis.  3.6 the  required  pattern.  may  features  reflect  the  continua  (R-«)  (Sn74,  9).  f o r d e t a i l s of  value  which  chloromethanes  model  4eg  Alternatively,  continuum  chapter  1s  the  interference  Weak  o f  above  10.3a)  structures.  EXAFS  i n the F  would  (Fig.  interpretation  (HB78b, 4.6  are observed  spectrum  spectra  A rather  energies  and  length.  considerably  of  S  simultaneous  are part  7  model,  (a)  the  (6 a n d 7 )  an  loss  and  (JP69).  i n  identified  spacing  6  also  as shake-up  maxima  to f i t a  EXAFS  13)  maxima  t o section  features  seem  spectra.  t h e F-F  interatomic  and  (W74)  consider  shown  weak  f o r t h e weak  been  energy  the  not  feature.  involving  interpreted  reflecting  does  12)  1s e n e r g y  t h e two  10.1  f o r  valence  weak  i n section  interpretation  (feature  processes  Two  outlined  features  t o  evidence,  i n  structure  at  be  reguired  t o  272  make  a  10.3  more  definite  Rydberg  Transitions  Early spectrum 176  optical  (ZF67,  and  182  forbidden  0.08 are in  eV in  general are  broad  early  S  0  some  existence In  of  been  are  by  to  with  an  loss  spectrum  phctoabsorption  6t  1  transition.  U  reported  i n  the  recently  obtained  (GKM77).  These  reported  to  6t-|  U  readily (GKM77). has  the  6 t  this  1  are in  spectrum  apparent  i n  the  this  high  Nakamura's  regarding  the  compared  a  the  in  the  orbital. S  2p  spectrum  r e s o l u t i o n of  figure has  GKM77.  previous  of  inner-well  u  instrumental  (NMH71)  i n  answered  situation  results  reported  Although  remains  with  spectra  transitions  validity  The  synchrotron  those  the  weak  apparently  than  not  between  transition.  u  2p  spin-orbit  energies  s t i l l  to  the  the  (GKM77)  c l a r i f y  energy  that  to  without  the  S  features  {N M H 71}  a l .  Gluskin  transitions  photoabsorption the  lower  concerning  examined The  except  uncertainty  order  et  assigned  spectrum (D72)  a l .  region  Gluskin  EXAFS.  the  2p—•6t-|  observed  2p  agreement  reported  r e s u l t ,  since  SF  of  broad  S  to  to  Spectrum  region  also  features,  questions  FWHM.  i s  a l l ~ 0 . 4 eV  resolution  has  this  investigations,  spectrum  et  assignable  r e s o l u t i o n by  NMH71  The  i n  the  structure  attributed  Nakamura  structure  2p  two  parity  features  of  only  the  structure  spectrum  found were  later,  this  S  which  Somewhat  Rydberg  the  eV  of  observing  in  of  investigations  BZF67)  components  Rydberg  assignment  to  10.4. linear  0.2  eV  Nakamura's Note  that,  wavelength  273  WAVELENGTH (A) 70  72  68  i  _J (0)  66  L  Nakamura et.al. (Photoabsorption)  (b)  present  work  1-OH  c 3  I  0-5-  >-  to UJ 1  172 Fig.  10.4a  2  3  45  6 7  176 ENERGY  8  1 1  180 L O S S (eV)  10  9  184  188  The photoabsorption spectrum of SFg in the S 2p region showing the Rydberg structure (NMH71).  Fig.  10.4b  The energy loss spectrum of SFg in the Rydberg region of  the S 2p spectrum ( A E = 0.20 eV FWHM).  274  scale  while  scale,  lines)  differences energies  are  not  between  has  over  Rydberg  those  a  (which  are  aligned  the l i m i t e d  range  f o r  a r e presented  sharp  spectrum  exactly  assignments  features  the four  loss  features  are small  and  spectral  are  energy  corresponding  vertical  of  the  the  reported  i n  by  although  the  involved.  the  The  energy  10. 1.  observed  energy  connected  electron  i n table  features  linear  The  energies  i n the  two  loss  spectrum  photoabsorption  studies. There energy  i s a  loss  intensities absorption was al.  and  peak  (GKM77)  i n Nakamura's  transitions  It  to  that  the  corresponding  has  6 and  i n  been  61-|  analysis  due  energy  to  although to  2p  3 / 2  8.  —»-4d  photo-  weak  and  Gluskin  parity  et  fordidden  photoabsorption  feature  s t i l l  of the  The  while  The  loss  electron  i s very  (NMH71)  o r b i t a l .  u  intensity assigned  i s  6  the  i n terms  feature  to feature  i t  to  between  spectra  possibly  corresponding  suggest  comparable  difference  photoabsorption  of feature  ignored  feature  noticeable  8  i s  more  noticeably  weaker.  transitions  (NWH71,  GKM77) . The  increased  electron  energy  significant  matrix  (K*=o.5  i n  element  momentum  loss  spectrum  Non-dipole the  eV  appears from  loss  i s s u f f i c i e n t l y  a t 180  these  features to  be  electric  t r a n s i t i o n s c a n have  energy  transfer au  of  contribution  transitions. intensity  intensity  spectrum large)  under  the  energy  loss).  a  (if the  because  of  experimental Feature  6  due  i n  the  t o  a  quadrupole significant appropriate the  f i n i t e  conditions  i s assigned  as  275  the  f i r s t  member  [ <5p= 1. 6 6 ( 5 ) ]  and  transition. in  The  excellent  1.2(1)  eV  the  have  agreement  spectra  energy  loss  absorption  3 / 2  b  —*-1p  t r a n s i t i o n s .  forbidden  i n  Oh  photoabsorption which by  i s  coupling  The  this  weak  that  i thas  6 t  By  inner-well level  a  In  u  a  states, 1s, S  by  f i r s t  inner-shell  to  feature  also  due  i n  or  allowed  (GKM77)  of  assigned have  occur  dipole  t r a n s i t i o n s  t o  dipole  energies,  refuted  that  6  t r a n s i t i o n ,  Gluskin  spectra,  be  may  t r a n s i t i o n s  those  photo-  e l e c t r i c  to a  c a n be  Rydberg  1s  loss  i s the  photon  leading  feature  S  would  high  s i m i l a r  and  energy  guadrupole  given  including 2s  transitions  t r a n s i t i o n s  at  a l l other  of  photoabsorption  loss  formally  d i r e c t  mechanism  contrast  of  t h e weak  energy  GKM77)  favoured  linewidth  s p l i t t i n g  molecule.  to  assignment  the  2.2), t h i s  such  i d e n t i f i e d as  i n the F  linewid  1  by  /2  the analysis  assignment,  Although  2p, —»>4p eV,  non-dipole  a  i n  photoabsorption  unambiguously G KM 7 7) .  either  series  1.22(5)  i n inner-shell  of  symmetry,  increasingly  a vibronic  process.  2  i s  t r a n s i t i o n i n the  above  figure  and  i n  see f i g u r e  equivalent  of  and 8  (SNJ69)  observed  the  feature  peak  2p  t o  Rydberg  spin-orbit  Although  spectrum  — * ~ n p  6  the  XPS  non-dipole  3 /  t c the corresponding  observed  (KTR77,  According  S  both  previously  of a  2p  o f peaks  GKM77).  o f atoms  electron  8  with  series  i d e n t i f i c a t i o n  (cf.  from  (NMH71,  the  feature  derived  been  of  separation  Rydberg  spectra  (n=4)  f o r  by  noting  the  peaks  (~0.1  eV i n  assigned to the much  to 6ti  u  greater  ths. addition,  the S  2p—»-6ti  u  transition  i s considered  276  to  be  clearly  as  a  The  dashed  broad  as  feature  line  exponential well  observed  selected  background  given  figure  loss S  orbit  U  the  10.4b  eV)  labelled  spin-orbit least  structure.  The  cf  f i t of  i s  underlying  Rydberg  structure at  ~179  Gluskin 6 t i  u  i s eV  et  a l .  are  figure  (GKM77), i n  actually  most  intense  The  widths  as  6ti  the  peaks  the i s  quite  a  10.4a). the  the  As  area  the  energy  show  lines  to  of  has  figure  the  earlier  optical  this  closer  same  broad  background out  assigned  spectra  broadened  a  structure  pointed  previously  on  two  underlying  On  the  been  the  with  broad  in  and  based  definite.  step  spin-  in  this  to  eV)  l o c a t i o n of  features  instrumentally  clearly  (173  1 g  spectrum,  downward  derived  i s  associated  presence  shell  assigned  to  6a  a  background  i n  transition  u  uncertainty  Rydberg and  the  estimate  peaks  the  as  i s  valence  with  an  eV  line  rigorously  dashed  photoabsorption  apparent (see  with  i s 171  This  expected  gaussian  large,  the  transitions  3ZF67), the  of  two  structure.  below  l o g i c a l l y  be  spectrum  10.4b  features  i s  may  the  the  determination  examination  4  Fig  eV.  mere  Rydberg  vertical  and  Although  the  and  Rydberg  points  178.5  loss  spectral intensity  analogy  components  squares  in  Even  feature  by  3  sharp  the  11. 2p  energy  underlying  above  S  transitions  peaks.  and  the  four  This  s p l i t t i n g  2t2g(184  175  of  10.4b,  spectrum.  2p—*-6t<|  at  chapter  underlying  the  spectrum  i t l i e s i n  electron  a l l experimental  estimate  given  in  the  points  background  observed  to  since  the  underlying  below  f i t  conservative  i n  by to  (ZF67,  versions  of  peaks. ratios  of  the  6a-|  g  and  2t g 2  spin-  277  orbit  components  f i t s  to  the  10.4b.  et  the  a l .  results  intensity  The  I t  intensity  ratio  to  the  5:7  of  the  the  S  2p  excited  into  of the  rate  of  2p  IP  the  energy  expected  the  outer-well  the are  seems  the  The  been  in  terms  to  be  2t2g(0.8  states S  2p  directly eV)  d i f f i c u l t  width to  S  This in  4e (4.5  eV)  g  of  a  accept.  6a  in  in of  a  S  2p the  1 g  Such  ( S 2 p . 4 e g) ]  rapid the  decay observed  features. satisfactory  continuum the  that  features  and  reflected  2p  than  autoionization  2 t ?g)  present  the  larger  the  rapid  [ (S2p,  and  of  the  a  exchange  rationalized,  continuum.  may  widths for  of  close  observation  chapter  has  i s  much  intense  throughout  11)  ratio  o r b i t a l s .  2  the  the  of  orbital  2t g  excited  spin-orbit  absence  fragmentation  ionized  explanation  of  the  (i.e.  by  and  g  discussed.  quasibound  the  the  Rydberg  widths  autoionization of  6a-|  exchange  spectrum)  rationalized  inner-well,  point  loss  in  of  thought  explanation  S  2  the  transitions  be  directly  Although  similar  i n  picture,  the  i s  widths  the  (HBW7 8,  state  decay  that  Rydberg  discussed  significant  note  ionic  continuum  as  to  spectrum  constant  spin-orbit  interesting  may  final  expected  and  the  along  Baranovskii  hole  This  localized, a  a  figure  by  explained  of  in  10.2  core  6:8  extent  As  the  table  reported  the  be  terms  in  squares  shown  2p  of  interactions.  spectrum  data i n  least  S  of  and  value  spatial  in  i s  optical  reversal  between  electron.  loss  from  summarized  can  (D72),  interaction  peaks  are  ratio  previously  determined  energy  corresponding  (BZF67).  of  also  electron  These  with  were  features,  peak an  below  a the  explanation  Table 10.2: Spin-Orbit S p l i t t i n g s , Widths and Intensity Ratios derived from least-squares f i t s to the 6a,  and 2 t  peaks in the S 2p spectrum.  9  6 a  , Parameter-  Present work  3  lq  2 t  BZF67  b  Present work  9  2q BZF67  E(3/2)(eV)  172.03  172.40  183.11  183.45  E(l/2)(eV)  173.20  173.55  184.27  184.55  (eV)  1.18(1)  1.15  1.17(1)  1.10  FWHM (eV)  0.79(3)  0.9  0.77(2)  0.9  FWHM (eV)  1.22(8)  1.2  0.86(5)  1.2  0.45(5)  0.80  0.46(2)  0.62  A.E  Spi n-orbi t Ratio ( 3 / 2 / h )  a. Both gaussian and lorentzian lineshapes were least-squares f i t t e d Fig.  10.4b.  b  to the spectrum shown in  The tabulated data i s derived from the lorentzian f i t s which were better than  the gaussian f i t s as may be expected from the fact that the peak widths are dominated by natural linewidths rather than by instrumental  factors.  b. The instrumental resolution was stated to be between 0.25 and 0.3 eV over the range of the S 2p photoabsorption spectrum reported in BZF67.  279  would  require  treating  underlying  valence  (S2_2,6a.|g)  state  ionization  continuum  the  6a  process This  in  geometries  since  significantly orbitals  of  the  outer  The  between  normally  the  virtual  orbital.  6a  However  well  o r b i t a l  makes  the  case  a  of  orbital. width  The  of  somewhat  more only  the  overlap  and  the  spectra  fact  even (NMH71,  i n  upper  that the  GKM77),  the  the  fragmentation  for  along  lines  ionization standing  considered  the  (HBW78, of  the  more  chapter  173  eV  into  a  the  11)  feature  f i r s t  in  larger  than  between  the  valence  6aig  less  inner-  than  as  a  S  for  Rydberg for  the  unresolved band  structure  shape. i s  not  photoabsorption  An of  should  examination each  obtained  lead  the  be  explanation  that  the  orbital  autoionizing  smooth  ionization  may  of  of  such  seriously.  of  spectator.  to  resolution  decay  overlap  involve  vibrational high  involving  explanation  would  blends  be  orbital  single  occupied  orbital,  the  depend  the  of  an  rates  orbitals  nature  alternate  probably ionic  in  normally  components  In  observed  decay  valence  a  terms  i s expected  a  plausible  s t r u c t u r e which  of  a  competing  d i f f e r e n c e somewhat  vibrational view  a  spatial  localized  diffuse  6a-jg  of  occupied  this  i n  basis,  into  i n  electrons involved  the  this  remained  unlikely  degree  orbital  1 g  On  of  electron  a,  spatial  resonance  decay  occurence  t> \g  the  transition. two  to  non-radiative  on  a  a non-radiative process the  the  as  continuum.  by  seems  peak  1 g  have  before  which  explanation  a  shell would  electron  1 g  the  to  a  2p  spectrum  of  valence for  further  S  2p  underof  SF . 6  280  11  CHAPTER ELECTRON-ION  COINCIDENCE  STUDIES  OF  SF  OF  THE  IONIC  FRAGMENTATION  6  "No man can be specialist without t h e s t r i c t s e n s e an  It  has  been  photoabsorption  known  continua  strongly  non-atomic  threshold  in  This  the  BF  3  is etc.  in  the  which  electronegative S74) by  ascribed a  speculated forces  apparently shell CO  the  i t  (DD75,  unlikely.  where  More  recently  PGG77) .  reasonably  resonances  can  that  diatomic a a  given  using  I t  was  centrifugal  pronounced  occur  in  same  the  F72,  less  the  such  phenomenon  picture,  be  of  quasibound  or  s i m i l a r  phenomena  shell  (N70,D72,  potential  quantitative  a  4  potential.  molecules  A  these  by  Coulcmb  unifying  SiP ,  0  force.  the  of now  repulsive  SF f  states  (Coulomb)  ionization of  accurate  interpretation  localized  above  structure.  like  surrounded  exhibit  just  localized  s i m i l a r structures  DD76a,b)  D76,  to  recognized  even  valence-shell  region  molecules  exchange  of  for  the  is  inner-shell  frequently  e f f e c t i v e molecular  was  spectra  f o r  that  interpretations  necessary  otherwise  decade  in  atom  Early  either  provided  Later,  central  the  a  prominent,  structure  i n  that  molecules  of  atoms.  barrier  of  especially  a  the  ever  behaviour  form  case  for  a pure being i n i d i o t " G.B. Shaw  well  multiple  and  2  seems  (HSB76,  provides  (KLW77a) terms  N  observed  molecules which  i n  inner-  as  was  but  a  physical of  shape  scattering  281  method  (DD75,  DD76a,b).  energies  at  electron  penetrates  i t  which  should  f i e l d  be  permits  partial  containing  SF  6  a  agreement  of  the  of  by  N of  and  continuum  the  outgoing  In of  this  the  allowed  by  of  shape  the  CO  but  which  are  experimental  in  molecular higher  atomic  also  scattering  regard  i n  dipole  resonance  for  electronegative  multiple  Ni76)  the  2  at  photoelectron  those  for  number  SPK74, with  wave  anisotropy  s u i t a b i l i t y  only  large  the  just  The  demonstrated (VKK74,  that  than  not  occur  i t s centrifugal barrier.  escape  rules.  description  been  the  resonances  particular partial  noted  waves  selection  a  Such  molecules  ligands  has  calculations  for  semi-quantitative  spectra  of  the  sulphur  2p  continuum. At  the  same  calculations peaks  in  time,  can  the  equally  continuum  v i r t u a l  o r b i t a l s of  moment  theory  accurate  MO  state  is  accident  calculations  approach  state  state,  MO  and  the  describe  i t .  descriptions From i t  is  can  since  quasidiscrete  of. v i e w  for  ground  continuum  excited  to  well  (e.g.  the  should  theoretical prediction  photoionization  no  i t  explain SF  (SL77) to  basis  set  is usually  a  matter  either  the  shape  i s  d i f f i c u l t  make  in  terms  provided the  of core  BO  recent the  most  nitrogen that  the  of  1s  an  MO  spectrum localized  resembles  s u f f i c i e n t l y between  a  bound  flexible the  two  semantics.  resonance to  absorption  fact  difference of  strong  inner-shell  portion  molecular  mainly  of  the  the  apparent  have  The  2  that  Furthermore  date  N .  noted  GGL72) ,  state.  describe  that  see  0  i n  The  not  of  be  or  excited  plausible  state  arguments  point as  282  to  why  vibrational  molecule pattern This  -  and  vary  chapter  when  sulphur  2p  of  of t h i s N  2  and  CO  of  occur  the  i n  through  this the  sulphur  straightforward.  2p  Since  there  fragmentation of the  i n  both  the  continuum.  i t  and  of SF&.  The  valence-shell  continua.  However,  s i t u a t i o n  i s  more  methods t o remove  background  i s possible  structured  i o n i c  ( D 7 2 , VKK7U)  f o r the  are reliable  more  pronounced  spectra  valence-shell  (KLW77a)  of  Very  the  was  possibly  behaviour  overlapping shell  and continuous  absorption  involved  f o r K-shell  hexafluoride  further,  absorption  rather cf  f o r a  the inner-shell  SIM77)  number  Sulphur  resonance.  both  be  not observed  energy  a  i n  were  (KLfl77b).  through  i t slarger  portions  nature  molecule  would  t o t a l  i o n i c  region.  test  smooth  of  swept  proposed  the  study  i s  (SIM71,  the  resonance.  energy  valence-shell  for  a  the excitation  fragmentation  with  through  experimental  excited  fragmentation  variations  test  structures  ionic  of  6  a suitable  dramatic,  i t s  inner-shell  search  i n  as  an  sweeping  an  SF ,  of  i n  Variations processes  when  reports  fragmentation  chosen  consequently  might  pattern  excitation  from  t o determine  and  the the  unstructured  283  11.1  Absorption  Oscillator  Measurements 5  t o 2 3 0 eV  obtained  demonstrated  the  can o f t e n  off  the  across  method. of  the  the  energy  at high  This  the  energy  energy were  made  measured ascribed  of  a target  by a the  the  parent  time-of-f  electrons,  I f a similar  was  i t  would  observed  as  discontinuity  i n  the  o s c i l l a t o r  strength  (black accuracy a  dots no  of such  gas dependent  compatible observed A  with  background t h e energy  r e l a t i v e from  validity  of  the  the dipole  term  the  time-of-flight  Within  the  i s observed.  loss  study  scattering Bethe  181 eV  light  dependence  be S?5  +  method  s t a t i s t i c a l  The absence  i n t h e S 2p e x c i t a t i o n  absorption  the  at  11.5b) .  discontinuity  i n the earlier  obtained  only  figure  i o n  gas-dependent  i n t h e present measurements  by  gas  largest  existed  measured  2  discontinuity  background  a  N  to incomplete suppression  scattered  losses.  earlier  spectra  i n  by  scattering In  f o r  aV)  background  from  loss  from  (160-230  analyser.  threshold  i n e l a s t i c a l l y  highest  losses  made  (gas absent)  region  was i n d i c a t e d  inner-shell  background,  spectrum  loss  energy  of  which  as  were  of any gas-independent  corrections  strength  intensity  background  of the inner-shell  low energy  at  2p  absence  background  o s c i l l a t o r  A  surfaces  (KLW77a)  dependent  S  arise  inner  measurements CO  loss.  the  which  and  of the scattered  energy  f o r  Strengths  of these  of  region i s effects  (KLW77a) . oscillator  strength  intensity  approximation  of the generalized  by (171),  curve  assuming and  o s c i l l a t o r  was the  retaining strength  284  (see  equation  2.3.7) .  scattering  angles  been  i n BTW75.  given Since  strength been  a  of  TRK  cross  sum  from  o s c i l l a t o r  and  et  normalization of  loss  o s c i l l a t o r  of  both  above  consistently  2p that  i n  derived  the  by  about  Zimkira  of  optical  normalization to  eV) the  i s  with  derived  from  with photo-  considerable  optical  measurements  of  measurements  LPJ77.  and  occurs  11.2).  the  the  However values  A the  i n the  I t should  synchrotron  at are  obtained  (see F i g . 11.1).  value  the  agreement  the values  than  this  With  15%  recent  (BHK72)  2p a b s o r p t i o n .  absolute  (figure  a l .  because  present  the absolute  (160-230  6  an  because  valence-shell  various  (VZ72)  to  only  curve  from  the  the  reasonable  i n figure  larger  chosen  and  eV  comparison  considering  the  i n terms  region  i s  was  et  the  shows  27  which S  absorption  eV  between  direct  v a l e n c e - s h e l l and the  11.1  by  at  energy  a l . (BHK72)  50  discrepancy results  et  value  has  reported  than  Blechschmidt  this  most  apparent  and  of  at  the  between  Vinogradov  This  data  measurements,  are readily  normalized  have  scale  previously  Figure  the  o s c i l l a t o r  eV, t h e a b s o l u t e to  over  zero  absorption  2.3).  eV  measurements  inconsistencies  energies  the  strengths  absorption  the  about  S.IM71) , r a t h e r  0.75.  Blechschmidt  normalization  which  of  allows  this energy  230  a l . (SIM71)  study  230  (BHK72,  to  other  angle  of  section  between  Sasanuma  results  (see 5  the integration  normalization  strength  agreement  above  sections  rule  results  of  by  of  the s o l i d  portion  occurs  obtained  optical  within  large  SF^  Details  by  similar present sulphur be  noted  measurements  of  SF  I.6H  C  i  \JUlK  Ld TD  S. 0  40  A  —i  80  1  Vinogradov and Zimkina  1  1 —  1  120  160  200  ENERGY LOSS (eV)  Fig.  11.1  x|0  Absorption o s c i l l a t o r strength for SF  fi  from 5 to 230 eV.  240  286  SF  fi  I6H CVJ  §12-  > LU TD  •o  8H —I 4-J ••— this work Blechschmidt et. al. • - - Zimkina and Fomichev  S2p  160  T  180  T  T  200  ENERGY LOSS  Fig.  11.2  —r~ 220  (eV)  Absorption o s c i l l a t o r strength f o r the S 2p region (160 to 230 eV).  SFg in  287  Lee,  P h i l l i p s  for  the  overall the  agreement  i n i t i a l  A  Judge  oscillator  comparison  curves  with  t h e data  results occurs  and i n  results  intense  spectral  of  the peaks  effects optical  respect  (171) w h i c h spectral  process,  Since line  196  eV  data.  of  reports  be  I t  i s  optically-derived  values  validity  to  i s  affect  optically,  not  i s an  different present  sulphur  6  the  line  than  noted  the  of the SF  greater  be  be  curves  with  saturation  whenever  a  resonant impact  between  the  between  measurements  j u s t i f i a b l y  the assumption  the  the natural  differences  loss  2p  various  the electron  discrepancies  cannot of  should  structure  the energy  background  considerably  scattering  the  from  considerably  optical  due  f o r sharp  obtained  derived  are  i n accord  s a t u r a t i o n cannot  strengths  the  may  electron  o s c i l l a t o r  question  similar  d i f f e r e n c e s among  bandwidth  Because  results  The  occur  results.  the  i n other  spectrum.  are  since  VZ72).  2p  i n F i g . .11.2  of data  given  absorption  to the non-structured  a r e more  the  BHK72.  the choice which  between  of  the two  measurments  linewidth.  and  However,  2  between  (BZF67,  optical  184  the  IDHK72).  reported  agreement  are  spectrum  at  shewn  i n the optical  shapes,  results,  shapes  0.68  f a c i l i t a t e  discrepancy  figure  taken  eV.  e t a l .  previously  of  improve  to  from  more  a r t i f a c t  50  were  eV,  t h e good  above  of the S  180  that  would  retained  serious  value  shape  below  i s the case  eV,  a  the relative  the relative  than  27  Blechshmidt  the  Although  with  report  values  was  of  more  who at  optical  normalization  with  optical  (LPJ77),  strength  potentially  present  The  and  used  of solely  and to  dipole  288  contributions  t o t h e energy  Support  f o r  the assumption  inferred  from  t h e agreement  S  2p  energy  loss  impact  and  i.e.  values  of  3  times  as  studies. the  as  electron-ion  occur  oscillator  present  spectral  transfer the  of  the  spectrum.  processes data  with  than loss  a b i l i t y  obtain  WWB77,  of  accurate  TBL78)  c o n s i d e r e d t o be previously  more  energy  demonstrated  (BWT75,  keV  1 0 . 1)  are  present  be the  2.5  (figure  to  can  using  which  apparatus  are  2p  obtained  6  previously  shapes any  dipole  S  present SP  i n  strengths  i n the  scattering  coincidence  optical  as  of  small angle  Considering the  trustworthy  cf the  t h e momentum  large  data  of only  spectrum  electron at  loss  the  at least  reported  as  optical  curves.  11.2  Ionic  Fragmentation  Figure obtained Peaks  i n  the  time.  expected  F  2  +  was i s an  of  to  both  exactly, the  due  Part  to  an or  ionization  energy  and  ionic  do  were  ionic  identified and  not  f l i g h t  follow  broad  peak  losses  to rise  this  i n  identification  the background  energy  i s known  electrons.  non-linearity  a l l of the since  spectrum  charged  b e t w e e n y/m/e'  unambiguous  at  loss  doubly  species  a slight  determined potential,  eV  positions  instrumental effect as  184  relation  peak  TAC,  i o n time-of-flight  singly The  linear the  possible.  coincidences, f i r s t  typical  observed.  Although  response  a  coincidence with  are  relationship  ions  shows  corresponding  fragments using  11.3  of  the the  labelled of  less  i n this  random  than  the  region.  SFfe E=l84eV SF  SF  +  I  6H  (F ) I 2+  SF |SF 2 +  2 + 2  S^SF  SFf- SFT SF*  + 2  I  I  I  I  2 + 4  hi  "4CO UJ  ^3 UJ Q  .  O  L*25  ? 2-  o o  H 0-  "I  2 Fig.  11.3  ~  l  1  1  1  3 4 ION TIME OF FLIGHT (/xsec)  5  Ion time-of-flight spectrum in coincidence with 184 eV energy loss electrons,  00  290  Even  though  gross  part  energy  of  the  production  area  was  less  studied.  with  maximum  energy  The  of 2%  than  energies  analysis.  of  0.4%,  yield  from  the  the  =  0  the  10.2)  If one  the  ion  efficiency  i s  (i.e. in unity)  kinetic  energy  at  threshold  (~35  one  w i l l  ion  eV be  in  no  0  +,  by  created  of  the  shown  will  the  20  has  been to  figure 165  due  eV  to  ionic  F )  were  +  strength  (fj)  determined  that  give  The  an  any  (f ) a  one  and  ionization the  true  ion  for  any  arising  from  situation double that  energy  by  ion.  generates  possibility  during  the  at  10  the  the  in  strength  of  where  above  2  betwen  and  then  event  (DTW75).  SF3 +,  in  of  1,2,4  (Xj)  than  +  a l l  leading  o s c i l l a t o r  loss  at  background  =  peak  to  values  was  yield  yield  SF6  o s c i l l a t o r  icn  The  observed  that  x  and  d i s c r i m i n a t i o n occurs  energies SF )  2 X  observed  included  yields  procedure  less  event  a l l  to  for  regions  this  ion  ionization  not  no  due  not  less  The  energy  since  complicated  SF  fractional  strength  single  5;  each  o s c i l l a t o r with  energy  absorption  ionizing  ion  distortion  areas. of  total  by  each  was  ions  2 +  zero.  peak  fractional  to  peak  production  multiplying (figure  x  X  be  was  corrections the  to  F  was  observed  similar  thirty  coincidences  computed  only  at  area  weak  ,  to  i n s t a b i l i t y  spectra  After  (SF +,  + 0  Jahn-Teller  obtained  species  SF  extreme  Time-of-flight  for  ion,  due  assumed  very  (DH66) .  random  was  +  the  The  eV.  peak  Also,  dissociation  225  the  total  to  and  2  be  the  attributed  were  F  of  may  of  parent  loss.  11.3  peak  dependence  thus  a  this  a i s  ionization more loss  than event  8H O o  7"  O  6-  o o o  5-  to  S +F +  +  7A  SF +F +  \  CO  +  4-  SF + F +  34  +  2  5  SF %F  _j  3  LU CE  rr o o o 3  < o-  1.0  2.0  4.0  3.0  ION T I M E - O F - F L I G H T DIFFERENCE (/ASeC) Fig. 11.4  Ion autocorrelation spectrum (integrated over a l l losses of 8 keV electron impact on S F ) . fi  energy M  292  i.e.  double The  dissociative following  dissociative highly  by  SF .  o f time  produced  background  due t o  background  due  line.  2  When  scattering the  each  ionic  event  difference  areas  under  enter  i n the production  in  The i o n s  11.1.  given  assignment  Msec, t i m e - o f - f l i g h t indicated From multiple the  the only  processes the  F  +  ions  may  sum  of  following two  F+  be