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- Library Home /
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Molecular inner-shell excitation studied by electron impact Hitchcock, Adam Percival 1978
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| Title | Molecular inner-shell excitation studied by electron impact |
| Creator |
Hitchcock, Adam Percival |
| Date Issued | 1978 |
| Description | Electron impact and electron spectroscopic techniques provide many useful tools for the examination of the physical structure of matter. One of these tools is electron energy loss spectroscopy (EELS). This thesis describes the application of EELS to studies of excitations of the inner-shell electrons of gaseous molecules. Preliminary, low resolution studies in the Department of Chemistry at UBC by G.B. Wight have demonstrated that the technique is experimentally feasible and that many interesting spectroscopic features occur in the inner-shell electron energy loss spectra (ISEELS) of molecules. The present work builds on this foundation and has provided significant extensions not only of the technique but also of its application. Improvements in the experimental apparatus have led to higher energy resolution and more flexible scanning arrangements. The molecular I SEE L spectra of several series of related molecules have been studied including investigations of all observable inner-shell excitation structure between 50 and 700 eV in the simplest saturated, unsaturated and aromatic hydrocarbons (CH₄, C₂H₆, C₂H₂, C₂H₂ and C₆H₆), the methyl halides (CH₃X, X = F, Cl, Br, I), the monohalobenzenes (C₆H₅X, X = F, Cl, Br, I), the chloromethanes (CHxCl₄-x, x = 0 to 4) and chloroethane. A number of specific investigations have been carried out in order to assist spectral interpretations and to further understand the physical nature of inner-shell excitation phenomena. Isotopic substitution has been used to aid the assignment of the carbon 1s spectra of CH₄ (CD₄) and CH₃Br (CD3Br). The first observation of the gas phase energy loss equivalent of extended X-ray absorption fine structure (EXAFS) is reported in the spectra of CH₂CI₂, CHCI₃ and CCI₄. Molecular electric quadrupole transitions have been identified in the sulphur 2p excitation spectrum of SF₆. The improved experimental resolution has led to observations of vibrational structure in the inner-shell excitation spectra of N₂, CO, C₂H₄ and the methyl halides. In addition to the ISEELS studies, electron-ion coincidence techniques have been used to study the ionic fragmentation following excitation and ionization of a sulphur 2p electron in SF₆. This experiment was performed at the FOM Institute for Atomic and Molecular Physics in Amsterdam. An attempt has been made to evaluate alternate theoretical descriptions of certain characteristic inner-shell excitation features in the light of both the electron-ion coincidence results and ISEELS studies of the chloromethanes and SF₆. |
| Subject |
Molecular spectra |
| Genre |
Thesis/Dissertation |
| Type |
Text |
| Language | eng |
| Date Available | 2010-03-02 |
| Provider | Vancouver : University of British Columbia Library |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
| DOI | 10.14288/1.0060983 |
| URI | http://hdl.handle.net/2429/21327 |
| Degree |
Doctor of Philosophy - PhD |
| Program |
Chemistry |
| Affiliation |
Science, Faculty of Chemistry, Department of |
| Degree Grantor | University of British Columbia |
| Campus |
UBCV |
| Scholarly Level | Graduate |
| Aggregated Source Repository | DSpace |
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