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X-ray photoelectron spectroscopy of gaseous atoms and molecules Perera, Josage Sudharman Henry Quintus 1980

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X-RAY PHOTOELECTRON SPECTROSCOPY OF GASEOUS ATOMS AND MOLECULES by  JOSAGE SUDHARMAN HENRY QUINTUS PERERA B.Sc,  U n i v e r s i t y o f S r i Lanka,  P e r a d e n i y a , 1974  A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES (Department o f Chemistry)  We a c c e p t t h i s t h e s i s a s c o n f o r m i n g to the required  standard  THE UNIVERSITY OF B R I T I S H COLUMBIA May,  1980  (c) J.S.H. Q u i n t u s P e r e r a , 1980  In presenting t h i s thesis in p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission f o r extensive copying of t h i s thesis f o r s c h o l a r l y purposes may be granted by the Head of my Department or by his representatives.  It i s understood that copying or p u b l i c a t i o n  of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission.  Department nf Chemistry The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  D a t e  May 29th,1980  ABSTRACT  A versatile spectrometer  gas phase x - r a y p h o t o e l e c t r o n  employing  a PDP 8/e m i n i c o m p u t e r  control the spectrometer lation  i s described.  Facilities  i n s i d e the spectrometer available,  f u n c t i o n s and d a t a  to accumu-  f o rheating materials  t o ^10 00°C a r e c u r r e n t l y  and t h e a d v a n t a g e s o f such  are s u i t a b l y  demonstrated. Core l e v e l Group I A m e t a l cesium cium,  x-ray photoelectron spectra o f the  atoms, sodium, p o t a s s i u m ,  and t h e Group I I A m e t a l s t r o n t i u m , and barium  provide the f i r s t  a t o m s , magnesium,  have been o b t a i n e d .  a c c u r a t e measurements  b i n d i n g energies f o r s e v e r a l o f these Experimental  rubidium, calThese  o f the core elements.  and t h e o r e t i c a l v a l u e s from t h e l i t e r a t u r e  a r e c o m p a r e d w i t h t h e p r e s e n t r e s u l t s . The f r e e b i n d i n g e n e r g i e s a r e f o u n d t o be g r e a t e r t h a n parative solid  state binding energies.  "phase t r a n s i t i o n  shifts"  theoretical estimates.  atom  t h e com-  The e x p e r i m e n t a l  a r e compared w i t h v a r i o u s  Multielectron excitation  satel-  l i t e s are also observed i n the spectra o f a l l these atoms.  T h o s e o b s e r v e d f o r t h e a l k a l i m e t a l atoms a r e  a s s i g n e d t o n s -*- ( n + l ) s t y p e m o n o p o l e  excitations  using the equivalent cores approximation. approximation f a i l s  This  to provide a satisfactory  assign-  ment o f t h e s a t e l l i t e s o b s e r v e d i n t h e s p e c t r a o f Group I I A a t o m s . X - r a y p h o t o e l e c t r o n s p e c t r a o f t h e T i 2p and 3p l e v e l s ,  and t h e h a l o g e n c o r e l e v e l s o f t h e gaseous  titanium t e t r a h a l i d e s , TiX^(X=F,C1,Br,I), are reported. S a t e l l i t e s a r e observed t o h i g h e r b i n d i n g e n e r g i e s from the halogen core l e v e l s , levels. some  a s w e l l a s t h e t i t a n i u m np  The o r i g i n o f t h e s e s a t e l l i t e s  i s discussed i n  detail. Gas p h a s e x - r a y p h o t o e l e c t r o n s p e c t r a o f some  t r a n s i t i o n metal acetylacetonates, M(AcAc) Ni(II),  Cu(II))j have been i n v e s t i g a t e d .  2  (M=Co(II),  The m e t a l  2p, 3 s , a n d 3p c o r e l e v e l s a n d t h e 0 I s a n d C I s b i n d i n g e n e r g i e s have been a c c u r a t e l y d e t e r m i n e d .  Satellite  s t r u c t u r e i s observed a t h i g h e r b i n d i n g e n e r g i e s from t h e m e t a l 2 p , 3s and 3p l e v e l s ,  and t h e 0 I s l e v e l s .  From a c o m p a r i s o n o f t h e s o l i d phase w i t h t h e p r e s e n t g a s p h a s e r e s u l t s , t h e e f f e c t s o f c h a n g e s i n symmetry upon s a t e l l i t e  s t r u c t u r e were s t u d i e d w i t h o u t c h a n g i n g  t h e c e n t r a l m e t a l atom o r t h e l i g a n d .  The r e s u l t s  - iv -  i n d i c a t e that the s a t e l l i t e s  seen  m e t a l 3s s p e c t r a ,  e n e r g i e s 4-6eV h i g h e r  at binding  i n these  transition  than the main peak, a r i s e from m u l t i e l e c t r o n r a t h e r than  from m u l t i p l e t  splitting.  excitati  - v -  TABLE OF CONTENTS  CHAPTER ONE:  INTRODUCTION References  CHAPTER TWO:  BASIC CONCEPTS OF X-RAY PHOTOELECTRON  Page 1 11  SPECTROSCOPY  14  2.1  Introduction  14  2.2 2.3  N - E l e c t r o n Wave F u n c t i o n s Molecular O r b i t a l C a l c u l a t i o n s For XPS S t u d i e s  15 21  2.4  Koopmans Energies  25  2.5  F u r t h e r B i n d i n g Energy C a l c u l a t i o n s . .  27  2.6  C o n f i g u r a t i o n I n t e r a c t i o n Method ....  29  2.7  T r a n s i t i o n P r o b a b i l i t i e s and Photoelectron Cross-Sections  31  2.8  Sudden Approximation  35  2.9  Sum Rules on Energy and Intensity  40  2.10  Core B i n d i n g Energy S h i f t s  43  2.11  R e l a x a t i o n E f f e c t s on B i n d i n g Energy  47  2.11.1  Atoms  48  2.11.2  Molecules  51  2.11.3  Solids  52  2.11.4  Core L e v e l B i n d i n g Energy S h i f t s i n Metals  54  2.12  1  Theorem and B i n d i n g  Multicomponent S t r u c t u r e i n XPS  60  2.12.1  Spin-Orbit S p l i t t i n g  60  2.12.2  Multiplet Splitting  62  2.12.3  M u l t i e l e c t r o n E x c i t a t i o n s ..  69  References  78  - v i-  CHAPTER THREE: THE GAS PHASE X-RAY PHOTOELECTRON SPECTROMETER; DESIGN AND PERFORMANCE  87  3.1  Introduction  87  3.2  The S p e c t r o m e t e r  90  3.2.1  The X - r a y S o u r c e U n i t  90  3.2.2  The Gas C e l l s  99  3.3  3.2.2.1 The O l d Gas C e l l  100  3.2.2.2 The New H i g h Gas C e l l  103  Temperature  3.2.3  The E i n z e l L e n s  109  3.2.4  The E l e c t r o n E n e r g y A n a l y s e r and t h e O p e r a t i n g Mode o f t h e Spectrometer I l l  3.2.5  Helmholtz C o i l s  114  3.2.6  The Vacuum S y s t e m  115  3.2.7  The D e t e c t o r S y s t e m  116  3.2.8  Performance  117  I n t e r f a c i n g o f a PDP 8/e M i n i c o m p u t e r t o t h e Gas P h a s e X - r a y P h o t o e l e c t r o n Spectrometer  118  3.3.1  The I n t e r f a c e  122  3.3.2  The S o f t w a r e  12 3  3.4  Calibration of Electron Spectra  127  3.5  Data A n a l y s i s  128  References  130  CHAPTER FOUR:  X-RAY PHOTOELECTRON SPECTROSCOPY OF GROUP I A AND I I A FREE METAL ATOMS  132  4.1  Introduction  132  4.2  Experimental  134  - v i i-  4.3  R e s u l t s and D i s c u s s i o n  139  4.3.1  139  Binding Energies  4.3.1.1 S o d i u m  139  4.3.1.2 P o t a s s i u m  144  4.3.1.3 R u b i d i u m  14 7  4.3.1.4 C e s i u m  151  4.3.1.5 M a g n e s i u m  154  4.3.1.6 C a l c i u m  157  4.3.1.7 S t r o n t i u m  162  4.3.1.8 B a r i u m  165  4.3.2  Phase T r a n s i t i o n AE  Shifts,  V  4.3.3 4.4  CHAPTER F I V E :  Multielectron Satellites  Excitation  170. 176  Conclusions  183  References  186  X-RAY PHOTOELECTRON SPECTROSCOPY OF TITANIUM TETRAHALIDE VAPORS  191  5.1  Introduction  19J.  5.2  Experimental  194  5.3  R e s u l t s and D i s c u s s i o n  196  5.4  Conclusion  215  References  217  CHAPTER S I X :  X-RAY PHOTOELECTRON SPECTROSCOPY OF C o ( I I ) , N i ( I I ) AND C u ( I I ) ACETYLACETONATE VAPORS  221  6.1  Introduction  221  6.2  Experimental  224  - vi ii 6.3  R e s u l t s and D i s c u s s i o n  226  6.4  Conclusions  259  References  261  CHAPTER SEVEN: SUMMARY AND PROGNOSIS  APPENDIX:  26 5  References  2 73  MULTI-CHANNEL SCALING PROGRAM; Symbolic Program L i s t i n g  276  - ix -  L I S T OF  TABLES Page  Table 4.1  A p p r o x i m a t e t e m p e r a t u r e s and t h e g a s c e l l window m a t e r i a l s u s e d t o o b t a i n t h e f r e e m e t a l atom x - r a y photoelectron spectra  135  4.2  Sodium I s l e v e l b i n d i n g e n e r g i e s  142  4.3  P o t a s s i u m 2p  4.4  R u b i d i u m 3p l e v e l b i n d i n g e n e r g i e s  4.5  C e s i u m 3d  4.6  Magnesium I s l e v e l b i n d i n g e n e r g i e s  4.7  Calcium  level  binding energies  ...  146  ....  150  l e v e l binding energies  2s and  2p  level  153 ...  binding  energies  160  4.8  Strontium  4.9  B a r i u m 3d and 4d l e v e l b i n d i n g energies E s t i m a t e d v a l u e s of phase t r a n s i t i o n s h i f t s f o r t h e g r o u p IA and I I A metals  4.10  156  3d  l e v e l binding energies  ...  164 168 173  4.11  Multielectron excitation satellites: s e p a r a t i o n s from the main l i n e s  179  5.1  T i 2p and 3p b i n d i n g e n e r g i e s TiX ( X = F , C l , B r ,1)  197  in  4  5.2  Halogen core l e v e l binding energies i n T i X , H X and X (X=F, C I , B r , I) 4  5.3  S a t e l l i t e separations,AE,and the r e l a t i v e i n t e n s i t i e s , I , i n t h e T i 2p and 3p s p e c t r a o f T i X (X=F,C1,Br,I) 4  5.4  S a t e l l i t e separations,AE,and the r e l a t i v e i n t e n s i t i e s , I , i n the halogen core l e v e l s p e c t r a of TiX ( F , C I , B r , I) 4  198  2  ..  205  206  - x -  Page  Table 6.1  6.2  6.3  6.4  B i n d i n g e n e r g i e s of the metal 2p,3s and 3p l e v e l s i n MCAcAc)vapors (M=Co,Ni,Cu) 7  227  S a t e l l i t e separations,AE,and r e l a t i v e i n t e n s i t i e s , I , i n the metal 2p s p e c t r a of M(AcAc)2 vapors (M=Co,Ni,Cu).  228  S a t e l l i t e separations,AE,and r e l a t i v e i n t e n s i t i e s , I , i n the metal 3s and 3p s p e c t r a of M(AcAc)^ vapors (M=Co,Ni,Cu).  229  0 Is and C Is b i n d i n g e n e r g i e s and s a t e l l i t e separations i n acetylacetone and M(AcAc) vapors (M=Co,Ni,Cu)  239  9  - xi -  L I S T OF FIGURES Page  Figure 3.1  Block diagram of the x-ray photoelectron spectrometer  88  3.2  The x - r a y p h o t o e l e c t r o n s p e c t r o m e t e r ...  91  3.3  The x - r a y t u b e a s s e m b l y s h o w i n g t h e f i l a m e n t , f i l a m e n t s u p p o r t , anode and t h e s t a i n l e s s s t e e l s h i e l d  92  3.4  The x - r a y t u b e a s s e m b l y  93  3.5  The x - r a y t u b e anode i n d e t a i l  94  3.6  Schematic diagram of the spectrometer s h o w i n g t h e x - r a y t u b e and t h e o l d gas c e l l  96  3.7  S c h e m a t i c d i a g r a m o f t h e new h i g h t e m p e r a t u r e gas c e l l  104  A p r e l i m i n a r y s p e c t r u m o f t h e Ag 3d r e g i o n r e c o r d e d a t 1100°C u s i n g t h e new h i g h t e m p e r a t u r e g a s c e l l  10 8  3.9  The t h r e e e l e m e n t l e n s  110  3.10  X-ray p h o t o e l e c t r o n spectrum o f t h e 0 I s r e g i o n from 0  119  3.11  B l o c k diagram of a microcomputerc o n t r o l l e d experiment  121  3.12  Major f u n c t i o n flow diagram of the m u l t i - c h a n n e l s c a l i n g program  125  4.1  P h o t o e l e c t r o n spectrum of t h e sodium Is r e g i o n from atomic sodium  140  P h o t o e l e c t r o n spectrum of the potassium 2p r e g i o n f r o m a t o m i c p o t a s s i u m  145  P h o t o e l e c t r o n spectrum of t h e rubidium 3p r e g i o n f r o m a t o m i c r u b i d i u m  148  3.8  2  4.2 4.3  - x i i -  Page  Figure 4.4 4.5 4.6 4.7 4.8 4.9 4.10  5.1  5.2  5.3  5.4  5.5  5.6  P h o t o e l e c t r o n spectrum of the cesium 3d r e g i o n f r o m a t o m i c c e s i u m  152  P h o t o e l e c t r o n s p e c t r u m o f t h e magnesium I s r e g i o n f r o m a t o m i c magnesium  155  P h o t o e l e c t r o n spectrum of the calcium 2s r e g i o n f r o m a t o m i c c a l c i u m  158  P h o t o e l e c t r o n spectrum of the c a l c i u m 2p r e g i o n f r o m a t o m i c c a l c i u m  159  P h o t o e l e c t r o n spectrum of the s t r o n t i u m 3d r e g i o n f r o m a t o m i c s t r o n t i u m  163  P h o t o e l e c t r o n spectrum of t h e barium 3d r e g i o n f r o m a t o m i c b a r i u m  166  P h o t o e l e c t r o n spectrum of the barium 4d r e g i o n f r o m a t o m i c b a r i u m  16 7  P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n f r o m t i t a n i u m t e t r a f l u o r i d e vapor  200  P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n f r o m t i t a n i u m t e t r a c h l o r i d e vapor  201  P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n f r o m t i t a n i u m t e t r a b r o m i d e vapor  202  P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n f r o m t i t a n i u m t e t r a i o d i d e vapor  203  P h o t o e l e c t r o n spectrum of the t i t a n i u m 3p r e g i o n f r o m t i t a n i u m t e t r a f l u o r i d e vapor  208  P h o t o e l e c t r o n spectrum of the i o d i n e 3d r e g i o n f r o m t i t a n i u m t e t r a i o d i d e vapor  209  - xiii  *-  Figure 5.7  6.1  6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13  Page V a r i a t i o n o f t h e T i ^V_/2 satellite s e p a r a t i o n s and t h e T i 2^2/2 and T i 3p binding energies with ligand  210  P h o t o e l e c t r o n spectrum of the c o b a l t 2p r e g i o n f r o m c o b a l t a c e t y l a c e t o n a t e vapor  230  P h o t o e l e c t r o n s p e c t r u m o f t h e n i c k e l 2p r e g i o n from n i c k e l a c e t y l a c e t o n a t e vapor  2 31  P h o t o e l e c t r o n s p e c t r u m o f t h e c o p p e r 2p r e g i o n from copper a c e t y l a c e t o n a t e vapor  2 32  P h o t o e l e c t r o n s p e c t r u m o f t h e c o b a l t 3s r e g i o n from c o b a l t a c e t y l a c e t o n a t e vapor  2 33  P h o t o e l e c t r o n s p e c t r u m o f t h e n i c k e l 3s r e g i o n from n i c k e l a c e t y l a c e t o n a t e vapor  2 34  P h o t o e l e c t r o n s p e c t r u m o f t h e c o p p e r 3s r e g i o n f r o m copper a c e t y l a c e t o n a t e v a p o r  235  P h o t o e l e c t r o n s p e c t r u m o f t h e c o b a l t 3p r e g i o n from c o b a l t a c e t y l a c e t o n a t e vapor  236  P h o t o e l e c t r o n s p e c t r u m o f t h e n i c k e l 3p region from n i c k e l a c e t y l a c e t o n a t e vapor  237  P h o t o e l e c t r o n s p e c t r u m o f t h e c o p p e r 3p r e g i o n from copper a c e t y l a c e t o n a t e vapor  2 38  P h o t o e l e c t r o n spectrum of the carbon I s r e g i o n from c o b a l t a c e t y l a c e t o n a t e vapor  2 40  Photoelectron spectrum of the 0 I s region from c o b a l t a c e t y l a c e t o n a t e vapor  2 42  P h o t o e l e c t r o n spectrum o f the 0 I s r e g i o n from n i c k e l a c e t y l a c e t o n a t e vapor  24 3  P h o t o e l e c t r o n spectrum o f the 0 I s r e g i o n from copper a c e t y l a c e t o n a t e vapor  244  - xiv -  ACKNOWLEDGEMENTS  I would l i k e t o take t h i s o p p o r t u n i t y t o e x p r e s s my a p p r e c i a t i o n t o my r e s e a r c h s u p e r v i s o r s , P r o f e s s o r D.C. F r o s t a n d P r o f e s s o r C A . M c D o w e l l for  t h e i r s u p p o r t , encouragement and i n t e r e s t  through-  out t h i s work. I am g r a t e f u l t o D r . M.S.. Banna a n d p a r t i c u l a r l y to  D r . B. W a l l b a n k f o r t h e i r h e l p a n d i n v a l u a b l e  b o r a t i o n d u r i n g my f o r m a t i v e d a y s a s an x - r a y  colla-  photo-  electron spectroscopist. My v e r y for  s p e c i a l thanks  go t o D r . N.P.C. Westwood  h i s f r e e l y a v a i l a b l e h e l p and encouragement d u r i n g  t h e p a s t y e a r s , a n d f o r m a k i n g v e r y u s e f u l comments on this  manuscript. I also like  Dr.  R. N a k a g a k i ,  ful  discussions.  machining  t o t h a n k P r o f . A. B r e e ,  D r . M. W h i t e a n d D r . S. W h i t e f o r u s e I t i s a p l e a s u r e t o acknowledge t h e  s k i l l s o f Mr. E m i l M a t t e r , Mr. C h a r l e s  a n d Mr. C e d r i c N e a l e .  McCafferty  I am a l s o t h a n k f u l t o M r . B r i n  Powell for h i s useful suggestions temperature  D r . C. K i r b y ,  i n designing the high  gas c e l l s .  I would a l s o l i k e  t o thank Mr. Joe S a l l o s f o r h i s  e l e c t r o n i c s t r o u b l e - s h o o t i n g , and t h e e v e r h e l p f u l in  the electronics  shop.  staff  -  XV  -  I w i s h t o t h a n k Mr. T.D.J. D u n s t a n a n d Ms. S. Gamage f o r p r o o f r e a d i n g a n d Ms. T i l l y S c h r e i n d e r s a n d Ms. Anna Wong f o r t y p i n g  this  manuscript. Finally of B r i t i s h  I would l i k e t o thank t h e U n i v e r s i t y  Columbia f o r the grant o f a graduate  f e l l o w s h i p w h i c h made t h i s  study a r e a l i t y ,  and t h e  U n i v e r s i t y o f S r i L a n k a , P e r a d e n i y a Campus f o r t h e leave o f absence.  This  thesis  i s dedicated  to  my  paven  - 1 -  CHAPTER ONE  INTRODUCTION  The  fundamental experiment i n p h o t o e l e c t r o n  s p e c t r o s c o p y i n v o l v e s i r r a d i a t i o n o f t h e sample by a beam o f n e a r l y m o n o e n e r g e t i c r a d i a t i o n  and then  observation o f the resultant emission of photoelectrons I f t h e energy o f the i r r a d i a t i n g photons i s hv, the e n e r g e t i c s o f t h e p r o c e s s a r e d e f i n e d by t h e E i n s t e i n p h o t o e l e c t r i c relation"'", assuming t h a t hv>E^(k) , t h e n  hv = £ ( k ) + E . E  k  where, ^ ( ) i s t h e i o n i z a t i o n E  k  (1.1)  n  energy  e n e r g y ) o f t h e k-th l e v e l a s r e f e r r e d l e v e l and  (or binding t o t h e vacuum  i s t h e k i n e t i c e n e r g y o f s u c h an e l e c t r o n  e j e c t e d by t h e e x c i t i n g  radiation.  -  2  -  Each p h o t o e l e c t r o n e m i t t e d d u r i n g t h i s i s c h a r a c t e r i z e d by i t s k i n e t i c emission  process  energy, d i r e c t i o n  of  w i t h r e s p e c t t o t h e specimen and t h e e x c i t i n g  radiation,  and, under c e r t a i n  conditions, i t s spin. photoelectrons  special  experimental  These t h r e e f e a t u r e s o f e m i t t e d  lead t o three basic photoelectron  expe-  riments.  (1)  The number d i s t r i b u t i o n k i n e t i c energy:  of photoelectrons  This k i n d o f experiment leads t o  an e n e r g y d i s t r i b u t i o n  curve  (EDC) o r a  t r o n s p e c t r u m and t h e i o n i z a t i o n thus obtained the eigenvalue  with  photoelec-  potentials  (IP's)  c a n be e q u a t e d t o t h e n e g a t i v e o f f o r t h e o r b i t a l under c o n s i d e r a t i o n  using the approximation  commonly known a s K o o p m a n s  theorem . 2  (2)  The d i s t r i b u t i o n angle  of photoelectron  of emission:  kinetic  intensity  with  These e x p e r i m e n t s i n v o l v e  energy d i s t r i b u t i o n  determinations  of s e v e r a l angles  of emission  photon propagation  direction  r e s p e c t t o t h e specimen"^' ^.  relative  a t each  to the  o r t o axes f i x e d  with  1  - 3 -  (3)  The  s p i n d i s t r i b u t i o n of the p h o t o e l e c t r o n  sity:  inten-  These measurements r e q u i r e a specimen t h a t  h a s b e e n m a g n e t i c a l l y p o l a r i z e d by an e x t e r n a l field. may  U n d e r t h e s e c o n d i t i o n s more p h o t o e l e c t r o n s  be e m i t t e d w i t h one  o f t h e two  possible spin  o r i e n t a t i o n s t h a n w i t h t h e o t h e r , and t h e numbers o f s p i n - u p and are then  relative  spin-down p h o t o e l e c t r o n s  measured.  Experimental l e s s common due  s t u d i e s of types  (2) a n d  (3)  t o e x p e r i m e n t a l c o m p l e x i t y and  are  the  long  time r e q u i r e d . S e v e r a l r e v i e w s h a v e a p p e a r e d r e c e n t l y , on  the 5-7  t h e o r e t i c a l and e x p e r i m e n t a l a s p e c t s o f s u c h and  studies  t h e s e w i l l n o t be d i s c u s s e d f u r t h e r h e r e .  work d e s c r i b e d i n t h i s t h e s i s i n v o l v e d f i x e d p h o t o e l e c t r o n s t u d i e s and cussed  The angle  t h i s technique w i l l  be  in detail. Two  types of e x c i t i n g r a d i a t i o n  used i n p h o t o e l e c t r o n spectroscopy.  are  commonly  These a r e  e s s e n t i a l l y m o n o c h r o m a t i c beams o f u l t r a v i o l e t p r o d u c e d by x-ray  sources.  use  either radiation  a d i s c h a r g e i n a s u i t a b l e r a r e gas o r Vacuum u l t r a v i o l e t r a d i a t i o n  e n e r g y r a n g e f r o m a b o u t 5 - 50eV, its  dis-  and  to the study of valence l e v e l s .  band w i d t h of such r a d i a t i o n  i s usually  this  soft  covers  the  restricts  However, the sufficiently  - 4 narrow to a l l o w the v a r i o u s v i b r a t i o n a l l e v e l s i n t h e i o n t o be d i s t i n g u i s h e d f o r s i m p l e m o l e c u l e s . 8 9 ( I n some s p e c i f i c c a s e s be p a r t i a l l y sources  '  resolved).  rotational  s t r u c t u r e may-  When t h e s e t y p e s o f  photon  a r e u s e d t h e t e c h n i q u e i s r e f e r r e d t o as  u l t r a v i o l e t p h o t o e l e c t r o n spectroscopy which  i s known  by t h e more common a c r o n y m s UPS, UVPES o r s i m p l y P E S . When s o f t x - r a y s  (^100 - 1500eV) a r e u s e d  t h e e x c i t i n g r a d i a t i o n t h e t e c h n i q u e i s more r e f e r r e d t o as ESCA  (Electron Spectroscopy  c a l A n a l y s i s ) , X-ray  the energy  commonly  f o r Chemi-  PES o r XPS.  S o f t x-rays are produced and  as  i n standard x-ray  o f the x-rays produced  anode m a t e r i a l b e i n g u s e d .  tubes  depends on t h e  Mg a n d A l a r e t h e m o s t  commonly u s e d anode m a t e r i a l s .  H o w e v e r , t h e u s e o f Na  and S i a n o d e s i n x - r a y t u b e s i s n o t uncommon"^'"'"''". All  f o u r o f these second  t r a which  a r e dominated  row atoms g i v e r i s e  to x-ray  spec-  by a v e r y s t r o n g , u n r e s o l v e d ,  K a ^ - K a d o u b l e t p r o d u c e d by t r a n s i t i o n s o f t h e t y p e 2P.^ -*ls ^ ^l/2^ P '- lY• mean e n e r g i e s 2  a n <  s  r e s  e c t ;  v e  T  n  e  2  o f the x-rays produced 1041.OeV ;  Mg K a  10  and S i K c ^ , 2  1  2  ,  i n s u c h x - r a y t u b e s a r e Na K a , , I, / 9  1253.6eV ; A l Kc^ ,  1739 . 5 e V  1 2  2  i:L  .  1486.6eV ; 1 3  -  When t h e s e radiation mental Ka^  -  sources are used as e x c i t i n g  the primary  resolution  2 line.  5  factor  determining the i n s t r u -  i s the natural  The f u l l  l i n e width of the  w i d t h a t h a l f maximum  intensity  (FWHM) o f t h e a b o v e m e n t i o n e d s o u r c e a r e a p p r o x i m a t e l y 0.4eV f o r Na K a ^ ° Al Ka^  , 0.7eV f o r Mg K a ^ °  2  a n d 1.0 - 1.2eV f o r S i K a j ^ .  3 2  such r a d i a t i o n  less  suited  as t h e b r o a d e x c i t i n g to  produced  the individual  themselves  T h i s makes level studies  closely  l e v e l s of thei o n  i s ejected. spaced  makes them v e r y u s e f u l  study o f i n n e r s h e l l i o n i z a t i o n the natural  i n the  w i d t h o f t h e Kct^  line  2  b e l o w Ne  f o r anode m a t e r i a l s a s t h e v a l e n c e 2p  l e v e l s o f these elements e f f e c t s , which  levels  processes.  w i t h t h e atomic number,the elements  are n o t s u i t a b l e  levels  However, t h e  s o f t x-rays t o reach the core  atoms a n d m o l e c u l e s  Although  In  valence  are often not distinguished.  o f these  decreases  , 0.8eV f o r  l i n e w i d t h makes i t i m p o s s i b l e  when a v a l e n c e e l e c t r o n  addition,  of  f o r valence  resolve the various v i b r a t i o n a l  ability  2  a r e b r o a d e n e d by  increases the natural  bonding  l i n e width of the  x-rays correspondingly. A more p r a c t i c a l way o f o b t a i n i n g n a r r o w e r excitation x-radiation  sources  i s the monochromatization  o f Ka^  by Bragg r e f l e c t i o n from a s u i t a b l e  2  single  14 crystal  .  Although  the loss of intensity during  such  - 6 -  monochromatization  p r o c e s s e s i s c o n s i d e r a b l e , photo-  e l e c t r o n peaks as narrow as 0.4eV have been observed 15 with mono chroma t i zed A l Ktx r a d i a t i o n  .  In f a c t , the  l i n e width o f these monochromatized e x c i t i n g sources are s u f f i c i e n t l y narrow, t h a t cases have been r e p o r t e d where v i b r a t i o n a l f i n e s t r u c t u r e was  r e s o l v e d i n the  core l e v e l s p e c t r a o f some s m a l l m o l e c u l e s ^ . In a d d i t i o n to these x-ray s o u r c e s , u l t r a x-rays produced by the M? the s e q u e n t i a l elements a l s o been used i n XPS  transition  soft  (^P3/2"*" 5/2^ 3d  ^  n  y t t r i u m t o molybdenum have  studies.  These cover the i n t e r e s t -  i n g energy range o f 100<hv<200eV, and the most f r e q u e n t l y used l i n e s o f t h i s type are those f o r Y  (hv=132.3eV,  FWHM=0.5eV) and Zr(hv=151.4eV, FWHM=0.8eV). These have been used s u c c e s f u l l y t o study both the v a l e n c e l e v e l s 10 18 19 and o u t e r core l e v e l s ' ' In some i n s t a n c e s , when a h i g h e r energy source i s r e q u i r e d , i n order to reach the deep l y i n g l e v e l s o f a sample, chromium and copper are used o c c a s i o n a l l y as the 20  x-ray source  (Cr Kc^ hv=5414.7eV  , FWHM=2.1eV; Cu  Ka^  20 hv=8047.8eV  , FWHM=2.6eV).  these sources e x c i t i n g x-ray  However, the a p p l i c a t i o n o f  i s l i m i t e d by the broad l i n e width o f the lines.  Another source t h a t has emerged over the few years i s t h a t of s y n c h r o t r o n r a d i a t i o n .  last  In a syn-  c h r o t r o n , e l e c t r o n s are c o n s t r a i n e d t o move i n a c l o s e d path by a magnetic  field.  c e n t r i p e t a l f o r c e normal  As they are a c c e l e r a t e d by the t o the d i r e c t i o n o f motion,  the  e l e c t r o n s r a d i a t e energy i n the form o f e l e c t r o m a g n e t i c radiation.  T h i s r a d i a t i o n appears as a c o n t i n u o u s  s p e c t r u m w i t h an i n t e n s i t y maximum a t a c r i t i c a l length,  X , a t which the r a d i a t i o n  i s almost  wave  100%  p o l a r i z e d i n the plane o f the o r b i t i n which the e l e c trons are t r a v e l l i n g .  A range o f photon e n e r g i e s from  a b o u t 10 t o 8000eV i s p r e s e n t l y a v a i l a b l e  from synchro-  t r o n s and phenomena d e p e n d e n t on p h o t o n e n e r g y  and/or  polarization  this  a r e much more e a s i l y s t u d i e d w i t h  21 r a d i a t i o n t h a n w i t h more s t a n d a r d s o f t x - r a y s o u r c e s A c c o r d i n g t o e q u a t i o n 1.1  one w o u l d e x p e c t a  s i n g l e p h o t o e l e c t r o n peak a s s o c i a t e d w i t h e a c h or molecular o r b i t a l .  atomic  However, t h e b i n d i n g e n e r g y  term,  E ^ ( k ) , o f e q n . 1 . 1 i s more a c c u r a t e l y d e f i n e d as t h e difference  i n t o t a l energy between the i n i t i a l  and t h e f i n a l  s t a t e p r o d u c e d by t h e  state,  ionization,  i.e. b  E  Here,  E  ^  (  ( )  t  )  i  N  o  K  =  s  E  t o t  t n e  (before i o n i z a t i o n )  (  N  _  1  ,  K  " tot  )  E  (  N  )  ( 1  t o t a l energy o f the ground and E ^ ( N - l , K ) o t  i s the corresponding b i n d i n g energy  t o t h e vacuum l e v e l . state results  2 )  state  i s the energy of  t h e K-th ( N - l ) - e l e c t r o n i o n i c s t a t e p r o d u c e d b y where E^(K)  '  ionization, referenced  T h e r e f o r e , i f more t h a n one  from removal o f a core e l e c t r o n ,  final  then  -  more t h a n one  l o w e s t v a l u e o f E^(K)  final  occur.  In the  t h e peak c o r r e s p o n d i n g t o  the  i s h e r e a f t e r r e f e r r e d t o as  the  a d d i t i o n a l peaks t h a t appear a t h i g h e r  b i n d i n g energy Various f i n a l  -  p h o t o e l e c t r o n peak w i l l  p h o t o e l e c t r o n spectrum  m a i n p e a k and  8  v a l u e s a r e r e f e r r e d t o as s a t e l l i t e state effects that w i l l  peaks.  result in multiple  s t a t e s (and h e n c e t h e m u l t i p l e s t r u c t u r e i n t h e  core e l e c t r o n i n Chapter  spectra) w i l l  be d i s c u s s e d i n some d e t a i l  Two.  X-ray  photoelectron spectroscopy i s presently  f i n d i n g a p p l i c a t i o n s i n the study o f e l e c t r o n i c t i e s o f a wide range o f m a t e r i a l s ;  solids  14  proper-  , vapors  14  '  22  23-25 and more r e c e n t l y l i q u i d s  .  XPS  t o m o l e c u l a r beams f r o m h o t m e t a l L i q u i d p h a s e XPS  has  a l s o been a p p l i e d 26  vapors  h a s , up t o now,  been a p p l i e d 23  o n l y t o low vapor  pressure l i q u i d s  ( v a p o r p r e s s u r e 0.01  - 0.02  s u c h as  t o r r a t room  formamide temperature)  25 and e t h y l e n e g l y c o l temperature).  ( V a p o r p r e s s u r e ^0.1  A number o f s a m p l i n g  t o r r a t room  techniques  are 25  presently available,  i n c l u d i n g the moving w i r e method 23 24  an.d t h e l i q u i d beam method Solid u s i n g XPS.  '  samples have been e x t e n s i v e l y s t u d i e d  Here the s o l i d  form o f probe which  i s u s u a l l y a t t a c h e d t o some  i s then i n t r o d u c e d i n t o the  chamber o f t h e s p e c t r o m e t e r .  sample  Powders a r e o f t e n mounted  - 9 -  by  spreading  tape.  An  a t h i n l a y e r onto double s i d e d  'scotch'  a l t e r n a t i v e method i s t o p r e s s t h e  powder  onto a conducting wire  mesh.  simply  o r p o l i s h e d i n t o shapes s u i t a b l e  be  cut, cleaved  f o r mounting i n the  specimen p o s i t i o n .  involving clean surfaces, vacuum e v a p o r a t i o n  Machineable s o l i d s  s a m p l e s may  be  For  can  studies  prepared  by  o f the m a t e r i a l o n t o a s u i t a b l e  27 28 substrate  '  .  For p r e c i s e  high  vacuum f a c i l i t i e s  face  contamination.  emission  studies,  are a n e c e s s i t y , to a v o i d  f r o m any  i s generally connected, e l e c t r i c a l l y , potential, V  u n e q u a l c h a r g e d i s t r i b u t i o n , may  t o the  r" i s t h e the  to the v a l u e s spatial  f o r the  coordinate  s p e c i m e n , eqn.  1.1  hv= £(k,r*) + E  = E  b  ( k )  °  +  E  can  be  rewritten  E . (?) k  kin  n  (  shifts  J  )  an specimen  with  uncharged s i t u a t i o n .  now  +  V  c  (  ?  )  to  sample  vary w i t h i n the  of the emission  a  specimen  , p r o d u c e d by  volume p r o d u c i n g a range o f e n e r g y l e v e l respect  of  In order the  net  to  possible building-up  reduce such p o t e n t i a l build-up, f o r s o l i d s ,  charging  the  sample c o n s t i t u t e s a  p o s i t i v e p o t e n t i a l i n the e m i t t i n g r e g i o n .  The  sur-  charge, i t i s u s u a l l y necessary  m i n i m i z e o r c o r r e c t f o r the  chamber.  ultra  D u r i n g t h e s e e x p e r i m e n t s , as  of e l e c t r o n s  loss of negative  surface  point as  If within  - 10 -  where E^(k)° and E^(k,r) are the b i n d i n g e n e r g i e s i n the absence and presence  o f charging, r e s p e c t i v e l y .  In most cases the r e s u l t of sample c h a r g i n g i s a broadened p h o t o e l e c t r o n s i g n a l .  To c o r r e c t f o r such  e f f e c t s s t u d i e s o f peak p o s i t i o n versus x-ray f l u x can be made. The work d e s c r i b e d i n t h i s t h e s i s i s p a r t i c u l a r l y r e l a t e d to the study o f atoms and molecules the vapor phase.  In o r d e r to study metal  h i g h temperature furnace was in this laboratory. the f i r s t  designed and  atoms, a constructed  The work presented here  represents  x-ray p h o t o e l e c t r o n s p e c t r o s c o p i c study i n  the vapor phase f o r most o f the atoms and reported.  in  molecules  Problems i n v o l v e d i n these h i g h temperature  gas phase s t u d i e s and the s p e c i a l advantages of  such  techniques w i l l be d i s c u s s e d i n the f o l l o w i n g c h a p t e r s .  - 11 REFERENCES  1.  A. E i n s t e i n , A n n . P h y s . 1 7 , 132 (1905)  2.  T. Koopmans, P h y s i c a 1, 104 (1934)  3.  K. S i e g b a h n , U. G e l i u s , H. S i e g b a h n , a n d E . O l s o n , Physica Scripta  4.  C.S. F a d l e y , a n d S.A.L. B e r g s t r o m , P h y s . L e t t . 35A, 375  5.  1, 272 (1970)  (1971)  C.R. B r u n d f e , and A.D. Baker, E d i t o r s ,  "Electron  Spectros-  copy - T h e o r y , T e c h n i q u e s and A p p l i c a t i o n s " V o l . 2 ( A c a d e m i c P r e s s , New Y o r k , 1 9 7 8 ) 6.  T.A. C a r l s o n , E d i t o r , copy"  "X-ray P h o t o e l e c t r o n  Spectros-  (Dowden, H u t c h i n s o n & R o s s I n c . , S t r o u d s b u r g ,  P e n n s y l v a n i a , 1978) 7.  M. Campagna, D.T. P i e r c e , F. M e i e r , L . S a t t l e r , a n d H.C. S i e g m a n n , A d v a n c e s i n E l e c t r o n i c s a n d E l e c t r o n P h y s i c s 4_1_, 113 (1976)  8.  R.N. D i x o n , G. D u x b u r y , J.W. R a b a l a i s , a n d L . A s b r i n k , M o i . P h y s . 3 1 , 423 (1976)  9.  L. K a r l s s o n , L. M a t t s s o n , R. J a d r n y , R.G. A l b r i d g e , S. P i n c h a s , T. B e r g m a r k , a n d K. S i e g b a h n , J . Chem. P h y s . 6 2 , 4745  10.  (1975)  M.S. B a n n a , a n d D.A. S h i r l e y , J . E l e c t r o n  Spectrosc.  R e l a t . Phenom. 8, 2 3 , 255 (1976) 11.  J . E . C a s t l e , L.B. H a z e l l ,  and R.D. W h i t e h e a d ,  J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 9_, 246 (1976)  - 12  12.  M.O.  K r a u s e , and J.G.  2007  -  F e r e i r a , J . P h y s . B 8_,  (1975)  13.  E. K a l l n e , a n d T. A b e r g , X - r a y S p e c t r . 4_, 26  14.  K. S i e g b a h n , C. N o r d l i n g , A. F a h l m a n , K. H a m r i n , S.-  J . Hedman, G. J o h a n s s o n , T.  R.  (1975)  Nordberg,  Bergmark,  E. K a r l s s o n , I . L i n d g r e n , and B. L i n d b e r g ,  "ESCA: A t o m i c , M o l e c u l a r , a n d S o l i d  State  Structure  S t u d i e d b y Means o f E l e c t r o n S p e c t r o s c o p y "  Nova  A c t a R e g i a e S o c . S c i . U p s a l i e n s i s , S e r I V , V o l . 20 ( A l m q v i s t and W i k s e l l s , 15.  16.  Stockholm,  1967)  K.  S i e g b a h n , J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 5_,  3  (1974)  U. G e l i u s , E. B a s i l i e r , S. S v e n s s o n , T. B e r g m a r k ,  and  K. S i e g b a h n , J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 2_, 405 17.  (1973)  U. G e l i u s , S. S v e n s s o n , H. and K. of  S i e g b a h n , E. B a s i l i e r , A. F a x a l v ,  S i e g b a h n , UUIP-860 ( U p p s a l a U n i v e r s i t y  P h y s i c s Report) March  Institute  1974  18.  M.O.  K r a u s e , Chem. P h y s . L e t t . 1 0 , 65  (1971)  19.  R. N i l s s o n , R. N y h o l m , A. B e r n d t s s o n , J . Hedman, and C. N o r d l i n g , J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 9_, 337  (1976)  20.  J.A.  Bearden,  21.  K.O.  H o d g s o n , and S. D o n i a c h , C h e m i c a l and E n g i n e e r i n g  News A u g .  Rev. Mod.  21, 1978,  p.26  Phys.  3_9_, 78  (1967)  - 13 -  22.  K. S i e g b a h n , C. N o r d l i n g , P.F.  H e d e n , K. H a m r i n ,  G. J o h a n s s o n , J . Hedman,  U. G e l i u s , T. B e r g m a r k ,  L.O. Werme, R. Manne, a n d Y. B a e r , "ESCA, to Free Molecules"  (North-Holland  Applied  Publishing  Company,  A m s t e r d a m , 1969) 23.  H. S i e g b a h n , a n d K. S i e g b a h n , J . E l e c t r o n R e l a t . Phenom. 2, 319  24.  H. F e l l n e r - F e l d e g g ,  26.  H. S i e g b a h n , L. A s p l u n d , P.  Y.S. K h o d e y e v , H. S i e g b a h n , K. H a m r i n ,  Siegbahn,  (1973)  S h i r l e y , P h y s . R e v . B 8, 3583  S h i r l e y , P h y s . Rev. B 1 1 , 600  C.S. F a d l e y , G.L. G e f f r o y , J.M. H o l l a n d e r ,  30.  a n d K.  (1973)  L. L e y , F.R. M c F e e l y , S.P. Kowalczyk, J.G. J e n k i n , D.A.  29.  R e l a t . Phenom. 1_,  S.P. Kowalczyk, L. L e y , F.R. M c F e e l y , R.A. P o l l a k , a n d D.A.  28.  Spectrosc.  Kelfve,  (1975)  Chem. P h y s . L e t t . __9, 16 27.  Spectrosc.  (1974)  a n d K. S i e g b a h n , J . E l e c t r o n 421  Hamrin,  a n d K. S i e g b a h n , J . E l e c t r o n  R e l a t . Phenom. 5, 1059 25.  (1973)  H. S i e g b a h n , L. A s p l u n d , P. K e l f v e , K. L. K a r l s s o n ,  Spectrosc.  Nucl.  (1975)  S.B.M. H a g s t r o m ,  I n s t . M e t h o d s 6_8, 177  J . F . M c G i l p , a n d I.G. M a i n , J . E l e c t r o n Phenom. 6, 397  (1975)  and  and (1969)  Spectrosc.  Relat.  - 14 -  CHAPTER  TWO  B A S I C CONCEPTS OF X-RAY PHOTOELECTRON  2.1  SPECTROSCOPY  Introduction  Since co-workers energies  1  the f i r s t observation  by Siegbahn and  a t Uppsala U n i v e r s i t y , that core  binding  show a d e f i n i t e d e p e n d e n c e o n c h e m i c a l  envi-  r o n m e n t , a l a r g e number o f d i f f e r e n t c h e m i c a l a n d p h y s i c a l e f f e c t s have been r e p o r t e d ture.  Successful  attempts are being  i n t h e XPS  litera-  made t o p r o v i d e  q u a n t i t a t i v e t h e o r e t i c a l models o f s u c h e f f e c t s , as revealed the  b y t h e l a r g e number o f p a p e r s t h a t a p p e a r i n  journals that deal with  this  subject.  Theoretical  a s p e c t s o f p h o t o e m i s s i o n p r o c e s s e s have a l s o been d i s cussed i n d e t a i l  i n a number o f b o o k s 1—5 , r e v i e w s 6 ' 7 8—10  and  conference proceedings  review o f the theory  .  o f XPS w i l l  T h u s , no d e t a i l e d be a t t e m p t e d  here,  - 15 although  some o f t h e c h a r a c t e r i s t i c f e a t u r e s o f s p e c t r a  reported i n this thesis w i l l  be d i s c u s s e d i n some  detail The in  primary  a i m o f most t h e o r e t i c a l models used  XPS i s t o i n t e r p r e t t h e e x p e r i m e n t a l  photoelectron  s p e c t r a u s i n g t h e now f a m i l i a r eqn. 1.2 which w i l l  E  b  where  t  be r e w r i t t e n h e r e f o r c o n v e n i e n c e , a s  ( K )  =  E  (N-l,K)  tot  (  N  - ' 1  K  " tot  )  E  (  N  )  2.2  ( 1  '  i s the t o t a l energy o f theK-th  electron i o n i c state corresponding final  (Chapter One),  2 )  (N-l)-  to the ( N - l ) - e l e c t r o n  s t a t e wave f u n c t i o n , p r o d u c e d b y p h o t o i o n i z a t i o n .  N-Electron  Wave  In g e n e r a l ,  Functions f o r a system w i t h N e l e c t r o n s the  t o t a l wave f u n c t i o n s c o n s i d e r e d spatial coordinates,  will  d e p e n d upon t h e  r ^ , and s p i n c o o r d i n a t e s , c k , o f  the N e l e c t r o n s and t h e s p a t i a l  coordinates  R , of the  P nuclei  'tot  =  ^tot  ( r  l' l' 2' 2-"- N N a  r  a  r  a  ;  W-V  The r e l e v a n t Hamiltonian o f the N - e l e c t r o n state  ( i n the n o n - r e l a t i v i s t i c  limit)  can be w r i t t e n  { 2  '  1 ]  - 16 -  H  2m  tot  +  N  2  E  V .  i=l  p  p  E  E  i  ZzZm  £=1 m>£  The  N -E 1=1  P E  N  £=1  r  i.  E  j >i  ID  e  (2.2)  T  ' £m  £=1  M  £  f i v e terms on the r i g h t hand s i d e o f t h i s  expression represent contributions  to the t o t a l H a m i l t o n i a n  from the k i n e t i c energy o f e l e c t r o n s , attraction, electron-electron repulsion  N  + E 1=1  electron-nuclear  repulsion,  nuclear-nuclear  and n u c l e a r k i n e t i c energy r e s p e c t i v e l y , where  m i s the e l e c t r o n i c mass,  i s t h e charge o f the £th  nucleus , r . =lr . -£„ I .r . . = I r. - r . I , r „ = I R~ -R I i£'i £ ' i j I j ' £m £ m and i s the mass o f the £th n u c l e u s . 1  1  Contributions  1  1  1  due to s p i n - o r b i t s p l i t t i n g are  u s u a l l y added as an e x t r a term, H , t o the t o t a l so' J  Hamiltonian i n eqn.  H  so f =  2.2 where  S(r.Hi- i S  = 1  f o r atomic o r b i t a l s .  '  <-> 2  Here t;(r^) i s a s u i t a b l e  3  function  o f the r a d i a l c o o r d i n a t e r ^, and £^ and s^ are the onee l e c t r o n o p e r a t o r s f o r o r b i t a l angular momentum and s p i n 12 angular momentum r e s p e c t i v e l y must s a t i s f y the r e l a t i o n s h i p  .  The t o t a l wave  function  - 17 -  tot  H  W  N  =  )  E  t o t  (  N  )  W  (  N  )  ( 2  '  4 )  12 13 According  t o t h e Born-Oppenheimer a p p r o x i m a t i o n  t h e t o t a l e i g e n f u n c t i o n V^ ^ Q  c a  n be s e p a r a t e d  p r o d u c t o f an e l e c t r o n i c f u n c t i o n , function, *tot  ( ?  Y  l'  a  n u c  '  into the  v, a n d a n u c l e a r  .  l " " N ' n ?  a  =  ;  ¥ ( ?  l'°l--- N' N ?  0  ) , i f  nuc l---V ( S  (2.5)  where  V(N) , t h e e l e c t r o n i c p a r t o f e q n . 2.5, depends  only  parametrically  on t h e i n s t a n t a n e o u s  the P n u c l e i .  ^(N) i s a s o l u t i o n t o e q n . 2.4 i n w h i c h  H  t Q t  s p a t i a l coordinates of  i s r e p l a c e d by H, where 2 -h F" i_  . H  =  H  . tot  +  2 v - W £=1 A p  E  ( 2  *  6 )  The t o t a l e n e r g y o f t h e s y s t e m , c a n now be w r i t t e n as  ^ = E + E tot nuc  (2.7)  - 18  -  Here, E i s the e l e c t r o n i c energy and ^  E  the energy due  to i n t e r n a l n u c l e a r motions which  vibrations, rotations lations) .  and  include  center-of-mass motions  (trans-  Furthermore, i f these d i f f e r e n t modes o f  n u c l e a r motions are rewritten  is nuc  J  independent, then eqn. 2.7  can  be  as  E  tot "  E  +  E  vib  +  E  rot  +  E  trans  (2.8)  T h i s demands t h a t the o v e r a l l quantum numbers describing  any  i n i t i a l or f i n a l s t a t e must i n c l u d e  a  complete s p e c i f i c a t i o n of a l l these modes o f motion. V i b r a t i o n a l e x c i t a t i o n s i n the give r i s e to v i b r a t i o n a l bands i n UPS i n the vapor phase.  final  state  ion  s t u d i e s o f molecules  These have a l s o been observed i n a 14-17  number o f h i g h r e s o l u t i o n XPS  studies  studies, c u r r e n t l y a v a i l a b l e i n s t r u m e n t a l not permit the i n the  detection  .  In  XPS  r e s o l u t i o n does  of d i f f e r e n t r o t a t i o n a l e x c i t a t i o n s  final ionic state. The  e f f e c t o f t r a n s l a t i o n a l motion of an atom or  molecule on e n e r g i e s determined by XPS  (and  UPS)  is  two  that,  for  fold. (i)  Conservation o f l i n e a r momentum r e q u i r e s  the  photoemission process  - 19 -  ?  hv  +  0  =  Pf  where P^ / P f a n d P v  +  r  Pr  ( 2  '  9 )  a r e t h e p h o t o n momentum,  photo-  e l e c t r o n momentum a n d t h e r e c o i l momentum o f t h e f i n a l state is  ionrespectively.  t a k e n t o be 0 ( z e r o ) f o r s i m p l i c i t y .  trons encountered to  i n XPS c a n be c o n s i d e r e d  state  The p h o t o e l e c non-relativistic,  a good a p p r o x i m a t i o n , and t h e r e f o r e one can w r i t e  P  for  Momentum o f t h e i n i t i a l  |£ _5L | P  h v  |  f  (2.10)  t h e extreme case o f t h e p h o t o e l e c t r o n s h a v i n g  energy  kinetic  approximately equal t o t h e photon energy ( i . e .  v a l e n c e p h o t o e m i s s i o n ) , where v a n d c a r e t h e v e l o c i t i e s of  t h e p h o t o e l e c t r o n and l i g h t r e s p e c t i v e l y .  | P ^ | <<|P_:| a n d P f ^ P v  ion  r  In general  i n d i c a t i n g that the f i n a l  state  r e c o i l s i n a direction opposite to the direction of 18  photoemission energy  .  The r e c o i l e n e r g y ,  and k i n e t i c energy  E , f o r a given photon r  o f p h o t o e l e c t r o n , c a n be w r i t t e n  as E  = p /2M *r 2  r  (2.11)  - 20  -  where M i s t h e mass o f t h e f i n a l t o a c a l c u l a t i o n by S i e g b a h n l i g h t e s t atoms H, He of E  state ion.  According  and c o w o r k e r s , o n l y t h e 1  and L i h a v e a s i g n i f i c a n t  magnitude  , where t h e r e c o i l e n e r g i e s a r e 0.9eV a n d O . l e V f o r  H a n d L i ( p h o t o i o n i z e d by A l Ka x - r a y s , hv = 14 86 .6eV) r e s p e c t i v e l y , i n c o m p a r i s o n w i t h t h e a v a i l a b l e XPS m e n t a l r e s o l u t i o n o f 0.4  (ii)  - l.OeV.  The . t h e r m a l t r a n s l a t i o n a l m o t i o n o f t h e  molecule  (or atom),  i n t h e gas p h a s e ,  p e a k w i d t h s d e t e r m i n e d by XPS broadening.  instru-  emitting  can i n c r e a s e  (and UPS)  due  to  the  Doppler  I t h a s b e e n shown t h a t t h e D o p p l e r w i d t h i s  p r o p o r t i o n a l t o t h e i n v e r s e o f t h e m o l e c u l a r mass o f  the  19 e m i t t i n g molecule  ( o r atom)  , and i t h a s b e e n e s t i m a t e d  t h a t t h e D o p p l e r w i d t h i s £ O.lOeV f o r m o l e c u l e s  with  m o l e c u l a r w e i g h t s ^ 10. For almost a l l cases, the e f f e c t of m o t i o n on XPS  e n e r g i e s , through r e c o i l energy  translational and  Doppler  broadening, i s c o n s i d e r e d i n s i g n i f i c a n t i n comparison typical  XPS  r e s o l u t i o n o f ^0.4  - l.OeV.  to  - 21 -  For these reasons, u s u a l l y i t i s adequate t o consider quantities relating only to electronic and eqn.1.2 i s now a p p r o x i m a t e d  (K) = E ( N - l , K ) f  2.3  motion  as  - E (N)  (2.12)  1  M o l e c u l a r O r b i t a l C a l c u l a t i o n s F o r XPS S t u d i e s  Most quantum m e c h a n i c a l  c a l c u l a t i o n s o f the  e l e c t r o n i c s t r u c t u r e o f m o l e c u l a r systems have been carried out using various molecular o r b i t a l  approximations.  A common s t a r t i n g p o i n t f o r s u c h c a l c u l a t i o n s i s t h e n o n relativistic  Hartree-Fock  (HF) s e l f c o n s i s t e n t f i e l d (SCF)  12 method  .  I n t h i s a p p r o x i m a t i o n i t i s assumed t h a t t h e  e l e c t r o n s move i n d e p e n d e n t l y o f e a c h o t h e r i n t h e f i e l d of  t h e n u c l e i , and i n d e p e n d e n t l y o f t h e average  of  the other electrons.  The HF(SCF) m e t h o d i s u s e d a t  d i f f e r e n t l e v e l s o f exactness wave f u n c t i o n s .  distribution  i n approximating N-electron  I n t h e s i m p l e s t f o r m , t h e wave  Y f o r a c l o s e d s h e l l N - e l e c t r o n system  function  i s approximated  as  a s i n g l e S l a t e r d e t e r m i n a n t , $,of N o r t h o n o r m a l o n e - e l e c t r o n s p i n - o r b i t a l s and each o f t h e s e one e l e c t r o n o r b i t a l s i n turn i s the product o f a s p a t i a l part,  <f>^(r) ( i = 1,2, ..,N) ,  - 22  and a s p i n p a r t ,  -  x-; » w h i c h i s e q u a l t o a(m =+—) , o r 2 1  3 ( ~2") • m  =  f  t h e n be w r i t t e n i n t e r m s o f t h e  c a n  3  s y m m e t r i z e r , A,  ¥ *  s  as  $ = A ( <t, , * x ' lXl  2  •••  2  '* X ) N  (2.13)  N  In the s p i n r e s t r i c t e d H a r t r e e - F o c k each  spatial orbital,  involved  of electrons The using  method,  <j>^, i s assumed t o h a v e a maximum  o c c u p a t i o n number o f two are  anti-  and h e n c e o n l y N/2  i n d e s c r i b i n g a system w i t h (in doubly-occupied  unique  an e v e n number  orbitals).  H a r t r e e - F o c k e q u a t i o n s a r e o b t a i n e d by  t h e quantum m e c h a n i c a l v a r i a t i o n a l p r i n c i p l e t o  determine  the optimum  $ f o r which  the t o t a l  energy  E = <$|HJ$> i s a minimum. These N e q u a t i o n s c a n be to determine well  <f>^ s  a s e l f - c o n s i s t e n t s e t o f o r b i t a l s <j> ^,  as t h e t o t a l e n e r g y E c o r r e s p o n d i n g t o t h e  described  by $.  In atomic u n i t s , the  equations i n diagonal  P(l)*  (1) ={-ly 1  used  z  2  1  -  £=i  + r  m  j=l = e * (l) i  as  ?  i  K .]}• .(1)  m J  state  Hartree-Fock  f o r m can be w r i t t e n  Z  as  m  si' sj m  , i=l,2,  3  1  ,N  (2.14)  - 23 -  where, J j and Kj are the Coulomb and exchange o p e r a t o r s respectively.  These o p e r a t o r s are d e f i n e d such  J V * (1) = / + / ( 2 ) » — j x j 12  (2) <f>,(l)dT  H  K-*.(1) = -*  (2)-i12  J  that  (2.15)  2  <J>. (2) * . ( l ) d T o  r  (2.16)  3  Thus, the matrix elements o f these o p e r a t o r s are the t w o - e l e c t r o n Coulomb i n t e g r a l s J ^ j and exchange integrals K^j:  J . . =<•. (1) | J . | * - (1) > = //*. * ( 1 ) <t>, * ( 2 ) - ^ - *. (1) 4> . ( 2 ) d T , d x I J x j x x j 12 3  (2.17)  K. . =<<|>. (1) |K . | <j). (1) > = //*. * ( 1 ) xj  x  j  x  x  j  * ( 2 ) - ^ - 4>. (2) <(.. ( l ) d x 12 (2 .18)  6  m . ,m . si' sj  i n eqn. 2.14 ^  i s the Kronecker d e l t a which by  definition i s  <X •1  *i  I _X •  >  =  =1  m<S .,m. si' sj =  0  f o r a a o r 66 f o r a3 or 8 a  (2.19)  dx„  - 24  The e x c h a n g e  interaction  orbitals  with parallel  6  i n eqn. 2.14  m  • /HI  si  -  i s o n l y p o s s i b l e between spins  allows  ( i . e . cm o r 38) for this.  spin  and  Once t h e  Hartree-  Sj  Fock e q u a t i o n s a r e s o l v e d t o the d e s i r e d c o n s i s t e n c y , orbital  e-  energies  c a n be o b t a i n e d  N e  i  =  e  i  +  E  < ij  5  J  3=1  m  J  for kinetic  from  K. . .,m . i n s i ' Sj  (2.20)  J  Here e ? i s the e x p e c t a t i o n v a l u e operator  the  e n e r g y and  o f the  one-electron  electron-nuclear  attraction  e?=<*. (1) l-i-V, 1  Now, by  1  2  p - I  2 -A"  SL=1  Z  r  U- (1)>  l l  (2.21)  1  the t o t a l energy o f the s t a t e approximated $  i s given  by  E = < $ | H | $> N =  I  i=l  N  n  e? 1  +  Z  N I  i=l j>i  P (J---<5 1 3  m  m  s i ' sj  K..) 1 3  +  I 1=1  P I m>l  7•  £m  z  m  (2.22)  - 25  -  H e r e , when a d d i n g t h e o n e - e l e c t r o n for  the N e l e c t r o n s i n the  with i<j  energies  together,  s y s t e m , a c o r r e c t i o n i s made  to avoid counting  the  Coulomb and  exchange terms  twice. In u s i n g the Hartree-Fock binding energies, compute t h e  2.4  t h e most a c c u r a t e  procedure i s to  d i f f e r e n c e b e t w e e n E ( N - l , K ) a n d E"*"(N)  corresponding and  method f o r c a l c u l a t i n g  f  to the Hartree-Fock  wave f u n c t i o n s  ^(N-ljK)  Y (N), respectively. 1  Koopmans' Theorem and  Binding  Energies  20 Koopmans one  theorem  1  electron orbitals,  are p r e c i s e l y equal <}>^, m a k i n g up  the  k-subshell hole. eqn.  2.22  and  <$>^, m a k i n g up  t o the  final  E^(k) b  K T  f i n a l one  E ^ ( N - l , k ) c a n now  be = E  1  energy of  the  d e t e r m i n a n t i* (N) 1  electron orbitals,  be  calculated using  b i n d i n g energy of the  k-th  c a l c u l a t e d as f  (N-l,k)-E (N)  i n the k-th  (2.23)  1  where E ^ ( N - l , k ) i s t h e e n e r g y o f t h e state with a hole  the  initial  state, $^(N-l,k), with a single  the Koopmans  e l e c t r o n c a n now  assumes t h a t t h e  lowest  subshell.  The  energy f i n a l binding  ionic  - 26  k-th e l e c t r o n as o b t a i n e d  -  from egn. 2.23  the negative o f the o r b i t a l energy as  i s equal  to  and t h i s i s known  'Koopmans'theorem'. The b i n d i n g e n e r g i e s c a l c u l a t e d u s i n g Koopmans'  theorem as d e s c r i b e d here, experimental reasons.  u s u a l l y d i f f e r from the a c t u a l  b i n d i n g energy v a l u e s due  to a number o f  F i r s t l y , i t i s expected t h a t the  (N-l) e l e c t r o n s  i n the f i n a l s t a t e w i l l not have the same s p a t i a l b u t i o n as those  i n 4' (N) due 1  ment around the k h o l e .  to r e l a x a t i o n o r  distri-  rearrange-  I t has been shown t h a t ,  the o v e r a l l change i n the s p a t i a l form o f the  although  passive  o r b i t a l s f o l l o w i n g i o n i z a t i o n i s not l a r g e , the  resulting  change i n energy can have a c o n s i d e r a b l e e f f e c t on  the  21 c a l c u l a t e d binding energies  .  Secondly,  relativistic  e f f e c t s g e n e r a l l y i n c r e a s e core e l e c t r o n b i n d i n g  energies  and t h e i r magnitudes depend on the r a t i o o f o r b i t a l 22 v e l o c i t y to the v e l o c i t y o f l i g h t initial  s t a t e SCF  .  T h i r d l y , as  c a l c u l a t i o n does not i n c l u d e  c o r r e l a t i o n between a given core e l e c t r o n and (N-l) e l e c t r o n s , the c a l c u l a t e d value of E (N) 1  the  favourable the  other  will  be  too l a r g e and hence the b i n d i n g energy c a l c u l a t e d u s i n g eqn. 2.12  would be too The  small.  approximate r e l a t i o n s h i p between the Koopmans'  b i n d i n g energy, -e^' and t h e r e f o r e , be w r i t t e n as  the true b i n d i n g energy  can,  - 27 -  E, (k) = -e, -<5E , + 5E , , + 6E b k relax relat corr  where < S the  E r e l a x  r  6  E r  e  i  a a  Koopmans' b i n d i n g  relativistic  n  d  5  E  t  C  orr  a  r  e  t  h  e  c  o  r  r  e  e n e r g y due t o o r b i t a l  e f f e c t s and e l e c t r o n - e l e c t r o n  c  (2.24)  tions  to  relaxation, correlation  respectively. The m o s t d i r e c t m e t h o d t o e v a l u a t e 6E carry and  out  final  SCF H a r t r e e - F o c k c a l c u l a t i o n s states  , i s to relax  f o r the i n i t i a l  a n d t h e n t o compare t h e E ^ ( k ) as  l a t e d by t h e t o t a l energy d i f f e r e n c e  method w i t h  calcu-  the  Kbopmans * b i n d i n g e n e r g y , - e - S i e g b a h n a n d coworkers" " h a v e c a l c u l a t e d a v a l u e o f %2 3eV f o r 6 E , f o r Ne I s relax ionization. C o r r e c t i o n s f o r r e l a t i v i s t i c e f f e c t s , 6E , ., ' relat' 22 a r e u s u a l l y made b y u s i n g p e r t u r b a t i o n t h e o r y . Direct 22 1  k  tabulation  o f these corrections  and  this correction  and  i s a b o u t 22eV o u t o f 3180eV  f o r C I s i s 0.2eV o u t o f 290eV  correlation correction, ^ shell  f o r a l l atoms a r e a v a i l a b l e  E c  o  r  r  /  (^0.69%) r  o  for Af I s .  (0.08%) The  c o r e l e v e l s i n c l o>um sed  r  s y s t e m s c a n be a p p r o x i m a t e l y c a l c u l a t e d  from a si  of fo r e lt ehcet rgorno u np da i rs t ac toer r oe lf a t ih oen s ey nsetregmi e .s e The ( i , j )e s tciamlactuelda tv eadl ue 2 3  f  o  r  2.5  6 E  corr'  u  s  i  n  9  t h i s m e t h o d , f o r Ne I s i s 1 . 9 e V .  F u r t h e r B i n d i n g Energy For  2 3  Calculations  the accurate c a l c u l a t i o n o f i o n i z a t i o n pob  ,  - 28 -  tials  (IP's) , t h e t h e o r e t i c a l method used must, i n  p r i n c i p l e , be c a p a b l e o f h i g h sets  u s e d i n t h e c a l c u l a t i o n s m u s t be l a r g e .  must be a b l e  to describe  Hartree-Fock l i m i t , and  a c c u r a c y and t h e b a s i s  wave f u n c t i o n s  They  close  both f o r the n e u t r a l  ground  i s Koopmans'  method used t o c a l c u l a t e I P ' s  t h e o r e m a n d , as d i s c u s s e d  main d i s a d v a n t a g e here i s t h e n e g l e c t c o r r e l a t i o n and  before,  included  reorganization.  individual ionic states  and t h e g r o u n d s t a t e ;  t h e so c a l l e d ASCF m e t h o d .  this  T h i s method has been v e r y  i n t h e case o f c o r e i o n i z a t i o n s where e l e c t r o -  ' . reorganization Ab i n i t i o  i s the predominant e f f e c t  24 25 '  c a l c u l a t i o n s are derived  from  p h y s i c a l concepts without reference data.  c a n be  b y c a r r y i n g o u t s e p a r a t e SCF c a l c u l a t i o n s f o r  successful nic  the  of electronic  The e f f e c t o f e l e c t r o n r e o r g a n i z a t i o n  is  state  f o r the i o n i c states. The s i m p l e s t  the  to the  basic  t o any e m p i r i c a l  F o r m o l e c u l e s , t h e ab i n i t i o m e t h o d i s g e n e r a l l y  b a s e d on t h e same f u n d a m e n t a l a p p r o a c h as t h a t u s e d by the  H a r t r e e - F o c k method f o r t h e c a l c u l a t i o n o f a t o m i c  o r b i t a l s and c a l c u l a t e s the energy o f a l l e l e c t r o n s . The s o l u t i o n o f m o l e c u l a r wave f u n c t i o n s , w h i c h i s a many c e n t r e  p r o b l e m d e p e n d i n g o n t h e number o f atoms i n  the  m o l e c u l e , c a n be v e r y e x p e n s i v e i n c o m p u t e r t i m e ,  but  i s expected to give  reliable  values.  - 29  Semiempirical Neglect of  -  m e t h o d s s u c h as  D i f f e r e n t i a l O v e r l a p ) c a n n o t be  c a l c u l a t e core l e v e l binding do  not  CNDO  consider  (Complete used  e n e r g i e s because  to  they  core o r b i t a l s e x p l i c i t l y .  A n o t h e r method t h a t i s b e i n g used t o l a t e i o n i z a t i o n e n e r g i e s i s the m u l t i p l e  calcu-  scattering 26  m e t h o d w h i c h makes use  of a m u f f i n - t i n p o t e n t i a l  A  i s the  further modification  Xa  s c a t t e r e d wave a p p r o x i m a t i o n  27-29 (XaSW)  i n which the  exchange terms o f  the  Hartree-  F o c k t o t a l e n e r g y a r e e x p r e s s e d as e x c h a n g e p o t e n t i a l s t h a t a r e l o c a l i z e d o r made p r o p o r t i o n a l of the t o t a l e l e c t r o n d e n s i t y . 30-32 Cederbaum and  others  to the  cube  have s u g g e s t e d  root  an  a l t e r n a t i v e t o Koopmans' t h e o r e m i n v o l v i n g G r e e n ' s functions  i n an e x p a n s i o n u s i n g p e r t u r b a t i o n  These c a l c u l a t i o n s i n c l u d e e n e r g y and  the e f f e c t s of both  c o r r e l a t i o n e f f e c t s , however the  p e r f o r m i n g such c o m p u t a t i o n s has to simple  2.6  relaxation  difficulty  restricted this  in  method  molecules.  Configuration  The  I n t e r a c t i o n Method  configuration  p r i n c i p l e , can of the  theory.  be  N-electron  i n t e r a c t i o n (CI)  used to approach the s y s t e m t o any  method, i n  e x a c t wave  degree o f  function  accuracy.  In  - 30 -  t h i s m e t h o d t h e N - e l e c t r o n wave f u n c t i o n ¥(N) i s r e p r e s e n t e d as a l i n e a r c o m b i n a t i o n o f S l a t e r minants  $j(N) c o r r e s p o n d i n g t o d i f f e r e n t N - e l e c t r o n  configurations. include  deter-  T h e s e S l a t e r d e t e r m i n a n t s , $j (N) ,  t h e H a r t r e e - F o c k c o n f i g u r a t i o n , and those  o t h e r S l a t e r d e t e r m i n a n t s t h a t c a n be f o r m e d b y e x c i t i n g electrons  f r o m one o r more o f t h e H a r t r e e - F o c k o r b i t a l s  into virtual orbitals. function  Now t h e e x a c t N - e l e c t r o n wave  c a n be w r i t t e n a s  ¥(N) =1  The  C  A  *_, (N)  (2.25)  c o e f f i c i e n t s Cj and perhaps  also the s e t  o f o n e - e l e c t r o n o r b i t a l s <J>. u s e d t o make up t h e o p t i m i z e d b y s e e k i n g a minimum i n t o t a l e n e r g y . c o e f f i c i e n t m u l t i p l y i n g the determinant the Hartree-Fock  configuration w i l l  are The  representing  u s u a l l y be t h e  dominant term i n t h e above e x p a n s i o n ,  and t h i s  coeffi-  c i e n t u s u a l l y h a s a v a l u e b e t w e e n 0.9 a n d 1.0 f o r c l o s e d 33 s h e l l atoms o r m o l e c u l e s Configuration final  states  i n t e r a c t i o n i n the i n i t i a l  i s frequently  and  b e i n g used i n the d e s c r i p t i o n  o f m u l t i e l e c t r o n e x c i t a t i o n e f f e c t s s e e n i n XPS ( a n d UPS)  -  spectra. the  This  section  will  31 -  be d e a l t  with  i n some d e t a i l i n  on m u l t i - c o m p o n e n t s t r u c t u r e ,  this  chapter.  2.7  Transition  later i n  P r o b a b i l i t i e s and P h o t o e l e c t r o n  Cross-Sections  The  photoelectric  cross  section,  a, i s defined  as  the t r a n s i t i o n p r o b a b i l i t y p e r u n i t  an  atom, m o l e c u l e o r a s o l i d  specimen  f r o m a s t a t e ^"""(N)  to  a state ¥ ^ ( N ) with  incident  photon  a unit  more c o n v e n i e n t q u a n t i t y , cross-section solid  for ejection  o f an e l e c t r o n  dfi, w i t h  respect  differential  or total  cross-sections  initial  elsewhere  state *  to e l e c t r o n do  34  .  flux.  in a  A  small  t o some f i x e d a x i s . c a n be  means o f t i m e d e p e n d e n t p e r t u r b a t i o n  discussed  for exciting  however, i s t h e d i f f e r e n t i a l  angle,  by  time  Such  calculated  theory and a r e  . . F o r a t r a n s i t i o n from t h e  (N) to a f i n a l  state * ^ ( N )  emission, the d i f f e r e n t i a l  corresponding  cross-section,  , can be w r i t t e n a s ,  dfi  (2 .26)  - 32 -  where, e * i s a u n i t v e c t o r i n the d i r e c t i o n o f p o l a r i zation  and k ^ i s  the wave v e c t o r o f p r o p a g a t i o n .  C,  here, i s a combination o f fundamental c o n s t a n t s , and g^ i s the degeneracy o f the i n i t i a l  state.  Other  terms i n the above equation have been d e f i n e d b e f o r e . If unpolarized radiation  i s used f o r e x c i t a t i o n , a  summation o r i n t e g r a t i o n  over the v a r i o u s  orientations and  possible,  •  da  o f e i s necessary i n d e r i v i n g g^-  the summation z i,f  I f the i n f l u e n c e  i s r e p l a c e d by £ ^ i,f,e  i n eqn.2.26.  o f the p e r t u r b i n g r a d i a t i o n  on the  n u c l e a r c o - o r d i n a t e s i s n e g l e c t e d and the BornOppenheimer approximation can  be r e w r i t t e n  l^frfc^ 1  (eqn. 2.5) i s v a l i d , then eqn. 2  as  7  I<  v f  IZ  (N)  1 / I  1 —  l  The  < y  exp(i.k .?.):. V . | T (N)> | i  hv  JL  vib<  P )  l^vib(  P ) >  !  (2-27)  2  squared o v e r l a p between the i n i t i a l  and f i n a l  v i b r a t i o n a l wave f u n c t i o n s i n t h i s e x p r e s s i o n i s c a l l e d the  Franck-Condon f a c t o r  and t h i s i s l a r g e l y  responsible  f o r the r e l a t i v e i n t e n s i t i e s o f the v i b r a t i o n a l bands i n . . photoionization transitions  35-37 .  As these  vibrational  e f f e c t s are observed i n XPS o n l y under s p e c i a l only the e l e c t r o n i c  situations  aspects are c o n s i d e r e d f u r t h e r  here.  -  33 -  I f the photon wave length  i s much l a r g e r than  the t y p i c a l dimensions o f the system, then by t r e a t i n g e x p ^ k ^ j r ^ ) as u n i t y i n the i n t e g r a t i o n , eqn. 2.26 can be r e w r i t t e n a s ,  af  h  =  hV  (  I '  Z  X  E  1  <^(N)!E  V.  fI  |. (N)>| I  1 — J.  (2.28)  and t h i s i s c a l l e d "the d i p o l e approximation". o f the m a t r i x element  F  N (N) | Z  i=l  i n eqn. 2.2 8 i s  . V.  |V  One form  ^ N ( N ) > = x- < Y ( N ) | Z  1  F  i=l  7 1  p.  |T (N) > 1  x  (2.29)  There are s e v e r a l l e v e l s o f accuracy t h a t can be used i n the e v a l u a t i o n o f matrix elements  such as those  shown i n eqn. 2.28. In g e n e r a l , the m a t r i x element  the i n i t i a l and f i n a l s t a t e s i n  can be d e s c r i b e d by s i n g l e determinant  Hartree-Fock wave f u n c t i o n s  f o r a closed s h e l l  system.  These can be c a l c u l a t e d a c c u r a t e l y t o i n c l u d e r e l a x a t i o n e f f e c t s , and now the a p p r o p r i a t e w r i t t e n as  wave f u n c t i o n s can be  - 34 -  V  y  The  l  (N) = A ( | ) x / 4> 2 ' • • • * ' x  (  f  ~  1  <t)  2  1  i  k k'  •••' N N^  x  <f)  f f ' ••*'*N N  (N) = A ( * ^ x » + 2 2 ' X  X  1  X  (2.31)  )  N - e l e c t r o n m a t r i x element f o r a general  transition  (2.30)  x  one-electron  o p e r a t o r t d e p e n d i n g o n l y on s p a t i a l  can now be w r i t t e n a s  N ) | EE < ¥ ((N) tt., | / i=l f  coordinates  38 39 ' ,  ( N )  >  =  m S^m  ( 1 )  |t|^ (D> n  D^ml.n)  1  (2.32)  where t h e d o u b l e sum on m a n d n i s o v e r orbitals  a n d D^ (m.'|'.n) i s an ( N - l ) x ( N - l ) p a s s i v e - e l e c t r o n 1  overlap determinant  and i s e q u a l  by r e m o v i n g t h e m-th row a n d n - t h determinant initialelement  t o the signed minor  D"^ whose e l e m e n t s a r e o v e r l a p s 1  (D  primary  f l  D f i  )  >pq  between The p q  c a n be w r i t t e n a s  "< • p X p l V q  excitation  "  i s d i s t i n g u i s h e d as b e i n g  <f>, a g i v e n c o r e o r b i t a l , a n d <f> , a h i g h - e n e r g y f  k  formed  c o l u m n f r o m t h e NxN  and f i n a l - s t a t e o n e - e l e c t r o n o r b i t a l s .  <  The  a l l occupied  <  2  '  3  3  >  between photo-  -  35  -  e l e c t r o n s t a t e and t h e terms i n v o l v i n g a l l m a t r i x elements o t h e r than t o be n e g l i g i b l e  N < V (N) | Z i=l  39  '  < <|> (1) | t|<j> (l)>  h a v e b e e n shown  k  40  .  This leads to the expression  „ . t . | ¥ (N) > =<* (1) | t | * ( l ) > D  f  f  k  f l  ( f |k)  1  (2.34)  An  analogous e x p r e s s i o n c a n a l s o be d e r i v e d b y u s i n g  the sudden  2.8  approximation-  Sudden  Approximation  Here, a s t r o n g l y o n e - e l e c t r o n c h a r a c t e r i s assumed f o r t h e p h o t o e m i s s i o n  process.  The  s t a t e i s r e p r e s e n t e d a s an a n t i s y m m e t r i z e d the  product o f  ' a c t i v e ' k - t h o r b i t a l <l> (l) f r o m w h i c h t h e p h o t o k  e l e c t r o n i s e m i t t e d , a n d an ( N - l ) - e l e c t r o n V (N-l) p  initial  remainder  representing the rest of the electrons:  ^(N)  = A(<f» (l) x ( D , k  k  f (N-l) ) R  (2.35)  - 36 -  The f i n a l  s t a t e , i n t h e weak c o u p l i n g l i m i t , c a n ,  s i m i l a r l y , be w r i t t e n a s t h e a n t i s y m m e t r i z e d  product  o f t h e c o n t i n u u m o r b i t a l <j>^(l) a n d t h e i o n i c wave function,  f (N-l), f  V (N)  = A(<f) (1)  f  f  f  x  (1) , * ( N - l ) )  F u r t h e r , i t i s assumed t h a t t h e p r i m a r y is  (2.36)  f  k+f t r a n s i t i o n  r a p i d o r 'sudden' w i t h r e s p e c t t o t h e r e l a x a t i o n t i m e s  o f t h e p a s s i v e e l e c t r o n s and so t h e t r a n s i t i o n e l e m e n t c a n now be w r i t t e n as  matrix  34 41 '  f -i f f <^ (N) i E t . | ^ ( N ) > = < < r ( l ) | t | * . ( l ) > < * ( N - l ) |Y •i=l N  1  r  1  R  (N-l)>  (2.37)  The u s e o f t h i s e x p r e s s i o n approximation"  i s o f t e n t e r m e d t h e "sudden  and t r a n s i t i o n p r o b a b i l i t i e s  and c r o s s -  sections i n t h i s l i m i t are p r o p o r t i o n a l to  | < / (1) | t | cj> (l) > | M 2  k  f  ( N - l ) | ¥ (N-1) > |  2  R  (2.38)  - 37  and  -  involve a one-electron  (N-l)-electron overlap wave f u n c t i o n  i n t e g r a l between the  f^(N-l) and  remainder T ( N - l ) .  m a t r i x element and  the  ionic  passive-electron  In o r d e r  n  an  f o r the o v e r l a p i n t e g r a l  t o be non-zero, the symmetry requirements demand t h a t both f ^ ( N - l ) and  Y (N-1) must correspond to the same R  o v e r a l l i r r e d u c i b l e representation  and  this  gives  r i s e to the w e l l known 'monopole s e l e c t i o n r u l e ' . T h i s w i l l be d i s c u s s e d The  simplest  later in this  chapter.  approximation f o r the  m a t r i x element comes from the Koopmans frozen o r b i t a l  1  transition  theorem o r  the  f i n a l s t a t e i n which d>^ = 4 > f o r j^-k  the s a i d m a t r i x element can  then be  and  approximated as  <¥ (N)|z t . | * ( N ) > = <<f> (1) |t | < | > , (1) > i=l f  1  T h i s l a s t method has  (2.39)  f  1  K  been used i n the m a j o r i t y  of  c r o s s - s e c t i o n c a l c u l a t i o n s to date. Configuration  i n t e r a c t i o n wave f u n c t i o n s  can  a l s o be used i n the c a l c u l a t i o n o f these m a t r i x elements and  c r o s s - s e c t i o n s , and  more accurate  these r e s u l t s u s u a l l y p r o v i d e  a  d e s c r i p t i o n o f the m u l t i e l e c t r o n processes 42  t h a t o f t e n accompany p h o t o i o n i z a t i o n  .  I t has  shown t h a t the c a l c u l a t e d i n t e n s i t i e s  can be  been  significantly  38  -  -  m o d i f i e d by t h e i n c l u s i o n o f c o n f i g u r a t i o n i n t e r a c t i o n in  the i n i t i a l  and f i n a l  s t a t e wave f u n c t i o n s .  For  computational convenience  t h e same s e t o f o r t h o n o r m a l  one  <j>,  is  electron orbitals  4^,  ^  2  u s e d i n m a k i n g up b o t h t h e i n i t i a l  M  (M>N)  usually  and f i n a l  state  configurations.  ^ (N)  = Z C j  1  3  /(N)  $ (N)  (2.40)  X  3  = Z C*; $ J ( N ) m m  Allowance  1  (2.41)  m  i s made f o r r e l a x a t i o n i n t h e f i n a l  u s i n g a l a r g e number o f c o n f i g u r a t i o n s c o e f f i c i e n t s C^" a n d 3  states.  Now,  3  with  s t a t e by  mixing  that are optimized f o r both *  f o r a s i n g l e p r i m a r y k-*f t r a n s i t i o n ,  t a k i n g a sudden a p p r o x i m a t i o n a p p r o a c h , t h e i n d i v i d u a l configurations  $ j ( N ) a n d *^(N) i n e q n s 2 . 4 0 a n d 2.41 c a n  be w r i t t e n as an a n t i s y m m e t r i z e d p r o d u c t a n a l o g o u s  t o eqns.  2.35 a n d 2.36:  4j(N) = A ( ^ ( 1 ) x ( D , $ j ( N - l ) l  (2.42)  $ ( N ) = A(<j> (1)  (2.43)  k  f  m  f x  (1) , *__(N-1))  - 39  If  the  are  (N-l)-electron  -  factors  i n d e x e d i n s u c h a way  i n these equations  that  ' j ( N - l ) = *^(N-1) f o r j=m  and t h u s  (2.44)  also,  < $7(N-1) |$ ( N - l ) > j m f  1  v  =  6 . jm  (2.45)  then the t r a n s i t i o n m a t r i x elements i n t h i s l i m i t written  can  be  as  f " i f f -i <* (N)|l t . | y ( N ) > = <4> (l) | t | <k ( 1 ) > [ Z ( C . ) * i=l j N  r  r  J  1  (2.46)  O n l y t h o s e c o n f i g u r a t i o n s w h i c h have a n o n - z e r o c o e f f i c i e n t in  both the i n i t i a l  ( (C?)* C j )  j = l dominates  the i n i t i a l  the m a t r i x element i n eqn.  f |<4< (N) | Z t . |4' (N)>| i=l N  r  state w i l l  p r o d u c t and i n the l i m i t i n g  configuration of  and the f i n a l  2  1  have a  case where a  1  single  s t a t e , the square  2.4 7 c a n be w r i t t e n  f He, !  non-zero  as,  2  (2.47)  - 40 -  for  a transition  2.9  Sum  to a given f i n a l  R u l e s on E n e r g y a n d  state.  Intensity  F o l l o w i n g t h e sudden a p p r o x i m a t i o n , experimentally  useful  spectral  . . , ,38,39,41,43 introduced . o u t by L u n d q v i s t the weighted  43  k-*f t r a n s i t i o n  -e,= k  ^. first  .. sum r u l e 41  average b i n d i n g energy over F  -e  sum r u l e s h a v e  , a n d Manne a n d A b e r g  i o n i c s t a t e s Y (N-1,K)  energy,  _, The  two been  . , pointed states that  a l l final  associated with a given  primary  i s s i m p l y e q u a l t o t h e Koopmans' b i n d i n g  k  I I E, (K) / K K b  Z K  I K  (2.48)  =  f  2  Z|<4< ( N - l ,K) | y ( N - l ) > | R  E (K) b  K where  I K  i s t h e i n t e n s i t y o f t h e peak p e r t a i n i n g t o  a transition e n e r g y Ej (K) . =)  rule  t o ¥^(N-1 ,K) , c o r r e s p o n d i n g t o a b i n d i n g Another  popular  form o f t h i s energy  sum  c a n be d e r i v e d by s u b t r a c t i n g t h e b i n d i n g e n e r g y  corresponding  to the lowest energy f i n a l  state,  E , Q  associated  with  eqn.  resulting i n  2.48,  " k - 0 £  E  t h e t r a n s i t i o n k->f, f r o m b o t h s i d e s  =  I W^V  / *  L  of  K  or  relax  5 E  where  6E  Koopmans state  1  = I  \  A  K  /  *  (2.49)  K  , i s the energy d i f f e r e n c e relax 3  between t h e  a p p r o x i m a t i o n e n e r g y , and t h e a c t u a l  e n e r g y , and i s d e f i n e d  final  by e q n . 2.24.  Since a l l the q u a n t i t i e s  on t h e r i g h t hand side  o f e q n . 2.49 a r e e x p e r i m e n t a l l y d e t e r m i n a b l e , i n p r i n c i p l e t h i s p r o v i d e s a method f o r e x p e r i m e n t a l l y the  relaxation  energy.  usually not possible over the shakeoff extracted  However, i n p r a c t i c e  finding  this i s  because the i n t e n s i t y d i s t r i b u t i o n  continuum  (see l a t e r ) i s n o t e a s i l y  from the spectrum. A more i m p o r t a n t i m p l i c a t i o n o f t h i s sum  is that,  i n order f o r relaxation  i n the f i n a l  occur i n forming the lowest binding excited  i o n i c states  state to  energy f i n a l  corresponding to binding  rule  state,  energies  - 42 -  higher than -e^ must a l s o a r i s e . ( S E  relax  w  e  r  e  z e r o  /  n  o  In o t h e r words, i f  s a t e l l i t e s would be observed  and  i n the case thatSE  , i s large, i n principle, re l a x  one  would observe an i n t e n s e s e t o f s a t e l l i t e s  the main peak, o r weak s a t e l l i t e s  near  f a r from the main  peak o r some t h i n g i n between these two extremes. The  second sudden approximation sum r u l e 3 8 39  which was f i r s t p o i n t e d o u t by Fadley  '  states that  the sum o f i n t e n s i t i e s o f a l l peaks a s s o c i a t e d w i t h the states  I  ^ ( N - l , K ) i s given by  =El =CE|<* (l) |t| * ( l ) > | K .K f  tot  K  k  where C i s a constant  2  2 |<* (N-l,K) | ? (N-1)>| f  R  f o r a given photon energy.  (2.50)  This  means t h a t the frozen o r b i t a l c r o s s - s e c t i o n s c a l c u l a t e d u s i n g eqn.2.39 a c t u a l l y r e p r e s e n t  the c r o s s - s e c t i o n s  summed over a l l f i n a l s t a t e s produced by the primary t r a n s i t i o n k->f. Thus, o r b i t a l i o n i z a t i o n c r o s s - s e c t i o n s calculated parable  u s i n g f r o z e n o r b i t a l s are not d i r e c t l y com-  to experimental  e l e c t r o n experiments.  c r o s s - s e c t i o n s observed i n photo-  - 43 -  2.10  Core B i n d i n g Energy S h i f t s  F o l l o w i n g the o b s e r v a t i o n s o f Siegbahn co-workers  1  t h a t core e l e c t r o n b i n d i n g e n e r g i e s e x h i b i t  c h e m i c a l l y induced s h i f t s , the most w i d e l y used of XPS  and  aspect  i s the experimental d e t e r m i n a t i o n o f these  shifts  f o r elements as a f u n c t i o n of chemical environment and subsequent use o f t h i s i n f o r m a t i o n i n q u a n t i t a t i v e q u a l i t a t i v e chemical a n a l y s i s .  The  chemical  and  shift  between the f r e e atom s t a t e , A, and a p a r t i c u l a r molec u l a r s t a t e , M,  f o r a given element, f o r the  ionization  o f the k-th e l e c t r o n can be w r i t t e n as  AE^(k) = (EJJ(k)^ - ( E ^ ( k ) )  (2.51)  A  A l a r g e number of models which vary from  strictly  t h e o r e t i c a l , to s e m i e m p i r i c a l , to p u r e l y e m p i r i c a l i n nature have been suggested  f o r the i n t e r p r e t a t i o n o f  p e r i m e n t a l r e s u l t s and the advanced p r e d i c t i o n o f  ex-  chemical  1 44-63 shifts  '  models here.  .  No attempt  w i l l be made to review  However, as no d i s c u s s i o n on XPS  these  i s complete  without a few words on chemical s h i f t models, a few r e s t i n g p o i n t s on these w i l l be brought  inte-  to the a t t e n t i o n  - 44 -  of  the reader. The most a c c u r a t e way o f c a l c u l a t i n g b i n d i n g  energy of  s h i f t s , must i n g e n e r a l , i n v o l v e t h e c a l c u l a t i o n  two b i n d i n g e n e r g i e s : i . e . a t o t a l o f two  s t a t e c a l c u l a t i o n s a n d two f i n a l s t a t e So,  f o r c a l c u l a t i o n s performed  initial  calculations.  a t a given l e v e l o f  accuracy, the p o s s i b l e e r r o r s i n s h i f t s  are, thus,  a p p r o x i m a t e l y t w i c e as l a r g e as f o r a s i n g l e b i n d i n g energy. The s i m p l e s t a n d t h e m o s t s t r a i g h t  forward  method f o r t h e c a l c u l a t i o n o f b i n d i n g e n e r g y  shifts  makes use o f a Koopmans' t h e o r e m a p p r o a c h .  Here i t i s  assumed t h a t t h e r e l a t i v i s t i c , c o r r e l a t i o n a n d r e l a x a t i o n e f f e c t s on t h e c o r e b i n d i n g e n e r g i e s r e m a i n t h e same f r o m o n e s i t e and  to another,  f o r a given core l e v e l .  s h i f t c a n be e q u a t e d  approximately  f o r a given  Now t h e b i n d i n g  element  energy  t o t h e d i f f e r e n c e i n t h e Koopmans'  t h e o r e m b i n d i n g e n e r g i e s f o r t h e two s i t e s .  The u s e o f  Koopmans' t h e o r e m i n e s t i m a t i n g t h e b i n d i n g e n e r g y from r e a s o n a b l y a c c u r a t e m o l e c u l a r o r b i t a l has p r o d u c e d  fairly reliable  shifts  calculations  values f o r w e l l  chosen  , 45,48,49 compounds The r e l a t i v i s t i c a n d c o r r e l a t i o n e f f e c t s , a s assumed h e r e , c a n h a v e a p p r o x i m a t e l y t h e same v a l u e  when  - 45 -  going be  f r o m one s i t e t o a n o t h e r .  H o w e v e r , t h e same c o u l d  t r u e o n l y t o a much l e s s e r d e g r e e i n t h e c a s e o f  relaxation effects.  T h e r e f o r e , i t i s important  able t o i n c l u d e r e l a x a t i o n e f f e c t s i n these shift calculations.  The t r a n s i t i o n  t o be  chemical  s t a t e method, deve-  47 l o p e d by G o s c i n s k i and co-workers e f f e c t s t o second order binding energies been found v e r y  , allows r e l a x a t i o n  i n p e r t u r b a t i o n t h e o r y , and t h e  c a l c u l a t e d by u s i n g t h i s m e t h o d h a v e reliable^  .  In t h e p o t e n t i a l model used i n t h e e a r l i e s t q u a n t i t a t i v e d i s c u s s i o n s o f chemical s h i f t s by Siegbahn 1 4 8 49 and c o - w o r k e r s , a n d F a d l e y a n d c o - w o r k e r s ' , the i n t e r a c t i o n o f a given core e l e c t r o n w i t h a l l the other e l e c t r o n s and n u c l e i i n a m o l e c u l e  or a solid i s divided  i n t o an i n t r a - a t o m i c t e r m a n d an e x t r a - a t o m i c T h i s a l l o w s one t o e x p r e s s sum o f two t e r m s , one  extra-atomic  a g i v e n b i n d i n g e n e r g y as a  one i n t r a - a t o m i c f r e e i o n t e r m a n d potential:  E?J(k) = E ^ ( k , q ) + V  The  first  term.  (2.52)  term i s the b i n d i n g energy o f the k - t h e l e c t r o n  i n the f r e e i o n o f charge q f o r the element under c o n s i -  - 46  d e r a t i o n , and  the  second term i s the c o n t r i b u t i o n t o  t h e b i n d i n g e n e r g y by o t h e r atoms .  -  t h e t o t a l p o t e n t i a l due  to a l l  S e v e r a l v a r i a t i o n s o f t h i s model have  been a p p l i e d t o a wide v a r i e t y o f s y s t e m s , w i t h s i d e r a b l e success 63 model Basch and  1 48 49 ' ' .  I n one v a r i a t i o n o f t h i s 51 Schwartz h a v e shown t h a t t h e s h i f t  i n the o r b i t a l energy o f a g i v e n o r b i t a l molecule  to another  i s nearly equal  to  from  (the  ' , can be  one  negative)  s h i f t i n t h e p o t e n t i a l a t t h e n u c l e u s , -AV q u a n t i t y , AV  con-  .  This  n  c a l c u l a t e d e a s i l y and  reasonably 52  a c c u r a t e l y , u s i n g CNDO wave f u n c t i o n s .  Davis  et_ a l  used t h i s approach to p r e d i c t b i n d i n g e n e r g i e s number o f s m a l l m o l e c u l e s  and  of  a  these p r e d i c t i o n s are  i n good agreement w i t h the e x p e r i m e n t a l  values.  This  p a r t i c u l a r approach u s i n g the p o t e n t i a l model i s termed GPM  (ground  p o t e n t i a l m o d e l ) as o n l y t h e g r o u n d s t a t e 55 56 p o t e n t i a l s are considered ' To i n c l u d e r e l a x a t i o n e f f e c t s i n t h e c a l c u l a t i o n 58 of b i n d i n g energy s h i f t s  Davis  and  r e l a x a t i o n p o t e n t i a l m o d e l , RPM, b i n d i n g energy s h i f t i s given A E ( k ) = -AV b  n  -  AV  R  Shirley  where the  used a corrected  as (2.53)  - 47  Here, A V and,  R  i s the  i n order  -  change i n p o t e n t i a l due  t o compute AV  they  to r e l a x a t i o n ,  used the  i\  cores' approximation  57  i n t r o d u c e d by  Jolly  assumed t h a t the e l e c t r o n s i n o r b i t a l n s h i e l d t h e e l e c t r o n s i n t h e n'>n T h i s w o u l d a l l o w one tial due  a t the nucleus t o the  'equivalent  shell  to approximate the  .  Here i t i s  completely from the  nucleus.  change i n p o t e n -  upon i o n i z a t i o n o f a c o r e e l e c t r o n ,  r e l a x a t i o n of o u t e r e l e c t r o n s , to the  that would occur Now,  i f the n u c l e a r  one  unit.  RPM  approximation V  R  D  V  R  i n equation  change  charge were i n c r e a s e d 2.53,  i s written in  by  the  as  = \ [V (* + 1) 2 n  - V  ] n  (2.54)  J  T h i s model g i v e s r e s u l t s i n good agreement w i t h 55 experimental are  2.11  in fairly  values  and  the v a l u e s  g o o d a g r e e m e n t w i t h ab  R e l a x a t i o n E f f e c t s on  The  Binding  calculated for initio  l e a d s to the  H  estimates^ .  Energy  r e d u c t i o n i n energy o f the p a s s i v e  f o l l o w i n g photoemission  AV  electrons  d e f i n i t i o n of  the  - 48 -  quantity  termed r e l a x a t i o n energy, and t h i s i s the  major c o n t r i b u t o r perimentally  to the d i f f e r e n c e between the ex-  observed b i n d i n g  Koopmans'theory based b i n d i n g  e n e r g i e s and the energies.  The  of o r b i t a l r e l a x a t i o n upon p h o t o i o n i z a t i o n  extent  varies  from atoms to molecules to s o l i d s , and the p h y s i c a l o r i g i n s o f the r e l a x a t i o n energy f o r these systems w i l l be b r i e f l y d i s c u s s e d  2.11.1  here.  Atoms  Core i o n i z a t i o n o f an atom r e s u l t s i n a p o s i t i v e h o l e i n the atomic o r b i t a l e l e c t r o n ,is e j e c t e d , electrons  to r e l a x  from which the  and t h i s causes the remaining  (towards the hole) i n o r d e r t o  minimize the t o t a l energy o f the system. l a x a t i o n energy, 6 E  The r e -  , , due to i o n i z a t i o n from re xax  o r b i t a l k can be w r i t t e n  as the sum o f three  terms  65 ,  SE,(k,n)=^5E , (n <n)-f6E , (n'=n)-ri5E , (n'>n) relax relax relax relax /  (2.55)  - 49 -  Wnere n and n' are the p r i n c i p a l quantum numbers o f the k-th o r b i t a l and the p a s s i v e  orbitals respectively.  $E_ , _ (n'<n) i s the c o n t r i b u t i o n  to the  i c XaX  r e l a x a t i o n energy due t o o r b i t a l s l y i n g deeper than the a c t i v e s h e l l , n.  T h i s term was ft  shown t o be  rr  n e g l i g i b l e by Hedin and Johansson l a t i o n s f o r Na, K and t h e i r i o n s .  by d i r e c t c a l c u The  contribution  from i n t r a - s h e l l r e l a x a t i o n t o the t o t a l energy i s o f i n t e r m e d i a t e magnitude.  relaxation  This term o r i g i -  nates from the f a c t t h a t the removal o f an e l e c t r o n the  s h e l l , n, causes a r e d u c t i o n  i n the average e l e c t r o -  s t a t i c r e p u l s i o n between the p a s s i v e 65 s h e l l . Hedin and Johansson  electrons  i n that  c a l c u l a t e d a value o f 2.9eV  f o r the L s h e l l o f sodium and a value o f 1.2eV M s h e l l o f potassium.  from  f o r the  The o u t e r s h e l l r e l a x a t i o n  i s by f a r the l a r g e s t c o n t r i b u t o r  to the t o t a l  term  relaxation  energy i n atoms as these o u t e r s h e l l e l e c t r o n s experience an i n c r e a s e unit.  i n the n u c l e a r charge by approximately one  The r e l a t i v e magnitude o f t h i s term decreases  with i n c r e a s i n g n, which i s understandable, and a c c o r d i n g t o Hedin and Johansson's  c a l c u l a t i o n on potassium, the  o u t e r s h e l l r e l a x a t i o n term p r o v i d e s 96 and 82% o f the t o t a l r e l a x a t i o n energy f o r Is and 2s i o n i z a t i o n s , respectively.  - 50 -  A number o f m e t h o d s a r e a v a i l a b l e estimation of relaxation  f o r the  energy f o r a t o m s ^ 66  The m e t h o d s u g g e s t e d b y S h i r l e y 70 sively  and l a t e r  u s e d by h i s c o - w o r k e r s  exten-  i s r e l a t i v e l y straight-  forward.  T h i s m e t h o d makes u s e o f t h e p o l a r i z a t i o n  potential  approach o f Hedin and J o h a n s s o n ^ , and t h e 5  equivalent cores  approximation  w h i c h was  first  used  57 by J o l l y  .  Essential  f e a t u r e s o f t h i s m o d e l c a n be  summarized by t h e f o l l o w i n g 6 E  relax  " k " b  =  e  where E ^ ( k ) a n d  E  (  k  equations < ' >  )  2  56  a r e t h e b i n d i n g and o r b i t a l e n e r g i e s  of the k-th o r b i t a l respectively.  Now  according to the fi 5  Hedin and J o h a n s s o n p o l a r i z a t i o n p o t e n t i a l  6  E  relax  (  k  )  =  1  ^k^pJV  model  ,  '>  (2  57  where,  V  Here, V  R  = E j£k  (V.(N-1,Z) - V . ( Z ) )  i s the 'relaxation  of the k-th o r b i t a l .  (2.58)  3  potential'  V^(z) r e p r e s e n t s  f o r the i o n i z a t i o n t h e Coulomb  plus  - 51 -  e x c h a n g e p o t e n t i a l due t o t h e j - t h o c c u p i e d  orbital  and V j ( N - l , j=f=k ,Z ) i s t h e Coulomb p l u s e x c h a n g e tial  due t o t h e j - t h o r b i t a l  a hole i n the k-th o r b i t a l . cores approximation  i n the ionic state with The u s e o f t h e e q u i v a l e n t  a l l o w s one t o r e p l a c e t h e h o l e s t a t e  i n t e g r a l s i n e l e m e n t Z by t h e c o r r e s p o n d i n g i n t e g r a l s i n element following  5 E  ground s t a t e  (Z+l) and t h i s r e s u l t s i n t h e  expression,  relax  Although,  poten-  =  7 ^  IV  the i n n e r - s h e l l  " *k I ^ R I Vz>  '>  <  (2  59  and i n t r a - s h e l l r e l a x a t i o n s  are n e g l e c t e d i n t h i s model, the r e s u l t s o b t a i n e d are i n good agreement w i t h b o t h  the values obtained  from  6 8  more e l a b o r a t e h o l e s t a t e c a l c u l a t i o n s The  and  experiment.  dominance o f o u t e r - s h e l l r e l a x a t i o n i n c o r e  i o n i z a t i o n processes s e r v a t i o n s t h a t 6E  i s f u r t h e r i l l u s t r a t e d by the ob-  , (k,n) d e c r e a s e s re l d x  i n c r e a s i n g n a n d <5 E  ,  uniformly  with  (k,n,Z) i n c r e a s e s w i t h i n c r e a s i n g  Z f o r a g i v e n k a n d n.  2.11.2  Molecules  Core l e v e l i o n i z a t i o n a t a p a r t i c u l a r centre o f a molecule  can l e a d t o a charge  atomic  redistribution  - 52 -  5 8 66 w i t h i n the molecule.  S h i r l e y and co-workers  have s u b - d i v i d e d the r e l a x a t i o n energy core i o n i z a t i o n process i n t o two  '  70 '  f o r a given  terms;  an  intra-  atomic term which can be t r e a t e d s i m i l a r to the case o f atoms, and an extra-atomic term which i n c l u d e s a l l r e l a x a t i o n p r o c e s s e s i n v o l v i n g e l e c t r o n s s i t u a t e d on o t h e r atomic c e n t r e s , due  to the charge  redistribution  caused by p o l a r i z a t i o n o f the e l e c t r o n s towards the positive hole.  Davis and S h i r l e y have c a l c u l a t e d the  f i n a l - s t a t e atomic charges u s i n g CNDO/2 m o l e c u l a r o r b i 56 t a l s i n the RPM  approach  , f o r a number o f s m a l l mole-  cules . The r e l a x a t i o n energy  f o r a given core l e v e l i s  expected to i n c r e a s e from a f r e e atom to a d i a t o m i c molecule and a d d i t i o n a l l i g a n d s would a l l o w f u r t h e r enhancement of 5E  , . relax  However, the r e l a x a t i o n  energy 3 J  does not i n c r e a s e i n d e f i n i t e l y w i t h i n c r e a s i n g m o l e c u l a r size.  For example the experimental b i n d i n g energy  shift  f o r C l s i n the alkane s e r i e s from CH^ and the same s h i f t f o r n - C H g  2.11.3  1 8  to  n - c  to n-C^H^^ i s 0.32eV 71 i3 28 0.08eV H  1 S  Solids  The extent and the nature o f r e l a x a t i o n upon core i o n i z a t i o n i n s o l i d s d i f f e r s from i n s u l a t o r s , to semi-  - 53  -  conductors, to conductors.  A c c o r d i n g to Fadley  and  49 co-workers  the  b i n d i n g energy a s s o c i a t e d  with  the  i o n i z a t i o n of an o r b i t a l k a t a p a r t i c u l a r s i t e i n a molecular o r i o n i c s o l i d can local contribution total relaxation can be  6 E  6E  relax  .. 3T6  sum  to l a t t i c e  = 6  E  above p r o c e s s , s i m i l a r l y . ,  of a l o c a l c o n t r i b u t i o n  term  ( k  '  l  o  c  a  l  term can  )+ 6 E  relax < ^ t i c e )  be  k  treated  as  f o r l a r g e molecules or ions the  energy i s r e p r e s e n t e d , mainly, by  (2.60)  discussed total  t h i s term.  relaxation  Contribution  to l a t t i c e p o l a r i z a t i o n i n m o l e c u l a r l a t t i c e s i s  known.  and  X 3.X  before and  due  The  polarization,  relax  (k,local)  separated i n t o a  a l a t t i c e contribution.  energy f o r the  given as the  a term due  The  and  be  However, the  little  s i t u a t i o n i s more s a t i s f a c t o r y i n  the  case o f i o n i c c r y s t a l s . the  49 Fadley and co-workers were the f i r s t to d i s c u s s p o l a r i z a t i o n energy term f o r i o n i c l a t t i c e s , based on 72  a model d e s c r i b e d by Mott and indicate  Gurney  , and  their results  t h a t t h i s term i s of the o r d e r of leV o r  f o r a s e r i e s o f potassium s a l t s .  The  less  l a r g e s t values  for  l a t t i c e p o l a r i z a t i o n i s expected f o r monovalent, mono-atomic ions.  Nothing more w i l l be  effects in solids.  As  s a i d here about  relaxation  a p a r t of the work d e s c r i b e d i n t h i s  - 54  thesis involved binding  -  the experimental d e t e r m i n a t i o n o f core  energy s h i f t s between f r e e metal atoms and  standard s t a t e , the r e l a x a t i o n e f f e c t s i n the s t a t e which are  largely responsible  t r a n s i t i o n s h i f t ' w i l l be  discussed  the  metallic  f o r the s a i d  'phase  next i n a separate  section.  2.11.4  Core L e v e l B i n d i n g Energy S h i f t s i n Metals  The  e x p e r i m e n t a l l y determined b i n d i n g  f o r conductors have been found to be than the  c a l c u l a t e d values,  energies  considerably  even a f t e r a l l o w i n g  lower for  66 f i n a l s t a t e r e l a x a t i o n , and  thus S h i r l e y  suggested  t h a t the phenomenon o f e x t r a - a t o m i c r e l a x a t i o n can used to e x p l a i n and  this difference.  co-workers^'  , the  be  A c c o r d i n g to S h i r l e y  t o t a l r e l a x a t i o n energy  f o l l o w i n g core i o n i z a t i o n i n a conductor can be  written  as, 6E  , (k) = 6 E . . + 6E ^ relax intra extra  (2 .61)  where SE. , i s the i n t r a - a t o m i c r e l a x a t i o n term which intra can be t r e a t e d as i n the case o f atoms, and 5  E  1 S  e  x  t  r  a  66 the e x t r a - a t o m i c r e l a x a t i o n .  The  procedure S h i r l e y  - 55  -  u s e d t o c a l c u l a t e t h e r e l a x a t i o n e n e r g y i n atoms  has  70 been a p p l i e d eqn.  2.59  to metals  c a n now  relax  be  2^  y  k  by L e y  and  rewritten R k  1  co-workers  as  Z+l  | y  and  y  k  R k  1  | y  Z' i n t r a (2.62)  + 7(<* |V IVz+l k  where the d i f f e r e n t t e r m s , I t i s now level binding v e r a l eVs 66 atoms  by now,  ^kl^K^extra  are  self-explanatory,  w e l l known t h a t t h e e x p e r i m e n t a l  energies of metals  lower  70  ~  R  are  core  systematically  than those o f the corresponding  se-  free  73—79  '  '  . This core b i n d i n g  phase t r a n s i t i o n s h i f t ) ,  energy s h i f t  (or  AE^(k,M,A) can be w r i t t e n  as  A £(k,M,A)=EjJ(k,A) - E^(k,M)  ( 2  E  w h e r e E ^ ( k , A ) a n d E ^ ( k M ) a r e t h e vacuum r e f e r e n c e d f  binding phase  energies  f o r the  (metallic state)  AE_J(k,M,A) i s p o s i t i v e The caused i.  by  f r e e atom and  respectively. 6  6  '  7  0  '  7  3  "  7  9  the The  core  condensed quantity,  .  phase t r a n s i t i o n s h i f t  a number o f f a c t o r s s u c h  i s believed  to  be  as  Screening of the vacant o r b i t a l  v i a extra-atomic  r e l a x a t i o n o f the metal  electrons.  valence  '  6 3 )  -  ii.  56  -  Changes i n the r e p u l s i v e p o t e n t i a l e x p e r i e n c e d by the core e l e c t r o n s i n metals.  iii.  Changes i n e l e c t r o n i c  configuration.  The l a t t e r i s important i n t r a n s i t i o n  metals  where the common c o n f i g u r a t i o n i n the vapor phase i s nd  x  (n+1)s  2  x+1 1 as opposed t o the nd (n+1)s configuration  t h a t r e p r e s e n t s the s o l i d .  Chromium which e x h i b i t s the  lowest phase t r a n s i t i o n s h i f t i n the 3d t r a n s i t i o n  metal  s e r i e s i s an e x c e p t i o n a l case where i t has the same ground s t a t e c o n f i g u r a t i o n i n , both, the f r e e atom and the metal These f a c t o r s are expected t o operate tially  differen-  to reduce the i n n e r core l e v e l b i n d i n g e n e r g i e s  more than those f o r the o u t e r l e v e l s and e x t r a - a t o m i c r e l a x a t i o n i s by f a r the s i n g l e l a r g e s t c o n t r i b u t o r to the phase t r a n s i t i o n  shift  6 6  '  7 0  '  '  7 6  7 8  .  Now c o n s i d e r i n g o n l y the extra-atomic  relaxation,  one can w r i t e f o r AE^(k,M A), r  AEb>,M,A)=  I^k^pJVz+l  "  ^kl^VzWra  (2  78 S h i r l e y and co-workers s h i f t f o r the f i r s t  c a l c u l a t e d the phase t r a n s i t i o n  t h i r t y elements  using t h i s  relation-  s h i p , and to e v a l u a t e these i n t e g r a l s they used a t h e o r e t i c a l model based on the assumption  that extra-atomic  '  64)  - 57  -  r e l a x a t i o n occurs through s c r e e n i n g o f the hole by the  formation  of a semilocalized exciton.  they assumed t h a t the e x c i t o n s t a t e has  state  Further,  the symmetry o f  the lowest unbound s t a t e i n the conduction band and  that  the e x c i t o n wave f u n c t i o n i s found only i n the neighbourhood o f the hole The  values  state. c a l c u l a t e d f o r phase t r a n s i t i o n s h i f t s  u s i n g t h i s model are l a r g e r than the experimental  values,  mainly because the atomic s t a t e on which i t i s based be more l o c a l i z e d than the e x c i t o n s t a t e .  should  However, t h i s  model p r e d i c t s the trends o f b i n d i n g energy s h i f t s  rather  a c c u r a t e l y , i n d i c a t i n g the v a l i d i t y o f the model. 76 Recently  Beck and N i c o l a i d e s  transition shifts e s s e n t i a l l y the  e s t i m a t e d the phase  f o r metals u s i n g the above model  same assumptions.  o f t h i s model i s as  Their i n t e r p r e t a t i o n  follows.  L e t the atomic c o n f i g u r a t i o n c h a r a c t e r i s t i c o f ni  hole  s t a t e i n the s o l i d (n&)  where ml"  4 £ + 1  and  the  be  (mI) (S,L) . ' min q  (q<4l+2) ^  i s the valence s u b - s h e l l of lowest energy which  i s not completely f i l l e d .  Now,  the  f r e e atomic  mation to the e x c i t o n i c s t a t e can be w r i t t e n  . (nz)  4 1 + 1  (mji)  q+1  (S,L)  as  approxi-  - 58 -  and the b i n d i n g energy  AE^ = E ( . . . ( n j c ) * 4  + 1  s h i f t can be w r i t t e n as  ...(mD (S,L). ) q  mm  D  E ( . . . (ru)  4  £  +  1  . . . (ml)  (S , L )  q + 1  m i n  )  (2.65)  AE^ i s e v a l u a t e d from separate ASCF c a l c u l a t i o n s  and  here i t i s p o s s i b l e to p r e c o r r e c t the b i n d i n g e n e r g i e s o f the two phases i n case there i s a c o n f i g u r a t i o n change upon going from f r e e atom to s o l i d .  T h i s method g i v e s  v a l u e s which are i n good agreement with experiment,  and  once a g a i n the p r e d i c t e d values are h i g h e r than the exper i m e n t a l values due  to reasons o  77  Johansson and Martensson to c a l c u l a t e the phase thermochemical  data.  discussed e a r l i e r .  used a Born-Haber c y c l e  t r a n s i t i o n s h i f t s using a v a i l a b l e In t h e i r model, the f i n a l  state  reached by the core i o n i z a t i o n a t a p a r t i c u l a r s i t e o f the metal, i s c o n s i d e r e d e q u i v a l e n t to the c r e a t i o n of an i m p u r i t y s i t e i n an otherwise p e r f e c t c r y s t a l . they used the approximation e q u i v a l e n t to a pure c r y s t a l  Then  that t h i s f i n a l state i s (Z) i n which an i m p u r i t y  Z+l i s d i s s o l v e d , and then used ground s t a t e thermochemical data a v a i l a b l e f o r Z and Z+l metals  to compute  the phase t r a n s i t i o n s h i f t .  T h i s method e m p i r i c a l l y  estimates the b i n d i n g energy  s h i f t s r e f e r e n c e d to the  Fermi l e v e l , and the p r e d i c t e d v a l u e s are i n reasonable 77 agreement with experiment  - 59 -  A l l thfree methods mentioned here use the e q u i v a l e n t cores approach to approximate the f i n a l s t a t e .  The  core  l e v e l b i n d i n g energy s h i f t s estimated by u s i n g the impu77 nty  model  do not depend on which p a r t i c u l a r i n n e r s h e l l  i s i o n i z e d because, the Z+l approximation,  when used in. the  s i m p l e s t way,  does not make any d i s c r i m i n a t i o n between the 75 core l e v e l s . T h i s was found to be a good approximation 1 81 Siegbahn and co-workers and C i t r i n and co-workers have determined core l e v e l b i n d i n g energies o f rare-gas atoms embedded i n metal  f o i l s and these values are 2-5eV 44  lower than those r e p o r t e d f o r f r e e atoms  .  As the  a c t i o n between the gas atoms and the host metal more o f a p h y s i c a l nature, t h i s s h i f t may the degree o f e x t r a - a t o m i c  inter-  atoms i s  be i n d i c a t i v e of  r e l a x a t i o n i n the m e t a l l i c  state. A c c o r d i n g to the energy sum i n t h i s chapter  (eqn. 2.48,  rule discussed e a r l i e r  2.49), o r b i t a l r e l a x a t i o n  r e s u l t i n multicomponent s t r u c t u r e i n the XPS  should  spectra.  T h i s w i l l be d i s c u s s e d i n some d e t a i l i n the next s e c t i o n , however, one o f metals  i n t e r e s t i n g f e a t u r e r e g a r d i n g the XPS  i s worth some mention here.  core i o n i z a t i o n of metals  spectra  As d e s c r i b e d b e f o r e ,  involves a large relaxation  energy which means t h a t there must be a f a i r l y l a r g e probability  for multiple e x c i t a t i o n processes.  d i s c r e t e peaks have been observed  However, no  i n the x-ray p h o t o e l e c t r o n  s p e c t r a o f metals. metals  T h i s may  be due  to the f a c t t h a t i n  the m u l t i p l e e l e c t r o n e x c i t a t i o n processes  ve the conduction bands, r e s u l t i n g i n a shake up  invol(and  shake o f f )  spectrum which i s e s s e n t i a l l y  continuous,  and i t may  be t h a t the r e l a x a t i o n energy i s manifested  as a broad background on the h i g h b i n d i n g energy s i d e o f the main peak.  2.12  Multicomponent S t r u c t u r e i n  XPS  The b i n d i n g energy o f an e l e c t r o n f o r a given i o n i z a t i o n p r o c e s s , as d e f i n e d by eqn.  1.2, depends on  the e n e r g i e s o f the i n i t i a l and the f i n a l s t a t e . initial  Various  s t a t e and f i n a l s t a t e e f f e c t s can a l t e r the  initial  s t a t e and the f i n a l s t a t e t o t a l e n e r g i e s , r e s u l t i n g i n a s e r i e s o f b i n d i n g e n e r g i e s f o r a given i o n i z a t i o n  process.  This l e a d s to multicomponent s t r u c t u r e i n u l t r a v i o l e t x-ray p h o t o e l e c t r o n s p e c t r a .  In t h i s s e c t i o n some o f  and these  e f f e c t s , as r e l a t e d to XPS w i l l be d i s c u s s e d b r i e f l y .  2.12.1  Spin-Orbit S p l i t t i n g  S p i n - o r b i t s p l i t t i n g a r i s e s from a c o u p l i n g o f s p i n and o r b i t a l angular momentum.  This i s a r e l a t i v i s t i c  per-  t u r b a t i o n which i s r e a d i l y i d e n t i f i a b l e i n the p h o t o e l e c t r o n s p e c t r a o f heavy atom systems.  In atoms, s p i n - o r b i t  splitting  - 61  -  has been w e l l c h a r a c t e r i z e d by r e l a t i v i s t i c c o n s i s t e n t wave f u n c t i o n s . two  For a c l o s e d s h e l l o f  l e v e l s a r i s e with j = Z+?j- and  r e f e r to o r b i t a l and  self£>0,  j = z—j where a and  t o t a l angular momentum.  The  j  j = £—j  l e v e l f o r which the s p i n - o r b i t p o t e n t i a l i s a t t r a c t i v e , i s more p e n e t r a t i n g  than the j=£+j l e v e l and  the former i s o f h i g h e r b i n d i n g These two  energy.  l e v e l s , therefore,  electron lines.  The  l e a d to two  s u b s h e l l are  subshell.  The  s p i n - o r b i t s p l i t peaks i s  mately equal to the s t a t i s t i c a l (2J+1) o f the two  photoelectron  e l e c t r o n c r o s s s e c t i o n of t h a t  m u l t i p l i e d by the occupancy of the s i t y r a t i o of the two  photo-  t o t a l i n t e n s i t i e s of a l l  peaks a r i s i n g from i o n i z a t i o n i n a given p o r t i o n a l to the one  as a r e s u l t  peaks.  subshell  intenapproxi-  r a t i o of l e v e l degeneracies,  Deviations  from the  statistical  r a t i o can occur, p a r t i c u l a r l y near the t h r e s h o l d , c r o s s s e c t i o n s of the two  pro-  as  the  l e v e l s are not n e c e s s a r i l y  the  same. The  two  amount (£+i-)£ where The  components are separated i n energy by according  to the Lande i n t e r v a l r u l e ,  i s the a p p r o p r i a t e  s p l i t t i n g increases  5 as a f u n c t i o n of Z .  s p i n - o r b i t coupling  w i t h the n u c l e a r  The  an  constant.  charge, Z,  . . . spin o r b i t coupling  roughly  constant  3  depends on the e x p e c t a t i o n and  value <l/r > f o r the  subshell  the r e s u l t a n t doublet s p l i t t i n g can be very l a r g e  for  -  core l e v e l s .  The  62  t r e n d i n doublet s e p a r a t i o n f o r sub-  s h e l l s o f a given p r i n c i p a l quantum number, namely np>nd>nf  can a l s o be e x p l a i n e d on the b a s i s o f a de-  crease i n p e n e t r a t i o n , and t h e r e f o r e a decrease i n <l/r  >, with i n c r e a s i n g azimuthal quantum number £.  2.12.2  Multiplet  Splitting  When atoms, molecules or s o l i d s w i t h i n c o m p l e t e l y f i l l e d o u t e r s u b s h e l l ( s ) are i o n i z e d , the u n f i l l e d l e f t behind by photoemission  shell  can couple with the p a r t i a l l y  f i l l e d o u t e r s h e l l s l e a d i n g to v a r i o u s p o s s i b l e nondegenerate  electronic states.  T h i s w i l l l e a d to m u l t i p l e  peaks i n the p h o t o e l e c t r o n s p e c t r a .  These m u l t i p l e t  e f f e c t s can occur f o r both c o r e and valence e m i s s i o n . M u l t i p l e t s p l i t t i n g of core l e v e l s p e c t r a have been r e p o r t e d f o r paramagnetic  free m o l e c u l e s ' and 83 84 systems c o n t a i n i n g both t r a n s i t i o n metal atoms ' and 85 86 r a r e e a r t h atoms ' . A few comprehensive reviews on 87 88  m u l t i p l e t s p l i t t i n g have appeared  4 4  elsewhere  '  8 2  , and  a simple case w i l l be c o n s i d e r e d here t o i l l u s t r a t e some i n t e r e s t i n g f e a t u r e s of t h i s e f f e c t . f o l l o w i n g photoemission  process,  L e t us c o n s i d e r the  63 -  (n£) (n' £ ' ) (filled) (L,S) q  hv  p  (n'£')  p  + photoelectron (2.66)  where, n£ i s the s u b s h e l l from which the e l e c t r o n i s emitted and n'£' i s the p a r t i a l l y shell .  f i l l e d valence sub-  L and S are the t o t a l o r b i t a l and s p i n angular  momenta, and  and S^ r e p r e s e n t the same i n the ( N - l ) -  electron final state.  The s e l e c t i o n r u l e  concerning  the o n e - e l e c t r o n angular momentum of the p h o t o e l e c t r o n , £p =£+l h  and the c o n s e r v a t i o n o f t o t a l s p i n and t o t a l  (2.67)  f  The  (2.68)  • •. ,  AL = L -L=0  t o t a l i n t e n s i t y o f a given f i n a l  s t a t e w i l l be p r o -  89 p o r t i o n a l t o i t s t o t a l degeneracy  I^(L ,S ) f  f  , so t h a t  - (2S +l) (2L +l) f  f  p ' ^ n  orbital  angular momenta r e q u i r e s t h a t f o r the f i n a l s t a t e i o n ,  AS  &  (2/69)  s  - 64 -  Now,  for s orbital  AS = S  f  - S = ± j  (.2,70)  AL = L  f  - L = 0  (.2.71)  and t h i s w i l l S  f  ionization,  l e a d t o two f i n a l  = S ± j , and the i n t e n s i t y  states,  corresponding t o  r a t i o o f the r e s u l t i n g  two  peaks w i l l be given by the r a t i o o f t h e i r m u l t i p l i c i t i e s  I _  (L,S + \) 2S + 2 — =  (.2.72)  The energy s e p a r a t i o n o f the two peaks i s given by Van V l e c k ' s theorem  90 ,  A [ E ( n s ) ] = E ( L , S - j) - E ( L , S + i.)  (2.73)  A [ E ( n s ) ] = (2S + 1) K  (2.74)  f  f  b  b  n s  A[E (ns)] = 0 for S = 0 b  Here K  ^ , n  £ l  for S ^ 0  (2.75)  _ , , i s the ns-n'£* exchange i n t e g r a l which can  calculated  0  from  - 65 -  2 K  a'  0000  ns,n'£' IFTT  oo n s P  =  ( r  l  ) P  n'£'  ( r  2  ) P  ns  ( r  2  ) P  n' l' J  ( r  l  )  ^  +  l  d  r  l  d  r  2  (2.76)  where P ( r ) / r and P ,„,(r)/r ns n l  are the r a d i a l wave f u n c t i o n s 87  for  the r e s p e c t i v e s u b s h e l l s and e i s the e l e c t r o n i c  r  and r  <  >  charge  are chosen t o be the s m a l l e r and the l a r g e r o f r ^  and r , r e s p e c t i v e l y . 2  Gaseous paramagnetic molecules such as NO and 0 ©electron  2  show  core b i n d i n g energy s p l i t t i n g s analogous t o those  d e s c r i b e d by eqns. 2.72 - 2.76, where t h e o r e t i c a l e s t i m a t e s of the s p l i t t i n g s from m o l e c u l a r o r b i t a l c a l c u l a t i o n s 44  give  values i n good agreement w i t h experiment However, the s i t u a t i o n i s l e s s s a t i s f a c t o r y i n the case o f systems w i t h t r a n s i t i o n metal atoms. 2+ p h o t o i o n i z a t i o n o f the 3s l e v e l o f the Mn to two f i n a l s t a t e s : 3S 3p 3 d S 6  5  5  5  7  F o r example, i o n can l e a d  (S = 2, L = 0)  or  3s 3 p  6  3d  S  (S = 3, L = 0)  A Hartree-Fock c a l c u l a t i o n o f the energy s p l i t t i n g these two f i n a l  between  s t a t e s , u s i n g eqn. 2.74 and 2.76 y i e l d s a  -  value of ol3eV°' . r  for MnF^  1  66  -  The e x p e r i m e n t a l l y observed  values  the same s p l i t t i n g r e p o r t e d by F a d l e y and S h i r l e y and MnO  value.  84  for  are approximately one h a l f o f t h i s p r e d i c t e d  These d i s c r e p a n c i e s between the s p l i t t i n g s  intensities  and  estimated from f r e e i o n c a l c u l a t i o n s and  experimental values o b t a i n e d f o r t r a n s i t i o n metal  the  compounds,  a r i s e from a number of sources,  i.  N e g l e c t o f the extent of d e c o u p l i n g i n the d o r b i t a l s  due  to s t r o n g f i e l d l i g a n d  ii.  Neglect of the extent t h a t the d e l e c t r o n s are d e l o -  c a l i z e d due  iii.  bonding.  to the nature o f the chemical bond.  Neglect of c o r r e l a t i o n  effects.  Bagus and co-workers have shown t h a t c o r r e l a t i o n e f f e c t s make the l a r g e s t c o n t r i b u t i o n to the discrepancy  91  .  T h e i r Hartree-Fock  observed  c a l c u l a t i o n on  Mn  3 +  f i n a l s t a t e s , u s i n g wave f u n c t i o n s w i t h c o n f i g u r a t i o n i n t e r a c t i o n produced ment with experiment, bonding e f f e c t s .  a r e s u l t which i s i n very good even without i n c l u d i n g the  agree-  chemical  A c c o r d i n g to these m u l t i c o n f i g u r a t i o n a l 7  Hartree-Fock  c a l c u l a t i o n s the  S multiplet i s essentially 5 unchanged by the c o n f i g u r a t i o n i n t e r a c t i o n . But, f o r S,  - 67 -  c o n f i g u r a t i o n s which r e s u l t from t r a n s f e r r i n g one 3p e l e c t r o n t o the 3S o r b i t a l and another 3p e l e c t r o n t o a 3d o r b i t a l the  ( i n a l l the d i f f e r e n t ways c o n s i s t e n t w i t h  angular momentum o f the m u l t i p l e t ) , can mix v e r y  s t r o n g l y with the o n e - e l e c t r o n c o n f i g u r a t i o n ,  $ ( S) = 5  1  3s ( S)3p ( S)3d ( S) 1  2  6  1  5  6  Here, the terms which r e s u l t from L,S c o u p l i n g o f the s u b s h e l l t o the l e f t are given i n p a r e n t h e s i s . The conf i g u r a t i o n s which mix s t r o n g l y w i t h $p  $ ( S) =  3s ( S)3p ( P)3d ( P )  $ ( S) =  3s ( S)3p ( P)3d ( P )  5  2  5  3  2  1  4  3  6  5  ( S) a r e ,  3  1  2  1  4  3  6  3  2  5 2 1 4 1 6 5 $ r S ) = 3s^( -S)3p*( D)3d rD) J  1  b  4  3 3 P-_ and ?  6 r e p r e s e n t two d i f f e r e n t ways i n which 3d can 3 couple to give P, which are l i n e a r l y independent. 2  T h i s c o n f i g u r a t i o n mixing w i l l r e s u l t i n a t l e a s t a f o u r f o l d manifold of  s t a t e s , and the lowest energy 7 component w i l l be moved toward S significantly. The c a l 7 c u l a t e d s e p a r a t i o n between S and the lowest energy 5S component i s 4.7eV  91  which i s i n b e t t e r agreement w i t h  - 68  the experimental value  -  of 6.5eV f o r MnF "* . 1  2  r e l a t i v e i n t e n s i t i e s of the peaks can now u s i n g the  be  The predicted  sudden approximation r e s u l t o f eqn.  2.4 7.  However, some of the peaks p r e d i c t e d by the above method may  be too weak to be e x p e r i m e n t a l l y  observed, i n f a c t  5 2+ four p o s s i b l e peaks f o r S of Mn 92 have been observed . These c o n f i g u r a t i o n i n t e r a c t i o n only three o f the  c a l c u l a t i o n s a l s o e x p l a i n the d e v i a t i o n of the  experimental  5  i n t e n s i t y r a t i o from the r a t i o of 5/7 by simple m u l t i p l e t theory The  (eqn.  a n a l y s i s of m u l t i p l e t - s p l i t s t r u c t u r e produced  by p h o t o i o n i z a t i o n of non-s core forward as t h a t d e s c r i b e d  Coupling  angular momentum and  s p i n of j  ways  l e v e l s i s not  as s t r a i g h t -  here f o r s i o n i z a t i o n of p a r a -  magnetic compounds.  partially  2.72)  7 S/ S p r e d i c t e d 2+ f o r Mn  for  o f the non-zero o r b i t a l o r  the na o r b i t a l w i t h  the  f i l l e d valence o r b i t a l ( s ) can occur i n v a r i o u s  leading  t o more than two  final states.  Here  again,  the s i m p l e s t procedure t h a t can be used f o r c a l c u l a t i o n 84 of s p l i t t i n g s i s n o n - r e l a t i v i s t i c atomic m u l t i p l e t  theory  For b e t t e r q u a n t i t a t i v e d e s c r i p t i o n s c o n f i g u r a t i o n  inter-  a c t i o n and  chemical e f f e c t s have to be i n c l u d e d and 87 93 are d i s c u s s e d i n d e t a i l elsewhere ' Extensive  satellite  these  s t r u c t u r e seen i n paramagnetic  t r a n s i t i o n metal compounds can a l s o be produced by  electron  - 69  shake up.  -  In f a c t i t i s b e l i e v e d t h a t most of t h i s  s t r u c t u r e i s due detection  t o shake up  and  t h i s makes the  of m u l t i p l e t s t r u c t u r e somewhat ambiguous  at times.  More w i l l be s a i d about t h i s l a t e r , i n  chapter on the x-ray p h o t o e l e c t r o n t r a n s i t i o n metal a c e t y l a c e t o n a t e  2.12.3  Multielectron  the  spectroscopy o f some vapors.  Excitations  I f an i o n i c s t a t e produced by p h o t o i o n i z a t i o n be d e s c r i b e d  can  by a wave f u n c t i o n t h a t i n c l u d e s e x c i t e d  f i g u r a t i o n s , then i t i s p o s s i b l e t h a t the i n t e r a c t with these e x c i t e d s t a t e s and p r o b a b i l i t y t h a t the excited states.  final  s t a t e may  ground s t a t e  there  end  con-  is a  up as one  There w i l l be a peak i n the  may  finite of these  photoelectron  spectrum c o r r e s p o n d i n g to each o f these e x c i t e d s t a t e s , t h e i r p o s i t i o n s and  intensities  with r e s p e c t  peak are r e l a t e d to the r e l a x a t i o n energy by rule discussed infinite  i n Section  2.9.  t o the  primary  the energy  There are, i n g e n e r a l ,  number of e x c i t e d s t a t e s a s s o c i a t e d with the  s t a t e , however, only a few which can be up t o 80% favourable  conditions.  and  sum an  primary  o f these have observable i n t e n s i t i e s  of the  i n t e n s i t y o f the main peak under  These peaks appearing i n the photo-  e l e c t r o n spectrum at h i g h e r b i n d i n g e n e r g i e s than the main (or primary) peak are u s u a l l y termed c o r r e l a t i o n or ration interaction s a t e l l i t e s .  configu-  - 70 -  The  first  s a t e l l i t e s o f t h i s type were  observed 94-97  for  Ne and Ar by C a r l s o n , Krause and co-workers  These s a t e l l i t e s were e x p l a i n e d i n terms o f t w o - e l e c t r o n transitions.  Two types o f t w o - e l e c t r o n t r a n s i t i o n s can  occur i n a photoemission (n£) (n*£') q  process  —(nO ~ (n £') ~ (n"£")  P  q  1  ,  P  1  1  + photoelectron (2.77)  (n£) (n' V ) q  P  —(n£) ~ (n Jl ) ~ (e£") q  1  ,  ,  p  1  + photoelectron (2.78)  The  f i r s t p r o c e s s i n v o l v e s the t r a n s i t i o n o f a second  e l e c t r o n i n t o an e x c i t e d , but bound, s t a t e r e s u l t i n g i n a p h o t o e l e c t r o n peak a t a k i n e t i c energy line.  lower than t h e main  T h i s p r o c e s s i s known as "shakeup" .  The second  process i n v o l v e s the e x c i t a t i o n o f a second e l e c t r o n t o a continuum s t a t e , e £ " , r e s u l t i n g i n a continuous on the low k i n e t i c energy  s i d e o f t h e main peak.  spectrum This i s  known as " s h a k e o f f " . If  i t i s assumed t h a t the i n i t i a l and the f i n a l s t a t e s  are d e s c r i b e d by a s i n g l e e l e c t r o n i c c o n f i g u r a t i o n , then t h e shakeup  and shakeoff  u s i n g eqn. 2.38. i „i  4>ii n  probabilities  can be c a l c u l a t e d  For a s t r i c t l y two-electron  transition,  / with a l l the o t h e r p a s s i v e o r b i t a l s  remaining  - 71 -  very nearly (i.e.  t h e same d u r i n g  frozen  the e x c i t a t i o n process  t h e p r o b a b i l i t y , P ,^, ^ „ „ 98 o f t h e s a i d t r a n s i t i o n c a n be a p p r o x i m a t e d a s  P  N  n  £  ^V^'V*'* I ' ' <- > 2  79  i s t h e o c c u p a t i o n number o f t h e n ' A ' s u b ^  and R ,„, and R „ „ a r e r a d i a l n £ n £  functions  n  initial eqn.  n  n ' £ ' + n»£» " n ' £ '  where N ,„, n £ shell  orbitals),  and f i n a l  2.79 w i l l  result i s often  states.  The o v e r l a p  be n o n - z e r o o n l y  f o r the  integral i n  i f £'=£", a n d t h i s  termed t h e o n e - e l e c t r o n  monopole r u l e .  The t o t a l  symmetries f o r the (N-l) e l e c t r o n s  predicted  t o f o l l o w a monopole r u l e a s i n d i c a t e d by  eqn.  are also  2.3 8  AJ  = A L= A S = A M  = A M ^ = A M = ATT = 0 G  (2.80)  where J i s t h e q u a n t u m number f o r L + S* a n d TT i s t h e overall state parity. For  example, t h e i o n i z a t i o n o f a core  f r o m t h e I s l e v e l o f Ne l e a d s  electron 2  t o an i o n i c s t a t e o f  S  symmetry w h i c h when c o u p l e d t o a c o n t i n u u m f u n c t i o n o f p s y m m e t r y r e s u l t s i n a -^P s t a t e i n a c c o r d a n c e w i t h t h e dipole selection rule f o r photoionization.  According t o  - 72 -  the monopole s e l e c t i o n r u l e s , t w o - e l e c t r o n e x c i t a t i o n s of the types  2p-*np a n d 2s-*-ns a r e a l l o w e d , a s t h e  r e s u l t a n t shakeup of the primary Although  s t a t e s a r e o f t h e same symmetry a s t h a t  state. these  o n e - e l e c t r o n d e s c r i p t i o n s c a n be  used t o p r e d i c t t h e s a t e l l i t e peak p o s i t i o n s f a i r l y r a t e l y , t h e s i t u a t i o n i s much l e s s of p r e d i c t e d i n t e n s i t i e s  .  accu-  s a t i s f a c t o r y i n the case  A l s o , some s a t e l l i t e s  observed  e x p e r i m e n t a l l y a r e much l e s s f a v o u r a b l y d e s c r i b e d b y t h i s mechanism. excitation two  final  F o r e x a m p l e , i n Ne, t h e 2p  np m o n o p o l e  accompanying t h e I s photoemission ionic states,  2 5 3 2 2s 2p n p ( S) l s ( S) a n d  2 5 1 2 2s 2p n p ( S) I s ( S ) , a n d b o t h overlap with the i n i t i a l  can l e a d t o  o f t h e s e would have  s t a t e i f t h e c a l c u l a t i o n s were  done u s i n g a s i n g l e d e t e r m i n a n t a l  initial  e m p l o y i n g Koopmans' a p p r o x i m a t i o n  f o rthe f i n a l  orbitals. 2  zero  However, two s a t e l l i t e s  s t a t e and state  corresponding to  5  l s 2 s 2p 3p In  are experimentally  observed.  t h e c a s e o f A r , t h e 3s p h o t o e l e c t r o n  spectrum  shows a b r o a d p e a k s e p a r a t e d  by about lOeV from t h e 99 m a i n peak t o t h e h i g h b i n d i n g e n e r g y s i d e , and from o p t i c a l d a t a , i t h a s b e e n shown t h a t t h i s s e p a r a t i o n 1 6 2 m a t c h e s t h e e n e r g y d i f f e r e n c e b e t w e e n 3s 3p ( S) a n d 2 3s  4  12  3p 3d ( S ) .  The two c o n f i g u r a t i o n s d i f f e r by two  o r b i t a l s a n d t h i s t r a n s i t i o n c a n n o t be f a v o u r a b l y cribed using a simple  s i n g l e c o n f i g u r a t i o n model.  des-  - 73  Spears and mix  co-workers  -  have shown t h a t these two  very s t r o n g l y with each other,  states  thereby making the  multielectron t r a n s i t i o n highly probable.  These  satellites  9 9  are c a l l e d c o n f i g u r a t i o n  interaction satellites  t h i s d e f i n i t i o n covers shakeup case where the  , and  s a t e l l i t e s as a s p e c i a l  corresponding t r a n s i t i o n i s a  one-electron  e x c i t a t i o n to a c o n f i g u r a t i o n i n t e r a c t i o n s t a t e . Martin  and  Shirley  have r e p o r t e d  i n t e r a c t i o n c a l c u l a t i o n s f o r Ne which are  to obtain  intensities  i n good agreement w i t h experiment.  l a t e d i n t e n s i t i e s are,  i n general,  mental values and Martin if  configuration  configuration  s t a t e , the  and  The  calcu-  lower than the  Shirley  have a l s o shown t h a t ,  i n t e r a c t i o n i s included  i n the  initial  c a l c u l a t e d v a l u e s become c o n s i d e r a b l y  b r i n g i n g them much c l o s e r to the experimental T h i s r e s u l t showed t h a t i n i t i a l action plays configuration  experi-  larger  values.  state configuration  a s i g n i f i c a n t r o l e along w i t h f i n a l i n t e r a c t i o n i n d e t e r m i n i n g the  inter-  state  satellite  intensities. Initial  state configuration  used to e x p l a i n the  i n t e r a c t i o n has  been  conjugate s a t e l l i t e s observed f o r  Valence l e v e l i o n i z a t i o n of Hg([core] 6 s (^S) ) 2 produces the primary i o n i c s t a t e [core] 6s( S) as w e l l as 2 mercury  1 0 0  .  the conjugate s t a t e r a t i o n s cannot mix  2  [core]  6p,(_.. )-r p  with each o t h e r .  and  these two  Berkowitz and  configucoworkers  - 74 -  have shown  that  the ground s t a t e  by a m i x t u r e o f t h e two n e a r l y [core]6s  state  configuration  between  ( S) and [ c o r e ] 6 p mixing leads  the i n i t i a l  This explains  degenerate  2 1  tions  state  o f Hg i s r e p r e s e n t e d  2 1  ( S) and t h i s  initial  t o a non-zero  overlap  and t h e c o n j u g a t e  the observed s a t e l l i t e  ponding to the conjugate s t a t e , have a l s o b e e n o b s e r v e d  configura-  state.  structure  and s i m i l a r  f o r cadmium *"* 1  1  corres-  structures  and lead *"* 1  2  vapors. S t r o n g s a t e l l i t e s have a l s o been o b s e r v e d f o r transition  m e t a l and r a r e - e a r t h  compounds ^  A l t h o u g h , t h e s e c a n be c o n s i d e r e d tellites  they are u s u a l l y  satellites, mental i.  1  1  .  as c o r r e l a t i o n s a transfer  of s p e c i f i c  experi-  a r e a b s e n t when t h e 3 d o r b i t a l s a r e  filled ^. 1  may be p r e s e n t when t h e 3 d o r b i t a l s  The s a t e l l i t e s  . 110  empty  iii.  Satellite  metal  i o n are d i f f e r e n t f o r d i f f e r e n t l i g a n d s ,  the  1  observations.  completely  are  3  l a b e l l e d as c h a r g e  m a i n l y due t o a number  The s a t e l l i t e s  ii.  1  separations  energy separation  main l i n e hedral  following  between  the s a t e l l i t e  the n e p h e l a u x e t i c  compounds ''" . 1  and i n t e n s i t i e s o f a  2  series  given  with  and t h e in octa-  - 75 -  These o b s e r v a t i o n s can be e x p l a i n e d f u l l y by a l i g a n d - t o - m e t a l charge  t r a n s f e r mechanism  which would accompany the p h o t o i o n i z a t i o n r e p r e s e n t i n g an attempt  to screen the core h o l e  by photoemission.  T h i s model was  by K i m  1 1 3  '  1 1 4  produced  f i r s t put  forward  and more q u a n t i t a t i v e d i s c u s s i o n s  , , and, Sugano _ 107 were f o ,l -l, o w e Jd UbyT Larsson 106 , and, Asada C  The charge  t r a n s f e r process has been shown t o obey  the monopole s e l e c t i o n r u l e . o c t a h e d r a l symmetry, the e  For example, i n •+  b  type t r a n s i t i o n i s  monopole allowed  (where the s u p e r s c r i p t s b and  a  r e f e r to bonding  and a n t i b o n d i n g r e s p e c t i v e l y ) .  F u r t h e r , these two  o r b i t a l s are represented by a  l i n e a r combination  o f metal d o r b i t a l s and  ligand  valence o r b i t a l s with e^ being mainly l i g a n d and  b e i n g mainly metal  3d type o r b i t a l .  orbital The  s t a t e i s c o n s i d e r e d t o be a l i n e a r combination two  107 configurations ,  *, = (core hole) 1  (e ) g  n  $  (e )  n _ 1  b  (e ) g a  m  and  9  =  (core hole)  b  (e ) a  m + 1  final o f the  - 76 -  where $^ i s the f i n a l s t a t e with no change i n valence s u b s h e l l occupations and $  l S  t  n  e  f  i  n  a  2  l  s t a t e r e s u l t i n g from a o n e - e l e c t r o n l i g a n d ^ t o - m e t a l charge  transfer.  The l i n e a r combination r e s u l t s i n two  4  A  =  =  C  C  final  l l h  21  $  1  This w i l l  +  +  C  C  final  states  states,  12  22  o f these two  $  $  2  2  l e a d to two  p h o t o e l e c t r o n peaks of which  the i n t e n s i t i e s can be c a l c u l a t e d by u s i n g eqn. 2.4 7. In t h i s model c o r r e c t i o n s  are made due  to hole  induced  covalency and the v a l u e s c a l c u l a t e d f o r r e l a t i v e i n t e n s i t i e s , peak p o s i t i o n s and widths  are i n reasonable  • , . _, .. . 106-107 agreement with the experimental r e s u l t s . u  been suggested  t h a t the shortcomings  . , I t has T  of t h i s model can  be remedied by i n c l u d i n g more than two  configurations  in  107 the f i n a l  state configuration  i n t e r a c t i o n scheme  These charge t r a n s f e r s a t e l l i t e s i n t r a n s i t i o n metal core l e v e l s p e c t r a w i l l be f u r t h e r d i s c u s s e d i n Chapters F i v e and S i x .  -  77  -  The study o f s a t e l l i t e  s t r u c t u r e can  obviously  help i n an understanding o f the m u l t i e l e c t r o n p r o cesses accompanying p h o t o i o n i z a t i o n . observations satellite  Experimental  r e v e a l a s t r o n g dependence o f the  s t r u c t u r e and i n t e n s i t y on the o x i d a t i o n  s t a t e and the chemical environment o f the metal i o n , making i t p o s s i b l e to use s a t e l l i t e finger printing  1  s t r u c t u r e i n the  o f 3d and 4 f metal compounds.  - 78  -  REFERENCES 1.  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B 1 1 , 2177  and  (1975)  Spectrosc.  - 87 -  CHAPTER THREE  THE GAS PHASE X-RAY PHOTOELECTRON SPECTROMETER; DESIGN AND PERFORMANCE  3.1  Introduction  I n e l e c t r o n s p e c t r o s c o p y an e x c i t a t i o n beam i r r a d i a t e s a t a r g e t sample, and t h e e x p e l l e d e l e c t r o n s originating  from p h o t o i o n i z a t i o n , Auger o r a u t o i o n i -  z a t i o n p r o c e s s e s t h e n e n t e r an e l e c t r o n where t h e y a r e e n e r g y detected. in  spectrometer  a n a l y s e d and s u b s e q u e n t l y  The r e s u l t a n t p u l s e s a r e c o u n t e d  a s u i t a b l e manner f o r s u b s e q u e n t  A block diagram  and s t o r e d  data analysis .  o f the x-ray photoelectron spectrometer  used i n t h e work d e s c r i b e d i n t h i s t h e s i s , t h e m a i n c o m p o n e n t s , i s shown i n F i g . 3.1. demands on s u c h an e l e c t r o n  illustrating The b a s i c  spectrometer are t h a t the  r e s o l u t i o n s h o u l d be s u f f i c i e n t t o r e v e a l b o t h t h e multicomponent  s t r u c t u r e and b i n d i n g energy  shifts  p r e v i o u s l y d e s c r i b e d , and t h a t the s e n s i t i v i t y  should  Block diagram of the g a s p h a s e x - r a y photoelectron spectrometer.  Fig.  3.1.  Block diagram of the x-ray p h o t o e l e c t r o n spectrometer i n use a t t h e U n i v e r s i t y of B r i t i s h Columbia,Department of Chemistry.  -  be as high as p o s s i b l e .  89  -  However, s e n s i t i v i t y  and  r e s o l u t i o n , as i n many forms o f s p e c t r o s c o p y , are two mutually c o n f l i c t i n g q u a l i t i e s and some s o r t of a compromise has to be reached when d e s i g n i n g such a spectrometer. There are a d d i t i o n a l problems i f the s p e c t r o meter i s t o be used i n gas phase s t u d i e s .  In the gas  phase, a high p r e s s u r e i s r e q u i r e d i n the r e g i o n of i o n i z a t i o n i n o r d e r to o b t a i n a reasonable s i g n a l strength.  At the same time the p r e s s u r e i n the r e s t  of the system has to be s u f f i c i e n t l y low t h a t the e j e c t e d e l e c t r o n i s prevented from s u f f e r i n g a c o l l i s i o n , p a r t i c u l a r l y , an i n e l a s t i c one, b e f o r e i t reaches the d e t e c t o r .  T h i s can be achieved, t o a  l a r g e e x t e n t , by employing  d i f f e r e n t i a l pumping.  S i m i l a r low pressure c o n d i t i o n s are necessary f o r e f f e c t i v e o p e r a t i o n of the x-ray s o u r c e . The gas phase x-ray p h o t o e l e c t r o n spectrometer used i n the work d e s c r i b e d i n t h i s t h e s i s was  con-  s t r u c t e d i n the Department of Chemistry at the U n i v e r s i t y of B r i t i s h Columbia.  In t h i s chapter the  spectrometer w i l l be d e s c r i b e d i n some d e t a i l with s p e c i a l r e f e r e n c e to the performance,data and h a n d l i n g .  acquisition  A b r i e f d e s c r i p t i o n o f the spectrometer  has a l s o appeared  elsewhere  1  - 90 -  3.2  3.2.1  The  Spectrometer  The X-ray Source U n i t  The x-ray tube used i n t h i s study i s o f the hot cathode type, where an anode o f a s u i t a b l e m a t e r i a l i s bombarded with e l e c t r o n s produced by t h e r m i o n i c emission from a hot f i l a m e n t t o y i e l d x-rays c h a r a c t e r i s t i c o f the anode m a t e r i a l . The cathode 0.18 mm-diameter  i n t h i s case i s a 'bent h a i r p i n ' o f tungsten w i r e , s e m i c i r c u l a r l y  bent  c o n c e n t r i c with the anode ( F i g s . 3 . 3 , 3.4). The f i l a m e n t leads are approximately 0.5 cm a p a r t , t h i s design m i n i m i z i n g c u r r e n t induced magnetic  fields.  A support rod i s p r o v i d e d at one end o f the f i l a m e n t to prevent d i s t o r t i o n upon h e a t i n g .  An AC c u r r e n t i s  used t o heat the f i l a m e n t . The anode i s made o f a copper tube with the f r o n t end s e a l e d .  T h i s s e a l e d f r o n t end has a l i p  which i s u n i f o r m l y 'pinched' around  a 0.3  cm-thick  d i s c o f the d e s i r e d anode m a t e r i a l o f the h i g h e s t grade p u r i t y  ( F i g . 3.5).  Although, the work d e s c r i b e d  h e r e i n employed A l K a x-rays, we have used Mg, Zr and Y anodes s u c c e s f u l l y .  T h i s simple design allows  s u f f i c i e n t thermal c o n t a c t between the water-cooled  F i g . 3.2. The U n i v e r s i t y of B r i t i s h Columbia,Department of Chemistry,x-ray p h o t o e l e c t r o n spectrometer.  Fig.  3.3.  The x-ray tube assembly showing the tungsten f i l a m e n t , f i l a m e n t leads and support,anode and the s t a i n l e s s s t e e l s h i e l d .  Fig.  3.4.  The  x-ray tube  assembly.  Fig.  3.5.  The  x-ray  tube  anode  in  detail.  - 95 -  copper tube and the t a r g e t m a t e r i a l . water pressure o f 70 p s i was  The  laboratory  found t o be more than  enough f o r c o o l i n g the anode under normal o p e r a t i n g conditions. The x-ray tube i s maintained at ^2x10  6  t o r r under  t y p i c a l o p e r a t i n g c o n d i t i o n s i n o r d e r to prevent v o l t a g e breakdown, and to i n c r e a s e the f i l a m e n t l i f e t i m e .  To  maintain t h i s low p r e s s u r e w i t h i n the x-ray tube i t i s i s o l a t e d from the n e i g h b o u r i n g source chamber Fig.  3.6)  by u s i n g a 0.0025 mm  ( s u p p l i e d by A l f a C h e m i c a l s ) . and  aluminum  (See  f o i l window  However, when z i r c o n i u m  y t t r i u m anodes are used, with t h e i r lower  energy  x - r a y s , and decreased a b i l i t y t o p e n e t r a t e matter, a 2.5  yg/cm  p o l y s t y r e n e f i l m i s employed i n s t e a d o f  the aluminum f o i l . A rubber or V i t o n to  s e a l the window to the x-ray tube.  '0' r i n g i s used An added advan-  tage o f i s o l a t i n g the x-ray tube from the sample chamber is  t h a t i t prevents the contamination o f the anode and  the f i l a m e n t by the c o r r o s i v e gases and hence enhances their respective  lifetimes.  To prevent the d e s t r u c t i o n o f the x-ray tube window by o v e r h e a t i n g , the x-ray tube w a l l i s w a t e r - c o o l e d .  The  window can a l s o be destroyed by e l e c t r o n bombardment  from  the f i l a m e n t , but t h i s can be prevented by a p p l y i n g a very h i g h p o s i t i v e p o t e n t i a l t o the anode w h i l e main-  - 96 -  g a s in  stainless steel tubing flange cooling \ brass flange 0 -ring heater (boron nitride)  heating wire  (chromel) stainless steel tubing  sample stainless steel heat shields  g a s cell demountable base aluminum windows  einzel lens to analyzer  Fig.  3.6.  Schematic diagram o f the spectrometer showing the x-ray tube and the o l d gas  cell.  - 97 -  t a i n i n g the f i l a m e n t a t , o r c l o s e t o , ground  potential.  T h i s p o s i t i v e p o t e n t i a l a l s o ensures t h a t e l e c t r o n s s c a t t e r e d from the anode are drawn back, and thus cannot s t r i k e the window.  Under normal  operating  c o n d i t i o n s the f i l a m e n t i s h e l d a t -170V and the t y p i c a l o p e r a t i n g power f o r an aluminum anode i s ^350W (10 kV , 35 mA) . A grounded  cylindrical stainless steel  shield  between the anode t u b i n g and the f i l a m e n t serves t o focus the e l e c t r o n beam from t h e cathode, onto the target surface  ( F i g . 3.3).  T h i s s h i e l d a l s o ensures  t h a t no e l e c t r o n s can reach the back s i d e o f the anode. I t i s necessary t o m a i n t a i n the anode as c l e a n as p o s s i b l e a t a l l times.  Most o f the anode contamination  comes from the tungsten f i l a m e n t i n the form o f both tungsten and absorbed i m p u r i t i e s i n the f i l a m e n t . T h i s contamination can be minimized by p o s i t i o n i n g the f i l a m e n t out o f d i r e c t s i g h t o f the anode, and the s t a i n l e s s s t e e l s h i e l d which i s used t o focus the e l e c t r o n s a l s o doubles as a p r o t e c t i v e  barrier.  The low p r e s s u r e i n s i d e the x-ray tube i s maintained by u s i n g a 2 85  i/sec.  o i l d i f f u s i o n pump.  The d i f f u s i o n  pump i s connected t o the x-ray tube through a water c o o l e d b a f f l e which prevents backstreaming o i l vapor from contaminating the anode.  98 -  The anode high v o l t a g e i s i s o l a t e d from the r e s t o f the system by u s i n g a " h y s o l " spacer ( F i g . 3.4)  and  the anode p a r t i s connected to the x-ray tube by u s i n g nylon  screws. As mentioned  i n Chapter One,  the primary  limita-  t i o n on i n s t r u m e n t a l r e s o l u t i o n i s the band width of the x - r a y s .  In a d d i t i o n to the x-ray l i n e s  characteris-  t i c o f the anode m a t e r i a l , a continuous spectrum dependent upon the primary e l e c t r o n energy i s a l s o i n these x-ray tubes.  produced  T h i s continuous spectrum i s  normally known as bremsstrahlung. The presence o f bremsstrahlung r a d i a t i o n  i n c r e a s e s the background  of the p h o t o e l e c t r o n spectrum.  level  However, the c o n t r i b u t i o n  from t h i s continuous spectrum t o the background  becomes  l e s s s i g n i f i c a n t at lower k i n e t i c e n e r g i e s ( i . e . core l e v e l spectra) as the p r o p o r t i o n o f background  from  i n e l a s t i c a l l y scattered photoelectrons increases. A more s e r i o u s problem lines.  i s t h a t of x-ray  satellite  F o r example, i n Mg and A l , i n a d d i t i o n to the  predominant  Ka, i,  0  z  l i n e which,  as mentioned  earlier, is  e s s e n t i a l l y an u n r e s o l v e d d o u b l e t , o t h e r l e s s i n t e n s e l i n e s are produced by x-ray t r a n s i t i o n s i n m u l t i p l y i o n i z e d anode atoms as w e l l as those t r a n s i t i o n s which i n v o l v e the valence l e v e l s . there are two  In the case o f A l (and  Mg)  s a t e l l i t e s about lOeV t o the h i g h energy  -  99  -  s i d e o f the main x-ray l i n e which are produced  by  t r a n s i t i o n s i n v o l v i n g the K hole of a doubly i o n i z e d (KL) atom.  These are denoted as K a ^ and K a ^ and  i n t e n s i t i e s are approximately 8% and 4%  their  respectively.  In the p h o t o e l e c t r o n s p e c t r a these K a ^ and K a ^ s a t e l l i t e s from s t r o n g peaks can i n t e r f e r e and obscure weak peaks and care has to be taken i n a s s i g n i n g p h o t o e l e c t r o n l i n e s produced by such r a d i a t i o n . Ka-j and K a ^ s a t e l l i t e s o f Au 4 f ^ p l e t e l y mask the Au 5p^y i s used t o o b t a i n the T h i s problem  2  For example, the 4 2  ^7/2  c  a  n  c o m  ~  l i n e i f A l o r Mg Ka r a d i a t i o n  spectrum.  can be s o l v e d by u s i n g a monochro-  2 3 mator ' .  However, the i n c r e a s e d r e s o l u t i o n due to  monochromatization  i s accompanied by a decreased  sensi-  t i v i t y as a r e s u l t o f the l o s s o f i n t e n s i t y d u r i n g the process.  T h i s l o s s i n s e n s i t i v i t y can be somewhat 3  minimized by u s i n g h i g h power x-ray tubes  .  These  employ r o t a t i n g anodes i n o r d e r to minimize anode o v e r heating. In the p r e s e n t case a s t a t i s t i c a l method i s used to c o r r e c t f o r the x-ray s a t e l l i t e s  3.2.2  The Gas  (see l a t e r ) .  Cells  Almost a l l r e a d i l y o b t a i n a b l e gases and l i q u i d s have been s t u d i e d by XPS  and UPS.  volatile  Higher tern-  - 100 -  p e r a t u r e s are t h e r e f o r e r e q u i r e d to generate the free atoms and molecules s t u d i e d i n t h i s p a r t i c u l a r work.  Two gas c e l l s were t h e r e f o r e designed to  s a t i s f y these experimental needs.  Both gas c e l l s  were designed so that s o l i d samples may be v a p o r i z e d and unstable gaseous s p e c i e s may be s t u d i e d . gas c e l l s w i l l be termed  the o l d and the new gas c e l l  respectively, in a purely chronological  3.2.2.1  The two  sense.  The O l d Gas C e l l  A schematic. diagram o f the o l d gas c e l l and a p a r t of the x-ray tube i s shown i n F i g . 3.6.  Note  the r e l a t i v e p o s i t i o n i n g o f the gas c e l l with r e s p e c t to  the x-ray tube. The heater c o n s i s t s o f a double threaded boron  n i t r i d e c y l i n d e r on which chromel wire i s n o n - i n d u c t i v e l y wound.  T h i s heater i s s l i p p e d around the s t a i n -  l e s s s t e e l t u b i n g l e a d i n g to the i o n i z a t i o n and so operates o u t s i d e the vacuum system,  chamber thus  a v o i d i n g d e s t r u c t i o n o f the h e a t i n g element by the gas under study. (see  The gas c e l l  is electrically  isolated  l a t e r ) from the source chamber by u s i n g a perspex  r i n g as a high v o l t a g e s t a n d - o f f .  A rubber  '0' r i n g  - 101 -  i s used t o s e a l the gas c e l l t o t h e source chamber and the  gas c e l l  i s h e l d i n p o s i t i o n by four nylon screws.  The gas c e l l  flange can be a i r o r water-cooled to p r e -  vent o v e r h e a t i n g o f the 'O' r i n g at gas c e l l t u r e s i n excess o f =400°C.  tempera-  Heat t r a n s f e r from the  i o n i z a t i o n chamber t o the b r a s s flange i s a l s o minimized by u s i n g a t h i n s t a i n l e s s s t e e l c y l i n d e r t o connect the two p a r t s . the  Here, the term i o n i z a t i o n chamber r e f e r s t o  bottom p a r t o f the gas c e l l w i t h i n which the vapor  i s exposed to the x - r a y s .  Heat l o s s e s from the i o n i z a -  t i o n chamber and from the h e a t e r are reduced by means o f stainless steel  shields.  Room temperature gases are i n t r o d u c e d from the t o p of  the gas c e l l through a s t a i n l e s s s t e e l tube as shown  i n F i g . 3.6, w h i l e s o l i d s t o be v a p o r i z e d are p l a c e d i n s i d e a s t a i n l e s s s t e e l cup which screws i n t o the top of  the i o n i z a t i o n chamber. X-rays e n t e r the i o n i z a t i o n chamber through a  window, having a l r e a d y passed through the x-ray tube window.  The f u n c t i o n o f t h i s second window i s t o prevent  e x c e s s i v e gas l o s s e s from the gas c e l l .  I t was found  t h a t even the s m a l l e s t p i n h o l e i n a window can decrease the  count r a t e c o n s i d e r a b l y .  Normally, 0.0025 mm A l f o i l  i s used as the gas c e l l window m a t e r i a l .  When Zr M c and  2 .Y ML, x-rays are used, 2.5 ug/cm used.  p o l y s t y r e n e f i l m can be  - 102 -  The it  i o n i z a t i o n chamber i s made o f pure copper and  i s important  t o have a l l the s u r f a c e s o f the i n s i d e  chamber w a l l s a t a constant work f u n c t i o n w i t h good conductivity.  In p a r t i c u l a r , i t i s d e s i r a b l e t o a v o i d  the formation o f a non conducting oxide l a y e r , and so the i n s i d e w a l l o f the gas c e l l  i speriodically  coated  with benzene soot to prevent d e t e r i o r a t i o n o f the copper w a l l s through  r e a c t i o n with the gas under study  and t o maintain f i e l d homogeneity w i t h i n the i o n i z a t i o n chamber. When p o l y s t y r e n e windows are used, the gas c e l l can o n l y be heated t o ^100°C.  However, when aluminum  windows are used i n c o n j u n c t i o n w i t h A l Ka x - r a y s , i t i s p o s s i b l e t o achieve temperatures  o f approximately  500°C o r h i g h e r with the upper l i m i t s e t to ^570°C (the  m e l t i n g p o i n t o f the s i l v e r s o l d e r used i n the  c o n s t r u c t i o n o f the gas c e l l ) . temperature  a t which a s p e c i e s has been s t u d i e d s u c c e s s -  f u l l y u s i n g t h i s gas c e l l was  To date the h i g h e s t  i s approximately  r e q u i r e d to study magnesium atoms.  c a l c i u m , s t r o n t i u m and barium  4 70°C.  Except  This  f o r the  s p e c t r a presented i n the  next chapter a l l the o t h e r atoms and molecules  reported  i n t h i s t h e s i s were s t u d i e d u s i n g t h i s gas c e l l . T h i s design o f the gas c e l l temperature  a l s o allows f o r v a r i a b l e  s t u d i e s s i n c e the h e a t e r may be removed and  - 103 -  the c a v i t y f i l l e d w i t h an a p p r o p r i a t e r e f r i g e r a n t such as l i q u i d n i t r o g e n o r a d r y i c e - a c e t o n e m i x t u r e . In  o r d e r t o study t r a n s i e n t s p e c i e s a threaded, 0.3 cm-  diameter hole i s p r o v i d e d i n the gas c e l l a t the l e v e l of for  the window.  A tube made o f the a p p r o p r i a t e m a t e r i a l  the s p e c i e s under study i s i n s e r t e d i n t o t h e opening  i n a d i r e c t i o n p e r p e n d i c u l a r t o the plane o f F i g . 3.6. A 1 cm-diameter e x i t hole i n the gas c e l l ,  covered with  wire mesh t o p r e s e r v e f i e l d homogeneity, i s l o c a t e d d i r e c t l y o p p o s i t e the i n l e t f o r sample pumping.  In t h i s  manner the gas can be f a s t pumped across the x-ray beam by t h e 2 85 £/sec d i f f u s i o n pump connected source chamber housing the gas c e l l . design allows f o r a s h o r t path  to the  The sample  inlet  ( =15 cm) between the  i o n i z a t i o n r e g i o n and the gas source.  3.2.2.2  The New High Temperature Gas C e l l  Although the o l d gas c e l l wide range o f moderately temperature  v o l a t i l e m a t e r i a l s i t s upper  range i s l i m i t e d .  most metals, temperature  can be used t o study a  To produce  vapors o f  i n excess o f 600°C are  r e q u i r e d , and so another h i g h temperature  gas c e l l was  designed and c o n s t r u c t e d . The primary aim was to design a gas c e l l  t o f i t the e x i s t i n g spectrometer and the  best s t a r t i n g p o i n t was the o l d gas c e l l .  F i g . 3.7 shows  - 104 -  2  1  Stainless steel tubing Thermocouple  9 10  Boron nitride heater holder Pt wire  3  Heater connection  4  Machinable ceramic support ring  5 6 7 8  Flange cooling Brass flange Viton 'o' ring Boron nitride support tubing  11 12 13 14 15 16 17  Bayonet fitting Removable heat-shield Sample holder (cup) Molybdenum nut Demountable cavity C window Window holder  3.7. A schematic diagram of the new temperature gas c e l l .  high  - 105  a schematic gas  cell.  those old  -  r e p r e s e n t a t i o n o f t h e new The  critical  high  dimensions are unchanged.  m a j o r c h a n g e s b e t w e e n t h i s new  gas  cell will  temperature  be m e n t i o n e d  gas  cell  and  c e l l , a new  h e a t e r was  designed.  3.7).  cup  (See  T h e s e a r e h e l d t o g e t h e r by  cement ( m e l t i n g p o i n t ^2000°C).  A  A Viton the source  These  t e m p e r a t u r e o f ^200°C.  of the brass was  f l a n g e was  100°C, t h e r e b y  The  temperature.  By  '0'  cell  r i n g s can w i t h s t a n d  d e s i g n i n g the top p a r t  prevented.  The  a of  overheating brass  c o u l d be m a i n t a i n e d  preventing deformation  to  of the  flange at below perspex  stand-off.  entire  gas  window h o l d e r and s a m p l e cup  refractory  t o r e s e m b l e a vacuum f l a s k ,  a l s o a i r c o o l e d , and  high voltage  a  '0' r i n g i s u s e d t o s e a l t h e gas  chamber.  cell  the i n s e r t i n  chromel-alumel  t h e r m o c o u p l e i s used t o measure the  t h e gas  with  This h e a t i n g element i s p l a c e d  a t h i n w a l l e d boron n i t r i d e  Fig.  main  g r o o v e on e a c h s i d e i n w h i c h p l a t i n u m w i r e i s  n o n i n d u c t i v e l y wound. in  in  The  element o f the h e a t e r i s a d i s c o f boron n i t r i d e a spiral  the  here.  Instead of the t u b u l a r boron n i t r i d e heater t h e o l d gas  Only  c e l l , except  f o r the b r a s s  flange,  t h e molybdenum n u t w h i c h h o l d s  i n p l a c e , i s made o f s t a i n l e s s  steel.  the A l l  - 106 -  the j o i n t s are welded and the use o f screws was avoided as these tend to s t i c k a t h i g h temperatures.  An a d d i -  t i o n a l heat s h i e l d was used t o prevent heat l o s s the heater and the i o n i z a t i o n  chamber.  from  To accomodate  t h i s a d d i t i o n a l heat s h i e l d , the o u t e r diameter o f the ionization  chamber had t o be reduced.  The  ionization  chamber i s a detachable cup which i s connected t o the r e s t of the gas c e l l by means o f a snug bayonet ensures s u f f i c i e n t heat  f i t t i n g which  transfer.  The r a t h e r low m e l t i n g p o i n t o f A l (660°C) l i m i t s the use o f 0.0025 mm A l f o i l as the window m a t e r i a l . 20 ug/cm  2  2 and 40 yg/cm C f o i l s were used i n s t e a d .  These  carbon f o i l s are prepared by vacuum s u b l i m a t i o n o f carbon onto 3" x 1" g l a s s s l i d e s , and were s u p p l i e d by Yissum Research  Development Company, I s r a e l .  These f o i l s are  separated from the s l i d e by f l o a t i n g on water, and are then mounted on a copper window h o l d e r and, b e i n g f r a g i l e are  a l l o w e d t o d r y i n the absence  disturbance. ring  o f any k i n d o f a  The window h o l d e r i s b a s i c a l l y a copper  (cross s e c t i o n i s shown i n F i g .  3.7) with  wires spot welded to form a s u p p o r t i n g mesh.  copper These  carbon windows are very f r a g i l e by v i r t u e o f t h e i r extremely s m a l l ,  ^0.0001 - 0.0002 mm,  hence have t o be handled extremely  t h i c k n e s s and  carefully.  - 107  I t was  -  found t h a t the e l e c t r i c a l r e s i s t a n c e o f  boron n i t r i d e breaks  down a t temperatures  higher  than  700°C, thus making the h e a t e r s h o r t to the gas c e l l r e t a r d i n g v o l t a g e s i n excess o f %1000V.  This r e s u l t s  a breakdown o f the r e t a r d i n g v o l t a g e used to scan electron energies.  T h i s problem was  at  s o l v e d by  in  the  isolating  the h e a t e r power supply from the main power l i n e u s i n g an i s o l a t i o n transformer.  The h i g h e s t temperature  by u s i n g t h i s gas c e l l was  1100°C.  r e g i o n o f s i l v e r atoms was  o b t a i n e d at t h i s  ( F i g . 3.8).  achieved  A spectrum o f the  3d  temperature  However, the h e a t i n g element burnt  out  b e f o r e s u f f i c i e n t l y good c o u n t i n g s t a t i s t i c s were a c h i e v e d . V a r i o u s types o f boron n i t r i d e heaters were t r i e d out,  but  none o f these l a s t e d l o n g enough at 1100°C to produce a good enough spectrum.  The  gas c e l l has been  maintained  at ^1025°C f o r days without burning out the h e a t e r ,  but  u n f o r t u n a t e l y , t h i s temperature i s not h i g h enough to produce a s i l v e r 3d spectrum.  I t can be concluded  that  1025°C i s the upper temperature l i m i t f o r a gas c e l l  of  t h i s d e s i g n , the l i m i t i n g f a c t o r b e i n g the m e l t i n g p o i n t of platinum.  The  c a l c i u m , s t r o n t i u m and barium s p e c t r a  r e p o r t e d i n t h i s t h e s i s were o b t a i n e d u s i n g t h i s new temperature gas  cell.  high  - 108  -  3 O  o  8 0 i  60-  40  H  20  H  50  60  70  Channel Fig.  3.8.  80  90  100  number  A p r e l i m i n a r y spectrum of the Ag 3d r e g i o n r e c o r d e d a t 1100°C u s i n g the new h i g h temperature gas c e l l . E x c i t a t i o n source i s A l Ka x - r a y s .  - 109 -  3.2.3  The E i n z e l  Lens  The e l e c t r o n s l e a v i n g the gas c e l l through the opening i n the bottom o f the gas c e l l are focused onto the entrance a p e r t u r e o f the a n a l y s e r by a three-element l e n s ( F i g . 3.9). The c h a r a c t e r i s t i c s o f such l e n s e s can 4 be found elsewhere  .  The three elements  are o f equal  diameter and the r a d i a l axes o f these c y l i n d e r s  include  the r a d i a l axes o f the e x i t hole from the gas c e l l and the entrance h o l e to the a n a l y s e r .  The top element i s  p r o v i d e d with f i v e rows o f h o l e s t o f a c i l i t a t e  pumping,  i n o r d e r t o enable the e l e c t r o n s to have a c o l l i s i o n path through the l e n s .  free  The middle element i s i s o l a t e d  from the upper and lower elements by means o f 2 mm-diameter sapphire The  balls. focusing  i s achieved by grounding the two  o u t s i d e elements while a p p l y i n g a p o s i t i v e v o l t a g e (between + 150V and + 7 00V;  determined e m p i r i c a l l y f o r  maximum counts and optimum l i n e shapes) t o t h e middle element.  Such a l e n s i s a l s o r e f e r r e d t o as ' e i n z e l ' o r  ' u n i p o t e n t i a l ' l e n s as opposed  t o an 'asymmetric  voltage'  l e n s i n which the three elements are s u p p l i e d with three different  voltages.  T h i s e i n z e l l e n s i s made o f b r a s s .  - 110 -  F i g . 3.9. The three element e i n z e l lens.The h o l e s i n the top element f a c i l i t a t e pumping.  - Ill -  3.2.4  The E l e c t r o n Energy A n a l y s e r and The Operating Mode o f the Spectrometer.  E l e c t r o n s focused by the e i n z e l l e n s e n t e r a h e m i s p h e r i c a l e l e c t r o s t a t i c a n a l y s e r i n which two dimensional  p o i n t - t o - p o i n t f o c u s i n g occurs a f t e r 180°  d e f l e c t i o n i n the f i e l d between the two c o n c e n t r i c hemispheres  ( F i g . 3.1). The e l e c t r o n d i s p e r s i o n p r o -  p e r t i e s and f o c u s i n g a c t i o n o f h e m i s p h e r i c a l  electro5  s t a t i c a n a l y s e r s were f i r s t i t has subsequently  d i s c u s s e d by P u r c e l l  been developed  , and  and i t s p r o p e r t i e s  d i s c u s s e d by a number o f r e s e a r c h e r s  6  1 0  .  With the a n a l y s e r s e t to pass e l e c t r o n s o f energy E (eV) R=  along a c i r c u l a r path o f r a d i u s R where, (3.1)  (R. + R out )/2 n  the p o t e n t i a l o f the i n n e r hemisphere, V ^ , should be n  set to  V.  i n  = E ( 3 - 2 R/R. ) Q  (3.2)  n  while t h a t on the outer hemisphere, V  out'  should be  set to V  out  = E ( 3 - 2R/R Q  out  )  (3.3)  - 112 -  where R radii  n  and R  o u t  r e f e r t o i n n e r and o u t e r hemisphere  respectively. F o r equal entrance and e x i t h o l e diameters, w, and  for  an e l e c t r o n beam e n t e r i n g the a n a l y s e r w i t h a h a l f  angle o f 0° then the a n a l y s e r r e s o l u t i o n AEj_/E  o  i s given  by  AE, E  o  w  = — 2R  (3.4)  where AE^ i s the f u l l width a t h a l f maximum (FWHM) o f the a n a l y s e r c o n t r i b u t i o n t o a peak i n a spectrum. i m p l i c a t i o n o f Eqn. depends on E . Q  An important  3.4 i s t h a t the FWHM o f a given peak  The a n a l y s e r c o n t r i b u t i o n t o the FWHM can  be kept constant f o r the e n t i r e range o f k i n e t i c e n e r g i e s of  the emitted e l e c t r o n s by p r e r e t a r d i n g o r p r e a c c e l e r a t i n g  the e l e c t r o n s t o the f i x e d a n a l y s e r pass energy, E . Q  The values f o r R. and R . f o r t h i s in out  spectrometer r  are 8.25 cm and 12.25 cm r e s p e c t i v e l y , the hemispheres being made o f s o l i d b r a s s .  These hemispheres are coated  with benzene soot, which improves the experimental r e s o l u t i o n c o n s i d e r a b l y , and a l s o g r e a t l y reduces t h e background due to s c a t t e r e d e l e c t r o n s . e x i t holes are 1.6 mm i n diameter r e s o l u t i o n c a l c u l a t e d u s i n g Eqn.  The entrance and  and the i n s t r u m e n t a l 3.4 i s =0.8%. F o r a  - 113 -  pass energy o f 50eV the i n s t r u m e n t a l the FWHM o f a peak i s - 0.4eV. 1 keV e l e c t r o n i s r e t a r d e d an absolute  contribution to  T h i s means t h a t i f a  t o 50eV  i t would produce  energy r e s o l u t i o n o f 0.4eV, o r a percentage  r e s o l u t i o n o f the i n i t i a l k i n e t i c energy o f 0.04%. A l though t h i s r e s o l u t i o n can be f u r t h e r improved by decreasing  the entrance and e x i t s l i t widths i t can  lead to a considerable The i n s t r u m e n t a l  loss i n s e n s i t i v i t y . c o n t r i b u t i o n t o the FWHM can be  changed by a l t e r i n g the a n a l y s e r can be achieved by a p p l y i n g  pass energy, E . Q  the a p p r o p r i a t e  This  voltages  t o the two hemispheres, which are s u p p l i e d by a H a r r i s o n 6205 B Dual DC Power Supply.  The r e t a r d i n g  voltage i s  a p p l i e d between the gas c e l l and the upper element o f the e i n z e l l e n s . binding  The r e t a r d i n g v o l t a g e  i s r e l a t e d t o the  energy o f an e l e c t r o n k, E^(k) by the Eqn.  Retarding V o l t a g e = x-ray energy - E ^ ( k ) - E - C Q  (3.5). where C i s a c o r r e c t i o n which i n c l u d e s  the work  function  of the chamber and the r e t a r d a t i o n e f f e c t s due t o a net p o s i t i v e charge i n the cone o f i o n i z a t i o n .  More w i l l be  s a i d about t h i s i n the s e c t i o n on energy c a l i b r a t i o n .  - 114 -  S p e c t r a l scanning i s t h e r e f o r e a c h i e v e d by v a r y i n g the r e t a r d i n g v o l t a g e and d e t e c t i n g the e l e c t r o n s e m i t t e d w h i l s t keeping the v o l t a g e s on the a n a l y s e r hemispheres, and hence the pass energy constant.  3.2.5  Helmholtz C o i l s  A magnetic f i e l d o f 1.OmG p e r s i o n o f about 0.2 mm  can r e s u l t i n a d i s -  f o r a hemispherical  electro-  s t a t i c a n a l y s e r w i t h a 20 cm-radius and a 1000e.V e l e c t r o n measured w i t h 0.04% resolution ''" T h i s makes i t 1  important t o keep the magnetic f i e l d as low as p o s s i b l e i n the region o f the source chamber and the a n a l y s e r . In  a d d i t i o n to the e a r t h ' s magnetic  f i e l d of approxi-  mately 500 mG, s t r a y f i e l d s caused by c e r t a i n tal  experimen-  arrangements, e.g. a wire wound furnace can be a  s e r i o u s problem.  These  f i e l d s can be c a n c e l l e d by  u s i n g Helmholtz c o i l s , o r f e r r o m a g n e t i c s h i e l d i n g such as Mu metal.  The l a t t e r i s i n c o n v e n i e n t due t o machining  and a c c e s s i b i l i t y and so i n t h i s case, three p a i r s o f Helmholtz c o i l s ,  four f e e t square, mounted a t r i g h t  angles to each o t h e r are used.  These c o i l s which com-  p r i s e 50 t u r n s o f 20 gauge i n s u l a t e d copper w i r e , are  - 115 -  powered by Lambda r e g u l a t e d DC power s u p p l i e s LH 122AFM) and may be i n d i v i d u a l l y  (Model  adjusted t o o b t a i n  optimum count r a t e s and peak shapes.  3.2.6  The vacuum System  T y p i c a l gas pressures -2 chamber are from 10  r e q u i r e d i n the i o n i z a t i o n  t o 1 t o r r . The pressure  i n the  r e s t o f the system has t o be c o n s i d e r a b l y lower than t h i s so t h a t the e j e c t e d e l e c t r o n s are d e t e c t e d before going c o l l i s i o n s .  The normal o p e r a t i n g p r e s s u r e  a n a l y s e r r e g i o n i s about 5 x 10 pressure  i s maintained  i n the  t o r r and t h i s low  by employing d i f f e r e n t i a l pumping  between the gas c e l l aperture and the a n a l y s e r slit.  under-  entrance  T h i s i s p r o v i d e d by an o i l d i f f u s i o n pump connected  to the source  chamber  (the same d i f f u s i o n pump i s used  f o r f a s t pumping sample  gases).  Since the source housing  communicates w i t h t h e  a n a l y s e r o n l y through the 1.6 mm-diameter opening, the a n a l y s e r , as w e l l as the d e t e c t o r , i s spared by c o r r o s i v e gases.  from attack  The r a t h e r cumbersome task o f frequent  c l e a n i n g o f the a n a l y s e r i s thus  avoided.  - 116  The  -  a n a l y s e r chamber i s pumped by a 1500  l/sec  o i l d i f f u s i o n pump. Under normal o p e r a t i n g c o n d i t i o n s the x-ray tube volume i s i s o l a t e d from the r e s t o f the spectrometer.  However the two  volumes can be  unified  by opening a v a l v e f o r rough pumping, thereby e l i m i n a t i n g rupture of the d e l i c a t e x-ray tube window. The pressure  i n the x-ray tube, source  and the a n a l y s e r housing separate a NRC  chamber  are monitored by u s i n g three  i o n i z a t i o n gauges (NRC  538,  i n conjunction  i o n gauge c o n t r o l u n i t , type 710B).  S t a r t i n g from  atmospheric pressure normal o p e r a t i n g p r e s s u r e s u s u a l l y be obtained  i n about 90 minutes.  3.2.7  System  Thfe D e t e c t o r  The  spectrometer  can  geometry i s such t h a t only  e l e c t r o n s e j e c t e d i n a d i r e c t i o n 90° to the  with  the  direction  of the e x c i t i n g r a d i a t i o n can e n t e r the a n a l y s e r .  The  energy analysed e l e c t r o n s leave the e x i t hole and  strike  the d e t e c t o r which i n t h i s case i s a channel e l e c t r o n multiplier mode.  ( M u l l a r d B319  A v o l t a g e of  the channeltron  AL)  +300V  o p e r a t i n g i n the s a t u r a t e d a p p l i e d t o the f r o n t end  a c c e l e r a t e s the e l e c t r o n s , and  the  of  signal  - 117 is amplified  across the d e t e c t o r by a p p l y i n g a  p o s i t i v e v o l t a g e o f +3.3kV  to the output.  Pulse  counting i s used f o r data a c q u i s i t i o n and c o n v e n t i o n a l p u l s e counting equipment i s used f o r t h i s purpose. s i g n a l from the m u l t i p l i e r i s passed through  The  a modified  V a r i a n type p r e - a m p l i f i e r to an a m p l i f i e r / a n a l y s e r (Nuclear E n t e r p r i s e s ) and a r a t e meter (Nuclear E n t e r prises) .  The p u l s e s are counted  as a f u n c t i o n o f r e -  t a r d i n g v o l t a g e , repeated scanning i s performed and the data s t o r e d i n a Nuclear Chicago  multichannel analyser.  T h i s was l a t e r r e p l a c e d by a PDP 8/e computer to a l l o w for  greater f l e x i b i l i t y .  F o r d e t a i l s see the s e c t i o n  on the i n t e r f a c i n g o f a PDP 8/e  minicomputer to the  spectrometer.  3.2.8  Performance  The peak width  AE^ measured from a spectrum i s  made up o f a c o n v o l u t i o n o f a number o f c o n t r i b u t i o n s . Assuming t h a t a l l these components have Gaussian shapes, the measured h a l f width by  line  can be approximated  12  AE  2  =  2 2 + AE k 'P  AE.  +  AE  2 a  (.3.6)  - 118  -  where AEj, i s the n a t u r a l width o f the l e v e l from which the e l e c t r o n was  e j e c t e d , and  AE p  and AE a  are the h a l f  widths of the photon source and the a n a l y s e r r e s p e c t i vely . A peak width o f 1.2eV  can be observed  Is l e v e l u s i n g A l K a x - r a y s . instrument  The  f o r the  Ne  r e s o l u t i o n o f the  i s high enough to d i s t i n g u i s h two peaks w i t h  a s e p a r a t i o n of as low as ^ l e V  under favourable con-  d i t i o n s depending on the r e l a t i v e i n t e n s i t i e s .  For  example, the m u l t i p l e t s p l i t t i n g of the 0 Is l e v e l of molecular oxygen can be observed  ( F i g . 3.10) .  At a  sample pressure of 0.1  t o r r , about 2000 counts/sec  be obtained f o r the Ne  Is l e v e l .  can  However, more weak  s a t e l l i t e peaks produced by m u l t i e l e c t r o n e x c i t a t i o n s u s u a l l y take a c o n s i d e r a b l y l o n g e r time to produce s a t i s f a c t o r y counting s t a t i s t i c s .  I t may  be p o s s i b l e  t o improve t h i s s i t u a t i o n by u s i n g p o s i t i o n d e t e c t o r s and thereby  sensitive  f u l l y u t i l i s i n g the two  dimensional  f o c u s i n g c a p a b i l i t y o f the h e m i s p h e r i c a l analyser ''". 1  3.3  I n t e r f a c i n g of a PDP  8/e Minicomputer to the  Phase X-ray P h o t o e l e c t r o n  Gas  Spectrometer  Time averaging with m u l t i - c h a n n e l s c a l e r s  (MCS)  is  o f importance i n x-ray p h o t o e l e c t r o n spectroscopy where  - 119 -  Oxygen  01s • •  • • •  • •  •  •  +-» C D  •  •  o  •  H-ievH • •  •  i 546 F i g . 3.10.  • •  •  ••  •  •  •  • •  i 544 Binding energy  •  1 542 (eV)  X-ray p h o t o e l e c t r o n spectrum of the oxygen Is r e g i o n from 0 obtained w i t h A l K a X-rays 9  - 120 -  the count r a t e i s low. Even when the count r a t e i s comparatively h i g h , a d d i t i o n a l f l e x i b i l i t y and p r e c i s i o n can be o b t a i n e d w i t h a d i g i t a l system.  The  e f f e c t o f low frequency n o i s e can be removed by accumulation o f data over a p e r i o d o f time, p e r f o r m i n g m u l t i p l e scanning where the counts o f one p a r t i c u l a r scan are added t o the sum o f counts from a l l p r e v i o u s scans.  When the c o u n t i n g s t a t i s t i c s are s u f f i c i e n t l y  good, accumulation o f data may be terminated and t h e data may be s t o r e d d i g i t a l l y f o r l a t e r use. A p a r t i c u l a r a p p l i c a t i o n o f a PDP 8/e minicomputer to t h i s data c o l l e c t i o n technique i s d e s c r i b e d here.  Such a computer i s p r e f e r r e d t o c o n v e n t i o n a l  m u l t i - c h a n n e l s c a l e r s f o r a v a r i e t y o f reasons.  The  data storage c a p a c i t y may be r a i s e d by t h e a d d i t i o n o f e x t r a 4K memory modules, and thereby r e s o l u t i o n can be increased.  The i n t e r f a c e and software may be c o n t i n u a l l y  upgraded t o p r o v i d e e x t r a f a c i l i t i e s . The  computer i s programmed t o c o n t r o l most o f  the spectrometer f u n c t i o n s .  A generalized block  diagram o f a microcomputer c o n t r o l l e d experiment i s given i n F i g . 3.11.  The i n t e r f a c e and software  be b r i e f l y d i s c u s s e d here.  will  Block diagram of a microcomputer-controlled experiment DATA ACQUISITION INTERFACE  MONITOR  EXPERIMENT  MICROCOMPUTER  EXPERIMENT CONTROL INTERFACE  g.  3.11.  B l o c k diagram of a m i c r o c o m p u t e r - c o n t r o l l e d  experiment.  - 122 -  3.3.1  The I n t e r f a c e  P u l s e s from the spectrometer channel m u l t i p l i e r are i n p u t to the 1 2 - b i t up/down c o u n t e r .  A device  code i s a s s i g n e d t o t h i s counter which enables the contents t o be t r a n s f e r r e d to the computer accumul a t o r a t a p p r o p r i a t e times d u r i n g the scanning r o u t i n e . The counts are then added t o those a l r e a d y s t o r e d i n the channel which i s b e i n g scanned a t t h a t p a r t i c u l a r The byte s i z e o f the PDP 8/e i s 12 b i t s .  time.  This necessi-  t a t e s the use o f double p r e c i s i o n storage and a r i t h m e t i c . A channel corresponds t o a n e i g h b o u r i n g p a i r o f 12 b i t bytes.  The maximum number o f counts t h a t can be accumu24  l a t e d per channel without c a u s i n g o v e r f l o w i s (2 or 16,777,215.  -1)  In p r a c t i c e t h i s i s never a c h i e v e d .  The spectrometer r e t a r d i n g v o l t a g e ramp  (analysing  energy f o r e l e c t r o n s ) i s c o n t r o l l e d through two d i g i t a l to analog c o n v e r t e r s (DAC) Z and X.  The r e t a r d i n g v o l t a g e  i s produced by a Spellman Super r e g u l a t e d h i g h v o l t a g e power supply (Model SRM3P10KD) which i s d r i v e n by the a p p r o p r i a t e programming v o l t a g e from the Z and X DAC's. The Z DAC produces the programming v o l t a g e w h i l e the X DAC p r o v i d e s the necessary v o l t a g e increments. i s a one t o one correspondence  There  between the number o f  - 123 -  v o l t a g e increments per scan and the number o f channels. The spectrum can be d i s p l a y e d on an o s c i l l o s c o p e ( T e k t r o n i x Type RM 504) o r on a r e c o r d e r  (Nuclear C h i -  cago X-Y P l o t t i n g System Model 7590 C ( S ) ) , both cont r o l l e d by two DAC's, X and Y.  The X DAC  (which a l s o  serves to increment the r e t a r d i n g voltage) c o n t r o l s the d i s p l a y i n the x - a x i s and the Y DAC  t h a t i n the y - a x i s .  These two d i s p l a y modes are c o n t r o l l e d by d i f f e r e n t software s u b r o u t i n e s . In a d d i t i o n , data can be output to a t e l e t y p e o r punched on paper t a p e .  The t e l e t y p e i s a l s o used to  i n p u t the spectrometer c o n t r o l commands.  3.3.2  The software  Computer programs are most c o n v e n i e n t l y w r i t t e n i n h i g h l e v e l languages such as FORTRAN. r e g a r d l e s s of how  However,  e f f i c i e n t these compilers may  be,  the code produced almost always o c c u p i e s more memory than assembler language code, and the v e r y nature o f the minicomputers  and the small amount o f main memory  a v a i l a b l e make the use o f such c o m p i l e r s i n e f f i c i e n t  and  cumbersome when compared to assembly language programming. The PDP  8/e minicomputer  used i n t h i s work has a memory  - 124 -  of  8K, 12 b i t w o r d s .  relatively  F o r more e f f i c i e n t u s e o f t h i s  s m a l l memory, t h e e n t i r e c o n t r o l p r o g r a m  was w r i t t e n i n P r o g r a m A s s e m b l y L a n g u a g e I I I (PAL I I I ) w h i c h was s p e c i a l l y d e v e l o p e d  f o r t h e PDP 8 l i n e o f  . . . computers by t h e D i g i t a l Equipment In d e s i g n i n g the software  . 13 Corporation  f o r multi-channel  scaling,  t h e e m p h a s i s h a s b e e n p l a c e d on e a s e o f o p e r a t i o n o f t h e spectrometer commands.  by u s i n g the t e l e t y p e t o g i v e t h e necessary  The c u r r e n t p r o g r a m o c c u p i e s  the f i r s t  4K o f  t h e memory o f w h i c h 15 36 l o c a t i o n s a r e p e r m a n e n t l y cated  f o r data  storage.  A software  allo-  flow diagram i s  g i v e n i n F i g . 3.12 w i t h o n l y t h e m a j o r f u n c t i o n s shown. T h i s program i s w r i t t e n i n t h e form o f a c o l l e c t i o n o f s u b r o u t i n e s , which p e r m i t s m o d i f i c a t i o n and/or update o f the software  w i t h t h e minimum amount o f r e s t r u c t u r i n g .  A maximum o f t h r e e r e t a r d i n g e n e r g y r e g i o n s c a n be s c a n n e d a t any g i v e n t i m e .  Seven s p e c t r o m e t e r  commands  a r e a v a i l a b l e ; A, B, C, D, E , F a n d G, c o r r e s p o n d i n g seven d i f f e r e n t r o u t i n e s .  Command A:  These a r e as f o l l o w s :  Initializing routine.  v o l t a g e , r a t e o f scan,  to  The i n i t i a l r e t a r d i n g  retarding voltage  increment,  number o f s c a n s r e q u i r e d a n d t h e number o f c h a n n e l s f o r  MAOOR FUNCTION FLOW DIAGRAM SET STARTING VOLTAGE  6ET  HAVE ALL SCANS BEEN COMPLETED J  SCAN SPEED SCAN REGIONS ALTERNATELY 1  H  U1  » DISPLAY DATA  Fig.  3.12.  Major f u n c t i o n f l o w diagram o f t h e m u l t i - c h a n n e l  scaling  program.  - 126 -  up t o three routine.  s p e c t r a l r e g i o n s can be i n p u t using  this  Scanning r a t e s o f 0.05 s e c . t o ( a maximum o f )  4 sec./channel are a v a i l a b l e .  The l a r g e s t v o l t a g e i n -  crement a v a i l a b l e i s 0.38V and each s p e c t r a l r e g i o n can have up t o 256 channels.  Command B: initial  T h i s enables a r o u t i n e to pre-check the  and f i n a l v o l t a g e s  Command C:  f o r each r e g i o n .  Scan r o u t i n e .  are requested,  When more than two regions  two o p t i o n s are a v a i l a b l e .  r e g i o n may be scanned a f t e r completing scans r e q u i r e d f o r the f i r s t scanned a l t e r n a t e l y .  The second  the number o f  r e g i o n o r these can be  T h i s second o p t i o n i s u s e f u l i n  the c a l i b r a t i o n o f b i n d i n g e n e r g i e s .  The program i n t r o -  duces a pause a t the s t a r t o f each scan f o r the purpose of f l y - b a c k suppression.  The r o u t i n e can be i n t e r r u p t e d  by t y p i n g any key-board c h a r a c t e r on the t e l e t y p e .  Command D:  Display routine.  l a t e d data t o be d i s p l a y e d . 0-4  T h i s allows the accumuComputer switch r e g i s t e r s  a l s o serve as gain c o n t r o l switches f o r t h i s r o u t i n e .  Command E:  Erase r o u t i n e .  storage l o c a t i o n s .  T h i s c l e a r s the a p p r o p r i a t e  - 127 -  Command F:  Three p o i n t smooth r o u t i n e .  smoothing r o u t i n e r e p l a c e s the contents channel,  This  digital  o f the i - t h  y. by y.' where,  (3.7)  i-1  However, the use o f such smoothing procedures can r e s u l t in undesirable  changes i n peak shapes and t h e r e f o r e  should be used with utmost  Command G:  care.  Data t r a n s f e r r o u t i n e .  The data can be  p l o t t e d on the x-y r e c o r d e r , typed on the t e l e t y p e , o r punched on paper The  tape.  complete symbolic  appendix.  program i s l i s t e d i n the  The number o f regions and/or the number o f  channels can be i n c r e a s e d without any d i f f i c u l t y  using  the p r e s e n t l y unused, second 4K block o f the memory.  3.4  Calibration of Electron  Eqn.  Spectra  3.5 i n s e c t i o n 3.2.4  r e l a t e s the r e t a r d i n g  energy t o the b i n d i n g energy o f a given e l e c t r o n . equation  This  can t h e r e f o r e be used to o b t a i n the experimental  - 128  -  b i n d i n g e n e r g i e s from the measured r e t a r d i n g v o l t a g e s . However, the c o r r e c t i o n f a c t o r , C, i n eqn.  3.5  depends  on the type o f sample and the pressure i n s i d e the 14 i o n i z a t i o n chamber determined  , which means t h a t C has to be  f o r each p a r t i c u l a r experimental c o n d i t i o n .  This can be achieved by mixing the sample gas w i t h a s u i t a b l e c a l i b r a n t gas and then o b t a i n i n g the electron spectra.  photo-  The core l e v e l b i n d i n g e n e r g i e s of  noble gases, and a few o t h e r more common gases such as N  2'  °2  a  r  e  a  c  c  u  r  a  t  e  x  Y  known ^, and these gases can 1  be  used as c a l i b r a n t s , and hence the c o r r e c t i o n f a c t o r C can be  3.5  calculated.  Data A n a l y s i s  I t i s o f t e n necessary to c o r r e c t the data o b t a i n e d by the methods d i s c u s s e d e a r l i e r i n t h i s chapter f o r background, and c o n t r i b u t i o n s from s a t e l l i t e  x-rays.  In o r d e r to o b t a i n accurate peak p o s i t i o n s ( b i n d i n g energies) and areas o f c l o s e l y spaced peaks, p a r t i c u l a r l y o f m u l t i p l e peak envelopes,  i t i s necessary to separate  these i n t o t h e i r component s i n g l e peaks.  For a c c u r a t e  peak d e c o n v o l u t i o n s i t i s necessary t o know the p r e c i s e peak shapes and background.  The peak shapes observed i n  x-ray p h o t o e l e c t r o n s p e c t r a are a c o n v o l u t i o n o f s e v e r a l f a c t o r s such as e x c i t i n g x-ray l i n e shape, a n a l y s e r l i n e  - 129  shape,possible  -  nonuniform specimen c h a r g i n g ,  a  L o r e n t z i a n h o l e - s t a t e l i f e t i m e c o n t r i b u t i o n and 14 Doppler broadening  .  A number o f mathematical  methods have been d i s c u s s e d elsewhere f o r the deconv o l u t i o n and  smoothing o f data  16  '  17  In t h i s work the s p e c t r a were f i t t e d u s i n g a 18 l e a s t - s q u a r e s program d e s c r i b e d by Fadley  .  Here  s e v e r a l b a s i c peak shapes o f Gaussian o r L o r e n t z i a n form are chosen, and an a s y m p t o t i c a l l y constant i n e l a s t i c t a i l o f v a r i a b l e h e i g h t i s smoothly added to get the best f i t .  The  e f f e c t o f x-ray  s a t e l l i t e s are  i n c l u d e d i n the b a s i c peak shape chosen. i s considered All  The  background  linear.  the b i n d i n g energy v a l u e s r e p o r t e d i n t h i s  t h e s i s were r e p r o d u c i b l e to w i t h i n O.leV, however, the u n c e r t a i n t y due  to v o l t a g e measurement i s  ±0.2eV.  - 130  -  REFERENCES  1.  M.S.  B a n n a , B. W a l l b a n k , D.C.  Frost, CA.  McDowell,  a n d J.S.H.Q. P e r e r a , J . Chem. P h y s . 6_8, 5459 2.  K. S i e g b a h n , C  (1978)  N o r d l i n g , A. F a h l m a n , R. N o r d b e r g ,  K. H a m r i n , J . Hedman, G. J o h a n s s o n , T. S. - E. K a r l s s o n , I . L i n d g r e n , Atomic, Molecular,  Bergmark,  a n d B. L i n d b e r g ,  and S o l i d S t a t e S t r u c t u r e  "ESCA:  Studied  b y Means o f E l e c t r o n S p e c t r o s c o p y " , N o v a A c t a R e g i a e Soc.  S c i . U p s a l i e n s i s , S e r I V , V o l . 20  ( A l m q v i s t and  W i k s e l l s , S t o c k h o l m , 1967) 3.  K. S i e g b a h n , J . E l e c t r o n S p e c t r o s c . 3  4.  (1974)  E. H a r t i n g , and F.H.  Read, " E l e c t r o s t a t i c L e n s e s "  ( E l s e v i e r , Amsterdam, E.M.  6.  J.A. S i m p s o n , Rev. S c i . I n s t .  7.  A.M. 1271  Skerbele,  P h y s . Rev. 5_4, 818  and E.N.  (1938)  35_, 1698  (1964)  L a s s e t t r e , J . Chem. P h y s . 40,  (1964)  J.A. S i m p s o n , a n d C E . 3805  9.  Purcell,  1976)  5.  8.  R e l a t . Phenom. 5_,  K u y a t t , J . A p p l . P h y s . 37,  (1966)  CE.  K u y a t t , a n d J.A. S i m p s o n , Rev. S c i . I n s t .  103  (1967)  10.  H.Z.  S a r - E l , Rev. S c i . I n s t . 4 1 , 561  11.  T.A.  Carlson,  (.1970)  " P h o t o e l e c t r o n and Auger  ( P l e n u m P r e s s , New  Y o r k , 19 75)  38,  Spectroscopy"  - 131 -  12.  A. B a r r i e ,  "Handbook o f X - r a y a n d U l t r a v i o l e t  electron Spectroscopy"  D. B r i g g s , E d i t o r  Photo-  (Heyden,  L o n d o n , 19 77) 13.  Introduction  t o Programming"  D i g i t a l Equipment C o r p o r a t i o n , 14.  K. S i e g b a h n , C. N o r d l i n g , P.F.  PDP-8 Handbook S e r i e s , Maynard, Massachusetts  G. J o h a n s s o n , J . Hedman,  H e d e n , K. H a m r i n , U. G e l i u s , T. B e r g m a r k , L.O. Werme,  R. Manne, a n d Y. B a e r , "ESCA A p p l i e d (North-Holland, 15.  G. J o h a n s s o n , J . Hedman, A. B e r n d t s s o n , M. K l a s s o n ,  295  (1973) R e l a t . Phenom. 6_  f  (1975)  H. E b e l , a n d N. G u r k e r , J . E l e c t r o n S p e c t r o s c . Phenom. 5, 799  18.  and  R e l a t . Phenom. 2_,  G.K. W e r t h e i m , J . E l e c t r o n S p e c t r o s c . 239  17.  Molecules"  A m s t e r d a m , 1969)  R. N i l s s o n , J . E l e c t r o n S p e c t r o s c .  16.  t o Free  C.S. F a d l e y , Berkeley  19 70  UCRL-19535)  Relat.  (1974)  Ph.D. T h e s i s ,  University of California,  (Lawrence B e r k e l e y L a b o r a t o r y  Report  - 132 -  CHAPTER FOUR  X-RAY PHOTOELECTRON SPECTROSCOPY OF GROUP I A AND  4.1  I I A FREE METAL ATOMS  Introduction  The t e c h n i q u e  of photoelectron spectroscopy  applied  t o gaseous systems p r o v i d e s a d i r e c t , unambiguous ment o f c o r e b i n d i n g e n e r g i e s .  F o r most atomic  measure-  species  a c c u r a t e b i n d i n g e n e r g i e s have o n l y been measured f o r 1-3 valence  levels.  The e x p e r i m e n t a l  situation with  regard  t o c o r e l e v e l s i s q u i t e u n s a t i s f a c t o r y s i n c e o n l y a few 4-7 atoms o t h e r t h a n t h e r a r e g a s e s h a v e b e e n s t u d i e d . a r e s u l t , w o r k e r s r e q u i r i n g f r e e atom c o r e b i n d i n g have had t o r e s o r t t o v a r i o u s a p p r o x i m a t i o n s v a l u e s from other p e r t i n e n t experimental  data  However, a s p o i n t e d o u t by S h i r l e y a n d  8 co-workers,  these  The m o s t  emission  v a l u e s from measurements on s o l i d s w i t h o p t i c a l f o r f r e e atoms.  energies  to obtain  data.  p o p u l a r o f t h e s e methods i s t o combine x - r a y  As  s u c h a n a p p r o a c h may r e s u l t i n a n e s t i m a t e  f o r t h e b i n d i n g energy which i s t o o low because o f  - 133 -  differential  extra-atomic r e l a x a t i o n i nthe hole states  involved i n x-ray emission.  As mentioned i n Chapter  Two t h e c o r e l e v e l b i n d i n g e n e r g i e s o f m e t a l s standard state are systematically t h o s e o f t h e f r e e atoms.  s e v e r a l eV l o w e r  than  The r e d u c t i o n i n b i n d i n g e n e r g y  for the inner core l e v e l s are expected than  i n the  t o be g r e a t e r  t h a t f o r t h e o u t e r c o r e l e v e l s and t h e r e f o r e t h e  f r e e atom x - r a y e n e r g i e s s h o u l d be s y s t e m a t i c a l l y  larger  than those of the corresponding t r a n s i t i o n s i n the m e t a l l i c s t a t e , thus r e s u l t i n g  i n lower values f o r estimated  free  atom b i n d i n g e n e r g i e s , when x - r a y e m i s s i o n d a t a f o r t h e solid  s t a t e are used.  S i n c e modern d a y b i n d i n g e n e r g y  c a l c u l a t i o n s are c a r r i e d out a t a greater p r e c i s i o n  than  9-11 ever b e f o r e ,  d i r e c t e x p e r i m e n t a l f r e e atom b i n d i n g  e n e r g i e s have become more a n d more d e s i r a b l e . The p r e s e n t w o r k i s a p a r t o f c o n t i n u i n g e f f o r t s this  l a b o r a t o r y to extend  spectroscopy  the realm of x-ray photoelectron  (XPS) t o a t o m i c  species. In t h i s chapter the  x-ray p h o t o e l e c t r o n s p e c t r a o f sodium, potassium,  rubidium,  cesium  (group  I A ) , magnesium, c a l c i u m , s t r o n t i u m and  barium  (group  IIA) are presented.  A p a r t o f t h e work 12  d e s c r i b e d i n t h i s c h a p t e r was p u b l i s h e d e l s e w h e r e . r e s u l t s permit examination core binding energies.  from  These  of various past estimates of  In conjunction with the corres-  ponding values i n the s o l i d  ( r e f e r e n c e d t o t h e vacuum  - 134 -  level)  these  r e s u l t s a l s o make p o s s i b l e t h e d e t e r m i n a t i  o f t h e 'phase t r a n s i t i o n s h i f t ' ,  AE^,  a  quantity of  c o n s i.d,e r a b,l,e c u r r e n t4.-4. i n t e r e s t4.. 11,13-16 S a t e l l i t e s due t o m u l t i e l e c t r o n e x c i t a t i o n observed a t higher binding energies i n most o f t h e c o r e will  level  be b r i e f l y d i s c u s s e d  of these  satellites  t h a n t h e main peak  s p e c t r a r e p o r t e d here. i n t h i s chapter,  quantitative discussion w i l l study  were  h o w e v e r , no  be a t t e m p t e d h e r e .  i n core  These  A  i o n i z a t i o n from the  s o l i d m e t a l s w o u l d be s e v e r e l y hampered by t h e p r e s e n c e of plasmon s t r u c t u r e s i n the r e g i o n o f the s a t e l l i t e s . Experimental next s e c t i o n .  conditions w i l l  The r e s u l t s w i l l  c u s s e d i n S e c t i o n 4.3. Section  4.2  be p r e s e n t e d  and  dis-  The c o n c l u s i o n s a r e g i v e n i n  Experimental  detail  u s e d i n t h i s w o r k was  i n Chapter Three.  Calcium,  b a r i u m w e r e s t u d i e d i n t h e new h i g h c e l l while the in  i n the  4.4.  The s p e c t r o m e t e r in  be d i s c u s s e d  other  t h e o l d gas c e l l  s t r o n t i u m and temperature gas  f i v e m e t a l s were s t u d i e d  (see Chapter  Three).  The t e m p e r a t u r e s u s e d t o o b t a i n t h e x - r a y e l e c t r o n spectra f o r d i f f e r e n t metal are l i s t e d  described  i n T a b l e 4.1.  photo-  atoms  These t e m p e r a t u r e s were  1  - 135 -  T a b l e 4.1  Approximate t e m p e r a t u r e s and t h e gas c e l l window m a t e r i a l u s e d t o o b t a i n t h e f r e e m e t a l atom x - r a y p h o t o e l e c t r o n  Metal  a  atom  spectra  Temperature/  Window  C  Sodium  240  Aluminum  Potassium  190  Aluminum  Rubidium  145  Aluminum  Cesium  140  Aluminum  Magnesium  470  Aluminum  Calcium  690  Carbon  Strontium  640  Aluminum  Barium  740  Carbon  A l u m i n u m windows w e r e 0.0025 m m - t h i c k  ( s u p p l i e d by A l f a 2  C h e m i c a l s ) a n d t h e c a r b o n w i n d o w s w e r e 40 ug/cm mm-thick Israel)  -4 =2x10  ( s u p p l i e d b y Y i s s u m R e s e a r c h D e v e l o p m e n t Company,  - 136  -  measured o u t s i d e the i o n i z a t i o n chamber and do not r e p r e s e n t the p r e c i s e sample  therefore  temperature,  however, t h i s d i f f e r e n c e i s not expected t o exceed 20-30°C.  At temperatures above 660°C carbon windows 2  (40 yg/cm ) were used.  I t was  found t h a t a l l t h r e e  higher temperature metal vapors, c a l c i u m , s t r o n t i u m and barium r e a c t w i t h the carbon windows. between carbon and c a l c i u m vapor was  The  reaction  c o n s i d e r a b l y slower  under the experimental c o n d i t i o n s and hence d i d not pose any major problem.  However, s t r o n t i u m seemed t o  r e a c t r a t h e r v i g o r o u s l y making i t i m p o s s i b l e t o use carbon windows. r e p o r t e d here was  For t h i s reason the s t r o n t i u m spectrum obtained u s i n g an aluminum  window  and hence a t l e s s than optimum o p e r a t i n g p r e s s u r e s . Although barium d i d not r e a c t as v i g o r o u s l y as s t r o n t i u m , the  carbon windows had t o be r e p l a c e d r a t h e r  frequently.  The r e a c t i o n between the metal atoms and the carbon windows was  indicated  by a drop i n the count r a t e .  Sodium and potassium were s l i c e d under then p l a c e d i n the gas c e l l the  toluene and  sample cup covered w i t h  same l i q u i d f o r subsequent h e a t i n g .  Ampoules of  rubidium and cesium were opened under petroleum e t h e r ( b o i l i n g range 65-110°C) and were loaded i n t o the gas c e l l w i t h the sample cup f i l l e d w i t h the same s o l v e n t .  - 137  In  -  a l l cases the s o l v e n t s were removed by pumping  i n s i d e the source chamber b e f o r e the sample heated.  99.9%  pure magnesium powder was  was  loaded  the spectrometer without any p r e c a u t i o n s being  into taken  w i t h regard t o s u r f a c e o x i d a t i o n .  The  same was  with >99.7% pure c a l c i u m f i l i n g s .  The  strontium  sample was rod  prepared by c u t t i n g >99.5% pure s t r o n t i u m  i n t o small p i e c e s .  extremely  done  r e a c t i v e and  oxide l a y e r .  A l l samples s t u d i e d here soon covered with  are  a surface  However, t h i s does not c o n s t i t u t e a  problem s i n c e the oxides do not produce a s i g n i f i c a n t vapor p r e s s u r e under the experimental c o n d i t i o n s used to  o b t a i n the x-ray p h o t o e l e c t r o n s p e c t r a .  barium was  found to be a d i f f i c u l t  Here,  case s i n c e , when  small amounts of the oxide were p r e s e n t , they to  form a r e d d i s h mass making i t d i f f i c u l t  tended  to maintain  an optimum p r e s s u r e i n s i d e the i o n i z a t i o n chamber. has been r e p o r t e d t h a t BaO  It  c r y s t a l s w i t h excess of metal 18  i n the l a t t i c e are deep r e d . mized by c l e a n i n g the barium and then immediately  T h i s problem was  mini-  p i e c e s i n a g l a s s bead j e t ,  immersing these i n n-hexane.  These p i e c e s were then loaded i n t o the gas c e l l under n-hexane and pumped out b e f o r e h e a t i n g . minimized  This  the formation of the s a i d red mass.  procedure  - 138  -  The p o s s i b l e presence of dimers was  r u l e d out  the b a s i s of the vapor p r e s s u r e data obtained  on  from  19 Nesmeyanov  f o r the temperatures r e q u i r e d to produce  the o p e r a t i n g p r e s s u r e s .  The  f o l l o w i n g monomer/dimer  r a t i o s are l i s t e d : Na/Na =71(600K), K/K =369(550K), 2  2  Rb/Rb =482(475K) and Cs/Cs =574(450K). 2  There seems to  2  be no s i m i l a r data on the composition e a r t h metal vapors.  The  of the  alkaline  Hel p h o t o e l e c t r o n s p e c t r a of  c a l c i u m , s t r o n t i u m and barium have been p u b l i s h e d Suzer and co-workers,  and  these do not show any  t h a t can be a t t r i b u t e d to dimers.  by peaks  I t i s concluded  t h e r e f o r e t h a t the dimer c o n c e n t r a t i o n i s n e g l i g i b l e i n a l l cases. two  The  s p e c t r a were recorded a t a minimum of  d i f f e r e n t temperatures  (and t h e r e f o r e pressures)  d i f f e r e n t i a t e between the i n e l a s t i c - l o s s peaks and  to  the  r e a l p h o t o i o n i z a t i o n peaks. A l l s p e c t r a were l e a s t - s q u a r e s f i t t e d to o b t a i n peak p o s i t i o n s , l i n e w i d t h s and  areas u s i n g the program  des-  20 c r i b e d by Fadley. Mg  C a l i b r a t i o n of the Na  Is and Ba 3d l e v e l s was  atom. The  K 2p  21  3d,  performed by i n t r o d u c i n g neon  w i t h the vapor under study and [870.37(9)eV]  I s , Cs  scanning  the Ne  Is l e v e l  a l t e r n t i v e l y with the l e v e l of the metal l e v e l s were s i m i l a r l y c a l i b r a t e d u s i n g  the C Is l e v e l of methane [ 2 9 0 . 9 ( 2 ) e V ] ,  22  while  - 139  the Rb  3p, Ca 2s and Ca 2p l e v e l s were r e f e r e n c e d  u s i n g the known Ar 2\?^^ The  -  Ba 4d and  b i n d i n g energy  [248.62(8)eV].  the Sr 3d l e v e l s were s i m i l a r l y  21  calibrated  with r e s p e c t to the known b i n d i n g energy of the Ne  2s  21 level  [48.47eV],  A l l b i n d i n g e n e r g i e s measured i n  t h i s work have an u n c e r t a i n t y of ±0.2eV.  4.3  R e s u l t s and  4.3.1  Binding  4.3.1.1  Discussion  Energies  Sodium  The  sodium Is spectrum i s shown i n F i g . 4.1.  a l k a l i metal atoms have an unpaired valence  e l e c t r o n i n the  s h e l l , m u l t i p l e t s p l i t t i n g should r e s u l t i n 3  levels  Since two  1 S and  S a r i s i n g from Is i o n i z a t i o n .  The mag-  n i t u d e of the m u l t i p l e t s p l i t t i n g i s o b v i o u s l y small seen i n the spectrum i n F i g . 4.1.  The  as  separation  3 1 between the S and S s t a t e s (AE) can be c a l c u l a t e d u s i n g Van V l e c k ' s theorem. (See S e c t i o n 2.12.2, Chapter 23 2). H i l l i g and co-workers calculated this s p l i t t i n g 24 employing the Hartree-Fock program of and obtained  a AE of 0.42eV.  t h e i r experimental  Froese-Fischer  From d e c o n v o l u t i o n  Auger l i n e s , they obtained  of  a value  - 140 -  1090  1085  1080  1075  Binding energy (eV) Fig.  4.1.  The I s l e v e l o f a t o m i c s o d i u m o b t a i n e d w i t h A l K a x - r a y s . T h e peak l a b e l l e d ' s a t ' i s due to m u l t i e l e c t r o n e x c i t a t i o n .  - 141  of 0.26eV f o r AE.  The  -  spectrum  i n F i g . 4.1  merely  shows an asymmetry on the h i g h b i n d i n g energy  side,  however, a l e a s t - s q u a r e s f i t u s i n g two L o r e n t z i a n peaks w i t h an area r a t i o of 3 t o 1 y i e l d s a s e p a r a t i o n of 0.4(l)eV, which i s i n reasonable agreement w i t h the c a l c u l a t e d value of H i l l i g multiplet  23 e t a_l.  For each of the 23 H i l l i g and co-workers calculated 25  states,  l i n e width of 0.27eV.  Banna and S h i r l e y  a  computed an  upper l i m i t f o r the Na K c t , „ emission l i n e from sodium of 0.42eV and assuming t h a t the ^2^3  solid  levels  i n v o l v e d i n t h i s t r a n s i t i o n have a n e g l i g i b l e width,  the  0.42eV v a l u e i s p r i m a r i l y a r e f l e c t i o n of the K l e v e l width.  The Na Is l i n e i n F i g . 4.1  width o f 1.2eV  due  to a d d i t i o n a l c o n t r i b u t i o n s  the A l Ka e x c i t i n g l i n e resolution  (=0.3eV  has a t o t a l l i n e  (=0.85eV) and the  a t ^50eV a n a l y s e r pass  from  spectrometer energy).  Sodium Is b i n d i n g e n e r g i e s from t h i s work and v a r i o u s other sources are l i s t e d Auger  i n Table 4.2.  and o p t i c a l v a l u e o f H i l l i g  The 23  and co-workers  was  e x p e r i m e n t a l l y obtained by combining the o p t i c a l l y known energy,  E[2s 2p ( D)3s (D )], 2  4  X  a b s o l u t e Auger energy, sodium atoms.  1  2  of 101.9eV, 1 2  27  w i t h the  E [ K L L 2 ( D) D], both f o r f r e e 2 3  3  The experimental v a l u e obtained i n t h i s  work by d i r e c t measurement  (107 9.lev)  i s 0.5eV higher  than the v a l u e o b t a i n e d by H i l l i g e t a l .  2 3  The  107 9.lev  - 142 -  Table 4.2  Sodium Is b i n d i n g e n e r g i e s (eV)  Is Experimental f r e e atom:  i.  T h i s work  10 79.1  ii.  Auger + O p t i c a l  iii.  X-ray emission + o p t i c a l  1078.6  3  1079.1  T h e o r e t i c a l f r e e atom:  Ref.  9  1078.2  Ref. 26  1079  Ref. 11  1079.3  Experimental standard state* :  10 74.0  Theoretical  1072.8  3  standard  state  a.  From Ref. 2 3  b.  From Ref. 17  c.  From Ref. 11  c  :  - 143 -  value l i s t e d  i n Table 4.2 f o r x-ray e m i s s i o n + o p t i c a l  data was taken from the work r e p o r t e d by Kowalczyk and 17 co-workers and i s the r e s u l t o f combining x-ray emission e n e r g i e s from the s o l i d 28 w i t h o p t i c a l data. 27 The agreement w i t h t h e x-ray p h o t o e l e c t r o n v a l u e i s e x c e l l e n t and theuse o f x-ray e n e r g i e s o b t a i n e d  from  the s o l i d does not r e s u l t i n too low an estimate i n t h i s case.  The f i r s t two t h e o r e t i c a l b i n d i n g e n e r g i e s  listed  i n Table 4.2 are t h e r e l a t i v i s t i c H a r t r e e - F o c k - S l a t e r r e s u l t s o f Huang e t a_l.9 and Siegbahn  e t a 1. 26 .Both  these v a l u e s correspond t o the d i f f e r e n c e i n t o t a l  energy  between the n e u t r a l ground s t a t e and the h o l e s t a t e and so t h e c o n t r i b u t i o n of i n t r a - a t o m i c r e l a x a t i o n i s i n c l u d e d . Agreement w i t h experiment Siegbahn 0.9eV.  i s e x c e l l e n t i n the case o f  e t a_l. but the value o f Huang e t a l . d i f f e r s by The ASCF Hartree-Fock  Nicolaides,  1 1  c a l c u l a t i o n o f Beck and  which i n c l u d e s the c o r r e c t i o n s f o r  r a d i a t i v e e f f e c t s i s 0.2eV higher than the experimental v a l u e ; however the two v a l u e s f a l l w i t h i n the quoted deviations. 17 Kowalczyk and co-workers b i n d i n g energy  have r e f e r e n c e d the Na I s  f o r s o l i d sodium t o the vacuum l e v e l and  o b t a i n e d a v a l u e o f 1074.OeV.  The f a c t t h a t the vacuum  l e v e l r e f e r e n c e d standard s t a t e b i n d i n g e n e r g i e s f o r  - 144 -  metals  i s i n v a r i a b l y lower than t h a t f o r the f r e e atom 14 15 19 30  i s now w e l l documented.  '  '  '  The measured phase  t r a n s i t i o n s h i f t s w i l l be d i s c u s s e d i n S e c t i o n 4.3.2. 4.3.1.2  Potassium  The K 2p l i n e s and accompanying s a t e l l i t e s t r u c t u r e due t o m u l t i e l e c t r o n e x c i t a t i o n are shown i n F i g . 4.2. The measured b i n d i n g e n e r g i e s are compared w i t h l i t e r a t u r e r e s u l t s i n Table 4.3.  A l l reported binding  e n e r g i e s are the average v a l u e s f o r the s p i n m u l t i p l e t s . Again the combination  of x-ray emission  28  and o p t i c a l  27  data g i v e s b i n d i n g e n e r g i e s which are i n very good agreement w i t h the experimental energies  (Table 4.3).  f r e e atom b i n d i n g  The t h e o r e t i c a l v a l u e s of  26 9 Siegbahn e t a l . and Huang e t a l . are a l s o i n e x c e l l e n t agreement w i t h experiment.  Once a g a i n the v a l u e s  c a l c u l a t e d by Beck and N i c o l a i d e s than the d i r e c t experimental  are s l i g h t l y h i g h e r  1 1  result.  31 Mansfield series 2 p ( P 5  2  1 / 2  o b t a i n e d a l i m i t t o the photoabsorption )3d[3/2] ns[1] x  1 / 2  3  /  2  of 303.9(2)eV i n  potassium vapor. T h i s i s 0.7eV higher than the d i r e c t experimental b i n d i n g energy of the 2p^y l e v e l . This 2  31 can be regarded as evidence t h a t M a n s f i e l d i n a s s i g n i n g the photoabsorption  i s correc  s e r i e s t o the above  - 145 -  F i g . 4.2.  The 2p l e v e l s of atomic potassium o b t a i n e d w i t h A l K a x-rays.The peaks l a b e l l e d 'sat' are due t o m u l t i e l e c t r o n excitation.  - 146 -  Table 4.3  Potassium 2p b i n d i n g e n e r g i e s (eV)  2 p  Experimental  l/2  2 p  3/2  f r e e atom:  I.  T h i s work  303.2  300.5  II.  Auger  303.7(1)  300.9(1)  303.2(4)  300.5(4)  303.0  300.2  Ref. 26  303  300  Ref. 11  303.7  300.9  :  299.6  296.9  :  29 8.6  295.7  a  I I I . X-ray emission + o p t i c a l  b  T h e o r e t i c a l f r e e atom : Ref.  9  Experimental  standard s t a t e  T h e o r e t i c a l standard s t a t e  a.  From Ref.  4  b.  From Ref.  8  c.  From Ref. 11  0  b  - 147  -  c o n f i g u r a t i o n r a t h e r than the s i n g l e s e r i e s 2p ( P , ) 4s [ 1/2 ] 5  2  1/  4.3.1.3  2  Q  x  excitation  nd.  Rubid ium  A spectrum  of the rubidium 3p l e v e l s and  the  accompanying m u l t i e l e c t r o n e x c i t a t i o n s a t e l l i t e s i s shown i n F i g . 4.3.  The  Rb 3p l i n e s are r a t h e r broad,  the l i n e w i d t h s o b t a i n e d by computer f i t t i n g 3. leV f o r the 3p^y  2  l i n e and  3. OeV  being  f o r the 3p^y  2  line.  32 Svensson and co-workers 1.80  and  have r e p o r t e d l i n e w i d t h s  1.48eV f o r the 3p-jy  2  and  3p^y  2  of  l i n e s of  Krypton obtained u s i n g monochromatized A l Ka x - r a y s . The 3 p j y l i n e i s broader than the ^2/2 l i n e due t o the f a c t t h a t M-jM^lSh and M,,M- 0^ type C o s t e r - K r o n i g 2  t r a n s i t i o n s are e n e r g e t i c a l l y p o s s i b l e f o r the 3p.jy 33 l e v e l , but not f o r the 3p^y  2  level,  2  34 '  and  also  a d d i t i o n a l super C o s t e r - K r o n i g t r a n s i t i o n s are e n e r g e t i c a l l y allowed f o r the former which are not allowed 32 f o r the l a t t e r . the energy  However, Svensson et aJL.  l i m i t f o r the M  2  ^M^  Kronig t r a n s i t i o n s l i e s a t Z=36(Kr).  state that  ^ super C o s t e r I f t h i s i s the  case, then the Rb 3p l i n e w i d t h s one would expect to o b t a i n w i t h monochromatized x-rays would be l e s s  than  - 148 -  Rubidium  i  i  i  i  260 250 Binding energy (eV)  i —  240  F i g . 4.3. The 3p l e v e l s of atomic rubidium obtained w i t h A l Ka x-rays.The peaks l a b e l l e d ' s a t ' are due to m u l t i e l e c t r o n excitation.  - 149  1.5eV.  -  Thus t h e l i n e w i d t h s o b t a i n e d  i n t h i s work  g r e a t e r t h a n t h o s e t h a t w o u l d be e x p e c t e d increased instrumental broadening  e v e n when t h e  of the  spectrometer  i s c o n s i d e r e d . These d a t a t h e r e f o r e i n d i c a t e  that  c o n f i g u r a t i o n i n t e r a c t i o n resonances through super  C o s t e r - K r o n i g t r a n s i t i o n s may  are  ^M^  ^M^  be p o s s i b l e b e y o n d  Z=36. Further evidence  for this  by c o m p a r i n g t h e o r e t i c a l and f o r t h e Rb  3p l e v e l s .  Rb  experimental  3p^y  f r o m t h i s w o r k and v a r i o u s  s u g g e s t i o n may  a n 2  d  ^V_/2  be  obtained  binding  energies  binding  other sources  energies  are l i s t e d  in  9 Table ^3eV  4.4.  The  t h e o r e t i c a l v a l u e s o f Huang e t a _ l .  g r e a t e r than  the d i r e c t experimental  s i m i l a r d i s c r e p a n c y b e t w e e n t h e o r y and 32 observed  for krypton.  For krypton  are  r e s u l t and  experiment  i t has  been  a  was found  t h a t t h e r e e x i s t s a l a r g e number o f s i n g l y i o n i z e d  con-  f i g u r a t i o n s w i t h two h o l e s i n t h e 3d l e v e l , o f t h e t y p e -2 -2 -2 -2 3d n s , 3d np (n^.5) , 3d nd and 3d n f (n^.4) w h i c h a r e 32 spaced w i t h i n a s m a l l energy range. Within these 2 c o n f i g u r a t i o n s , a number o f P s t a t e s e x i s t w h i c h can 2 i n t e r a c t w i t h e a c h o t h e r and r e s u l t s presented  w i t h 3p( P)  here s t r o n g l y suggest  states. that  similar  c o n f i g u r a t i o n i n t e r a c t i o n e f f e c t s are important t h e Rb  3p l e v e l s a s  well.  The  for  - 150 -  Table 4.4  Rubidium 3p b i n d i n g e n e r g i e s (eV)  3 p  Experimental  T h i s work  ii.  X-ray emission + o p t i c a l  a.  3/2  3  254.3  245.4  254.3  245.4  257.1  247.9  250 .9  242.0  f r e e atom:  Ref. 9  Experimental  3p  free atom:  i.  Theoretical  l/2  standard state* : 3  C a l c u l a t e d u s i n g x-ray e m i s s i o n v a l u e s from Ref. 2 8 and o p t i c a l v a l u e s from Ref. 27  b.  C a l c u l a t e d u s i n g x-ray emission v a l u e s from Ref. 28, s o l i d s t a t e photoemission  v a l u e s from Ref. 35 and a work f u n c t i o n  o f 2.3eV from Ref. 36  - 151  -  The b i n d i n g e n e r g i e s e s t i m a t e d  from x-ray  emission''  27 and  optical values  a r e i n e x c e l l e n t agreement w i t h the  d i r e c t experimental potassium. 4.3.1.4  (Table  r e s u l t a s i n t h e c a s e o f s o d i u m and 4.4)  Cesium  The c e s i u m 3d l e v e l s a r e shown i n F i g . 4.4 the experimental  and  f r e e atom b i n d i n g e n e r g i e s a r e c o m p a r e d 28  with values  obtained using x-ray  emission  and  optical  27 results  i n Table  4.5.  Again  t h e r e i s good a g r e e m e n t  b e t w e e n t h e s e r e s u l t s a l t h o u g h t h e r e i s some  evidence  i n t h i s case t h a t the x-ray emission + o p t i c a l  values  are lower  because o f d i f f e r e n t i a l e x t r a - a t o m i c  relaxation  i n the hole states involved i n x-ray emission.  However, 28  values f o r the L jN  , L^M  a n d NjyOj-j- e m i s s i o n  lines  w e r e u s e d t o c a l c u l a t e t h e 3d b i n d i n g e n e r g i e s and t h e e r r o r s i n v o l v e d i n s u c h an i n d i r e c t method a r e p r o b a b l y o  at least and  0.4eV.  The t h e o r e t i c a l v a l u e s o f Huang et. a l .  Beck and N i c o l a i d e s ' ' " a r e i n e x t r e m e l y 1  with the experimental i n t h i s work  (3d ^ , 3  2  good a g r e e m e n t  f r e e atom b i n d i n g e n e r g i e s 745.8eV;  3&_/ ' 2  7 3  obtained  1• eV)(Table g  4.5).  - 152  F i g . 4.4.  -  The 3d l e v e l s of atomic cesium o b t a i n e d w i t h A l K a x-rays.The peaks l a b e l l e d ' s a t ' are due to m u l t i e l e c t r o n excitation.  - 153 -  Table  4.5  Cesiurr, 3d b i n d i n g e n e r g i e s (eV)  3 d  Experimental  T h i s work  ii.  X-ray  emission  free  + optical  3  74 5.8  731.8  745.4  731.4  atom:  9  745.8  731.9  Ref.  11  745 .8  732 . 0  742.2  728 .2*  standard  state:  742 . 9  Theoretical  state :  values  from  R e f . 28 ar.d  using x-ray emission  values  from  Ref. 28,  v a l u e s from  R e f . 35 and a work  o f 2.1eV from R e f . 36  Front R e f . 37.  These v a l u e s a r e f o r Cs atoms a d s o r b e d  N i , c a l c u l a t e d u s i n g a work f u n c t i o n  6.  727.8  R e f . 27  state photoemission  function  727.9'  C  741.6  d  using x-ray emission  v a l u e s from  Calculated solid  c.  standard  Calculated optical  b.  5/2  Ref.  Experimental  a.  3 d  f r e e atom:  i.  Theoretical  3/2  Prom R e f . 11  o f 1.9eV.  on  - 154  4.3.1.5  Magnesium  The Ka  -  spectrum  x-rays  measured  o f t h e Mg  i s presented  Is l e v e l obtained with  i n F i g . 4.5  Is l e v e l b i n d i n g energy  l i t e r a t u r e values i n Table between t h e d i r e c t and  28  and  t h e Mg  the  directly  i s compared  with  T h e r e i s good  experimental  the b i n d i n g energy  emission  4.6.  and  measurement  estimated  Al  agreement  (1311.5eV)  u s i n g v a l u e s from  2p b i n d i n g e n e r g y  o f Newsom.  x-ray 38  39 The Mg  I s b i n d i n g energy  o b t a i n e d u s i n g Auger d a t a ,  2p b i n d i n g e n e r g y ^ 3  and  experimental  coulomb  the integrals  i s l e v t o o low. However, t h e e r r o r q u o t e d f o r t h i s 39 41 d e t e r m i n a t i o n i s ±leV. More r e c e n t l y , Breuckmann used  the a b s o l u t e e n e r g i e s of the K-I^  transitions atoms and from for  from  a higher r e s o l u t i o n  M 3  i  and  Auger  spectrum  the e n e r g i e s of the c o r r e s p o n d i n g  o p t i c a l data, t h e Mg  to calculate  Is b i n d i n g energy.  This value  agreement w i t h the e x p e r i m e n t a l t h i s work  (Table  a value of  XPS  final  in  i s i n good  value reported i n  binding  et a l .  agreement w i t h the r e p o r t e d  energy.  theoretical  v a l u e o f Siegbahn  However L e y  v a l u e and  and  estimated  the e f f e c t  6  is  experimental  co-workers  1 6  of  used  Mg  states  4.6).  theoretical  reasonable  of  1311.3(3)eV  2 The  K-M^M^  this  electron  4 0  - 155  F i g . 4.5.  -  The Is l e v e l of atomic magnesium obtained w i t h A l K a x-rays.The peaks l a b e l l e d ' s a t ' are due t o m u l t i e l e c t r o n e x c i t a t i o n .  - 156 -  Table 4.6  Magnesium Is b i n d i n g e n e r g i e s (eV)  Is  Experimental  f r e e atom:  i.  T h i s work  ii.  X-ray emission + o p t i c a l  1311.5 3  1311.2  i i i . Auger + o p t i c a l + coulomb integrals  Theoretical  Ref.  f r e e atom:  9  1310.6  Ref. 26  1312.0  Ref. 16  1312.6  Experimental  a.  1310.5(10)  standard  state  1306.7  C a l c u l a t e d u s i n g x-ray emission values from Ref. 2 8 and o p t i c a l v a l u e s from Ref. 38  b.  From  Ref. 39  c.  From  Ref. 16  - 157  -  c o r r e l a t i o n t o a r r i v e a t a t h e o r e t i c a l b i n d i n g energy o f 1312.6eV w h i c h i s 1 . l e V h i g h e r t h a n t h e b i n d i n g energy measured i n t h i s work. 9 Huang et_ a l . value.  i s 0.9eV l o w e r  The t h e o r e t i c a l r e s u l t o f than the experimental  Thus i t seems t h a t i f a s i m i l a r  correlation 9  c o r r e c t i o n was a p p l i e d t o t h e r e s u l t o f Huang et. a l . e x c e l l e n t agreement between t h e o r y and e x p e r i m e n t be  might  obtained.  4.3.1.6  Calcium  The c a l c i u m 2s and 2p l e v e l s a n d t h e a s s o c i a t e d multielectron excitation Fig.  4.6 and 4.7  statellites  a r e shown i n  r e s p e c t i v e l y and t h e measured b i n d i n g  e n e r g i e s a r e compared w i t h v a l u e s from v a r i o u s sources  i n Table  the f i r s t  4.7.  In this  c a s e where t h e  other  study calcium e x e m p l i f i e s  binding energies  estimated  u s i n g t h e x - r a y e m i s s i o n v a l u e s f o r t h e s o l i d and t h e o p t i c a l data  for  atoms, d i f f e r  m e n t a l r e s u l t , where t h e former Although, as mentioned e a r l i e r ,  from the d i r e c t e x p e r i i s lower  by 5.0 t o 5.2eV.  i t i s expected  that the  e m p i r i c a l f r e e atom c o r e l e v e l b i n d i n g e n e r g i e s  estimated  using s o l i d state x-ray emission values may be somewhat g low, the observed discrepancy i s c o n s i d e r a b l y l a r g e r  - 158  F i g . 4.6.  -  The 2s l e v e l of atomic c a l c i u m obtained w i t h A l Ka x-rays.The peak l a b e l l e d 'sat' i s due to multielectron excitation.  - 159 -  o  CVJ  in O  o  365  Binding energy (eV)  355  F i g . 4.7. The 2p l e v e l s of atomic c a l c i u m obtained w i t h A l K a x-rays.The peaks l a b e l l e d 'sat' are due to multielectron excitation.  - 160 -  T a b l e  4 . 7  C a l c i u m  2s  a n d  2p  l e v e l  b i n d i n g  e n e r g i e s  fl E x p e r i m e n t a l  f r e e  i .  T h i s  i i .  A u g e r  i i i .  T h e o r e t i c a l  R e f .  e m i s s i o n  3  s t a t e  a .  d  o n  d .  F r o m  3 5 9 . 6  3 5 6 . 0  b)  3 6 0 . 0 ( 1 )  b)  3 5 6 . 4 ( 1 )  c)  3 6 1 . 1 ( 1 )  b)  3 5 7 . 4 ( 1 )  442  .5  449  .8  (20)  354  . 7 ( 2 0 )  351  .1  3 6 0 . 5  356  .9  4 4 1 ( 1 )  3 5 3 . 6 ( 5 )  R e f . 4  W h e t h e r  a s s i g n m e n t  R e f .  (20)  443  354  3 5 0 . 0 ( 5 )  s t a n d a r d  :  t h e  3  s t a n d a r d  :  F r o m  P /2  a t o m :  9  T h e o r e t i c a l  2  l / 2  +  3  f r e e  E x p e r i m e n t a l  S t a t e  4 4 7 . 5  3  o p t i c a l *  p  a t o m :  work  X - r a y  2  (eV)  8  o f  b)  o r  A u g e r  c)  a r e  l i n e s  t h e  t o  c o r r e c t  f i n a l  350  v a l u e s  A u g e r  d e p e n d s  s t a t e s .  - 161  -  than what one would have a n t i c i p a t e d .  Despite  the  f a c t t h a t most of the estimated b i n d i n g e n e r g i e s u s i n g t h i s method have shown e x c e l l e n t agreement w i t h  the  f r e e atom b i n d i n g e n e r g i e s measured i n t h i s l a b o r a t o r y u s i n g XPS,  the present d i s c r e p a n c y may  be  considered  a warning t h a t such i n d i r e c t methods should be used only w i t h great c a r e . 4  Mehlhorn and co-workers  have given two  s e t s of  f r e e atom b i n d i n g e n e r g i e s f o r the 2p l e v e l s of calcium  (Table 4.7),  the c o r r e c t s e t of v a l u e s  depending upon the proper assignment of Auger l i n e s to f i n a l Auger s t a t e s . The two d i f f e r by 1.0  - 1.leV with the lower energy s e t only  0.4eV higher than the XPS laboratory.  s e t s of b i n d i n g e n e r g i e s  v a l u e measured i n t h i s  C o n s i d e r i n g the nature of agreement t h a t  has been shown to e x i s t between XPS Spectroscopy  (AES)  and Auger E l e c t r o n  i n the d e t e r m i n a t i o n of b i n d i n g  e n e r g i e s , the present r e s u l t suggests  t h a t the  assignment of the Auger l i n e s to f i n a l Auger s t a t e s 4  l e a d i n g to the lower i s correct. not  set of v a l u e s by Mehlhorn e t a l .  D e t a i l s of t h i s assignment are, however,  available. The  t h e o r e t i c a l f r e e atom b i n d i n g e n e r g i e s from  relaxed-orbital  relativistic  Hartree-Fock-Slater  - 162  -  c a l c u l a t i o n s by Huang e t a_l.  are compared w i t h the  experimental r e s u l t s i n Table 4.7.  The  calculated  v a l u e s are 0.9eV h i g h e r than the experimental  values  f o r the 2p l e v e l s , and the c a l c u l a t e d v a l u e f o r the Ca 2s l e v e l i s 2.3eV l a r g e r . due  T h i s d i f f e r e n c e may  be  t o the n e g l e c t of c o n f i g u r a t i o n i n t e r a c t i o n .  initial  The  s t a t e s of the c l o s e d s h e l l group IIA atoms are  2 known t o possess near degenerate c o n f i g u r a t i o n s np 2 2 and ( n - l ) d ( f o r Ba, 4f i s a l s o p o s s i b l e ) which can mix  s t r o n g l y w i t h the ground s t a t e , ns  4.3.1.7  The  2  , configuration.  3  Strontium  3d l e v e l of atomic  s t r o n t i u m and the a s s o c i a t e d  s a t e l l i t e s t r u c t u r e i s shown i n F i g . 4.8. mental 3d b i n d i n g energy v a l u e s i n Table 4.8.  The e x p e r i -  i s compared w i t h the  literature  Core l e v e l b i n d i n g e n e r g i e s of  s t r o n t i u m atoms have been determined 4 Mehlhorn and co-workers,  p r e v i o u s l y by  and were repeated  in this  l a b o r a t o r y mainly to compare the b i n d i n g e n e r g i e s measured i n t h i s l a b o r a t o r y w i t h those measured u s i n g the same technique. XPS  As seen i n Table 4.8  v a l u e s d i f f e r by 0.5eV, but f a l l w i t h i n the  errors.  As mentioned i n S e c t i o n 4.2  elsewhere the  two  quoted  earlier in this  - 163  -  150  140  Binding energy (eV) F i g . 4.8.  The 3d l e v e l of atomic s t r o n t i u m obtained with A l Ka x-rays.The peak l a b e l l e d 'sat' i s due to multielectron excitation.  - 164 -  T a b l e  4.8  S t r o n t i u m  3d  b i n d i n g  e n e r g i e s  (eV)  3d E x p e r i m e n t a l  i .  T h i s  a t o m :  w o r k  1 4 2 . 6  A u g e r  11.  i i i  f r e e  .  i v .  v .  142  X - r a y  e m i s s i o n  1  5  T h e o r e t i c a l  X P S  f r e e  142  a  a t o m :  s t a n d a r d  a .  F r o m  R e f .  b .  C a l c u l a t e d  b i n d i n g  d.  The  two  s t a t e  e  :  1 4 2 . 8  1 3 7 . 0 ( 1 0 )  4  u s i n g  e n e r g i e s  R e f .  1 4 4 . 0 ( 2 )  .9  1 4 1 . 1 ;  E x p e r i m e n t a l  F r o m  ;  1 4 3 . 1 ( 7 )  R e f .  c .  (2)  1 4 2 . 8 ( 1 1 )  P h o t o a b s o r p t i o n  O t h e r  .3  x - r a y  o f  e m i s s i o n  f r e e  atoms  v a l u e s  f r o m  f r o m  R e f .  R e f .  2 8  a n d  4p  4  42  v a l u e s  shown  a r e  f o r  3d ^  t h e  5  a  n  2  d 3 d  3/2  s  P i  n  -  o  r  b  i  t  d o u b l e t .  e .  F r o m  R e f .  f u n c t i o n  a v e r a g e  4 3,  o f  r e f e r e n c e d  2 . 7 ( e V )  b i n d i n g  f r o m  e n e r g y  t o  t h e  R e f .  f o r  t h e  vacuum  l e v e l  u s i n g  a  The  v a l u e  shown  i s  44.  s p i n - o r b i t  d o u b l e t  work  t h e  3ds/2  a n d  3d3/2•  - 165  chapter,  -  the u n c e r t a i n t y o f the b i n d i n g energy measured  i n t h i s l a b o r a t o r y i s ±0.2eV.  The  binding  energy 28  estimated and  using s o l i d  state x-ray emission r e s u l t s 4 known 4p b i n d i n g e n e r g i e s i s i n e x c e l l e n t agreement  w i t h the present  r e s u l t , as w e l l a s t h a t o b t a i n e d  from  42 photoabsorption  by M a n s f i e l d and 4  M e h l h o r n e t a_. s p l i t t i n g o f 1.7eV  Connerade.  have r e p o r t e d  f o r the  3d  level  a  spin-orbit  from the  Auger  s p e c t r u m w h i c h i s i n good a g r e e m e n t w i t h t h e 9  theoretical  r e s u l t o f Huang e t a_l.  (Fig.  I n t h e XPS  t h i s i s s e e n a s an a s y m m e t r y on energy s i d e of the  peak. 9  c u l a t e d b i n d i n g energy result. 4.3.1.8  The  the higher  4.8)  binding  w e i g h t e d a v e r a g e of the c a l -  i s i n good a g r e e m e n t w i t h t h e  XPS  Barium  x-ray  photoelectron  of atomic barium are tively.  The  spectrum  The  s p e c t r a of the  shown i n F i g . 4.9  binding energies  those  from v a r i o u s other  4.9.  Binding energy values  and  3d and 4.10  levels  respec-  measured i n t h i s work  sources  4s  and  are c o l l e c t e d i n Table 4  d e t e r m i n e d by AES  and  photo-  i n good  agree-  45 absorption  methods f o r the  ment w i t h t h e e x p e r i m e n t a l  4d  XPS  l e v e l s are result.  However no  such  - 166  -  Barium 3d  T  810  '  1  1  5/2  r  800  790  Binding energy (eV) Fig.  4.9. The 3d l e v e l s of atomic barium o b t a i n e d w i t h A l Ka x-rays.The A l K q x-ray s a t e l l i t e s of the 3 d ^ l i n e are seen next t o the 3d,-^ l « 3  4  2  i n e  2  - 167 -  "no  '  TOO  R  Binding energy (eV) F i g . 4.10.  The 4d l e v e l s of atomic barium o b t a i n e d w i t h A l Ka x-rays.The peak l a b e l l e d 'sat' i s due to m u l t i e l e c t r o n excitation.  - 168 -  T a b l e  4 . 9  B a r i u m  3d  and  4d  3  E x p e r i m e n t a l  f r e e  T h i s  i i .  A u g e r  i i i .  X - r a y  i v .  P h o t o a b s o r p t i o n  R e f .  work  d  3  8 0 3 . 6  e m i s s i o n  f r e e  1  d  5 / 2  4  7 8 8 . 2  8 0 4 . 3 ( 1 1 )  3  7 8 9 . 0 ( 1 1 )  0  d  (eV)  3 / 2  4  d  5 / 2  1 0 0 . 9  9 8 . 3  1 0 1 . 0 ( 1 )  9 8 . 5 ( 1 )  1 0 0 . 7 ( 9 )  9 8 . 1 ( 9 )  1 0 1 . 0 ( 2 )  9 8 . 3 ( 2 )  1 0 0 . 5  9 7 . 9  a t o m :  9  8 0 4 . 6  7 8 9 . 3  7 9 8 . 6 ( 2 0 )  7 8 3 . 2 ( 2 0 )  s t a n d a r d  =  a .  F r o m  R e f .  b .  C a l c u l a t e d  u s i n g  5p  e n e r g y  9 5 . 0 ( 2 0 )  9 2 . 4 ( 2 0 )  4  b i n d i n g  c .  F r o m  R e f .  45  d .  F r o m  R e f .  4 3 ,  f u n c t i o n  3 / 2  e n e r g i e s  a  E x p e r i m e n t a l  s t a t e  d  b i n d i n g  a t o m :  i .  T h e o r e t i c a l  l e v e l  o f  x - r a y  o f  e m i s s i o n  f r e e  r e f e r e n c e d  2 . 5 ( e V )  f r o m  atoms  t o  t h e  R e f .  44  r e s u l t s  f r o m  f r o m  R e f .  vacuum  R e f .  28  a n d  4  l e v e l  u s i n g  a  w o r k  - 169 -  v a l u e s are a v a i l a b l e f o r the 3d l e v e l s of atomic barium. Of the two s p i n - o r b i t s p l i t components of the 4d l i n e , the 4d^^2 component appears i n the x-ray p h o t o e l e c t r o n spectrum as a shoulder on the h i g h b i n d i n g energy s i d e of the 4d peak.  T h i s can be e a s i l y deconvoluted  two peaks with a s e p a r a t i o n of 2.6eV.  into  This separation  shows e x c e l l e n t agreement w i t h the t h e o r e t i c a l  spin-  o r b i t s p l i t t i n g o f the 4d l e v e l of Ba c a l c u l a t e d by 9 Huang e t al_. The 4d s p i n - o r b i t s p l i t t i n g observed by 4 45 AES and photoabsorption are 2.5 and 2.7eV r e s p e c t i v e l y . The f r e e atom b i n d i n g e n e r g i e s estimated u s i n g x-ray 28 emission data f o r the s o l i d 4 f o r the f r e e atoms  and the 5p b i n d i n g e n e r g i e s  are i n v e r y good agreement w i t h the  experimental XPS v a l u e s f o r the 4d l e v e l s , whereas the estimated 3d b i n d i n g e n e r g i e s are 0.7 t o 0.8eV higher than the experimental v a l u e .  The x-ray emission v a l u e s  r e p o r t e d f o r Ba have been o b t a i n e d e x p e r i m e n t a l l y u s i n g 2 8 43 Ba(N0 )2 3  energies  '  and  t  n  e  e s t i m a t i o n o f the f r e e atom b i n d i n g  (as w e l l as the standard s t a t e b i n d i n g energies)  was c a r r i e d be maintained  out assuming t h a t these emission v a l u e s would i n the  metal.  D e s p i t e the f a c t t h a t the  experimental XPS b i n d i n g e n e r g i e s of the 3d l e v e l s w i t h i n the quoted minimum p o s s i b l e  fall  e r r o r of the v a l u e s  estimated u s i n g these x-ray emission r e s u l t s , as w i l l be  - 170 -  indicated later,  t h e r e i s reason t o b e l i e v e t h a t  these estimated v a l u e s are i n e r r o r . The t h e o r e t i c a l l y estimated b i n d i n g e n e r g i e s  9  for  barium f r e e atoms show good agreement w i t h the e x p e r i mental v a l u e s f o r the 4d l e v e l s .  The b i n d i n g e n e r g i e s  9  c a l c u l a t e d by Huang e t a_.  are 1.0 to 1.leV higher  than the experimental v a l u e . 4.3.2  Phase T r a n s i t i o n S h i f t s ,  I t i s now sition shift,  AE^  p o s s i b l e t o c a l c u l a t e the phase t r a n AE^, f o r the metals d i s c u s s e d so f a r ,  u s i n g the experimental  f r e e atom b i n d i n g e n e r g i e s i n  c o n j u n c t i o n w i t h the corresponding v a l u e s i n the s o l i d (referenced t o the vacuum l e v e l ) .  The f r e e atom b i n d i n g  e n e r g i e s measured i n t h i s work are compared w i t h the a p p r o p r i a t e standard s t a t e v a l u e s i n Tables 4.2-4.9. To o b t a i n K 2p b i n d i n g e n e r g i e s r e f e r e n c e d t o the vacuum l e v e l f o r the s o l i d , S h i r l e y and co-workers used x-ray emission v a l u e s f o r KCl and a work f u n c t i o n of 2.3eV.  To the author's knowledge t h e r e has been no  x-ray photoemission r e l i a b l e values  study of potassium metal t o g i v e more  f o r the s o l i d s t a t e b i n d i n g e n e r g i e s . g  Thus, the v a l u e s  of S h i r l e y e t a_l.  were used w i t h the  f r e e atom b i n d i n g e n e r g i e s measured i n t h i s work t o  - 171  c a l c u l a t e a AE^ o f 3.6eV.  -  Similarly  the standard  state  b i n d i n g e n e r g i e s f o r s o d i u m , magnesium and c a l c i u m were o  o b t a i n e d f r o m t h e d a t a o f S h i r l e y and c o - w o r k e r s .  b i n d i n g e n e r g i e s f o r t h e Rb 3p l e v e l s i n t h e s o l i d  The state  28 have been o b t a i n e d u s i n g x - r a y e m i s s i o n r e s u l t s  and t h e  b i n d i n g e n e r g y v a l u e s f o r Rb 4p l e v e l s r e p o r t e d by 35 Ebbinghaus e t a_l. r e f e r e n c e d t o t h e vacuum l e v e l 36 a w o r k f u n c t i o n o f 2.3eV. determined  When t h e s o l i d  state values  t h i s way a r e c o m b i n e d w i t h t h e f r e e atom  b i n d i n g e n e r g i e s a AE^ o f 3.4eV i s o b t a i n e d . standard  using  The Cs 3d  s t a t e b i n d i n g e n e r g i e s were c a l c u l a t e d  i n the  same way a s t h e Rb 3p l e v e l s w i t h t h e Cs 5p b i n d i n g 35 e n e r g i e s o f E b b i n g h a u s e_t a l . and a w o r k f u n c t i o n o f 36 v 2.leV b e i n g u s e d . A v a l u e o f 3.6eV f o r AE^ was e s t i m a t e d 37 t h i s way.  Krishnan et a l .  b i n d i n g energies o f cesium surface. and  have d e t e r m i n e d atoms a d s o r b e d  These v a l u e s o b t a i n e d  on a n i c k e l  from x-ray  a w o r k f u n c t i o n o f 1.9eV a r e a l s o l i s t e d  H o w e v e r , i t i s t o be n o t e d  t h e 3d  photoemission i n Table  that the spin-orbit 37  o f t h e 3d l e v e l r e p o r t e d by K r i s h n a n e t a l _ .  (100)  4.5.  splitting i s 15.0eV  w h e r e a s t h e same s p l i t t i n g o b t a i n e d f r o m t h e e x p e r i m e n t a l and  t h e o r e t i c a l r e s u l t s f o r b o t h t h e f r e e a t o m s and t h e  standard  s t a t e a r e b e t w e e n 13.8 a n d 14.0eV.  37 e t a_l. report a 3d^^  2  Krishnan  l e v e l b i n d i n g energy which  shows  - 172  -  good agreement w i t h both the t h e o r e t i c a l e s t i m a t i o n by Beck and N i c o l a i d e s x-ray emission The  (Table  1 1  and the v a l u e o b t a i n e d u s i n g  4.5).  standard s t a t e b i n d i n g e n e r g i e s r e p o r t e d i n  Tables 4.8  and  4.9  f o r s t r o n t i u m and barium  are the  43 v a l u e s r e p o r t e d by Bearden and Burr.  These v a l u e s  were c a l c u l a t e d from x-ray emission r e s u l t s and r e ferenced t o the vacuum l e v e l by u s i n g work f u n c t i o n s of 44 2.7  and  2.5eV  f o r s t r o n t i u m and barium  respectively.  The phase t r a n s i t i o n s h i f t s c a l c u l a t e d f o r the group IA and IIA metals u s i n g the f r e e atom b i n d i n g e n e r g i e s measured i n t h i s work, and the  theoretically  estimated v a l u e s , are c o l l e c t e d i n Table 4.10.  The  author c o u l d not f i n d any t h e o r e t i c a l e s t i m a t e of c o r e l e v e l b i n d i n g e n e r g i e s f o r the standard s t a t e s of rubidium,  s t r o n t i u m and  barium.  A l l the t h e o r e t i c a l v a l u e s r e p o r t e d i n Table are based on a model f i r s t put forward by 14 Ley and coworkers.  4.10  Shirley,  (See S e c t i o n 2.11.4, Chapter  In t h i s model i t i s assumed  t h a t the hole s t a t e  by core l e v e l i o n i z a t i o n of metals  2 9 , 4 6  Two). produced  i n the standard  i s screened by the v a l e n c e e l e c t r o n gas forming a  state semi-  l o c a l i z e d e x c i t o n by the dropping down of a conduction band below E^.  T h i s i s the essence of a model put  - 173 -  T a b l e  4 . 1 0  P h a s e  t r a n s i t i o n  m e t a l s ,  e n e r g i e s  i n  s h i f t s ,  e s t i m a t e d  m e a s u r e d  AE^,  u s i n g  i n  t h e  t h i s  f r e e  w o r k .  b  (  E x p e r i m e n t a l  I s  K 2  K  2  l / 2  p  p  3 / 2  Rb 3  p  3  p  3  d  3  d  A l l  b i n d i n g  s h i f t s  e  V  )  T h e o r e t i c a l  5 . 1  5 . 3  3.6  3  3.6  3  4 . 2  5 / 2  3.6  4 . 2  5 . 1  Ca  2s  6  .5  7  6  .0  7  6  .0  7  2  p  S r  3 / 2 '  5 . 6  5 . 0 3  d  3  d  4  d  4  d  Ba  3 / 2 5 . 0  5 / 2  5.9  Ba  Ba  C  C  l / 2  3d  Ba  5 . 0  3.6  4 . 8  Ca  6 . 5  5 . 0  C  I s  p  a  C  Mg  2  a r e  b  b  b  b  3 / 2  Cs  Ca  I I A  3.4  3 / 2  Cs  atom  a n d  3.4  l / 2  Rb  I A  e V .  E  Na  g r o u p  3 / 2 5 . 9  5 / 2  a .  F r o m  R e f .  17  b .  F r o m  R e f .  11  c.  F r o m  R e f  d .  F r o m  R e f .  .  8 16  C  d  b  - 174  -  forward by F r i e d e l . **' '**° Beck and Nicolades^" " use a 1  ASCF method o u t l i n e d i n Chapter  Two  to e v a l u a t e the  phase t r a n s i t i o n s h i f t whereas a l l the other v a l u e s r e p o r t e d i n Table 4.10 atomic  are c a l c u l a t e d i n terms of  two-electron i n t e g r a l s .  procedures make use of the  '^  Both c a l c u l a t i o n  'equivalent cores' approxi-  1129 mation  '  and t h i s t h e o r e t i c a l model e s t i m a t e s the  core l e v e l b i n d i n g energy  s h i f t due  to extra-atomic  r e l a x a t i o n . The t h e o r e t i c a l b i n d i n g energy i n Table 4.10,  shifts  listed  t h e r e f o r e , r e p r e s e n t the estimated v a l u e s  f o r extra-atomic r e l a x a t i o n .  The phase t r a n s i t i o n  i s caused by a number of f a c t o r s  (Chapter Two)  shift  of which  extra-atomic r e l a x a t i o n i s the major c o n t r i b u t o r .  The  v a l u e s estimated by Beck and Nicolaides ''" are l a r g e r 8 16 1  than those c a l c u l a t e d by S h i r l e y and co-workers. '  17 '  A l l the t h e o r e t i c a l e s t i m a t e s are l a r g e r than the e x p e r i mental v a l u e s w i t h the e x c e p t i o n of the v a l u e estimated f o r K by S h i r l e y e t a_.  Although,  the ' s e m i l o c a l i z e d  e x c i t o n ' model seems t o overestimate the  extra-atomic  r e l a x a t i o n , the t r e n d s of b i n d i n g energy  shifts predicted  by t h i s model are i n e x c e l l e n t agreement w i t h The b i n d i n g energy  experiment.  s h i f t s p r e d i c t e d f o r Na I s , Mg  Ca 2s agree w i t h the experimental v a l u e s t o w i t h i n 0.2-0.5eV.  Is and  - 175 -  The b i n d i n g energy  s h i f t s are expected  to increase  slowly when going from outer core l e v e l s t o i n n e r core 8 16 levels  '  and t h i s can be seen i n c a l c i u m f o r which  the b i n d i n g e n e r g i e s of t h r e e separate l e v e l s were measured.  However, t h i s t r e n d i s r e v e r s e d i n barium  where the b i n d i n g energy 0.9eV l e s s than  s h i f t f o r the 3d l e v e l s i s  t h a t f o r the 4d l e v e l s .  T h i s may have  been caused by the use of i n c o r r e c t standard s t a t e core l e v e l b i n d i n g e n e r g i e s which were c a l c u l a t e d from the 43 x-ray emission v a l u e s f o r BaCNO^^-  As mentioned  e a r l i e r , a s i m i l a r d i s c r e p a n c y i s seen between the experimental XPS f r e e atom b i n d i n g e n e r g i e s and the v a l u e s estimated f o r the 3d l e v e l s of atomic  barium  u s i n g the same s e t of x-ray emission r e s u l t s where the estimated value i s higher than the experimental one. Such a d i s c r e p a n c y c o u l d be caused  by m e t a l l i c  barium  having d i f f e r e n t x-ray e m i s s i o n r e s u l t s than those f o r BaCNO-^as the r e l a x a t i o n mechanisms i n the two s o l i d s are not n e c e s s a r i l y the same.  However, the author  c o u l d not f i n d an a l t e r n a t e s e t of x-ray emission v a l u e s or a d i r e c t x-ray photoemission  study of m e t a l l i c barium.  F u r t h e r d i s c u s s i o n of t h i s p o i n t , t h e r e f o r e , w i l l not be considered. D i r e c t comparison o f the experimental f r e e atom  - 176 -  b i n d i n g e n e r g i e s and the b i n d i n g energy of such atoms adsorbed  on v a r i o u s s u r f a c e s can be expected  t o produce  d i r e c t i n f o r m a t i o n r e g a r d i n g the nature of the adsorbatesubstrate i n t e r a c t i o n s .  By combining the f r e e atom  b i n d i n g e n e r g i e s o f cesium w i t h the b i n d i n g e n e r g i e s of cesium atoms adsorbed  on a n i c k e l  (100) s u r f a c e  37 determined  by Krishnan e t a l . ,  b i n d i n g energy  shifts  of 2.9eV and 3.9eV can be c a l c u l a t e d f o r the 3d^^  a  n  d  "^5/2 l l respectively. Unfortunately t h i s s h i f t cannot be d i s c u s s e d i n a meaningful way due t o the unexpected d i f f e r e n c e i n the 3d s p i n - o r b i t s p l i t t i n g e  v  e  s  37 between t h i s work and the work of Krishnan e t a l . .  4.3.3  Multielectron Excitation  In any study of s a t e l l i t e  Satellites  s t r u c t u r e on the h i g h  b i n d i n g energy s i d e o f the main peaks i t i s important to d i s t i n g u i s h energy l o s s peaks from peaks due t o multielectron  'shakeup' events.  However, e l e c t r o n 4 9 50  impact  s t u d i e s o f the a l k a l i metal vapors,  '  as w e l l  as u l t r a v i o l e t p h o t o e l e c t r o n spectroscopy r e s u l t s ^ t h a t the most i n t e n s e t r a n s i t i o n s i n  the n e u t r a l atoms 49  have e n e r g i e s i n the range l-3eV  (2.09eV f o r Na,  1.6lev  and 1.41eV f o r C s  f o r K,  49  1.58eV f o r R b ,  50  show  1  Of course, i t i s c o n c e i v a b l e t h a t the r e l a t i v e  5 0  ).  intensities  - 177  of the  energy  -  l o s s t r a n s i t i o n s may change w i t h  k i n e t i c energy of the e x c i t i n g e l e c t r o n .  the  In the  case  50 of potassium,  H e r t e l and Ross  established that at  ^100eV e l e c t r o n energy, the 1.61eV t r a n s i t i o n i s still  ^100  times g r e a t e r than any of the o t h e r s .  It  seems p l a u s i b l e t h a t the s i t u a t i o n would be more or  less  the same f o r the ^1200eV e l e c t r o n s i n v o l v e d i n t h i s  x-  ray p h o t o e l e c t r o n study. the other metal atoms. IIA and  IIB vapors,  Similar situations exist for In a r e c e n t UPS 3  Suzer  peaks a t e n e r g i e s 2 . 9 ,  2.7  et a_l. and  study of group  reported  inelastic  2.2eV higher than the main  peak f o r c a l c i u m , s t r o n t i u m and barium , r e s p e c t i v e l y . No  s i g n i f i c a n t changes i n the s a t e l l i t e  were observed  f o r a l l these group IA and  intensities  IIA atoms when  s p e c t r a were o b t a i n e d a t d i f f e r e n t o p e r a t i n g p r e s s u r e s . I n t e n s i t i e s of the peaks due are expected  to i n e l a s t i c  to be p r e s s u r e dependent.  scattering  In a d d i t i o n ,  a l t e r n a t e scans of the Ne Is and Na Is r e g i o n s i n a mixture  of neon gas and  s t r u c t u r e ^8eV  sodium vapor gave no evidence f o r  from the Ne Is peak.  Because the  kinetic  energy o f the p h o t o e l e c t r o n s from the Ne I s and Na l e v e l s d i f f e r by o n l y ^200eV, the i n e l a s t i c  scattering  c r o s s s e c t i o n s should be more or l e s s s i m i l a r . procedure  was  repeated w i t h the cesium 3d  Is  levels  This  - 178  where the k i n e t i c energy  -  from the Ne I s and Cs  l e v e l s d i f f e r by ^130eV, and the r e s u l t s t h a t the peaks observed  3d  confirmed  a t e n e r g i e s of about 5eV  higher  than the main l i n e s of the cesium  3d spectrum  due t o m u l t i e l e c t r o n e x c i t a t i o n .  However, i t i s p o s s i b l e  t h a t some s t r u c t u r e corresponding to energy present i n the s p e c t r a shown here,but led  'sat  are indeed  loss i s  the f e a t u r e s l a b e l -  i n the metal atom s p e c t r a are d e f i n i t e l y  1  due  to m u l t i e l e c t r o n e x c i t a t i o n . The  s e p a r a t i o n between the s a t e l l i t e s and the main  peaks f o r the d i f f e r e n t atoms are l i s t e d In the o n e - e l e c t r o n p i c t u r e and initial action  s t a t e and/or f i n a l  i n Table  4.11.  i n the absence of  state configuration i n t e r -  (an o b v i o u s l y o v e r s i m p l i f i e d  s i t u a t i o n ) , and i n  order t o a s s i g n the main shakeup t r a n s i t i o n s i n v o l v e d , it  i s u s e f u l t o c o n s i d e r the e l e c t r o n i c s t a t e s of the  'equivalent core i o n ' corresponding to the atom under study, w i t h a core' h o l e .  Values f o r the  excitation  27 energies  o b t a i n e d f o r the monopole s e l e c t i o n  rule  allowed t r a n s i t i o n s ns-*- (n+1) s and ns+(n+2)s i n t h i s e q u i v a l e n t cores approximation 4.11.  are a l s o l i s t e d  (For example, t o o b t a i n the energy  i n Table  corresponding  t o the 3s-*4s t r a n s i t i o n i n core i o n i z e d sodium, the e x c i t a t i o n energy  f o r the same t r a n s i t i o n i n 3s i o n i z e d  - 179 -  T a b l e  4 . 1 1  M u l t i e l e c t r o n  e x c i t a t i o n  f r o m  l i n e s  t h e  m a i n  s a t e l l i t e s :  (eV)  E q u i v a l e n t E x p e r i m e n t a l  Na  I s  2 p  1  /  K  2 p  3  /  Rb  Cs  3d  Cs  3d  Mg  I s  2s  Ca  2p  2p  S r  3d  Ba  1 1 . 5 0  6 . 4 7  8 . 7 6  5 . 9 2  8 . 0 5  5 . 2 5  7 . 1 9  6 . 0  3/2  5.2  3/2  ) 5.4  5/2  6 . 1 ,  9  1 2 . 3  3  S  1 1 . 3 2  14  .89  S  1 1 . 8 2  15  .05  S  7.22  S  7.60  .1  9 . 8  1/2 Ca  8 . 6 5  6 . 0  L  Ca  ns->(n+2)s  6 . 3  2  1/2 3p  e x c i t a t i o n s  6 . 3  2  3p  Rb  c o r e  n s * ( n + l ) s  8 . 4  K  S e p a r a t i o n s  1 0 . 0  3/2  1 1 . 0  4d  9 . 7  a .  F r o m  b .  The  v a l u e  a n d  t h e  R e f .  b  2 7  g i v e n  w e i g h t e d  h e r e  i s  b i n d i n g  t h e  s e p a r a t i o n  e n e r g y  o f  t h e  b e t w e e n  4d  t h e  s p i n - o r b i t  s a t e l l i t e  d o u b l e t .  - 180 -  Mg  i s sought).  The c a l c u l a t e d v a l u e s corresponding  c a l c i u m and barium are not l i s t e d author  i n Table 4.11 as the  could not f i n d the a p p r o p r i a t e  energies f o r S c  to  transition  and L a .  +  +  There i s e x c e l l e n t agreement between the e x p e r i mental v a l u e s and the ns->-(n+l)s e x c i t a t i o n e n e r g i e s f o r a l l the a l k a l i metal vapors.  Of the a l k a l i n e e a r t h metals  the a p p r o p r i a t e data a r e a v a i l a b l e o n l y f o r magnesium and  strontium.  In the case of the Ca 2s, 2p, Sr 3d, and  Ba 4d x-ray p h o t o e l e c t r o n s p e c t r a t h e r e i s o n l y one s a t e l l i t e peak a s s o c i a t e d with a given main peak w i t h an energy s e p a r a t i o n of ^ 9 - l l e V , whereas f o r magnesium two s a t e l l i t e peaks were observed  at binding  energies  6.1 and 12.3eV higher than the main peak  (Table 4.11).  The s a t e l l i t e  spectrum may be  a t 12.3eV i n the magnesium  assigned t o a 3s->-4s t r a n s i t i o n u s i n g the e q u i v a l e n t cores approximation.  However the agreement here i s  not as good as t h a t o b t a i n e d f o r the a l k a l i metal atoms. The s a t e l l i t e  a t 6.1eV cannot be a s s i g n e d with any con-  f i d e n c e t o any t r a n s i t i o n u s i n g t h i s  approximation.  However, t h e r e i s a 3s-v4p t r a n s i t i o n i n n e u t r a l magnesium with an e x c i t a t i o n energy of 6.1eV i n d i c a t i n g t h a t t h i s peak may be due t o energy l o s s .  But, as i n d i c a t e d e a r l i e r ,  no s i g n i f i c a n t change i n the r e l a t i v e i n t e n s i t y o f t h i s peak was observed  on changing the o p e r a t i n g p r e s s u r e o f  - 181  -  the magnesium vapor making such an assignment questionable.  Comparison of t h i s r e s u l t w i t h the  s o l i d s t a t e s p e c t r a o f magnesium i s complicated, because of the presence  of s u r f a c e and bulk plasmons a t  16 7.3  and  10.7eV.  However, KLL Auger s p e c t r a of the  39 f r e e atom  do show d i s t i n c t f e a t u r e s due t o m u l t i -  electron excitation i n Although,  the  i n i t i a l hole s t a t e .  the e x c i t a t i o n source and the f i n a l s t a t e s  i n v o l v e d i n the two processes are r a t h e r d i f f e r e n t  an  i n t e r e s t i n g comparison can be made between the present 39 41 r e s u l t s and the Auger r e s u l t s ' f o r magnesium atoms. 39 Breuckmann and Schmidt  observed  satellites in  the Auger s p e c t r a of magnesium atoms, w i t h s e p a r a t i o n s of 5.5  and 11.7eV from the main l i n e s which were assigned  to 3s->-4s shakeup and shakeoff on the b a s i s of H a r t r e e Fock c a l c u l a t i o n s i n c l u d i n g c o n f i g u r a t i o n i n t e r a c t i o n . These Auger s p e c t r a were o b t a i n e d u s i n g a 3.8  keV  e l e c t r o n beam and the r e l a t i v e i n t e n s i t i e s of the s a t e l l i t e s to the main l i n e s were r e p o r t e d t o be  0.22  f o r the 5.5eV s a t e l l i t e and  one.  0.12  f o r the 11.7eV  The r e l a t i v e i n t e n s i t i e s of the two  s a t e l l i t e s at  6.1eV  and 12.3eV i n the x-ray p h o t o e l e c t r o n s p e c t r a o b t a i n e d i n t h i s work are 0.71  and  0.87  respectively.  the counting s t a t i s t i c s of the spectrum  Although,  shown i n F i g . 4.5  - 182  -  are not v e r y good, r e s u l t i n g  i n rather large errors  on t h e a b o v e v a l u e s , i t i s o b v i o u s t h a t t h e h e r e a r e much more i n t e n s e t h a n t h e A u g e r  satellites  satellites  39 r e p o r t e d by B r e u c k m a n n and  Schmidt.  i n e x c i t a t i o n e n e r g i e s may  p a r t l y be  t h i s discrepancy.  The  A l Ka  The  The  ^170eV  3.8keV e l e c t r o n s  threshold.  5s->-6s s h a k e u p t r a n s i t i o n e n e r g y e s t i m a t e d  s t r o n t i u m using the e q u i v a l e n t cores c o n s i d e r a b l y lower  found i n the  The  approximation  a l k a l i n e earth metals,  f a i l u r e of  so v a l i d  not  the  i n the case of  while being  is  A suitable  5s->-7s t r a n s i t i o n c o u l d  literature.  equivalent cores  for  approximation  than the observed v a l u e .  e x c i t a t i o n energy f o r the be  responsible for  r a d i a t i o n i s only  above t h e t h r e s h o l d e n e r g y w h i l e t h e a r e w e l l above the  difference  the  for  the  f o u r a l k a l i m e t a l atoms s t u d i e d , i s i n d i c a t i v e o f breakdown o f the o n e - e l e c t r o n former.  Such breakdowns can  configuration interaction configuration  interaction  p i c t u r e i n the case of be  c a u s e d by  (ISCI), f i n a l (FISCI)  configuration interaction.  h a v e o n l y one  f i n a l core  and  initial  ionic  the  state  state  continuum s t a t e  I n the group IA  a F I S C I m e c h a n i s m i s e x p e c t e d t o be u n i m p o r t a n t as t h e  the  elements  comparatively  ionized ionic  states  electron outside a closed s h e l l ,  whereas  - 183  -  i n g r o u p I I A e l e m e n t s w i t h two e l e c t r o n s i n t h e o u t e r incompletely f i l l e d  s h e l l a n d l o w l y i n g np and  (n-l)d  empty s u b s h e l l s , t h e r e i s a g r e a t e r p o s s i b i l i t y o f I S C I and F I S C I .  I t i s p o s s i b l e t h a t these c o n f i g u r a t i o n  i n t e r a c t i o n mechanisms a r e p l a y i n g an i m p o r t a n t determining  the s a t e l l i t e  role i n  s t r u c t u r e i n the a l k a l i n e  e a r t h atom c o r e l e v e l p h o t o e l e c t r o n s p e c t r a .  I n any  k i n d of a q u a n t i t a t i v e assignment of these m u l t i e l e c t r o n excitation  satellites  ( p o s i t i o n and i n t e n s i t y ) t h e  contribution to satellite shakeup  1  s t r u c t u r e through  a  'conjugate  m e c h a n i s m may h a v e t o be i n c l u d e d a s was  found  52 t o be t h e c a s e w i t h m e r c u r y .  4.4  Conclusions  The c o r e  b i n d i n g e n e r g i e s o f g r o u p I A and I I A m e t a l  atoms w e r e d e t e r m i n e d copy.  using x-ray photoelectron spectros-  T h i s w o r k shows t h a t e s t i m a t e s o f c o r e  energies obtained from a combination  of s o l i d  binding state  x - r a y e m i s s i o n a n d o p t i c a l d a t a f o r f r e e atoms c a n produce r e s u l t s which,  f o r favourable cases, are i n  e x c e l l e n t agreement w i t h t h e d i r e c t e x p e r i m e n t a l However, i n t h e case v a l u e i s lower  result.  o f c a l c i u m atoms, t h e e s t i m a t e d  by a b o u t 5eV f o r a l l l e v e l s f o r w h i c h  t h e c o m p a r i s o n s a r e made, and i n t h e c a s e o f b a r i u m  - 184  -  atoms, although the estimated v a l u e s agree w i t h the experiment  w i t h i n the quoted  e r r o r s , the accuracy of  the e s t i m a t i o n i s r a t h e r d o u b t f u l .  This  suggests  t h a t although x-ray emission v a l u e s f o r the  solid,  coupled w i t h f r e e atom o p t i c a l v a l u e s can be used  to  estimate f r e e atom b i n d i n g e n e r g i e s reasonably w e l l i n most cases, such i n d i r e c t e s t i m a t i o n s should be used only with g r e a t c a r e . The  importance  of the phase t r a n s i t i o n s h i f t between  the core b i n d i n g e n e r g i e s i n the s o l i d and vapor well recognized. may  For example,this  b i n d i n g energy  prove u s e f u l i n s t u d y i n g a d s o r b a t e - s u b s t r a t e  actions.  is  now  shift inter-  The phase t r a n s i t i o n s h i f t s f o r group IA and  IIA metals  (except f o r L i and Be) were estimated u s i n g  the experimental f r e e atom core l e v e l b i n d i n g e n e r g i e s measured i n t h i s work. photoemission  Due  t o l a c k of r e l i a b l e  r e s u l t s , v a l u e s from i n d i r e c t  x-ray  estimates  were used as the standard s t a t e b i n d i n g e n e r g i e s f o r 36 potassium,  rubidium, cesium,  c a l c i u m and barium. Poole  r e p o r t e d v a l u e s f o r the a l k a l i metal conduction band r e l a x a t i o n e n e r g i e s obtained s e m i e m p i r i c a l l y .  These  v a l u e s , though much s m a l l e r than those r e p o r t e d i n Table 4.10,  do show the same t r e n d  Rb 2.00eV, and Cs 2.02eV).  (Na 2.54eV, K 2.03eV,  T h e o r e t i c a l estimates of  - 185  -  extra-atomic r e l a x a t i o n based on a s e m i - l o c a l i z e d ex29 c i t o n model put forward by S h i r l e y ,  46 '  Ley  and  14 co-workers  are a l l ,  i n g e n e r a l , h i g h e r than the  experimental v a l u e s , however, the agreement can  be  c o n s i d e r e d good when the s i m p l i c i t y of the above model i s taken i n t o account.  T h i s model p r e d i c t s the t r e n d  of the phase t r a n s i t i o n s h i f t s f o r the elements s t u d i e d here r a t h e r a c c u r a t e l y , i n d i c a t i v e of the predominant r o l e p l a y e d by the extra-atomic i n determining the phase t r a n s i t i o n  relaxation  shift.  As reasonable peak-background r a t i o s were o b t a i n e d i n t h i s work i t was  a l s o p o s s i b l e t o study the m u l t i -  e l e c t r o n e x c i t a t i o n s a t e l l i t e s a s s o c i a t e d w i t h the main peaks.  Such a study can be extremely d i f f i c u l t on  the  s o l i d s t a t e s p e c t r a of these s p e c i e s because of the presence  of plasmons.  I t was  found t h a t the  satellites  could be a s s i g n e d to a ns-> (n+1) s type shakeup e x c i t a t i o n u s i n g the e q u i v a l e n t cores approximation atoms. could  The not  for a l k a l i  metal  s a t e l l i t e s found i n a l k a l i n e e a r t h metal atoms be assigned unambiguously u s i n g a simple  e l e c t r o n p i c t u r e , where the s i t u a t i o n i s c o m p l i c a t e d , p o s s i b l y , by i n i t i a l configuration  s t a t e and  interaction.  final ionic  state  one  - 186 -  REFERENCES 1.  J.M. Dyke, N.K. Fayad, A. M o r r i s , and I.R. 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These authors were able to r e s o l v e three  t i o n a l components w i t h a s e p a r a t i o n o f 0.4 3eV and i n t e n s i t i e s 0.61,  0.33  and 0.06.  The v e r t i c a l  p o t e n t i a l was observed a t 290.72 (15) .  vibrarelative  ionization  The value quoted  here i s a weighted mean o f the three components. 23.  H. H i l l i g ,  B. C l e f f , W. Mehlhorn, and W. Schmitz,  Z. Phys. 268, 225 24.  (1974)  C. F r o e s e - F i s c h e r , Hartree-Fock Program with C o n f i g u r a t i o n M i x i n g , U n i v e r s i t y o f Waterloo, O n t a r i o , Canada, 196 8  25.  M.S.  Banna, and D.A.  R e l a t . Phenom. 8, 23 26.  Shirley, J . Electron  Spectrosc.  (1976)  K. Siegbahn, C. N o r d l i n g , A. Fahlman,  R. Nordberg, K.  Hamrin,  J . Hedman, G. Johansson, T. Bergmark, S. - E. K a r l s s o n , I. L i n d g r e n , and B.J. L i n d b e r g , "ESCA: Atomic, M o l e c u l a r and S o l i d State S t r u c t u r e S t u d i e d by Means o f E l e c t r o n Spectroscopy", Nova A c t a Regiae Soc. S c i . U p s a l i e n s i s , Ser IV, V o l . 20 27.  (Almqvist and W i k s e l l s , Stockholm,  C.E. Moore, "Atomic Energy L e v e l s " C i r c u l a r No. 462  (1949, 1952  N a t l . Bur. Stand.  and 1958), V o l s .  28.  J.A. Bearden, Rev. Mod.  29.  D.A.  S h i r l e y , Chem. Phys. L e t t . 16_, 220  30.  P.H.  C i t r i n , a n d D.R.  301  (1973)  Phys. 39_, 78  1967)  1-3  (1967) (1972)  Hamarmann, Chem. Phys. L e t t .  22,  - 189 -  31.  M.W.D. M a n s f i e l d , Proc. R. Soc. London A 346, 555 (JL9.75).  32.  S. Svensson, N. Mclrtensson, E. B a s i l i e r , P.A. Malmquist, U.  G e l i u s , and K. Siegbahn, P h y s i c a S c r i p t a 14_, 141 (.19 76).  33.  E. McGuire, Phys. Rev. A 5 , 1043 (JL972)  34.  E. McGuire, Phys. Rev. A 5, 1052 (.1972).  35.  G. Ebbinghause, W. Braun, and S. Simon, B 31, 1219 (1976).  Z. N a t u r e f o r s c h .  The b i n d i n g e n e r g i e s o f the 4p l e v e l s  i n Rb and the 5p l e v e l s i n Cs have a l s o been r e p o r t e d by R.G. Oswald, and T.A. C a l l c o t , Phys. Rev. B 4_, 4122 (1971).. The v a l u e s o f Oswald and C a l l c o t t d i f f e r by 0.1 - 0.3eV from those o f Ebbinghaus e t al_. , b u t are w i t h i n the e r r o r s quoted by the former. Ebbinghaus e t al_.  The more r e c e n t v a l u e s o f  have been used i n t h i s study.  36.  R.T. Poole, Chem. Phys. L e t t . 42, 151 (.19 76).  37.  N.G. K r i s h n a n , W.N. Delgass, and W.D. Robertson, J.  Phys. F 7, 2623 (.1977).  38.  G.H. Newsom, A s t r o p h y s . J .  166 , 243  (.1971)  39.  B. Breuckmann, and V. Schmidt, Z. Phys. 268, 2 35  40.  W. Mehlhorn, and W.N. Asaad, Z. Phys. 191, 231 (.1966).  41.  B. Breuckmann, J .  42.  M.W.D. M a n s f i e l d , and J . P . Connerade, Proc. Roy. Soc.  (19 74).  Phys. B 12_, L609 (.19 791  London A 342, 421 (19 75). 43.  J.A. Bearden, and A.F. Burr, Rev. Mod. Phys. 39_. 125 (1967)  44.  American I n s t i t u t e o f P h y s i c s Handbook, 3rd E d i t i o n , Chap. 9, p. 172  (1972).  - 190 -  45.  D.L. E d e r e r , T.B. L u c a t o r t o , E.B. Saloman, R.P. Madden, and J . Sugar, J . Phys. B 8, L21 (_1975)_  46.  D.A. S h i r l e y , Chem. Phys. L e t t . 1 7  47.  J . F r i e d e l , P h i l o s . Mag. 43_, 153 (1952).  48.  J . F r i e d e l , Adv. Phys. 3, 446 (1954).  49.  I.V. H e r t e l , and K.J. Ross, J . Phys. B 2, 285 (_1969)_  50.  I.V. H e r t e l , and K.J. Ross, J . Phys. B 2, 484 (.1969).  51.  T.A. W i l l i a m s , and A.W.  f  312 (19 72),  Potts, J . Electron Spectrosc.  R e l a t . Phenom. 8, 331 (.19 76). 52.  J . Berkowitz, J . L . Dehmer, Y.K. Kim, and J.P. Desclaux, J . Chem. Phys. 61, 2556 (.1974)  - 191  -  CHAPTER F I V E  X-RAY PHOTOELECTRON SPECTROSCOPY OF  5.1  TITANIUM TETRAHALIDE VAPORS  Introduction  X-ray p h o t o e l e c t r o n  spectroscopy  (XPS)  has  used e x t e n s i v e l y t o study the p r o p e r t i e s of t r a n s i t i o n m e t a l compounds. w o r k has  A great  solid  d e a l of  this  b e e n c o n c e r n e d w i t h t h e phenomenon o f  m u l t i e l e c t r o n e x c i t a t i o n ( s h a k e u p ) and of  been  satellite  the  l i n e s i n the p h o t o e l e c t r o n  appearance  spectra  of  the  1 — 16 metal core l i n e s , p a r t i c u l a r l y However, s y s t e m a t i c  studies  the  i n the  2p  shell.  solid  state/of  s o m e t i m e s r a t h e r weak s a t e l l i t e s a s s o c i a t e d e l e c t r o n e x c i t a t i o n h a v e b e e n hampered by  the  with multi-  the  o f l a r g e b a c k g r o u n d s due  to i n e l a s t i c  and  I t i s , therefore, possible  plasmon e x c i t a t i o n .  e l i m i n a t e the the  electron  presence  i n t e r f e r e n c e o f t h e s e e f f e c t s by  compounds i n t h e v a p o r I n t h i s c h a p t e r a gas  collisions  studying  phase. phase x - r a y  to  photoelectron  - 192 -  spectroscopic  study of the 3 d  0  compounds T i X ^ (X=F,  CI, Br, I) w i t h p a r t i c u l a r emphasis on the s t r u c t u r e due  t o shakeup e x c i t a t i o n w i l l be p r e s e n t e d .  complication  A  o f t e n encountered i n a study o f t h i s  i s the presence of s t r u c t u r e on the metal core to m u l t i p l e t s p l i t t i n g . complication  i s present  kind  l i n e s due  However, no such a d d i t i o n a l i n the d° compounds  considered  here. Strong s a t e l l i t e s i n the inner  s h e l l XPS s p e c t r a o f 6 7  3d°  compounds were f i r s t observed by Wallbank et_ a l . ' .  The  s a t e l l i t e s were i n t e r p r e t e d as due t o shakeup from  the l i g a n d v a l e n c e o r b i t a l s t o the empty 3d o r b i t a l s of the metal i o n (e^ -»- e* s a t e l l i t e s i n other i n the same way. 3d°  4  i n 0^ symmetry) .  Similar  t r a n s i t i o n metal i o n s were  explained  L a t e r experimental w o r k ^ ' ^ on the 1  systems showed a s a t e l l i t e  structure  1  somewhat  d i f f e r e n t from t h a t known p r e v i o u s l y as shakeup e x c i t a t i o n s of the type t g 2  Molecular  t*g  a l s o seemed t o be  o r b i t a l c a l c u l a t i o n s have shown t h a t  present. high  s a t e l l i t e i n t e n s i t i e s may be expected f o r shakeup 17-21 t r a n s i t i o n s of the l i g a n d - t o - m e t a l I t should  3d type.  a l s o be mentioned t h a t , more r e c e n t l y ,  ligand-to-metal  4s or 4p shakeup t r a n s i t i o n s have a l s o 22-24 been suggested as the o r i g i n o f s a t e l l i t e s , on the  - 193  -  b a s i s of m u l t i p l e s c a t t e r i n g c a l c u l a t i o n s .  These  assignments of the shakeup t r a n s i t i o n s are made wholly on the b a s i s of the agreement between the experimental data and separations  the c a l c u l a t e d hole  s t a t e energy  f o r these types of t r a n s i t i o n s . However, 21  i t has  been suggested  t h a t such t r a n s i t i o n s would  not produce s a t e l l i t e s w i t h any  appreciable i n t e n s i t y .  From the above d i s c u s s i o n i t i s obvious t h a t  the  assignment of the shakeup t r a n s i t i o n s i n the t r a n s i t i o n metal core l e v e l s p e c t r a i s s t i l l an r e s o l v e d problem.  incompletely  I t i s hoped t h a t t h i s study of  the  t i t a n i u m t e t r a h a l i d e s i n the vapor phase w i l l  shed some  l i g h t on the problem s i n c e the e f f e c t s on the  satellites  of changing the l i g a n d s without changing the the c e n t r a l metal i o n  symmetry of  ( a l l four compounds are known to 25-28  have t e t r a h e d r a l symmetry i n the gas phase  )  be examined.  symmetry  A l s o , the e f f e c t of changing the  without changing the metal i o n or l i g a n d s may  may  be  considered  by comparing the gas phase d a t a f o r T i F ^ with t h a t published  f o r the  solid,  the  s t r u c t u r e of which i s  thought t o be c h a i n - l i k e w i t h the t i t a n i u m having 27 29 co-ordination.  '  already  six-fold  30 '  A p a r t of t h i s work has  elsewhere. Experimental d e t a i l s w i l l be d i s c u s s e d  appeared  31  i n the  next  - 194  section.  -  The r e s u l t s w i l l be presented and d i s c u s s e d  i n S e c t i o n 5.3.  The c o n c l u s i o n s are g i v e n i n S e c t i o n  5.4.  5.2  Experimental  The spectrometer used i n t h i s study has been d e s c r i b e d i n d e t a i l i n Chapter Three. TiF^, T i C l  4  Samples of  and T i B r ^ were o b t a i n e d commercially  (K and  K L a b o r a t o r i e s Inc.) and used without f u r t h e r  purification.  T i l ^ was  iodide with  prepared by the r e a c t i o n of hydrogen 32  t i t a n i u m t e t r a c h l o r i d e i n benzene was  p u r i f i e d by s u b l i m a t i o n .  moisture s e n s i t i v e , and  and the sample o b t a i n e d  A l l four t e t r a h a l i d e s are  so were handled at a l l times i n  a dry, i n e r t atmosphere. The t e t r a c h l o r i d e and the tetrabromide were i n t r o d u c e d i n t o the spectrometer from a g l a s s m a n i f o l d f i t t e d w i t h a t e f l o n stop-cock, the  c h l o r i d e being mantained  a t 0°C  to help c o n t r o l the vapor p r e s s u r e and the bromide being s t u d i e d at room temperature.  T i F ^ and T i l  4  were p l a c e d  i n s i d e the spectrometer and heated to 'vlOCC and ^75°C, r e s p e c t i v e l y , t o obtain a s u f f i c i e n t vapor p r e s s u r e (^3x10 -2 torr).  Samples were then i r r a d i a t e d w i t h A l Ka x-rays t o  o b t a i n the p h o t o e l e c t r o n s p e c t r a .  - 195 -  In the f i r s t few hours a f t e r sample l o a d i n g i t was  observed  t h a t the r a t i o s of the halogen core  l e v e l s t o the t i t a n i u m l e v e l s were much g r e a t e r  than  33 was expected  i n d i c a t i n g the presence of the hydrogen  h a l i d e s and/or f r e e halogens.  T h e r e f o r e , the samples  were l e f t a t the o p e r a t i n g c o n d i t i o n s f o r s e v e r a l hours before data were taken t o ensure t h a t a l l HX and/or X were removed and t h a t the s u r f a c e s of the gas c e l l had become ' c o n d i t i o n e d ' . that data obtained  2  spectrometer  To f u r t h e r ensure  f o r the halogen core l e v e l s were not  contaminated w i t h HX o r X , s p e c t r a of the t i t a n i u m 2p and 2  3p l e v e l s were taken before the halogen data were o b t a i n e d thus m a i n t a i n i n g a p e r i o d o f a t l e a s t three days between l o a d i n g the sample and studying the halogen core Spectra of hydrogen i o d i d e and molecular taken  levels.  i o d i n e were a l s o  f o r comparison with T i l ^ . The  T i 2p l e v e l s were r e f e r e n c e d t o the N I s l e v e l 34  of  N  (409.93eV  2  ), which was i n t r o d u c e d  w i t h the gas i n q u e s t i o n .  simultaneously  The T i 3p, Br 3d and I 4d  l e v e l s were s i m i l a r l y r e f e r e n c e d u s i n g the known Ne 2s 34 b i n d i n g energy (48.47eV ). The F I s and I 3d l e v e l s 35 were r e f e r e n c e d t o the F I s l e v e l of SFg (695. (MeV and the C l 2p,Br 3p and I 4s l e v e l s t o the S 2p.^ of  SF  (180.28eV ). 36  6  2  ) level  - 196  All  -  s p e c t r a were l e a s t - s q u a r e s  p e a k p o s i t i o n s , l i n e w i d t h s and  fitted  to  obtain  areas using the  program  37 d e s c r i b e d by  5.3  Fadley.  R e s u l t s and  The  binding energies  l e v e l s , and Tables  Discussion  5.1  o f t h e t i t a n i u m 2p and  v a r i o u s halogen l e v e l s are and  5.2  respectively.  titanium binding energies  The  summarized i n s h i f t s of  f o r each l e v e l  e l e c t r o n e g a t i v i t y t r e n d of the  the  f o l l o w the  halogens with a  c h a n g e b e t w e e n t h e t e t r a f l u o r i d e and  3p  large  t e t r a c h l o r i d e and  s m a l l e r changes between t h e t e t r a c h l o r i d e , -bromide - i o d i d e , as w o u l d be certain  expected.  l e v e l s i n the  The  h a l i d e s may  v i o u s l y published data  and  binding energies  be c o m p a r e d w i t h  f o r the halogens, X , 2  and  of  pre-  the  38 h y d r o g e n h a l i d e s , HX, i n the present 5.2)  study  (X=F,Cl,Br), f o r HI and  and  I,,.  the data  I t can  t h a t the t e t r a h a l i d e b i n d i n g energies  from those halogen core  f o r HX  and  X , 2  products  and  are  seen  (Table  different  i n d i c a t i n g t h a t the  l e v e l s p e c t r a a r e n o t due  decomposition  be  obtained  recorded  to h y d r o l y t i c or  thus confirming  that  the  methods used f o r o b t a i n i n g the T i X ^ s p e c t r a as o u t l i n e d i n S e c t i o n 5.2  were s a t i s f a c t o r y .  binding energies  reported  Comparison of  here w i t h p r e v i o u s l y  the  published  - 197 -  T a b l e  5 . 1  T i  2p  a n d  3p  b i n d i n g  e n e r g i e s ( e V )  i n  T i X  4  ( X = F , C l , B r , 1 )  b 2  T i F  4  T i C l  4  T i B r  4  T i l  4  p  l / 2  3  2  P  3  / 2  a  4 7 3 . 8  4 6 8 . 6  4 7 . 5  4 7 1 . 5  4 6 5 . 4  4 4 . 6  4 7 0 . 5  4 6 4 . 4  4 3 . 7  4 6 9 . 8  4 6 3 . 8  4 2 . 6  a  R e f e r e n c e d  t o  t h e  N  b  R e f e r e n c e d  t o  t h e  Ne  I s  2s  l e v e l  o f  b i n d i n g  N  2  ( 4 0 9 . 9 3 e V  e n e r g y  3  4  ( 4 8 . 4 7 e V  )  3  4  )  Table  5.2  Halogen  a  F Is 692.8 693.  2p 1/2  C l 2p  3/2  core b i n d i n g energies  B r 3p  1/2  B r 3p  3/2  (eV) i n T i X , HX a n d X-, (X=F,C1 , B r ,1) 4  3/2  I 3d5/2  I 4s  637.3°  625.9°  193.9^  I 3d  Br 3d  I 4d  3/2  I 4< d  5/2  a  ft  696.2  b  207.7°  206.6^ 207.2 207.6<T 196.9^  189. B  76.5  U  77.06" 77.10 1  57.9"  56 57 57  a  Referenced t o t h e F I s l e v e l o f SFg (695.04eV  b  From R e f . 38  c  R e f e r e n c e d to t h e S 2 p  d  R e f e r e n c e d t o t h e Ne 2s l e v e l (48.47eV  3 / 2  level of SF  35, )  36, (180.28eV ") J  g  3 4  )  - 199 -  data  i s p o s s i b l e o n l y f o r t h e C l 2p  tetrachloride.  Avanzino et a l .  3/2  l e v e l of titanium  have o b t a i n e d  a value  o f 205.77eV f o r t h i s b i n d i n g e n e r g y w h i c h i s i n v e r y agreement w i t h t h e p r e s e n t v a l u e s t u d y t h e C l 2p l e v e l o f SFg  (206.6eV).  poor  In this  3/2 l e v e l was r e f e r e n c e d t o t h e S 2p 3/2  ( C l 2p-S 2p s e p a r a t i o n i s o n l y ^26eV) a n d  so some u n c e r t a i n t y due t o l e a s t - s q u a r e s f i t t i n g  of the  r a t h e r p o o r l y r e s o l v e d S 2p d o u b l e t  However,  it  i s not expected  that this  i s present.  should exceed  ±0.2eV.  39 U n f o r t u n a t e l y , A v a n z i n o e t a_l. used t o r e f e r e n c e t h e i r  do n o t r e p o r t t h e m e t h o d  spectrum.  S p e c t r a o f t h e T i 2p r e g i o n s o f e a c h o f t h e t e t r a h a l i d e s a r e shown i n F i g s . 5 . 1 - 5 . 4 . lines  labelled  electron  ' s a t ' i n these  energy l o s s  these  t h e p o s s i b i l i t y o f p e a k s due t o S p e c t r a were  pressures, but the r e l a t i v e  s a t e l l i t e s d i d n o t change  that they are indeed To f u r t h e r t e s t  multi-  However, i n any s t u d y o f  h a s t o be c o n s i d e r e d .  at d i f f e r e n t  photoelectron  F i g u r e s a r e due t o  (shakeup) e x c i t a t i o n .  r a t h e r weak s a t e l l i t e s ,  The  obtained  i n t e n s i t i e s of  significantly,indicating  due t o m u l t i e l e c t r o n e x c i t a t i o n .  t h i s conclusion, the N I s x-ray  photo-  e l e c t r o n s p e c t r u m o f g a s e o u s n i t r o g e n was o b t a i n e d presence of t i t a n i u m t e t r a c h l o r i d e pressure.  The N I s l i n e i n N  2  at a typical  i s separated  f r o m t h e T i 2p l i n e s , a n d i t i s e x p e c t e d  i n the  operating  by o n l y  that the  ^60eV scattering  - 200 -  10-  Tif^  2  P /2 3  •  •  8  o  Sin 6 +->  c  ZJ O  u  4  A' 1  2  sat/ \ sat.  2-  1  V  J  sat. if  •*/  \  /\  % \ V  1  X  •/  V  ^»-^  T»  >  1I .  480  \  I  i1—  470  Binding energy (eV) F i g . 5.1.  P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n from t i t a n i u m t e t r a f l u o r i d e obtained w i t h A l K a x-rays.The peaks l a b e l l e d ' s a t ' are due to multielectron excitation.  - 201 -  480 Fig.  470 Binding energy (eV)  5.2. P h o t o e l e c t r o n spectrum of the t i t a n i u m 2p r e g i o n from t i t a n i u m t e t r a c h l o r i d e obtained with A l K a x-rays.The peaks l a b e l l e d 'sat' are due t o multielectron excitation.  - 202  480 Fig.  5.3.  -  470 Binding energy (eV)  P h o t o e l e c t r o n s p e c t r u m o f t h e t i t a n i u m 2p r e g i o n from t i t a n i u m t e t r a b r o m i d e o b t a i n e d w i t h A l Ka x - r a y s . T h e p e a k s l a b e l l e d ' s a t ' a r e due t o multielectron excitation.  -  480 Fig.  5.4.  203  -  470 Binding energy (eV)  P h o t o e l e c t r o n s p e c t r u m o f t h e t i t a n i u m 2p r e g i o n from t i t a n i u m t e t r a i o d i d e o b t a i n e d w i t h A l Ka x - r a y s . T h e p e a k s l a b e l l e d ' s a t ' a r e due t o m u l t i e l e c t r o n e x c i t a t i o n .  - 204  cross-section of T i C l the photoelectron constant. present  -  o v e r such a s m a l l change i n  4  k i n e t i c energy i s  Thus any  s t r u c t u r e due  i n t h e T i 2p  the N I s spectrum.  approximately  to i n e l a s t i c  spectrum should No  collisions  a l s o be o b s e r v e d i n  s t r u c t u r e was  o b s e r v e d a t ^4  and  ^9.5eV h i g h e r b i n d i n g e n e r g y t h a n t h e N I s p e a k . Therefore,  the  s a t e l l i t e s w i t h the  r e l a t i v e i n t e n s i t i e s given  separations  i n T a b l e 5.3  can  and  be  a t t r i b u t e d to m u l t i e l e c t r o n e x c i t a t i o n processes  with  certainty. I n a l l f o u r t i t a n i u m t e t r a h a l i d e s two observed  on t h e T i 2 p , 3 /  w h i l e o n l y one  2  peaks  ( a t 7-13eV and  i s o b s e r v e d on t h e  q u i t e p o s s i b l e t h a t t h e r e a r e two w i t h the  2p^y  separations  p e a k s , and  2  ^-"9-^/2  are not r e s o l v e d from the  s a t e l l i t e w o u l d be  expected to f a l l  2  satellite  e a  2p ^ 3  for a l l four  2  ^ * s  smaller  (this  r e p o r t e d on intensities.  the  second  w i t h i n ^ l e V of  (Table  5.3  and  the  l i n e s but w i t h 5.4).  photo-  halogen core  same s e p a r a t i o n s  b o t h o f t h e T i 2p  with  tetrahalides).  e l e c t r o n s p e c t r a o f t h e T i 3p and have a p p r o x i m a t e l y  s  associated  S a t e l l i t e s are a l s o observed i n the x-ray  and  i  I t  satellites  peaks  The  o b s e r v e d a t 2-7eV h i g h e r b i n d i n g e n e r g i e s  are  2-7eV)  t h a t the ones w i t h  from the  3  P  satellites  7-13eV s e p a r a t i o n s  2p ^  satellites  levels,  as  those lower  satellites than  the  -  Table  5.3  Satellite  separations,  intensities, of  AE,  (eV)  and  I , i n t h e T i 2p a n d  3p  relative spectra  TiX (X=F,Cl,Br,I) 4  AE  TiF  -  205  2p  1  /  2  (I)  13.9(0.43).  4  TiF,(solid) 4  AE  2p  3  /  2  (I)  AE  13.0t.19) ,7.1(.12)  3p(I)  13.3(.27)  14.7(.ll)  3  TiCl  4  9. 8 (0 .41)  9.4 (. 16) ,4. 0 ( .14)  9. 7 (.09)  TiBr  4  8.9 (0 .40)  8.5 ( .14) , 3. 3 ( . 0 6 )  9 . 3 (.13)  7 . 3 ( 0 .25)  7.2 (.18) ,2 .1 (.06)  Til  4  a  F r o m Re f .  b  A s a t e l l i t e on observed  -  b  8  t h e T i 3p l i n e  of T i l  4  because of i n t e r f e r e n c e from  e x c i t e d by A l K a ^ r a d i a t i o n . 4  could I 4d  not  be  electrons  Table  5.4  s ^ i i t e TJXQ  F I s (I) TiF  (X=F,Cl,Br,I)  2p  1 / 2  (I)  a  2p3/2(1)  Br 3 p y ( I ) 1  2  Br  3py (I) 2  Br 3d(I)  I  3d  3 / 2  (I)  I  3(^^(1)  I 4d  3 / 2  (I)  I 4d  5 / 2  (I)  12.3(.04)  4  TiCl  a  s e p a r a t i o n s (eV) and r e l a t i v e i n t e n s i t i e s , I , i n the halogen oore l e v e l s p e c t r a of  4  10.6(.09)  11.2(.04) 8 . K . 0 5 )  TiBr Til,  9.6(.09)  9.5(.06)  10.5(.03)  4  6.6 (.06)  6.5 (.05)  6.6(.04)  6.7 (.02)  O  - 207  2p^2  l i n e s were not  -  observed i n the  3p  spectra.  (Fig.  5.5).  8—  Recent m u l t i p l e NiFg"  1 8  '  2 1  s c a t t e r i n g c a l c u l a t i o n s on TiOg  p r e d i c t the  3p s a t e l l i t e s to be ^50-80%  as i n t e n s e as those on the  2p l i n e s , i n reasonable  agreement w i t h the data presented here. of the  I 3d r e g i o n  The  spectrum  of T i l ^ i s shown i n F i g u r e 5.6.  bromine core l e v e l s i n i B r ^ showed s i m i l a r T  s a t e l l i t e s but  and  The  well-defined  those observed f o r the t e t r a f l u o r i d e  and  t e t r a c h l o r i d e were somewhat broader. V a r i a t i o n of the T i 2p^y  satellite  and  the T i 2p^y  the  l i g a n d i s shown i n F i g . 5.7.  a n c 2  r e s u l t s i n four  ^  2  t n e  T  i ^p b i n d i n g  separations,  energies with  I t can  essentially parallel  be  seen t h a t  l i n e s showing  a good c o r r e l a t i o n between l i g a n d e l e c t r o n e g a t i v i t y satellite  T i F ^ i n the  spectra  s o l i d state  t h a t both the  of the T i 2p r e g i o n s of  w i t h the present data shows  s a t e l l i t e separation  and  intensity  are  s e n s i t i v e t o changes i n symmetry w h i l e the metal i o n  For  remain the a precise  assignment of the observed  undertaken no  satellites  energy s e p a r a t i o n s  w e l l as the i n t e n s i t i e s are r e q u i r e d . p r o j e c t was  and  same.  hole s t a t e c a l c u l a t i o n s of the  f o r any  and  separation.  Comparison of the  ligands  this  as  At the time t h i s  such c a l c u l a t i o n s were a v a i l a b l e  of these molecules, but  the  subsequent  publication  -  I  208  .  -  I  l_J  60 50 Binding energy (eV) Fig. 5.5.  P h o t o e l e c t r o n spectrum of the t i t a n i u m 3p r e g i o n from t i t a n i u m t e t r a f l u o r i d e obtained with A l Ka x-rays.The peak l a b e l l e d ' s a t ' i s due t o m u l t i electron excitation.  - 209 -  640 630 Binding energy (eV) F i g . 5.6. P h o t o e l e c t r o n spectrum of the i o d i n e 3 d r e g i o n from t i t a n i u m t e t r a i o d i d e obtained w i t h A l K a x-rays.The peaks l a b e l l e d 'sat' are due t o multielectron excitation.  - 210 -  F Fig.  5.7.  Cl  Ligand  Br  V a r i a t i o n of the T i 2p-. s a t e l l i t e separations ( • and 0 ) and the T i 2 p , (A) arid T i 3p ( A ) b i n d i n g e n e r g i e s w i t h ligana.Note,the o r d i n a t e only g i v e s r e l a t i v e b i n d i n g e n e r g i e s . 3 /  - 211 -  of these r e s u l t s  31  has l e d t o a SCF Xa molecular  o r b i t a l c a l c u l a t i o n of the ground s t a t e and T i 2p core 40 ion state f o r T i C l ^ w i l l be d i s c u s s e d  .  The r e s u l t s of t h i s c a l c u l a t i o n  later.  In c o n s i d e r i n g  the assignment  of the s a t e l l i t e s , and i n the absence of hole  state  c a l c u l a t i o n s , as i n the cases of T i F , T i B r ^ and T i l ^ , 4  i t might be thought u s e f u l t o compare the s e p a r a t i o n the  s a t e l l i t e s w i t h the ground s t a t e o r b i t a l  of  separations.  However, the s e p a r a t i o n s of the v a l e n c e o r b i t a l s can 22-24 change d r a s t i c a l l y on i o n i z i n g a core e l e c t r o n . Some i n f o r m a t i o n may a l s o be gained by c o n s i d e r i n g the r e s u l t s of a v a i l a b l e hole s t a t e c a l c u l a t i o n s on the octahedral  3d° systems T i F  2 -  and TiOg".  1  7  '  1 8  '  2 1  '  2  2  17 18 21 Larsson  '  '  has concluded from h i s c a l c u l a t i o n s  t h a t the s a t e l l i t e s are due t o l i g a n d - t o - m e t a l 3d charge t r a n s f e r t r a n s i t i o n s of the types t ~ -* t„ and/or 2g 2g * e g ->- e g . He has observed t h a t the i n t e n s i t*y of t h i s J j r  type of t r a n s i t i o n i s very dependent on the amount of charge t r a n s f e r r e d from the l i g a n d s  t o the c e n t r a l i o n  upon i o n i z a t i o n , whether or not the c e n t r a l i o n component of the mainly l i g a n d o r b i t a l i s small b e f o r e i o n i z a t i o n . I t i s i n t e r e s t i n g t o note t h a t here one has two competing f a c t o r s s i n c e a more c o v a l e n t  l i g a n d has a l a r g e r c e n t r a l  i o n component b e f o r e i o n i z a t i o n , but leads t o more charge being t r a n s f e r r e d from the l i g a n d s  t o the c e n t r a l i o n  - 212 -  upon  ionization.  F o r t h e m o l e c u l e s s t u d i e d i n t h i s work t h e t r a n * * s i t i o n s a n a l o g o u s t o t h e e -y e and t _ -*- t„ g g 2g 2g y  transitions * e  i n octahedral  e , respectively.  symmetry, a r e t  In the octahedral  •+ t ^  2  T i (IV)  2— 8— compounds, T i F , and T i O , , t h e m o s t p r o m i n e n t b b were a s s i g n e d  t o t h e e^ -»- e*  and  satellites  t r a n s i t i o n although  b a s i s o f t h e i n t e n s i t i e s c a l c u l a t e d by L a r s s o n  on t h e  i t i s not  p o s s i b l e t o r u l e o u t t h e t„ t„ transitions. Itis 2g 2g very tempting t o assign the s a t e l l i t e s w i t h the l a r g e r s e p a r a t i o n s o b s e r v e d i n t h e T i 2p s p e c t r a o f t h e T i ( I V ) *  h a l i d e s a s b e i n g due t o t h e t  t r a n s i t i o n s and * separations to e e . However,  the ones w i t h s m a l l e r  2  •> t  2  4-  t h e c a l c u l a t i o n s on T i F g sitions field t  2  should  s u g g e s t t h a t t h e two t r a n -  o n l y be s e p a r a t e d 17  s p l i t t i n g o f a b o u t 3eV  levels  should  by t h e o r d i n a r y l i g a n d  , s i n c e the lower  have a p p r o x i m a t e l y  e^ a n d  t h e same e n e r g y .  I f t h i s i s the case f o r the t e t r a h e d r a l molecules  studied  here,  separated  by the  then the t  approximately satellites  2  and e s a t e l l i t e s 4/9 o f t h i s ,  should  o n l y be 41  i . e . , ^1.5eV.  observed f o r the T i 2 p y 3  2  However,  l e v e l s of the  f o u r t*i t a n i u m t e t r * a h a l i d e s a r e s e p a r a t e d by 5-6eV, a n d 2 2 doubtful. t h i s makes t h e a s s i g n m e n t o f t h e two s a t e l l i t e s t o t  t  a  n  d  e  e  r  a  t  n  e  r  - 213 -  . At t h i s  p o i n t i t i s i n t e r e s t i n g t o c o n s i d e r the 22-24  arguments of Tossell observed  who a s s i g n s the s a t e l l i t e s  i n T i 0 , MnF 2  and M n l  2  2  t o be l i g a n d - t o - m e t a l  4s or -4p t r a n s i t i o n s on the b a s i s o f the hole s t a t e energy  s e p a r a t i o n s o b t a i n e d from m u l t i p l e s c a t t e r i n g  calculations.  In the p r e s e n t case then, one c o u l d  a s s i g n the w e l l separated s a t e l l i t e s t o t h i s type o f t r a n s i t i o n and the o t h e r s t o the l i g a n d - t o - m e t a l 3d *  type  ( e i t h e r the t -+ t  *  t r a n s i t i o n or both) . 2In f a c t the m u l t i p l e s c a t t e r i n g c a l c u l a t i o n s on T i F ^ * show an e  -»• e  o r e -> e  t r a n s i t i o n energy  o f 7.6eV which  i n d i c a t e s t h a t the 7.1eV s e p a r a t i o n observed  for TiF^  i n the present study i s o f the r i g h t magnitude f o r a 40 l i g a n d - t o - m e t a l 3d t r a n s i t i o n . performed  Tossell  has r e c e n t l y  SCF X a MO c a l c u l a t i o n s on the ground s t a t e and  the T i 2p c o r e i o n s t a t e f o r T i C l ^ and has estimated s a t e l l i t e s e p a r a t i o n s o f 3.0 and 4.6eV f o r l i g a n d - t o * * metal  3d type e  The weighted  e  average  and t  2  t  2  excitations respectively.  o f these s e p a r a t i o n s , 3.7eV, agrees 40  v e r y w e l l w i t h the experimental v a l u e o f 4.0eV.  Tossell  has a l s o estimated t h e e n e r g i e s f o r two monopole t r a n s i t i o n s from the l i g a n d t o the C13p-Ti 4s/4p a n t i b o n d i n g o r b i t a l s which a r e a t 9.9 and 10.6eV higher b i n d i n g  energy  than the main l i n e . Although, these v a l u e s agree v e r y w e l l  - 214 -  with the experimental i n d i c a t e t h a t these transitions will  v a l u e o f 9.4eV, B r a g a a n d L a r s s o n  l i g a n d - t o - c o n d u c t i o n band  be v e r y weak.  Despite  the fact  t h e l i g a n d - t o - m e t a l 3d t y p e c h a r g e - t r a n s f e r t r a n s i t i o n s a r e supposed t o  type that  shakeup  be t h e s t r o n g e r  multi-  17 18 21 electron transitions, here,  '  '  i n the molecules  studied  the s a t e l l i t e s with the larger separations are the  more i n t e n s e . So f a r t h e d i s c u s s i o n h a s c o n s i d e r e d the b a s i s o f o n e - e l e c t r o n  transitions.  the data  on  However, M a r t i n  42 and  Shirley  have s u g g e s t e d  that c a l c u l a t i o n s of  e l e c t r o n shakeup p r o b a b i l i t i e s ration mixing  i n both  should  the i n i t i a l  include configu-  and f i n a l s t a t e s .  Complete breakdown o f t h e o n e - e l e c t r o n model has a l s o been o b s e r v e d  i n t h e p h o t o i o n i z a t i o n o f t h e 4p s u b s h e l l 43 44  i n Xe a n d a d j a c e n t necessary  elements.  '  Therefore  i t may be  t o c o n s i d e r many e l e c t r o n e f f e c t s i n t h e c o r e  photoelectron  spectra of titanium t e t r a h a l i d e s i n order  to e x p l a i n the observed  satellite  s e p a r a t i o n s and  intensities. From T a b l e  5.1, i t c a n be s e e n t h a t t h e s e p a r a t i o n  o f t h e 2p s p i n - o r b i t d o u b l e t  i s 5.2eV i n t i t a n i u m  t e t r a f l u o r i d e while f o r the other t e t r a h a l i d e s i t i s 6.0eV.  T h i s i s t o o l a r g e a change f o r c h e m i c a l  effects  - 215  -  as these would be expected to be o n l y ^O.leV. The 9 explanation separation  10 '  f o r changes i n the  spin-orbit  i n t r a n s i t i o n metal compounds i s m u l t i p l e t  s p l i t t i n g but  t h i s cannot be the case here.  p o s s i b l e t h a t i n T i F ^ we the  usual  It i s  a l s o have a breakdown of  s i n g l e p a r t i c l e d e s c r i p t i o n of  the  photoionization  process. 5.4  Conclusion  In t h i s work i t was may  shown t h a t  be observed on the h i g h b i n d i n g  l i n e s i n the gas  satellite  structure  energy s i d e o f c o r e  phase p h o t o e l e c t r o n s p e c t r a  of  titanium 31  tetrahalides.  When t h i s work was  f i r s t published  s t a t e c a l c u l a t i o n s were not a v a i l a b l e f o r any four t e t r a h a l i d e s , and  i t was  one  hole of  the  hoped t h a t these data 40  would s t i m u l a t e reported  the  such c a l c u l a t i o n s .  r e s u l t s of SCF  Xa MO  T i 2p core i o n s t a t e f o r T i C l it  i s now  Recently, T o s s e l l c a l c u l a t i o n s of  the  Using t h i s r e s u l t  4 >  p o s s i b l e t o a s s i g n the  s a t e l l i t e peak a t a  b i n d i n g energy of 4.OeV higher than the main l i n e i n the T i 2p ^2 spectrum of T i C l , to l i g a n d - t o - m e t a l 3d * * 40 type t r a n s i t i o n s e -> e and ^2 2 * Tossell also used t h i s SCF Xa r e s u l t to s e m i e m p i r i c a l l y estimate 3  4  t  the c o r r e s p o n d i n g s a t e l l i t e s e p a r a t i o n s f o r TiBr„  and  - 216 -  Til^  t o be 2.9 a n d 1.7eV r e s p e c t i v e l y , w h i c h a r e  i n good agreement w i t h t h e e x p e r i m e n t a l 3.3 and 2.1eV.  B a s e d o n t h e same c a l c u l a t i o n t h e  higher energy s a t e l l i t e TiCl^  values of  i n t h e T i 2p s p e c t r u m o f  c a n be a s s i g n e d t o a l i g a n d - t o - c o n d u c t i o n b a n d  type m u l t i e l e c t r o n e x c i t a t i o n .  However, t h e o b s e r v e d  i n t e n s i t y o f t h i s p e a k i s much h i g h e r t h a n e x p e c t e d f o r 21 such a t r a n s i t i o n i n t h e o n e - e l e c t r o n Although  i t has been s u g g e s t e d  between t h e s a t e l l i t e Tie-  8— o  picture.  that the disagreement  intensities calculated  using  2— a n d T i F , c l u s t e r m o d e l s and t h e e x p e r i m e n t a l b  r e s u l t s from the s o l i d  s t a t e s t u d i e s o f T i G ^ and T i F ^  i s due t o t h e i m p o r t a n c e  o f second n e a r e s t  neighbor  18 effects i n the solid,  no s u c h c o n s i d e r a t i o n w o u l d  h a v e t o be made f o r t h e v a p o r p h a s e m o l e c u l e s  studied  here. T h e r e f o r e , t h e v a l i d i t y o f t h e o n e - e l e c t r o n model for the d i s c u s s i o n of core photoelectron spectra of these molecules of these  data.  s h o u l d be c o n s i d e r e d  i n the l i g h t  - 217 REFERENCES  1.  A. 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P e r r y , I n o r g . Chem. 1 3 , 2686 (.1974) Jolly,  M.S. L a z a r u s , W.B.  Perry,  R.R. R i e t z , a n d T.F. S c h a a f , I n o r g . Chem. 1_4, 1595 (1975) 40.  J . A . T o s s e l , Chem. P h y s . L e t t . 6 5 , 371 (1979).  - 220 -  41.  C.J. B a l l h a u s e n , 'Introduction t o Ligand F i e l d  Theory"  (McGraw-Hill, New York, 1962). p. 110 42.  R.L. M a r t i n , and D.A. S h i r l e y , " E l e c t r o n Spectroscopy: Theory, Techniques, and A p p l i c a t i o n s " e d i t e d by A.D. Baker, and C.R. Brundle (Academic, London, 1977).  43.  S. Svensson, N. Martensson, E. B a s i l i e r , P.A. Malmquist, U, G e l i u s , and K. Siegbahn, Physica S c r i p t a 1_4, 141 (1976).  44.  G. Wendin, and M. Ohno , P h y s i c a S c r i p t a 1_4, 148 (.1976)  - 221 -  CHAPTER SIX  X-RAY PHOTOELECTRON SPECTROSCOPY OF C o ( I I ) , N i ( I I ) AND Cu(II) ACETYLACETONATE VAPORS  6.1  Introduction  The phenomena o f m u l t i e l e c t r o n e x c i t a t i o n and m u l t i p l e t s p l i t t i n g a r i s i n g from c o r e i o n i z a t i o n o f t r a n s i t i o n metal compounds have been s t u d i e d i n considerable classified  d e t a i l w i t h the m a j o r i t y  of work  i n t o two main groups:-  a) The study of s a t e l l i t e s t r u c t u r e as a f u n c t i o n of the c e n t r a l metal. b) The study o f s a t e l l i t e  ^ s t r u c t u r e as a f u n c t i o n  5-13 of the l i g a n d . Although the s a t e l l i t e s t r u c t u r e i s expected t o 14 vary w i t h the l i g a n d and the symmetry o f the complex very l i t t l e work has been performed  on compounds w i t h  the same c e n t r a l metal i o n and l i g a n d , but w i t h d i f f e r e n t symmetry about the c e n t r a l metal i o n .  - 222  -  Strong s a t e l l i t e s observed i n the i n n e r s h e l l x-ray p h o t o e l e c t r o n s p e c t r a o f f i r s t row t r a n s i t i o n metal compounds o f o c t a h e d r a l symmetry have been a t t r i b u t e d to  l i g a n d ( L ) t o metal charge t r a n s f e r t r a n s i t i o n s of *  *  and/or t g  ^2q'  the  type e^ ->• e^  the  c o n f i g u r a t i o n o f the ground s t a t e and the nature  2  depending upon  2 3 5 9 11 15 of  the l i g a n d s .  ' ' ' '  '  These assignments have  been confirmed by s e l f - c o n s i s t e n t m u l t i p l e calculations  scattering  which p r e d i c t h i g h i n t e n s i t i e s f o r shakeup 16 — 21  t r a n s i t i o n s of l i g a n d - t o - m e t a l 3d type.  However,  i t has a l s o been suggested t h a t t r a n s i t i o n s such as l i g a n d - t o - m e t a l 4s or for  4p o r b i t a l s may 22-24  the observed s a t e l l i t e s .  be r e s p o n s i b l e  This suggestion i s  based on SCF-Xa s c a t t e r e d wave MO c a l c u l a t i o n s , and no attempt was made t o e x p l a i n the observed 20 Braga and L a r s s o n  intensities.  consider that high r e l a t i v e  i n t e n s i t y f o r s a t e l l i t e peaks cannot be expected for  L ->- metal 4s or 4p e x c i t a t i o n s . The s a t e l l i t e s t r u c t u r e seen i n the 3s and 3p core  s p e c t r a o f paramagnetic compounds of f i r s t  row  tran-  s i t i o n metals i s c o n s i d e r e d t o be due mainly t o m u l t i p l e t s p l i t t i n g and c o n f i g u r a t i o n effects. the  interaction  T h e o r e t i c a l assessment of the magnitude of  s p l i t t i n g due to  such e f f e c t s has been attempted  - 223 -  by  several workers.  H o w e v e r , b a s e d on m u l t i p l e 19  s c a t t e r i n g c a l c u l a t i o n s , L a r s s o n and Braga that f o r N i ( I I ) , satellite  , argue  a n d p o s s i b l y a l s o Co ( I I ) s a l t s , t h e  s t r u c t u r e i n t h e 3s s p e c t r u m a t a  separation  o f 4-7eV a r i s e s f r o m a s h a k e u p m e c h a n i s m , w h e r e a s t h e m u l t i p l e t s p l i t t i n g o f t h e main l i n e s i s so s m a l l it  c a n n o t be r e s o l v e d In t h i s chapter,  reported  with  easily. a g a s p h a s e s t u d y o f some  metal acetylacetonate  v a p o r s , M(AcAc)2  transition  (M=Co,Ni,Cu), i s  s p e c i a l e m p h a s i s on t h e s a t e l l i t e  seen i n t h e i r c o r e l e v e l p h o t o e l e c t r o n Co(AcAc)2 i s t e t r a m e r i c Co atom p o s s e s s i n g  that  structure  spectra.  i n t h e s o l i d phase w i t h t h e  sixfold coordination.  I n t h e gas  phase i t i s monomeric w i t h t e t r a h e d r a l Co i s h i g h on  spin  the other  coordination. 28 (s=3/2) i n b o t h p h a s e s . NijAcAc^/  h a n d , c h a n g e s b o t h symmetry a n d s p i n  when g o i n g i n t o t h e v a p o r p h a s e .  The s o l i d  i s trimeric  and  high  and  t h e d i a m a g n e t i c v a p o r i s monomeric and square  planar. planar  s p i n w i t h N i showing s i x f o l d  state  In the solid  coordination.,  s t a t e , Cu(AcAc)2 i s almost  square  and undergoes m i n i m a l s t r u c t u r a l change i n 28 2 9  going t o the planar  monomeric v a p o r phase.  b o t h p h a s e s , Cu h a s one u n p a i r e d This  '  In  electron.  study of the t r a n s i t i o n metal acetylacetonates 11 12 thus a f f o r d s a comparison of s o l i d ' and g a s p h a s e  - 224  x-ray p h o t o e l e c t r o n  -  spectra. I t i s anticipated that  t h i s should y i e l d i n f o r m a t i o n on the s e n s i t i v i t y of s a t e l l i t e s to changes i n symmetry and the o r i g i n of observed s a t e l l i t e  structure.  r o l e s of exchange s p l i t t i n g and may  In a d d i t i o n , the shakeup i n 3s  relative  spectra  be examined. In the next s e c t i o n the experimental  described. and  the  The  details  are  r e s u l t s are d i s c u s s e d i n S e c t i o n  6.3  the c o n c l u s i o n s are presented  i n S e c t i o n 6.4.  This  work w i l l appear e l s e w h e r e . ^  6.2  Experimental  The  spectrometer used i n t h i s study has been  d e s c r i b e d i n d e t a i l i n Chapter Three. The a c e t y l a c e t o n a t e s were prepared 31 methods.  Cu,  Ni and  Co  by p r e v i o u s l y e s t a b l i s h e d  32 '  A l l the compounds were p u r i f i e d by vacuum  sublimation. For an optimum count r a t e a vapor p r e s s u r e  of  -2 ^3x10  t o r r i n the i o n i z a t i o n c e l l was  required.  T h i s p r e s s u r e was  produced by h e a t i n g the sample i n s i d e  the spectrometer,  i n the o l d high temperature gas  d e s c r i b e d i n d e t a i l i n Chapter Three. Co(AcAc)- s p e c t r a were recorded  Gas  phase  at ^90°C, and  the  cell  - 225 -  spectra of Cu(AcAc) respectively.  2  and N i ( A c A c )  a t ^100 and 'vl25°C,  2  The compounds were i r r a d i a t e d w i t h A l  Ka x-rays t o o b t a i n the p h o t o e l e c t r o n s p e c t r a . Sample decomposition  a t the o p e r a t i n g  temperature  was monitored by comparing the r e l a t i v e count r a t e s o f 33 metal core l e v e l s t o those o f the 0 I s l e v e l . comparison showed n e g l i g i b l e decomposition  This  over the  p e r i o d o f r e c o r d i n g t h e s p e c t r a , as i n p r e v i o u s 31 34 studies. recorded  '  At l e a s t three separate  s p e c t r a were  f o r each core l e v e l t o make sure t h a t the  sometimes weak peaks were r e p r o d u c i b l e . the s p e c t r a were measured a t d i f f e r e n t  In a d d i t i o n , operating  p r e s s u r e s , i n order to be a b l e to d e t e c t energy l o s s s t r u c t u r e . There was none d e t e c t e d .  The s p e c t r a o f the  C and 0 I s l e v e l s o f f r e e a c e t y l a c e t o n e were a l s o taken f o r comparison with those o f the metal a c e t y l a c e t o n a t e s . Metal  2p l e v e l s were r e f e r e n c e d t o the I s l e v e l o f 35  Ne (870.37eV)  , and the 3s and 3p s p e c t r a were  r e f e r e n c e d t o t h e Ne 2s l e v e l  (48.47eV) . 35  The C I s  l e v e l s o f a c e t y l a c e t o n e and the metal a c e t y l a c e t o n a t e s 3 fi were r e f e r e n c e d t o t h e C I s l e v e l o f C 0 (297.5eV), and the 0 I s l e v e l s o f these compounds were s i m i l a r l y 36 r e f e r e n c e d t o the 0 i l e v e l o f C 0 (540.8eV). In a l l cases the r e f e r e n c e gas was i n t r o d u c e d s i m u l t a n e o u s l y 2  s  2  - 226 -  i n t o the spectrometer  w i t h the sample under  investi-  gation . All  s p e c t r a were l e a s t - s q u a r e s f i t t e d t o o b t a i n 37  peak p o s i t i o n s , l i n e widths and areas.  6.3  R e s u l t s and D i s c u s s i o n The  2p, 3s and 3p b i n d i n g e n e r g i e s o f Co, N i and  Cu i n M(AcAc) The  2  (M=Co,Ni,Cu) are shown i n Table  6.1.  s a t e l l i t e s e p a r a t i o n s and r e l a t i v e i n t e n s i t i e s a r e  summarized i n Tables 6.2 and 6.3.  A l l the b i n d i n g  energy measurements r e p o r t e d i n t h i s work were r e p r o d u c i b l e t o w i t h i n ±0.1eV.  Spectra o f the 2p l e v e l s  of Co, N i and Cu a r e shown i n F i g s . 6.1 - 6.3 and those of the 3s and 3p l e v e l s i n F i g s . 6.4 - 6.6 and 6.7 -6.9 respectively. B i n d i n g e n e r g i e s observed  f o r the C I s and 0 ]_  s  l e v e l s i n the three t r a n s i t i o n metal a c e t y l a c e t o n a t e s and  f r e e a c e t y l a c e t o n e are l i s t e d  C Is spectrum f o r C o ( A c A c )  2  i n Table  6.4.  The  i s shown i n F i g . 6.10 which  i s r e p r e s e n t a t i v e o f the C I s s p e c t r a of the compounds studied.  I t can be seen  (Table 6.4) t h a t the C I s and  0 Is b i n d i n g e n e r g i e s observed  f o r the t h r e e  transition  metal a c e t y l a c e t o n a t e s a r e d i f f e r e n t from those o f f r e e  Table  6.1  (eV) o f m e t a l 2p, 3s and 3p l e v e l s  Binding energies (M  =  i n H(AcAc)  2  vapors  Co, N i , Cu)  2p'  Co(AcAc)  2  Ni(AcAc)  2  Cu(AcAc)2  3s  2p 1/2  3/2  3-  k  P  786.5  802.0  10 8.5  66.4  860.5  877.9  118.2  73.5  940.0  960.0  129 .6  84.9, 82.4  (  AcAc = a c e t y l a c e t o n a t e Re f e r e n c e d Re  t o t h e Ne  Is l e v e l  f e r e n c e d t o the Ne 2s l e v e l  (870.37eV) (48.47eV)  The Cu 3p peak c o u l d be d e c o n v o l u t e d s e p a r a t i o n o f 2.5eV between the 3 p  1 / 2  35  35  i n t o 2 peaks w i t h and 3 p  3 / 2  levels.  a ratio  1:2.04 and a  T a b l e  6 . 2  S a t e l l i t e  Of  M ( A c A c )  s e p a r a t i o n s  0  (M  =  ,flE / (eV)  and  r e l a t i v e  i n t e n s i t i e s ,  I ,  i n  t h e  m e t a l  AE.  (I)  2 P  3 / 2  2  v a p o r  s o l i d  4 . 2  ( 0 . 5 6 )  4 . 8  ( 0 . 6 0 ) '  5.0  (0.60)  N i  .  5 . 5  ( 0 . 2 8 )  4 . 3  ( 0 . 6 2 )  5.9  (0.23)  5 . 0  ( 0 . 6 9 )  5.2  (0.72)  1 0 . 0  ( 0 . 4 9 )  9 . 7  (0.48)  F r o m  R e f .  1 1 .  H e r e  t h e  ( s a t e l l i t e  F r o m  R e f .  12  r e l a t i v e  peak  t o  i n t e n s i t y  m a i n  peak)  l / 2  s o l i d  .  5.2,  (I) p  v a p o r  C o ( A c A c )  C u ( A c A c ) .  s p e c t r a  C o , N i , C u )  AE  (AcAc)  2p  9 . 3  i s  ;  00  C  5 . 3 ,  g i v e n  a s  t h e  r a t i o  o f  peak  9 . 1  h e i g h t s  1  Table  6.3  Satellite  separations,  spectra of M(AcAc)  A E , and r e l a t i v e  (M =  2  E  3s  (  I  )  & E  vapor 4.1  I , i n t h e m e t a l 3s a n d  3p  Co,Ni,Cu)  A  CofAcAc),  intensities,  (0.39)  solid  3p  ( I )  vapor  4.8  solid  3.0  (0.41)  6.5  (0.09)  ,  4.4  (0.04)  K>  3.3  (0.08)  3.2, Ni(AcAc)n  4.5  (0.15)  Cu(AcAc),  4.8  (0.49) 4.2 ,  1  a  10.1 a  D.C.  F r o s t , C.A.  b  From R e f . 13.  a  N o t e , no p e a k s w i t h  8.7 Tapping (unpublished any d e t e c t a b l e  than lOeV from the main  . 7.5 , b  (0.23)  M c D o w e l l a n d R.L.  higher  8.6  5.2  line  (0.08)  23.5  . 15.0  b  b  results)  intensity  were found a t e n e r g i e s  i n t h e gas phase  spectra.  ^ I  - 230 -  Co(AcAc)2  810 Fig.  ' 800 790 Binding energy (eV)  6.1. X-ray p h o t o e l e c t r o n spectrum of the c o b a l t 2p r e g i o n from c o b a l t (II) a c e t y l a c e t o n a t e . T h e peaks l a b e l l e d ' s a t ' are due t o m u l t i e l e c t r o n excitation.  - 231 -  890 F i g . 6.2.  '  880 870 ' 860 Binding energy (eV)  X-ray p h o t o e l e c t r o n spectrum of the n i c k e l 2p r e g i o n from n i c k e l (II) a c e t y l a c e t o n a t e . The peaks l a b e l l e d ' s a t ' are due t o m u l t i electron excitation.  - 232  -  970 ' 960 ' 950 ' 940 ' Binding energy (eV) F i g . 6.3.  X-ray p h o t o e l e c t r o n spectrum of the copper 2p r e g i o n from copper (II) a c e t y l a c e t o n a t e . The peaks l a b e l l e d ' s a t ' are due t o m u l t i electron excitation.  - 233 -  F i g . 6.4.  X-ray p h o t o e l e c t r o n spectrum of the c o b a l t 3s r e g i o n from c o b a l t (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d ' s a t ' i s due t o m u l t i e l e c t r o n excitation.  - 234  -  125 120 115 Binding energy (eV) F i g . 6.5.  '  X-ray p h o t o e l e c t r o n spectrum of the n i c k e l 3s r e g i o n from n i c k e l (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d 'sat' i s due to m u l t i electron excitation.  - 235 -  Cu(AcAc)  2  3s  1  .  1  !  1  1  '  140 130 Binding energy (eV) X-ray p h o t o e l e c t r o n spectrum of the copper 3s r e g i o n from copper ( I I ) a c e t y l a c e t o n a t e . The peaks l a b e l l e d 'sat' are due to m u l t i electron excitation.  - 236 -  Co (Ac Ac )  2  3p  *  1  •  1  >  1  " — •  75 70 65 Binding energy (eV) F i g . 6.7.  X-ray p h o t o e l e c t r o n spectrum of the c o b a l t 3p r e g i o n from c o b a l t (II) a c e t y l a c e t o n a t e . The peaks l a b e l l e d 'sat' are due to m u l t i electron excitation.  - 237 -  Ni(AcAc)  1  2  ,  80 70 Binding energy (eV) F i g . 6.8.  1  X-ray p h o t o e l e c t r o n spectrum of the n i c k e l 3p r e g i o n from n i c k e l (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d ' s a t ' i s due to m u l t i electron excitation.  - 238 -  95 Fig.  6.9.  90 85 80 Binding energy (eV)  X-ray p h o t o e l e c t r o n spectrum of the copper 3p r e g i o n from copper (II) a c e t y l a c e t o n a t e . The peaks l a b e l l e d 'sat' are due t o . m u l t i electron excitation.  Table  6.4  O I s and  C Is binding  acetylacetone  and  the s a t e l l i t e  peak  M(AcAc)  and  s a t e l l i t e separations,  (M = C o , N i , C u ) .  Relative  AE  (eV)  in  intensity,  I, of  i n parentheses.  l s ' ' a  (eV)  vapors  2  i s given C  Acetylacetone  energies  b  0  C  2 9 2 . 6 , 290.4  ls (FWHM) d  537.7 537.3  AEQ  e  (3.15)  ( 1 . 6 5 ) 538.8  (1.95)  ( I ) L G  3.6  (.04)  g  f  Co(AcAc),  2 9 1 . 8 , 290.0  536.6  (1.8)  4.9  (.08)  Ni(AcAc)  2  2 9 2 . 0 , 290.2  536.5  (1.9)  4.8  (.07)  Cu(AcAc)  2  2 9 1 . 8 , 290.0  5 36.4  (1.8)  3.8  (.09)  I a  b  Referenced The  C Is signal  energy: c d  No  to the C I s l e v e l of C0 c o u l d be  low b i n d i n g  e  Full  f  From R e f .  g  See  to the O  width at half  Ref.  38 39  (297.5eV)  deconvoluted into  2 peaks w i t h a r a t i o  1:1.5  (high  energy)  s a t e l l i t e s of detectable  Referenced  2  3 6  intensity  Is l e v e l of C0 maximum  2  were o b s e r v e d (540.8eV)  i n the C Is  spectra  3 6  (FWHM) o f t h e p e a k i s g i v e n  i n parentheses.  binding  - 240 -  C0  2  Co(AcAc)  2  CIs  300 ' 290~ Binding energy (eV) F i g . 6.10.  X-ray p h o t o e l e c t r o n spectrum of the C Is r e g i o n from c o b a l t (II) a c e t y l a c e t o n a t e . C 0 was used as the r e f e r e n c e gas. 2  - 241 -  a c e t y l a c e t o n e , i n d i c a t i n g t h a t decomposition d i d not take p l a c e and t h a t the methods used f o r o b t a i n i n g the M(AcAc)2  (M=Co,Ni,Cu) s p e c t r a as o u t l i n e d i n Sec.  are s a t i s f a c t o r y .  6.2  I t i s p a r t i c u l a r l y i n t e r e s t i n g to note  t h a t the 0 Is l i n e observed f o r a c e t y l a c e t o n e i s v e r y much broader than t h a t observed f o r the metal a c e t y l a c e 40 tonates  (Table 6.4)  .  The broadening of the 0 Is s i g n a l  of a c e t y l a c e t o n e has been e x p l a i n e d i n terms of an e q u i l i b r i u m mixture of keto and e n o l forms i n the vapor phase.  '^  In f a c t the broad 0 I s l i n e o f  a c e t y l a c e t o n e has been deconvoluted i n t o two peaks 38 separated by 1.5eV.  The reduced f u l l width a t h a l f  maximum (FWHM) o f the 0 I s s i g n a l i n the metal a c e t y l a c e t o n a t e s , compared t o t h a t o f f r e e a c e t y l a c e t o n e , i n d i c a t e s a disappearance of the chemical non-equivalence of the two  0 atoms o f  the e n o l i c a c e t y l a c e t o n a t e l i g a n d  as a r e s u l t o f complex f o r m a t i o n .  In a d d i t i o n , the 0 i s  s p e c t r a of a l l these a c e t y l a c e t o n a t e s and f r e e a c e t y l a c e tone show an a d d i t i o n a l peak a t 3.5-5.0eV h i g h e r b i n d i n g e n e r g i e s than the main peak  ( F i g . 6.11-6.13, Table 6.4).  T h i s cannot o r i g i n a t e from i m p u r i t i e s such as ^ 0 (53 9.7 36 36 38 eV) or 0 (543.leV). Brown has a l s o r e p o r t e d s i m i l a r s t r u c t u r e i n the 0 I s spectrum of a c e t y l a c e t o n e 2  about 3.6eV t o h i g h e r b i n d i n g energy than the main l i n e .  -  242  -  Co (Ac Ac )  •  1  545 F i g . 6.11.  •  2  1  '  1  •  540 535 Binding energy (eV)  X-ray p h o t o e l e c t r o n spectrum of the 0 Is r e g i o n from c o b a l t (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d ' s a t ' i s due to m u l t i electron excitation.  - 243 -  Ni (AcAc)  ~"  F i g . 6.12.  2  540 535 Binding energy (eV)  X-ray p h o t o e l e c t r o n spectrum of the 0 Is r e g i o n from n i c k e l (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d ' s a t ' i s due t o m u l t i electron excitation.  - 244 -  545 F i g . 6.13.  540 535 Binding energy (eV)  X-ray p h o t o e l e c t r o n spectrum o f the 0 Is r e g i o n from copper (II) a c e t y l a c e t o n a t e . The peak l a b e l l e d ' s a t ' i s due t o m u l t i electron excitation.  - 245  -  In t h a t work the source o f t h i s a d d i t i o n a l l i n e unknown. T h i s s t r u c t u r e was  a l s o r e p o r t e d i n the 0 i s  s p e c t r a of a number of 1,3-dicarbonyl the r e l a t i v e i n t e n s i t y  was  compounds, w i t h  and p o s i t i o n dependent on  the  38 compound i n v e s t i g a t e d .  The o r i g i n of t h i s  additional  s t r u c t u r e w i l l be d i s c u s s e d l a t e r . The  C Is s p e c t r a of a c e t y l a c e t o n e and  i t s transition  metal complexes s t u d i e d i n t h i s work d i d not show s a t e l l i t e s t r u c t u r e at higher b i n d i n g e n e r g i e s .  In  a l l of these s p e c t r a the C I s l i n e c o n s i s t e d of a doublet ( F i g . 6.10)  which c o u l d be deconvoluted  with the i n t e n s i t y  i n t o two  peaks  r a t i o ^1:1.5 (high b i n d i n g energy  peak: low b i n d i n g energy peak).  The h i g h b i n d i n g energy  component of t h i s doublet can be a s s i g n e d to the c a r b o n y l C atoms. two  I t i s to be noted t h a t the s e p a r a t i o n of the  components  1.8eV 6.4).  (2.2eV i n a c e t y l a c e t o n e ) decreases  i n the t r a n s i t i o n metal a c e t y l a c e t o n a t e s T h i s decrease  i s largely  due  to  (Table  to a decrease  in  the b i n d i n g energy of the c a r b o n y l carbon atoms upon complex formation. S a t e l l i t e s were observed  a t higher b i n d i n g e n e r g i e s  than the main l i n e i n the metal  2p,  s p e c t r a of a l l three complexes(Tables The r e l a t i v e  intensity  3s and 6.2,  3p p h o t o e l e c t r o n 6.3) ( F i g . 6.1-6.9).  of the peaks d i d not change w i t h  - 246  -  p r e s s u r e , and t h e r e f o r e the a d d i t i o n a l  structure  appearing i n these p h o t o e l e c t r o n s p e c t r a can be c o n f i d e n t l y a t t r i b u t e d t o shakeup and/or  multiplet  s p l i t t i n g , and so the r e l a t i v e importance e f f e c t s w i l l now  of these  be d i s c u s s e d .  Cu(AcAc)-  Cu(AcAc)2 d i f f e r s from the other two a c e t y l a c e t o n ates s t u d i e d h e r e , i n t h a t i t shows two  satellites for  both the 2p^y2  approximately  a n (  ^  ^^1/2  i i  n  e  s  '  a n c  ^  ^  a s  the same s t r u c t u r e i n both the s o l i d and the vapor  phases.  S a t e l l i t e s t r u c t u r e i s expected t o vary w i t h the l i g a n d 14 and the symmetry of the complex. Tables 6.2  and 6.3,  Thus, as shown i n  the s a t e l l i t e s e p a r a t i o n s observed  f o r Cu(AcAc)2 vapor show a c o n s i d e r a b l e s i m i l a r i t y to those observed f o r the s o l i d , p a r t i c u l a r l y i n the case of the 2p and 3s s p e c t r a . S a t e l l i t e s p r e s e n t i n the 2p s p e c t r a of s o l i d Ni(AcAc)2 and Co(AcAc)2  have been e x p l a i n e d as a r i s i n g  from shakeup t r a n s i t i o n s of a 1igand-to-meta1 charge transfer n a t u r e . ^ i n t h a t i t has  However, Cu(AcAc)2 i s d i f f e r e n t ,  been suggested t h a t i n 2+  s a t e l l i t e s seen i n Cu  the case o f  s p e c t r a , t h i s i s more l i k e l y  to be due to a m e t a l - t o - l i g a n d charge  transfer  - 247 -  e x c i t a t i o n , as the core i o n i z e d completed  'ground s t a t e ' has a  3d s h e l l due t o an i n f l u x o f e l e c t r o n s  from  17 42 the l i g a n d .  '  T h i s i s d e s p i t e the f a c t t h a t  ground s t a t e e l e c t r o n i c s t r u c t u r e o f n e u t r a l compounds i s c h a r a c t e r i z e d by a vacant which i n D ,  symmetry i s a mainly d  Larsson"*" ' ^  has suggested  0  8  Cu(II)  spin o r b i t a l orbital.  t h a t i n core l e v e l  of Cu(II) compounds the main peak corresponds a d ^  the  spectra closely to  c o n f i g u r a t i o n and i t should not show any l a r g e  m u l t i p l e t s p l i t t i n g , whereas the s a t e l l i t e which 9 corresponds  closely to a d  c o n f i g u r a t i o n should show  multiplet splitting.  However, the s e p a r a t i o n  the two 2p s a t e l l i t e s  ( f o r both 2p.jy  for Cu(AcAc)  2  ^ P3/2^  observed  2  i n the gas phase i s much too l a r g e  to be due t o m u l t i p l e t s p l i t t i n g . the observed  a n < 2  between  In the present case .  FWHM v a l u e s f o r the Cu 2p^^  2  main l i n e ,  and the s a t e l l i t e a t 5.2eV higher b i n d i n g energy 2.4  and 3.9eV r e s p e c t i v e l y w i t h the s a t e l l i t e 40  having a FWHM o f 2.8eV.  (^5eV)  are  a t 9.7eV  Despite the f a c t t h a t the  r e l a t i v e valence o r b i t a l e n e r g i e s o f t r a n s i t i o n metal compounds are somewhat changed by core hole or c r y s t a l f i e l d o r b i t a l i o n i z a t i o n , based on e l e c t r o n i c s p e c t r a and molecular  orbital  - 248  -  c a l c u l a t i o n s f o r the n e u t r a l molecules  it  i s not unreasonable t o a s s i g n the lower b i n d i n g energy  s a t e l l i t e of both 2p and 3s s p e c t r a as due t o  a m e t a l - t o - l i g a n d charge t r a n s f e r type shakeup t r a n s i t i o n . T h i s assignment  supports Larsson's views r e g a r d i n g the  o r i g i n of s a t e l l i t e s  i n Cu(II) compounds.  The  r e l a t i v e broadening o f t h i s low b i n d i n g energy  large satellite 43  may  be e x p l a i n e d i n terms of m u l t i p l e t s p l i t t i n g ,  s u p p o r t i n g Larsson's views c o n c e r n i n g s a t e l l i t e s 2p s p e c t r a .  The s a t e l l i t e peak a t 'vlOeV may *  from a d i f f e r e n t source such as a IT ->- TT F u r t h e r support f o r these assignments  also i n Cu  originate  transition. i s provided  by the 3s s a t e l l i t e s e p a r a t i o n s being almost  identical  to those i n  w e l l known  the 2p s p e c t r a .  t h a t the s a t e l l i t e is  s t r u c t u r e caused by e l e c t r o n shakeup 14  not dependent on the exact core e l e c t r o n  one can a s s i g n both s a t e l l i t e s to  Since i t i s now  seen i n the 3s s p e c t r a  shakeup r a t h e r than m u l t i p l e t s p l i t t i n g .  s e p a r a t i o n between the two  satellites  be due to m u l t i p l e t s p l i t t i n g ,  ejected,  Again, the  i s too l a r g e to  and the low b i n d i n g energy  s a t e l l i t e has a FWHM of 6.7eV which i s c o n s i d e r a b l y broader 40 than the main peak (FWHM, 3.2eV). Both peaks are broader than the c o r r e s p o n d i n g 2p peaks, mainly due t o enhanced 43 c o r r e l a t i o n e f f e c t s i n the 3s peak, again c o n s i s t e n t w i t h  - 249  -  Larsson's view t h a t m u l t i p l e t s p l i t t i n g i s more s i g n i f i c a n t i n shakeup s a t e l l i t e s than i n the main peak i n the case o f Cu(II) compounds.  I t may  be o f s i g n i f i c a n c e  t o note t h a t the FWHM of the s a t e l l i t e at l O . l e V i s 2.9eV i n the  3s s p e c t r a compared to t h a t of 2.8eV f o r the  corresponding s a t e l l i t e i n the  2p s p e c t r a .  T h i s confirms  the view t h a t t h i s s a t e l l i t e o r i g i n a t e s from a d i f f e r e n t mechanism than t h a t of the The 6.9)  3p p h o t o e l e c t r o n  s a t e l l i t e at  ^5eV.  spectrum of Cu(AcAc)2  i s remarkably d i f f e r e n t from t h a t of the  levels.  In t h i s work no  (Figure 2p and  3s  s a t e l l i t e s of d e t e c t a b l e i n t e n s i t y 13  c o r r e s p o n d i n g to those m energies  higher  weak peak was  state  than lOeV were observed.  observed at 3.3eV higher  than the main l i n e . The i n t o two  the s o l i d  at  However, a  binding  main l i n e could be  This separation  energy  deconvoluted  components w i t h a r a t i o of 1:2.04 and  s e p a r a t i o n of 2.5eV.  binding  a  i s comparable to  the c a l c u l a t e d s p i n - o r b i t s p l i t t i n g of 2.8eV between 46 the Cu 3p ^2 P3/2 However the p o s s i b i l i t y a  n  d  3  l  e  v  e  l  s  1  t h a t t h i s s t r u c t u r e i s due  to m u l t i p l e t s p l i t t i n g cannot  be completely excluded as the c a l c u l a t e d m u l t i p l e t s t r u c t u r e of the Cu(II) 3p l e v e l i n d i c a t e s t h a t 40% the t o t a l i n t e n s i t y of a m u l t i p l e t - d e r i v e d 18 merges w i t h the main peak.  satellite  of  - 250  Co (AcAc)  2  and  Ni.(AcAc.)  -  2  S a t e l l i t e s e p a r a t i o n s observed Ni(AcAc)  2  for Co(AcAc)  2  and  vapors are d i f f e r e n t from those r e p o r t e d f o r 11 12  the corresponding  solids.  '  13 '  t r a t e s the dependency of s a t e l l i t e symmetry of the complex.  T h i s s t r o n g l y demonss t r u c t u r e on  Both Ni and Co  the  acetylacetonates  have s i x - f o l d c o o r d i n a t i o n i n the s o l i d s t a t e w h i l e , mentioned b e f o r e , the two  as  compounds are square p l a n a r  and t e t r a h e d r a l r e s p e c t i v e l y , i n the vapor phase. Shakeup t r a n s i t i o n s i n v o l v e o n l y those o r b i t a l s  having  the same symmetry s i n c e these f o l l o w the monopole s e l e c t i o n rules.  For charge t r a n s f e r , i n 0^  symmetry,  allowed  t r a n s i t i o n s are L nt- -> M d t ~ and L oe + M de , 2g 2g g g' whereas i n T^ symmetry, the corresponding t r a n s i t i o n s  are  9  L ne + M de and L t  2  -»- M t « 2  T h e r e f o r e , one would a n t i -  c i p a t e d i f f e r e n t s a t e l l i t e s t r u c t u r e f o r compounds of d i f f e r e n t symmetry even when the metal and i n v o l v e d are the same. the s o l i d and be noted.  s i m i l a r i t y between  the vapor phase s p e c t r a of Co(AcAc)2  should  In both phases the s a t e l l i t e s are of high  i n t e n s i t y which may spin  However, one  ligands  be due  t o the f a c t t h a t Co i s high  (s=3/2) i n both phases. A strong shakeup s a t e l l i t e i s favoured  by two  factors:  - 251 -  (i)  the amount o f t o t a l charge t r a n s f e r r e d from the  l i g a n d t o the c e n t r a l metal i o n through o r b i t a l s o f the  c o r r e c t symmetry, and ( i i ) whether or not the  c e n t r a l i o n component o f the mainly l i g a n d o r b i t a l i s small b e f o r e i o n i z a t i o n .  In diamagnetic complexes  covalency of the bonds i s s t r o n g e r , r e s u l t i n g i n a l a r g e c e n t r a l i o n component b e f o r e i o n i z a t i o n ,  explaining  why such compounds show weaker s a t e l l i t e s than c o r r e s ponding paramagnetic in  the s o l i d phase  compounds.  For example, N i ( A c A c ) ^  (Ni i n a h i g h s p i n s t a t e ) shows s t r o n g  satellites"'"''" whereas i n the gas phase the diamagnetic molecule shows c o n s i d e r a b l y weaker s a t e l l i t e s 6.2).  However, i t i s important t o  compound w i t h paramagnetic  incompletely f i l l e d  (Table  note here, t h a t a 3d l e v e l s need not be  t o show s t r o n g s a t e l l i t e s t r u c t u r e .  Carlson  et  al."^  have r e p o r t e d the presence o f s t r o n g s a t e l l i t e s  in  the 2p p h o t o e l e c t r o n s p e c t r a of c o b a l t i n K^Co (C2 4)3 0  d e s p i t e the f a c t t h a t t h i s compound i s known t o be d i a magnetic. of  The most important requirement f o r the presence  s a t e l l i t e s t r u c t u r e i n the p h o t o e l e c t r o n s p e c t r a o f  t r a n s i t i o n metal compounds i s an i n c o m p l e t e l y f i l l e d subshell.  3d  T h i s has been confirmed by the presence o f  s a t e l l i t e s i n S c ( I I I ) and T i ( I V ) compounds where the 3d s u b s h e l l i s f o r m a l l y empty  15 47 ' and the absence o f  - 252 -  satellites has  i n Cu(I)  compounds w h e r e t h e g r o u n d s t a t e  a 3d*^ c o n f i g u r a t i o n .  results for Ni(AcAc) understanding  2  I t i s hoped t h a t  vapor w i l l  these  help i n a better  o f the r o l e o f paramagnetism/diamagnetism  i n t h e shakeup mechanism as t h i s a f f o r d s a c o m p a r i s o n between t h e d i a m a g n e t i c magnetic s o l i d  Ni(AcAc)  (Table 6.2).  v a p o r and t h e p a r a -  2  I n a d d i t i o n one c o u l d  compare t h e s e r e s u l t s w i t h t h e s p e c t r a r e p o r t e d by C a r l s o n et  a l * f o r Ni(SacSac)  solid.  1  2  d i s u l f u r analogue o f Ni(AcAc)2 is  Ni(SacSac)  i sthe  2  and i s d i a m a g n e t i c . I t  i n t e r e s t i n g t o note here t h a t , although t h e s a t e l l i t e  s e p a r a t i o n i s d i f f e r e n t f o r t h e two d i a m a g n e t i c the s a t e l l i t e (Reported  i n t e n s i t i e s a r e o f t h e same order*"*".  v a l u e s f o r A E . and r e l a t i v e i n t e n s i t y f o r sa t  the 2 p ^ 2 s a t e l l i t e  i n Ni(SacSac)  2  solid  a r e 4.4eV a n d  0.22 r e s p e c t i v e l y a n d t h e v a l u e s o b t a i n e d for  Ni(AcAc)  2  2  i n this  work  v a p o r a r e 5.5eV a n d 0.28.)  Another important Ni(AcAc)  compounds  o b s e r v a t i o n i n t h e case  vapor r e s u l t s i s the presence  i n t h e 3s s p e c t r u m . T h i s s a t e l l i t e t e n s i t y o f t h e main peak  satellite  has 15% o f t h e i n -  (Table 6.3).  v a p o r i s known t o be d i a m a g n e t i c ,  of a  of the  As N i ( A c A c )  2  this structure i s  d e f i n i t e l y n o t due t o m u l t i p l e t s p l i t t i n g . c a n be a t t r i b u t e d t o a s h a k e u p t r a n s i t i o n .  This  satellite  By c o m p a r i n g  - 253  the  relative  intensity  -  o f t h i s s a t e l l i t e peak w i t h the  corresponding s a t e l l i t e i n the s o l i d s t a t e  spectrum,  one should be a b l e t o get a meaningful answer t o the  problem of r e l a t i v e r o l e s of shakeup and  s p l i t t i n g i n the 3s s p e c t r a o f paramagnetic  multiplet transition  metal compounds. Based on atomic c a l c u l a t i o n s  48 49 48 ' C a r l s o n e t a_l  have suggested t h a t the 3s-3p s a t e l l i t e i n t e n s i t y i s o n l y one t h i r d t h a t o f the 2s-2p s a t e l l i t e  ratio  intensity.  20 On the other hand, Braga and L a r s s o n ,  based on a  m u l t i p l e s c a t t e r i n g m o l e c l a r o r b i t a l treatemnt, have suggested t h a t the s a t e l l i t e i n t e n s i t y  r a t i o f o r 3s-3p  l e v e l s c o u l d be as high as 50-70% t h a t of the 2s-2p levels.  Using t h i s l a t t e r estimate as the upper  limit,  and from s o l i d s t a t e data f o r the Ni(AcAc)2 2p l e v e l , one would a n t i c i p a t e a s a t e l l i t e i n t e n s i t y the  3s l e v e l of s o l i d N i ( A c A c ) . 2  of 31-43% f o r  A v a l u e i n the same  range c o u l d be p r o j e c t e d by u s i n g the observed  intensity  of  2  15% f o r the 3s l e v e l of diamagnetic N i ( A c A c )  and the f a c t t h a t the 2 p y 3  2  s a t e l l i t e of the  vapor  paramagnetic  s o l i d i s twice as i n t e n s e as t h a t of the diamagnetic vapor. For  the paramagnetic C o ( A c A c )  2  vapor  observed s a t e l l i t e s are of h i g h i n t e n s i t y  (s=3/2), the f o r both 3s and  - 254 -  3p l e v e l s . of  The s e p a r a t i o n of 3eV between the main peak  the 3p spectrum and i t s n e a r e s t s a t e l l i t e i s too  l a r g e t o be due to s p i n o r b i t s p l i t t i n g of the 3p subshell. As mentioned  i n the i n t r o d u c t i o n , the h i g h b i n d i n g  energy component o f the 3s s p e c t r a o f paramagnetic  Ni(II)  and Co(II) compounds (at 4-7eV) has been i n t e r p r e t e d as due t o m u l t i p l e t s p l i t t i n g .  25  L a r s s o n and Braga  19  have  r e c e n t l y suggested t h a t the i n t e n s i t y of the h i g h b i n d i n g energy component of the 3s s p e c t r a of paramagnetic and Co (II)  Ni(II)  compounds belongs t o a shakeup s a t e l l i t e ,  whereas the m u l t i p l e t s p l i t t i n g of the main l i n e  i s so  small t h a t i t cannot be r e s o l v e d e a s i l y . The Co (II) spectrum of C o ( A c A c )  2  3s  vapor o b t a i n e d i n t h i s work w i l l  now be d i s c u s s e d i n the l i g h t of these s u g g e s t i o n s . The Co 3s spectrum shows a s a t e l l i t e a t 4.leV h i g h e r b i n d i n g energy than the main peak, w i t h i n t e n s i t y of 39%.  T h i s energy s e p a r a t i o n i s d i f f e r e n t  from that of the 4.8eV observed f o r s o l i d (Table 6.3).  a realtive  Co(AcAc)  2  For s e v e r a l reasons these r e s u l t s on  Co(AcAc)2 i n d i c a t e t h a t the s a t e l l i t e observed i n the 3s spectrum i s due t o shakeup r a t h e r than m u l t i p l e t splitting: (i) The magnitude o f the s a t e l l i t e s e p a r a t i o n s i n  - 255  both the 2p^^2  a n <  ^  -  ^s s p e c t r a f o r Co (AcAc) ^ vapor are  more or l e s s the.same.  This s i m i l a r i t y  (but not  the  p r e c i s e magnitude) i s common to the s o l i d s t a t e r e s u l t s also.  The  s a t e l l i t e s i n the 2p s p e c t r a are known to  o r i g i n a t e from a shakeup transition."'""'"  As mentioned  e a r l i e r the energy of a shakeup t r a n s i t i o n i s more or l e s s independent of the o r i g i n a l core hole s t a t e , and t h i s , c o u p l e d with the o b s e r v a t i o n of s i m i l a r separations,suggests with the 2p and  satellite  t h a t the s a t e l l i t e s a s s o c i a t e d  3s core l i n e s o r i g i n a t e from the same  mechanism. T h i s statement i s i n c o r r e c t o n l y i f the m u l t i p l e t s p l i t t i n g of the 3s l e v e l i s of the same order as t h a t of the shakeup t r a n s i t i o n . o b s e r v a t i o n s more or l e s s exclude  However, the f o l l o w i n g this  possibility.  ( i i ) Shakeup t r a n s i t i o n s are more s u s c e p t i b l e to changes i n symmetry than m u l t i p l e t s p l i t t i n g . s o l i d phase, Co(AcAc)^ e x i s t s as a tetramer  In  and  o c t a h e d r a l symmetry whereas the monomeric gas s p e c i e s i s of t e t r a h e d r a l symmetry. Co i s i n a high s p i n s t a t e . s a t e l l i t e i s due  Therefore,  the s a t e l l i t e  or l e s s i d e n t i c a l i n both phases.  phases.  phase  i f the  3s  separation  should be more  As mentioned above,  the p r e c i s e magnitude of the s a t e l l i t e d i f f e r e n t i n the two  shows  In both phases  to m u l t i p l e t s p l i t t i n g , the  between the main peak and  the  separation i s  This difference i n  - 256  -  s a t e l l i t e s e p a r a t i o n cannot be due d e n s i t y a t Co when going  to a change i n s p i n  from the s o l i d to the vapor  phase as such changes would be of much s m a l l e r magnitude. 7  E a r l i e r work i n t h i s l a b o r a t o r y t h i s observation.  on C o F  2  and CoF^  confirms  Here the 3s s a t e l l i t e s e p a r a t i o n  changed by o n l y 0.2eV when going number of unpaired  from C o F  to C o F ,  2  the  3  e l e c t r o n s i n c r e a s i n g from 3 to 4.  On  the other hand, the observed d i f f e r e n c e i n s a t e l l i t e s e p a r a t i o n between  the s o l i d and vapor phase 3s  spectra  could be e a s i l y e x p l a i n e d by a shakeup mechanism. ( i i i ) The  relative  intensity  i n the vapor phase i s 0.39. the r a t i o 5:3  The  of the Co value  expected f o r the two  f o r the r e l a t i v e i n t e n s i t y 25 by V n n i k k a and Ohrn,  3s s a t e l l i t e  i s different  s p i n s t a t e s . Values  of 3s s a t e l l i t e s c a l c u l a t e d  which i n c l u d e c o n f i g u r a t i o n  mixing are not i n agreement with t h i s r e s u l t . understandable because these v a l u e s do not effects  due  intensity  from  to covalency.  This i s  include  T h i s d e v i a t i o n from the  r a t i o between the main peak and  5:3  the s a t e l l i t e  i n the 3s s p e c t r a i s seen i n other Co compounds which 7  were s t u d i e d p r e v i o u s l y i n t h i s l a b o r a t o r y .  For  example, the r e l a t i v e i n t e n s i t i e s of the 3s s a t e l l i t e s of s o l i d C o F , C o C l 2  r e s p e c t i v e l y . The  2  and  CoBr  2  are 0.63,  value f o r CoF^  i s 0.58.  0.86  and  1.12  Therefore,in  - 257 -  the l i g h t o f t h i s p r e s e n t work, these r e s u l t s t h a t the s a t e l l i t e s seen i n Co(II) 3 s s p e c t r a ,  suggest 4-6eV  removed from the main l i n e are due t o shakeup r a t h e r than due t o m u l t i p l e t  splitting.  The FWHM o f the main peak and the s a t e l l i t e peak i n the 3 s spectrum o f C o ( A c A c ) respectively.  2  vapor are 3.6 and 4.OeV  The 3 s main peak o f Co i s broader than t h a t  o f Cu i n the 3 s spectrum o f C u ( A c A c ) . 2  This observation 19  supports the view put forward by Larsson and Braga, who  suggested t h a t the m u l t i p l e t s p l i t t i n g o f the 3 s  s p e c t r a o f N i ( I I ) and p o s s i b l y Co (II) s a l t s i s so s m a l l t h a t i t cannot be r e s o l v e d e a s i l y .  However i t i s t o be  noted t h a t the FWHM o f the Co (II) 3 s s a t e l l i t e i s l e s s than t h a t o f the Cu(II) 3 s spectrum,  t h i s being the  o p p o s i t e o f what one would have expected from g n e e r a l considerations of multiplet  splitting.  0 Is  The 0 I s s p e c t r a o f a l l t h r e e a c e t y l a c e t o n a t e s s t u d i e d i n t h i s work show a s a t e l l i t e a t b i n d i n g e n e r g i e s higher than the main peak  (Table 6.4).  I t has been r e p o r t e d 38  t h a t a c e t y l a c e t o n e a l s o shows a s i m i l a r s t r u c t u r e t h i s i s confirmed by the p r e s e n t work. As s t a t e d  and earlier,  -  258  -  t h i s f e a t u r e has a l s o been observed 1,3-dicarbonyl  compounds.  i n a number of  I t i s important  to note  here t h a t no such s a t e l l i t e s of any a p p r e c i a b l e  intensity  have been r e p o r t e d f o r 3 , 3 - d i m e t h y l a c e t y l a c e t o n e , the two methyl groups a t the c e n t r a l carbon e n o l i z a t i o n . The  satellite  where  prevent  s e p a r a t i o n s i n the 0 i s  s p e c t r a of the metal a c e t y l a c e t o n a t e s are a l l higher than t h a t o f f r e e a c e t y l a c e t o n e . suggest due  These o b s e r v a t i o n s  the p o s s i b i l i t y t h a t the observed  satellites  to a shakeup t r a n s i t i o n which i s mainly  character. observed  The  of  are  LTT+LTT*  c a l c u l a t e d e l e c t r o n i c s t r u c t u r e , and  e l e c t r o n i c s p e c t r a of a c e t y l a c e t o n e and i t s  anion i n d i c a t e the presence o f o r b i t a l s of the c o r r e c t 50 symmetry and energy o r d e r i n g f o r such t r a n s i t i o n s . However, as the r e l a t i v e energy l e v e l s of  molecular  o r b i t a l s can change c o n s i d e r a b l y on core l e v e l the exact nature of confirmed  ionization,  the shakeup t r a n s i t i o n c o u l d  o n l y a f t e r hole s t a t e c a l c u l a t i o n s are  out on these molecules.  The p o s s i b i l i t y t h a t  l l i t e s i n metal a c e t y l a c e t o n a t e s are due  0  be carried  Is s a t e -  t o metal to  l i g a n d charge t r a n s f e r remains t o be excluded.  I f the  shakeup t r a n s i t i o n i n v o l v e d i s a c t u a l l y of L T T ^ - L T T * nature, t h i s may  p a r t l y e x p l a i n the enhanced  satellite  s e p a r a t i o n i n the 0 Is s p e c t r a of metal a c e t y l a c e t o n a t e s compared to t h a t of a c e t y l a c e t o n e , s i n c e back  donation  - 259  -  o f e l e c t r o n s from the metal t o the l i g a n d bonding o r b i t a l s levels  relative  TT*  i s expected t o d e s t a b i l i z e t o bonding  TT l e v e l s .  antiligand  Lowering  IT*  of the  c a r b o n y l c a r b o n I s b i n d i n g e n e r g y on c o m p l e x f o r m a t i o n is  6.4  a l s o noted,  i n accord with expectations.  Conclusions  From t h e s t u d i e s o f t h e gas p h a s e x - r a y electron structure  spectra, seen  i t was  shown t h a t  i n t r a n s i t i o n metal  d e p e n d s on t h e symmetry  the  photo-  satellite  acetylacetonates  o f t h e complex.  As b o t h N i and  Co a c e t y l a c e t o n a t e s u n d e r g o a change i n symmetry going from the s o l i d in  symmetry  to the vapor, the e f f e c t  on s a t e l l i t e  s t r u c t u r e c o u l d be  o f change  studied  w i t h o u t c h a n g i n g t h e c e n t r a l m e t a l atom a n d / o r At  least  i n the case of CuCAcAc^f  atom e f f e c t s were the s a t e l l i t e  when  ligand.  the second n e a r e s t  f o u n d t o be u n i m p o r t a n t  i n determining  structure.  Present r e s u l t s  strongly  suggest that  s e e n i n t h e 3s s p e c t r a o f p a r a m a g n e t i c compounds p a r t i c u l a r l y  t h o s e o f Co  2+  the  satellite  transition  , Ni  2+  and Cu  metal 2+  , at  b i n d i n g e n e r g i e s 4-6eV h i g h e r t h a n t h e m a i n peak a r e due t o shakeup r a t h e r  than m u l t i p l e t  splitting.  The  main  - 260 -  e f f e c t of m u l t i p l e t s p l i t t i n g to be broadening o f the peaks. more predominant  i n these s p e c t r a seems T h i s broadening i s  i n the s a t e l l i t e  peaks.  The two s a t e l l i t e peaks found i n the 2p and 3s spectra of CufAcAc^  a r i s e from two d i f f e r e n t  shakeup  processes and i t i s l i k e l y t h a t the low b i n d i n g  energy  s a t e l l i t e r e s u l t s from a m e t a l - t o - l i g a n d charge t r a n s f e r t r a n s i t i o n as opposed t o t r a n s f e r type shakeup  the l i g a n d - t o - m e t a l  mechanism proposed  charge  f o r the  s a t e l l i t e s found i n 2p and 3s s p e c t r a o f Co and N i acetylacetonates.  In the case o f the l i g a n d ,  satellite  s t r u c t u r e i s seen o n l y i n the 0 Is s p e c t r a , and i s p o s s i b l y due t o a L T T + L T T * type shakeup t r a n s i t i o n .  Hole  s t a t e c a l c u l a t i o n s f o r these molecules are not a v a i l a b l e , and t h i s makes i t d i f f i c u l t t o a s s i g n unambiguously the shakeup peaks t o s p e c i f i c shakeup t r a n s i t i o n s . hoped t h a t t h i s study w i l l  It i s  s t i m u l a t e such c a l c u l a t i o n s .  - 261 REFERENCES  1.  D.C. F r o s t , C A . McDowell, and R.L. Tapping, J . E l e c t r o n Spectrosc.  R e l a t . Phenom. 7, 297 (1975)  2.  K.S. Kim, and N. Winograd, Chem. Phys. L e t t . 31, 312 (19 75)  3.  D.C 40,  4.  F r o s t , C A . McDowell, and B. Wallbank, Chem. Phys. L e t t . 189 (1976)  J . C Carver, G.K. Schweitzer, and T.A. C a r l s o n ,  J . Chem. Phys.  57_, 973 (1972) 5.  B. Wallbank, I.G. Main, and C E . Johnson, J . E l e c t r o n Spect r o s c . R e l a t . Phenom. 5, 259 (1974)  6.  M.A. B r i s k , and A.D. Baker, J . E l e c t r o n S p e c t r o s c .  Relat.  Phenom. 6, 81 (19 75) 7.  D.C. F r o s t , C A . McDowell, and I.S. 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Weigold, and C M . Barrow, J . Phys. Chem. 72_, 4631 (1968).  - 263 -  30.  J.S.H.Q. Perera, D.C. F r o s t , and C.A. McDowell, J . Chem. Phys. 7_2 (19 80). To be p u b l i s h e d  31.  R.G. C h a r l e s , and M.A. Pawlikowski, 440  J . Phys. Chem. 62,  (1958)  32.  J.B. E l l e r n , and R.O. Ragsdale,  33.  J.H. S c o f i e l d , J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 8_, 129  34.  Inorg. Synth. XI 82 (1968)  (1976)  M.Z. Gurevich, T.M. Sas, N.E. Lebedeva, V.V. Zelentsov, and B.D. S t e p i n , Russian J . Inorg. Chem. 17. 556 (.1976).  35.  G. Johansson, J . Hedman, A. Berndtsson, R. N i l s s o n .  M. K l a s s o n , and  J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 2_, 295  (1973) 36.  K. Siegbahn, C. N o r d l i n g , J . Johansson, J . Hedman, P.F. Heden, K. Hamrin, U. G e l i u s , T. Bergmark, L.O. Werme, R. Manne, and Y. Baer,"ESCA A p p l i e d t o f r e e molecules"  (North H o l l a n d ,  Amsterdam, 1969) 37.  C.S. Fadley, Ph.D. t h e s i s , U n i v e r s i t y o f C a l i f o r n i a , LBL  Berkeley,  Report No. 19535 (1970)  38.  R.S. Brown, J . Am. Chem. Soc. 9_9 , 5497 (1977)  39.  T h i s value was estimated from the r e s u l t s r e p o r t e d i n Ref. 38  40.  FWHM values r e p o r t e d here are the values o b t a i n e d u s i n g the 37 curve  f i t t i n g program  the A l Ka e x c i t i n g l i n e  , and i n c l u d e the c o n t r i b u t i o n s from (^0.8eV) and the spectrometer  r e s o l u t i o n (^0.3eV) 41.  A. Schweig, H. Vermeer, and U. Weidner, Chem. Phys. L e t t . 26, 229  (1974)  - 264 -  42.  S. Larsson, Chem. Phys. L e t t . 32, 401 (1975).  43.  S. L a r s s o n , P h y s i c a S c r i p t a 16, 381 (1977)  44.  F.A. Cotton, C.B. H a r r i s , and J . J . Wise, Inorg. Chem. 6_, 909  (1967)  45.  F.A. Cotton, and J . J . Wise, Inorg. Chem. 6_, 917 (1967)  46.  K. Siegbahn, C. N o r d l i n g , A. Fahlman, R. Nordberg, K. Hamrin, J . Hedman, G. Johansson, T. Bergmark, S. - E . K a r l s s o n , I . Lindgren, and B. L i n d b e r g , Nova  Acta  Regiae  Soc. S c i . U p s a l i e n s i s , Ser IV, V o l . 20 (196 7) 47.  B. Wallbank, J.S.H.Q. P e r e r a , D.C. F r o s t , and C.A. McDowell, J . Chem. Phys. 69, 5405 (1978)  48.  T.A. C a r l s o n , J.C. Carver, and G.A. Vernon,. J . Chem. Phys. 62_, 932 (1975)  49.  M. Mehta, C.S. Fadley,and  P.S. Bagus.  Chem. Phys. L e t t .  3_7, 353 (1976) 50.  H. N a k a n i s h i , H. M o r i t a , and S. Nagakura, Soc. Japan 50, 2255 (1977)  B u l l . Chem.  CHAPTER SEVEN  SUMMARY AND  The  a p p l i c a t i o n of e l e c t r o n spectroscopy i n the  i n v e s t i g a t i o n of now  PROGNOSIS  the e l e c t r o n i c s t r u c t u r e of matter i s  a w e l l e s t a b l i s h e d f i e l d of research.  spectroscopy has  Electron  been a p p l i e d to a l l known p h y s i c a l 1-3  s t a t e s of matter, and  however, the  study of f r e e atoms  molecules i s p a r t i c u l a r l y rewarding as most of  inherent  f e a t u r e s o f the s p e c t r a can be  investigated  i n the absence of condensed phase e f f e c t s . comparison of the  the  Then, by  f r e e atom/molecule r e s u l t s w i t h those  o b t a i n e d f o r the condensed s t a t e , v a l u a b l e  information 3  4  p e r t a i n i n g t o condensed phase e f f e c t s can be o b t a i n e d . ' Gas  phase x-ray p h o t o e l e c t r o n  spectroscopy, i n p a r t i c u l a r ,  i s i n v a l u a b l e as a t o o l f o r s y s t e m a t i c a l l y i n v e s t i g a t i n g  -  -  266  multielectron e x c i t a t i o n processes ionization.  In the s o l i d  accompanying photo-  s t a t e , such s t u d i e s are  o c c a s i o n a l l y hampered by the presence of l a r g e backgrounds caused by i n e l a s t i c s c a t t e r i n g , plasmon e x c i t a t i o n e t c . S t r u c t u r e due  to i n e l a s t i c  collisions  i n the vapor phase s p e c t r a can, however, be  readily  i d e n t i f i e d and c o r r e c t e d . The work d e s c r i b e d i n t h i s t h e s i s has i n v o l v e d the development and o p e r a t i o n of a gas phase x-ray p h o t o e l e c t r o n spectrometer.  A high temperature range  of upto ^ 1 0 0 0 ° C i s a v a i l a b l e f o r v a p o r i z i n g i n v o l a t i l e s o l i d s and metals, manipulation  and e f f i c i e n t data a c q u i s i t i o n  i s handled  by a P D P 8 / e minicomputer  faced t o the spectrometer.  inter-  T h i s work t h e r e f o r e r e p r e s e n t s  an e x p e r i m e n t a l i s t ' s viewpoint of x-ray  and  of some important  p h o t o e l e c t r o n spectroscopy.  aspects  More f u l l y  q u a n t i t a t i v e i n t e r p r e t a t i o n s of these r e s u l t s  can  now  For most  be attempted by f u l l - t i m e t h e o r e t i c i a n s .  s p e c i e s , the s p e c t r a r e p o r t e d i n t h i s t h e s i s r e p r e s e n t the f i r s t x-ray p h o t o e l e c t r o n s p e c t r o s c o p i c study i n the vapor phase. Core l e v e l b i n d i n g e n e r g i e s of Group IA and  IIA  f r e e atoms, e x c e p t i n g l i t h i u m and b e r y l l i u m , were determined a c c u r a t e l y and the r e s u l t s are r e p o r t e d i n  - 267  -  Chapter Four. These b i n d i n g energy v a l u e s can be i n c o n j u n c t i o n w i t h the corresponding standard b i n d i n g e n e r g i e s to estimate the shifts.'  The  used  state  'phase t r a n s i t i o n  f r e e atom b i n d i n g e n e r g i e s and the phase  t r a n s i t i o n s h i f t s determined  t h i s way  can be used t o t e s t  the v a l i d i t y of v a r i o u s s e m i - e m p i r i c a l and  theoretical  5-7 models.  The observed v a l u e s of phase t r a n s i t i o n  s h i f t s are lower than those v a l u e s c a l c u l a t e d f o r e x t r a 6 8 9 atomic r e l a x a t i o n u s i n g a s e m i l o c a l i z e d e x c i t o n model. ' ' However, the t r e n d s o f these phase t r a n s i t i o n s h i f t s are r a t h e r a c c u r a t e l y p r e d i c t e d , i n d i c a t i n g the dominant r o l e p l a y e d by extra-atomic r e l a x a t i o n i n determining shifts. Chapter  these  The d i r e c t l y measured b i n d i n g e n e r g i e s of Four are, i n most cases, i n good agreement w i t h  those estimated i n d i r e c t l y by combining  x-ray emission data  f o r s o l i d s and o p t i c a l r e s u l t s f o r f r e e atoms. However, f o r a l l l e v e l s of c a l c i u m , t h i s i n d i r e c t method g i v e s values ^5eV  lower than the XPS  b i n d i n g e n e r g i e s . Although  good agreement i s o b t a i n e d between the XPS of barium  binding energies  and v a l u e s estimated u s i n g x-ray emission  results  and f r e e atom o p t i c a l data, there are i n d i c a t i o n s t h a t the e s t i m a t e s are l e s s than r e l i a b l e .  These r e s u l t s , t h e r e -  f o r e , s t r o n g l y suggest t h a t extreme care should be  taken  i n u s i n g such i n d i r e c t l y estimated f r e e atom b i n d i n g energies.  - 268 -  M u l t i e l e c t r o n e x c i t a t i o n s a t e l l i t e s were observed i n a l l core l e v e l s p e c t r a o f the f r e e atoms r e p o r t e d i n Chapter Four.  In the case o f the group IA elements, the  observed s a t e l l i t e s can be c o n v e n i e n t l y a s s i g n e d t o a ns-*(n+l)s type shakeup t r a n s i t i o n , u s i n g the ' e q u i v a l e n t c o r e s approximation'.  However, the s i t u a t i o n i s l e s s  s t r a i g h t f o r w a r d i n the case of the Group I I A  metal atoms.  M a r t i n and S h i r l e y ^ have suggested t h a t both s t a t e and f i n a l i o n i c s t a t e c o n f i g u r a t i o n  interaction  can be important i n d e t e r m i n i n g the s a t e l l i t e The r e s u l t s from the Group I I A  initial  structure.  metal atoms are s t r o n g  i n d i c a t i o n s o f the incompleteness o f the o n e - e l e c t r o n t r a n s i t i o n d e s c r i p t i o n of the shakeup p r o c e s s . X-ray p h o t o e l e c t r o n s p e c t r a o f the t i t a n i u m 2p and 3p l e v e l s , and the halogen core l e v e l s from t i t a n i u m h a l i d e vapors, T i X Five).  4  ( X = F , C l , B r , I ) were o b t a i n e d  (Chapter  Two s a t e l l i t e s a s s o c i a t e d w i t h the T i 2 p ^ 3  were observed f o r a l l four t e t r a h a l i d e s .  tetra-  2  level  The s a t e l l i t e  a t lower b i n d i n g e n e r g i e s can be a s s i g n e d t o a l i g a n d to-metal 3d type charge t r a n s f e r t r a n s i t i o n e+e* or t -Hr* t r a n s i t i o n , or b o t h ) . 2  ( e i t h e r the  A r e c e n t SCF Xa hole  s t a t e calculation''"''" f o r 2p i o n i z e d T i C l ^ c o n f i r m s t h i s assignment.  T h i s c a l c u l a t i o n has estimated an e x c i t a t i o n  energy f o r C l 3p  T i 4s, T i 4p t r a n s i t i o n , which i s i n  - 269 -  good a g r e e m e n t w i t h t h e s e p a r a t i o n b e t w e e n t h e h i g h e r energy s a t e l l i t e one-electron to  and t h e main peak.  p i c t u r e these  However, i n t h e  t r a n s i t i o n s are expected  be v e r y weak when c o m p a r e d t o l i g a n d - t o - m e t a l  3d t y p e  12 transitions  d e s p i t e t h e f a c t t h a t t h e f o r m e r was  o b s e r v e d t o be t h e s t r o n g e r  satellite  tetrahalides.  state calculations including  Further  hole  i n a l l four  c o n f i g u r a t i o n i n t e r a c t i o n may be o f some u s e i n e x p l a i n i n g the observed  intensities.  New e x p e r i m e n t a l Six  e v i d e n c e was p r e s e n t e d  strongly indicating that the s a t e l l i t e  i n Chapter  structure  s e e n i n t h e 3s s p e c t r a o f p a r a m a g n e t i c t r a n s i t i o n m e t a l 2+ 2+ 2+ compounds, p a r t i c u l a r l y t h o s e o f Co , Ni and Cu , at binding energies  4-6eV h i g h e r  t h a n t h e m a i n p e a k , a r e due 13  to  shakeup r a t h e r t h a n m u l t i p l e t s p l i t t i n g .  e v i d e n c e came f r o m a s t u d y acetonates, vapor phase.  M(AcAc)2  of t r a n s i t i o n metal  (M=Co(II),Ni(II),Cu(II))  B o t h N i a n d Co a c e t y l a c e t o n a t e s  a c h a n g e i n symmetry when g o i n g vapor. the  I n t h e case o f Co(II)  from t h e s o l i d  and C u ( I I )  This acetyli nthe undergo to the  acetylacetonates,  s p i n s t a t e s o f t h e m e t a l atoms a r e u n c h a n g e d when  going  from t h e s o l i d  acetylacetonate diamagnetic.  t o t h e vapor, whereas f o r N i ( I I )  the s o l i d  i s high  s p i n , and t h e v a p o r i s  A l lthree acetylacetonates  have b e e n  - 270  -  previously s t u d i e d i n the s o l i d state" "' ' 1  of  1  xD  and  comparison  the vapor phase s p e c t r a w i t h those i n the s o l i d phase  p r o v i d e d i n f o r m a t i o n both on the s e n s i t i v i t y of to  satellites  changes i n symmetry about the metal atom without  changing the l i g a n d , and the r e l a t i v e r o l e s of exchange s p l i t t i n g and shakeup i n t r a n s i t i o n metal 3 s s p e c t r a . The experimental r e s u l t s on Cu(II) a c e t y l a c e t o n a t e can be e x p l a i n e d i n terms of a m e t a l - t o - l i g a n d type charge t r a n s f e r e x c i t a t i o n as opposed t o  the l i g a n d - t o - m e t a l  charge t r a n s f e r mechanism proposed  f o r the other t r a n s i t i o n 16  metal compounds, an o b s e r v a t i o n s u p p o r t i n g Larsson's views on the o r i g i n of s a t e l l i t e s i n the t r a n s i t i o n core l e v e l  17 '  metal  spectra.  The main t h e s i s o f t h i s t r e a t i s e has, t h e r e f o r e , been the experimental d e t e r m i n a t i o n of s e v e r a l core l e v e l b i n d i n g e n e r g i e s and the a s s o c i a t e d s a t e l l i t e The present spectrometer has demonstrated  structure.  a c a p a b i l i t y to  e f f e c t i v e l y gather i n f o r m a t i o n on such e l e c t r o n i c of  f r e e atoms and molecules.  and should be done to improve and f l e x i b i l i t y of the For  However, f u r t h e r work can, the performance,  sensitivity/  system.  example, the s t u d i e s of m u l t i e l e c t r o n  excitation  s a t e l l i t e s have shown t h a t f o r a g i v e n core l e v e l are  properties  these  c h a r a c t e r i s t i c of the molecule, and hence can be used  - 2 71  as a of  'finger print'.  -  H o w e v e r , due  t o t h e weak n a t u r e  these processes, several m o d i f i c a t i o n s could  made t o i m p r o v e t h e d a t a c o l l e c t i o n , t h e t i m e t o r e c o r d s p e c t r a , and c a u s e d by v o l t a g e d r i f t ,  be  thereby reducing  eliminating  problems  sample d e c o m p o s i t i o n ,  and  c o a t i n g o f t h e x - r a y t u b e and g a s c e l l w i n d o w s .  Thus  c e r t a i n s p e c t r a r e c o r d e d i n t h i s t h e s i s r e q u i r e d up 48 h r s . t o a c c u m u l a t e .  This decreased  to  sensitivity is  c a u s e d by t h e s m a l l e r d i a m e t e r o f t h e e n t r a n c e and  exit  h o l e s of the a n a l y s e r , w h i c h i s r e q u i r e d t o enhance r e s o l v i n g power o f t h e s p e c t r o m e t e r  (Chapter  Three).  P a r a m o u n t amongst m e t h o d s f o r r e m e d y i n g t h i s w o u l d be t h e u s e o f a p o s i t i o n  the  situation  sensitive multidetector  system, i n s t e a d of the simple channel e l e c t r o n  multiplier  at  capitalize  p r e s e n t employed.  A m u l t i c h a n n e l p l a t e can  on t h e two d i m e n s i o n a l f o c u s i n g power o f t h e h e m i s p h e r i c a l e l e c t r o n energy a n a l y s e r .  A number o f d i f f e r e n t  d e t e c t o r d e s i g n s a r e a v a i l a b l e a t p r e s e n t and  multi-  are  used  in conjunction with electron spectrometers.* '*^ Recently 8  20 H i c k s e t a_l. employing  have d e v e l o p e d  a charge-coupled  sensitive detection.  an e l e c t r o n  spectrometer  imaging device f o r p o s i t i o n  This i s claimed to give a  (con-  s e r v a t i v e ) i m p r o v e m e n t o f more t h a n a f a c t o r o f 100 s e n s i t i v i t y over the best e x i s t i n g  spectrometers.  in With  - 272  -  such a multidetector system one would be a b l e t o make f u l l use of the data a c q u i s i t i o n c a p a b i l i t i e s o f the minicomputer.  Such a m o d i f i c a t i o n would be  particularly  u s e f u l i n the study of very h i g h temperature  species i . e .  >1000°C, which p l a c e much more s t r i n g e n t requirements  on  the spectrometer, n e c e s s i t a t i n g s h o r t e r scanning times. Thus, the p r e l i m i n a r y spectrum could have been s u b s t a n t i a l l y Between 1000 of  improved.  and 2000°C, there are s e v e r a l s p e c i e s  h i g h temperature  first transition  of Ag atoms (Chapter Three)  i n t e r e s t , e.g. metal atoms of the  series.  A d d i t i o n a l l y , an improved  data a c q u i s i t i o n  system  would a s s i s t i n the study of t r a n s i e n t and u n s t a b l e s p e c i e s , where atoms and molecules e x i s t i n unusual bonding  s i t u a t i o n s and where l a r g e chemical s h i f t s of  core l e v e l s may  be expected.  Such s t u d i e s would t h e r e -  f o r e complement the e x c e l l e n t work t h a t i s being done i n 21 UPS.  - 273 -  REFERENCES 1.  K. Siegbahn, C. N o r d l i n g , A. Fahlman,  R.  Nordberg,  K. Hamrin; J . Hedman, G. Johansson, T. Bergmark, S.-E.  K a r l s s o n , I . L i n d g r e n , and B. L i n d b e r g , "ESCA:  Atomic, M o l e c u l a r , and S o l i d S t a t e S t r u c t u r e S t u d i e d by Means o f E l e c t r o n Spectroscopy", Nova A c t a Regiae Soc. S c i . U p s a l i e n s i s , Ser. IV, Vol.20 W i k s e l l s , Stockholm, 2.  (Almqvist and  1967)  K. Siegbahn, C. N o r d l i n g , G. Johansson, J . Hedman, P. F. Heden, K. Hamrin, U. G e l i u s , T. Bergmark, L. 0. Werme, R. Mann, and Y. Baer, "ESCA, A p p l i e d t o Free  3.  Molecules"  (North-Holland P u b l i s h i n g Company,  Amsterdam,  1969)  H. Siegbahn, L. Asplund, P. K e l f v e , K. Hamrin, K a r l s s o n , and K. Siegbahn, J . E l e c t r o n R e l a t . Phenom. 5, 1059  4.  L.  Spectrosc.  (1974)  M. S. Banna, B. Wallbank, D. C. F r o s t , C. A.  McDowell,  and J . S. H. Q. Perera, J . Chem. Phys. 68_, 5459 (1978). 5.  P. A l b e r t s e n , and P. Jo'rgensen, J . Chem. Phys.  70,  3254 (1979) 6.  D. R. Beck, and C. A. N i c o l a i d e s , NATO Adv. I n s t . Ser., Ser. C (1978) (Pub. 1979) S t a t e s Quantum Chem.) p.329  C46  Study (Excited  - 2 74 -  B. Johansson, and N. Mortensson, t o be p u b l i s h e d L. Ley, F. R. McFeely, S. P. Kowalczyk, J . G. J e n k i n , and D. A. S h i r l e y , Phys. Rev.B 11, 600 (1975) D. A. S h i r l e y , R. L. M a r t i n , S. P. Kowalczyk, F. R. McFeely, and L. Ley, Phys. Rev.B 15, 544  (1977)  R. L. M a r t i n , and D. A. S h i r l e y , Phys. Rev. A 13, .1475  (1976)  J . A. T o s s e l l , Chem. Phys. L e t t . 6_5, 371 (1979) M. Braga, and S. Larsson,  I n t . J . Quantum Chem.  Symp. 11, 61 (1977) J . S. H. Q. Perera, D. C. F r o s t , and C. A. McDowell, J . Chem. Phys. 7_2,  (1980)  T. A. C a r l s o n , J . C. Carver, L. J . Saethre, Santibanez, Relat.  F. G.  and G. A. Vernon, J . E l e c t r o n S p e c t r o s c .  Phenom. 5, 247 (1974)  D. C. F r o s t , C. A. McDowell, and R. L. Tapping, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom.  347 (1975)  S. Larsson, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 8_, 171  (1976)  S. L a r s s o n , Chem. Phys. L e t t . 3_2, 401 (1975) C. D. Moak, S. Datz, F. G. Santibanez,  and T. A. C a r l s  J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. (>, 151 (1975) S. T. Hood, and E. Weigold, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 15, 237 (1979)  - 275 -  20.  P. J . H i c k s , t o be  21.  S. D a v i e l , B. W a l l b a n k , a n d J . Comer,  published  D. C. F r o s t , S. T. L e e , C. A. M c D o w e l l , and N. P. C. Westwood, J . E l e c t r o n S p e c t r o s c . 95  (1977)  R e l a t . Phenom. 1 2 ,  APPENDIX  MULTI-CHANNEL SCALING PROGRAM  Symbolic Program L i s t i n g  /MCS  / C O M P L E T I N G T H E NUMBER O F S C A N S / R E Q U I R E D FOR REG I . I F C R FOLLOWED /C REGIONS ARE SCANNED ALTERNATELY. /AMY C H A R A C T E R T Y P E D DUHING A SCAN / S T O P S T H E R O U T I N E AT T H E END OF / T H E SCAN  PROGRAM  /MAXIMUM  OF  3  REGIONS  /EACH NOT E X C E E D I N G 2 5 5 CHANNELS / I N I T I A L L I Z E T H E COMPUTER /WHEN  A  IS  TYPED  COMPUTER  ASKS  /FOR I N I T I A L V O L T A G E ( T Y P E IN T H E /RETARDING VOLTAGE),DWELL TIME / C U R R E N T I N C R E M E N T , N O . OF SCANS /AND /INC.  N O . OF C H A N N E L S . ( F O R CUH. COMPUTER TAKES VALUES FROM  /2-I 6;ANY /CUR.  OTHER  INC.  NUMBER  TAKE  THE  TYPED  VALUE  /TO PROGRAM DWELL TIME / T Y P E I N A N Y N U M B E R FROM /AND  THE  COMPUTER  WILL  /DWELL T I M E ACCORDING /FOLLOWING TABLE. / /  NUMBER  TYPED  :  / /  SEC•/CHANNEL  I  /IN  REQUIRED  0  SET TO  7  THE  THE  0 .05  1 .5  2 1.0  3 1.5  4 2.0  ADDITION  /TO T H I S COMPUTER /INSTRUCTIONS.  TAKES  C M TO START SCAN D U E .  /SCANNING  WITH  2  STARTS  / S T A R T S WITH ONE /D:DISPLAY; AFTER  4.)  TO  TYPE NEXT  BELLS;  / E N D OF SCANNING I S S I G N A L L E D B Y /5 B E L L S ; A F T E R I N T E R R U P T SCANNING  MAKES  OF  /AFTER INTERRUPT /SCANNING AT T H E  FOLLOWING  /BiCHECK I N I T I A L AND FINAL VOLTAGE / A F T E R B T Y P E T H E NUMBER OF T H E R E G I O N /OF INTEREST.COMPUTER WILL SET THE /STARTING VOLTAGE.ANY KEYBOARD CHARACTER /OTHER THAN RETURN S E T S T H E F I N A L VOLTAGE, / T Y P E ANY C H A R . , B U T CR TO RESET. / C A R R I A G E RETURN TERMINATES THE ROUTINE. / C : S C A M ROUT IN E : 2 O P T I O N S ; IF ANY / C H A R A C T E R O T H E R T H A N CR F O L L O W E D C /SECOND REGION IS SCANNED AFTER  7 2.  BELL. TYPING  . D  / C O M P U T E R W A I T S FOR T H E NUMBER /OF THE REGION T O BE DISPLAYED. /ANY KEY BOARD C H A R . TYPED  M ^  /TERMINATES THE ROUTINE. / E : C L E A R STORAGE LOCATIONS / A F T E R E C O M P U T E R W A I T S FOR / T H E REGION NUMBER.  I  /F:3  POINT  SMOOTHING  OF  DATA  / T Y P E T H E NUMBER OF T H E R E G I O N / OF INTEREST AFTER F / G l P R I N T OR P L O T D A T A . ' W H E N G I S /  TYPED  / / /  T Y P E ANY K E Y B O A R D C H A R A C T E R FOLLOWED BY T H E R E G I O N O F I N T E R E S T T O P R I N T OUT D A T A . T O PLOT D A T A T Y P E  TELETYPE  PRINTS  /  RETURN  /  THE  FOLLOWED  REGION  OF  B Y THE  "PRINT"  NUMBER O F  INTEREST.AT  THE  / P L O T T Y P E R E T U R N TO T E R M I N A T E / ROUTINE. / A F T E R F OR G T Y P E I N T H E / R E G I O N NUMBER /J.S.H.O.PERERA  END O F THE  >50  esse  5455  0051  5456  JMP  I  CC  0052  54 57  JMP  I  DD  00 53  JMP  1 EE  JMP  I  005S  5460 5461 1245  BB.  1245  ce*6  4414  CC.  4 4 14  0057  1000  DD»  1000 1 1  0054  eeec  1  137  JMP  EE,  I  BB  1042  Ff,  1042  0062  1200  EEE,  0e63  1205  CURINC.  1200 1205  0ee4  oece 1226  NUMSC. CETSET,  0  0e65 cet6  00ee  DUELL2,  0  0026  ORDER,  0026  0070  0e00  C O U N T 1,  0e7i  ezee  OPTION,  0 0  0e72  I N D E X 1,  0 3 13  0073  0313 cee0  ee74  0000  007 5  0000  0100 0 000 0000 0101  REGNO 1,  OPT  1,  37  1226  0067  NUMREG,  FF  0  0 0  • 100  REGNO,  0  KPSTO,  0  0102  0000  HP,  0  0103  00e0  LP,  0  0ie4  0341 0330  A L P H A 1,  0341  LISTI,  0105  0106  eeea  N U M S C 1,  0330  0 0  /NO.  0110  0000 0000  0111  6eoe  DECPRT,  6000  01 1 2 01 1 3  0105  0000  K 105,  0105 0  0107  0114 0115  0 DWELL,  0000  M5,  6046 0724 0000  UDPRHT,  0116 0117 0120 C 2 0 0 012 1 7520  SPOT. LPSTO,  /IS  SCANS STORED  /UNSIGNED  COMPLETED HERE  DECIMAL  PRINT  R START,  0200  HM260,  7  520  0137 0555 5200  KI37,  6200  0140 0141 0142 0143 0144 0145 0146 0147 01 50 0151 01 52 0153 01 5 4 0 1 55 01 5 6 0157 0l6e  0342 0000  K6200, • 140  /DOUBLE  PR.  DEC  CONVERSION  0 137 0555 5200 6200  PPICK. DT.  0342 0 0 0 0 0 0 0 0 '  AALPHA,  0000 e»00  0ee0 0000 0000 0000 0000 0000 0000 0000 0000 0000  /STORE  /STORE  AND LAST  HERE  N O . OF  SCANS  HERE M  /STORE  CUR. INC.  /STORE  DWELL  INITIAL  TIME  HERE  HERE  0HO0 0000 0000  /STORE  0000  0162 0163 0164 0165 01 66 01 6 7 01 7 0  /HERE  0000  0172 0173 0174 0175 0176 0177  FIRST  /CHANNELS  0161  017 1  0  6046 0724 0  0122 0123 0124 0125  0000  0 LI SN,  6e32 603 1 5165  0  /SUBROUTINE  KCC  /BOARD  INPUT  KSF JMP  6C36  . - 1  K RB  6046  TLS  5563 0000  VOLTAGE  JMP TYPE,  I  LISN  0  604 1  TSF  5173  JMP  6046  TLS  7200  CL A  5572  JMP  /SUBROUTINE  .-I 1  TYPE  FOR K E Y  00  . 2 0 0 0200  7 3 0 0  020 I  6046  0202  1320  START,  C L A TAD  0203  6046  T L S  0204  4722  JMS  0205  3317  DCA  0206  1 3 17  TAD  0207  1316  TAD  02  10  7 5 1 0  SPA  02 1 1  5213  J M P  02  5200  J M P  12  C L L  T L S K 2 7 6  02 52  3703  DCA  I  02 53  1302  TAD  K 1 4 0 0  02 54  370 1  DCA  I  0255  1300  TAD  02 56  3677  DCA  SC K K I 4 0 0  STCHAN I  02 57  1 1 40  TAD  A A L P H A  0260  3341  DCA  A L P H A  I N S T  02 61  4 3 3 0  JMS  I N S T  G262  1313  TAD  / T Y P E S I  >  L L I S N  A  1,  LI  0263  472 1  J M S  4330  JMS  . * 2  0265  4676  JMS  I  SSICON  START  0266  37 1 1  DCA  I  IB  / N E G .  C O D E  FOR  H  I  T T Y P E  L I S T  02  13  3 3 1 5  DCA  CHECK  0267  23  11  ISZ  14  2 3 1 5  I S Z  CHECK  0270  4 3 3 0  JMS  L I  ST  02  15  52  J M P  .+2  027 1  4 52 4  JMS  I  DT VI  0216  5740  J M P  I  G  0272  3707  DCA  I  2 3 1 5  I S Z  CHECK  0273  2307  I S Z  VI  0220  5222  J M P  .+2  0274  567 5  J M P  I  022 1  5727  J M P  I  0275  0 4 0 0  K 4 0 0 ,  0222  2 3 1 5  I S Z  CHECK  e223  5225  J M P  .+2  0276  6200  SSI  0224  5726  J M P  E  0277  0 5 0 5  S T C H A I ,  0 5 0 5  C22 5  2 3 1 5  0300  0141  STCHAN,  0141  e226  5230  J M P  0301  0506  K K 1 4 0 0 /  0227  5725  J M P  I  0302  1400  K 1 4 0 0 ,  0230  231  I S Z  CHECK  0303  0510  S O  0231  5233  J M P  .+2  0304  0147  S S C ,  0  0232  5724  C  0305  051 1  C I ,  0511  0233  2 3 1 5  I S Z  CHECK  0306  0 1 52  C C I ,  0152  0234  5236  J M P  .  *2  0307  0 0 0 0  V I ,  0  0235  5723  J M P  I  B  03  0 1 55  WW I ,  0236  2 3 1 5  I S Z  0237  5200  0240  5241  024 1  1314  0242  3313  DCA  0243  1312  TAD  0244  331 1  DCA  0 2 4 5  1310  TAD  0246  3307  DCA  0247  1306  TAD  CCI  02 50  3 7 0 5  DCA  I  0 2 51  1304  TAD  I  I S Z  5  J M P  A,  CHECK .+2  I  D  /DT"  K 4 0 0  10  0 5 0 6 0 5 1 0 147  0  155  0  J M P  START  03  0 1 60  I I B,  0 1 6 0  J M P  A  0313  0000  INDEX,  0  TAD  K261  0 3 14  026 1  K 2 6  026 1  INDEX  0315  0 0 0 0  CHECK,  0  03  7 4 7 0  MH,  7 4 7 0  0317  0 0 0 0  I N S T ,  0  VVI  0320  0276  K 2 7 6 ,  0 2 7 6  VI  032 1  0  T T Y P E ,  0  0322  0163  L L I S N ,  0 1 63  0323  0050  B,  0 0 5 0  0324  0051  C,  0051  CI  / D E C I M A L  1400  I D,  SSC  R3  12  16  172  1,  AND  172  //•- 3 1 0  FOR  i  IB=  6 2 0 0  0 0 0 0  IB  R 1 , R 2  / C O N S T A N T S CON,  03 1 1  IB  / T Y P E S / T Y P E S  0 4 0 0  CHECK  I  STORAGE  I B  0217  F  S T A R T I N G  CHANNEL  ST  02 64  MH  FOR  / F I N A L  INDEX  02  17  / P O I N T E R  STCHA1  H  TO  BINARY  CONV.  0052  D»  0 0 5 2  0326  0053  E»  0 0 5 3  0400  47  J M S  I  L L I S T  0327  0054  ft  0 0 5 4  040 1  4463  JMS  I  CURINC  L I S T ,  0402  371 1  DCA  I  0403  23 1 1  ISZ  CI I  JMS  I  L L I S T  JMS  I  S S S I C O  032  5  • 400  0330  0000  0331  1741  TAD  I  A L P H A  0332  4721  J M S  I  T T Y P E  0404  47  0333  174 1  TAD  I  A L P H A  0405  4712  0334  2341  ISZ  A L P H A  0406  3710  0335  7 7 1 0  SPA  C L A  0407  2310  0336  5730  J M P  I  04 1 0  4713  JMS  I  L L I S T  0337  5331  JMP  LI  04 1 1  47  JMS  I  S S S I C O  0340  0540  G,  034 1  0342  A L P H A,  0342  0 2 1 5  02 1 5  0343  02  02  12  0  13  / S U B R O U T I N E  L I S T ST*1  0 5 4 0  DCA ISZ  12  CI I  I  SCC  0 4 12  3307  DCA  CHAN  1307  TAD  CHAN  /CR  04 1 4  7  CLL  RAL  /LF  04 1 5  3307  DCA  CHAN  /R  104  0344  4322  4 3 2 2  04 1 6  1306  TAD  0345  0 2 1 5  02  15  04  3705  DCA  0346  02  02  12  0420  2 3 0 5  ISZ  SSTCHA CHAN  12  17  SSTCHA  0347  031 1  03 1 1  /1  042 1  1307  0 3 0 2  /B  TAD  0302  0422  700 1  I AC  0351  4 2 7 5  4 2 7 5  /=  0423  1306  TAD  03 52  02  15  02  1 5  0424  3 7 0 5  DCA  0353  02  12  02  12  042 5  1304  TAD  03 54  0 3 0 4  0 3 0 4  /D  0426  1306  TAD  T 1 4 0 0  0 3 5 5  0324  0 3 2 4  /T  0427  3306  DCA  T 1 4 0 0  0356  4 2 7 5  4 2 7 5  /=  0430  1306  TAD  T 1 4 0 0  03 57  0 2 1 5  02 1 5  043 1  3303  DCA  MLSTCH  0360  02  02  0432  1303  TAD  MLSTCH  0361  0 3 0 3  0 3 0 3  0433  704 1  C I A  0362  031 1  03 1 1  0363  4 2 7 5  4 2 7 5  0364  02 1 5  02  15  02  12  12  12 /C /I  /=  T 1 4 0 0 I  SSTCHA  K I 0 0 0  0434  1705  TAD  I  0435  7710  SPA  CLA  0436  5243  J M P  SSTCHA CLL  . + 5  0365  02  0437  4316  JMS  REDO  0366  0 3 2 3  0 3 2 3  / S  0440  5677  J M P  I  0367  0303  0 3 0 3  /C  044 1  7000  0370  4 2 7 5  4 2 7 5  /=  NOP  0442  7000  NOP  037 1  0 2 1 5  02 1 5  0443  2 3 0 5  ISZ  0372  0212  02  0444  6031  0373  0303  0 3 0 3  /c  KSF  0445  5244  J M P  0374  0310  03  /H  0446  6036  KRB  0375  4 2 7 5  4 2 7 5  /=  0447  33  14  DCA  WAIT  0376  02  02  04 50  13 14  TAD  WAIT  0377  42 1 5  0451  1275  TAD  M264  12  12  10 12  42 1 5  M S T A K E ,  /CH«  T 1 4 0 0 I  0350  12  /sc»  SCC  04 1 3  0 3 4 2  12  13  / C I '  SSTART  SSTCHA . - 1  00  o  C525  2332  ISZ  E X I T  .+2  0526  77  SPA  CLA  J M P  M S T A K E  0527  57 1 6  TAD  WAIT  0530  5322  053 1  0533  X,  0 5 3 3  0532  0000  E X I T ,  0  0533  0277  L L I S T  0534  02  I  S S T A R T  0535  42 1 5  I  I I N D E X  0536  4000  0537  5000  0540  4737  054 1  1352  0452  7710  SPA  0453  5255  J M P  e454  5237  0455  1314  0456  1300  TAD  0457  7 6 4 0  SZA  CLA  0460  5263  J M P  . + 3  e46t  47  JMS  I  13  C L A  M2  C L L  56  10  JMP  I  JMP  0277 02  12  12  42 1 5  5677  J M P  0463  1676  TAD  C464  704 1  C I A  0465  1314  TAD  WAIT  0466  7 7 5 0  SPA  SNA  e467  5237  J M P  M S T A K E  0542  3504  DCA  I  WAIT  0543  4 50 5  JMS  I  I I N D E X  0544  0462  CLA  4 0 0 0 C H O I C E ,  5000 JMS  I  TAD  C H O I C E  K 6 0 0 ALPHA 1 L I S T 1  0470  1314  TAD  047 1  3676  DCA  I  0472  47  J M S  I  L L I S T  0545  1112  TAD  0473  5674  J M P  I  AA1  0546  3 3 5 4  DCA  ST  0474  02  0547  1754  TAD  I  0 4 7 5  13  TAD  1 100  REGNO K 1 0 5 ST  A A 1 ,  02  7 5 1 4  M 2 6 4 ,  7 5 1 4  0550  451 1  JMS  I  DECPRT  0476  0 3 1 3  I  03  0551  57 53  J M P  I  CONT  0 2 0 0  0552  0 6 0 0  K 6 0 0 ,  0 6 0 0  7  522  0553  063 1  CONT,  063 1  172  0554  0000  ST,  0  P I C K ,  0  57  I N D E X ,  57  REDO  RED0+4  13  0477  0 2 0 0  S S T A R T ,  0500  7522  M2  0501  0172  T T T Y P E ,  0  0502  0163  L L L I S N ,  0 1 6 3  0555  0000  0503  0 0 0 0  M L S T C H ,  0  0556  7300  CLA  56,  / S U B R O U T I N E CLL  0504  1000  K  0557  6031  K S F  0 5 0 5  0 0 0 0  S S T C H A ,  0  0560  5357  JMP  0506  0 0 0 0  T 1 4 0 0 ,  0  0561  6036  KRB  0507  0000  CHAN,  0  0562  6 0 4 6  T L S  0510  0000  sec  0  0563  3100  DCA  REGNO  051 1  0000  CI  0  0564  1676  TAD  I  0 S I 2  6200  S S S I C O ,  6 2 0 0  0565  704 1  CI  0513  0330  E L I ST,  0 3 3 0  0566  1 100  TAD  REGNO  0514  0000  WAIT,  0  0567  7750  SPA  SNA  0  0 57 0  5372  J M P  .+2  0 57 1  5237  JMP  MSTAKE  0572  1 100  TAD  REGNO  0573  112 1  TAD  MM260  051  5  1000,  I ,  0 0 0 0  1000  0  0516  0000  0517  7 3 0 0  CLA  0520  1331  TAD  052 1  3332  DCA  0522  1732  TAD  0523  470 1  0524  1732  REDO,  C L L X  . - 1  IINDEX  A CLA  0574  7550  SPA  SNA  I  E X I T  0 57 5  5237  JMP  M S T A K E  J M S  I  T T T Y P E  0576  3100  DCA  REGNO  TAD  I  E X I T  0577  5755  J M P  I  E X I T  PICK  0652  1375  TAD  K 7 7 7 7  0653  1376  TAD  HOLDI  0654  7110  CLL  RAR  0655  451 1  JMS  I  DECPRT  0656  1 50 1  TAD  I  HPSTO  /A  0657  3 102  DCA  HP  /N  0660  1370  0 3 2 3  /S  0661  4 2 7 5  4 2 7 5  /=  0610  0 2 1 5  02 1 5  061 1  0212  02  0612  0304  0 3 0 4  /D  06 1 3  0327  0327  /V  0614  0 3 0 5  0 3 0 5  0615  0314  0616  • 600  0600  0 2 1 5  060 I  0 2 12  02  0602  0323  0 3 2 3  /S  0603  0 3 0 3  0303  /c  06C4  030 1  030 1  0605  03 16  0 3 16  0606  e323  0607  02 15 12  N X L I N E ,  TAD  K77I  3504  DCA  I  0662  4505  JMS  I  L I S T I  0663  1 50 1  TAD  I  HPSTO  0664  704 1  CIA  0665  1 1C2  TAD  0666  7110  CLL  RAR  / E  0667  451 1  JMS  I  0 3 14  /L  0670  7307  0 3 1 4  03  /L  067 1  700 1  I AC  e 6 17  4 2 7 5  427  /=  C I A  0620  02  062 1 0622  12  14  0672  704 1  02 1 5  0673  3114  0212  0 2 12  0674  1 102  0 2 4 3  0 2 4 3  /#  0675  700 1  15  5  HP  CLA  R E P E A T ,  ALPHA 1  DECPRT C L L  DCA  M5  TAD  HP  I AC  0623  0240  0240  / S P A C E  0676  3 103  DCA  L P  0624  0303  0 3 0 3  /C  0677  1357  TAD  K 7 6 0  e62 5  03  03  /H  0700  3504  DCA  I  10  10  I AC  00  to  ALPHA1  0626  030 1  0301  /A  070 1  4505  JMS  I  L I S T I  0627  4 2 7 5  4 2 7 5  /=  0702  4515  JMS  I  UDPRNT  0703  0 102  0 102  0704  4516  JMS  I  SPOT  0705  110 1  TAD  HPSTO  0706  700 1  I AC  0707  3117  DCA  L P S T O I  0630  4 0 0 0  4 0 0 0  063 1  4 5 0 5  JMS  0632  7000  NOP  I  L I S T I  ee33  4777  e&34  704 1  C I A  e635  451 1  J M S  I  DECPRT  07 10  1517  TAD  e636  4 5 0 5  J M S  I  L I S T I  07 1 1  704 1  C I A  0637  1 100  TAD  1 103  TAD  L P  0640  7104  C L L  RAJ-  0 7 13  7650  SNA  C L A  064 1  1 122  TAD  K 137  07 14  5322  JMP  0642  3101  DCA  HPSTO  07 1 5  2102  I SZ  et43  1101  TAD  HPSTO  07 16  2 1 02  ISZ  HP  0644  3374  DCA  H0LD2  0 7 17  2 114  I SZ  M 5  0645  1774  TAD  I  0720  5274  JMP  REPEAT  0646  704 1  C I A  072 1  5260  JMP  N X L I N E  0647  3376  DCA  HOLD 1  0722  4505  JMS  I  L I S T I  06 50  2 3 7 4  ISZ  H0LD2  0723  5520  JMP  I  RSTART  065 1  1774  TAD  I  0724  0000  JMS  I  DTPRNT  REGNO  H0LD2  H0LD2  0 7 12  SSPOT,  0  L P S T O  .+6 HP  // S : UBROUTINE  FOR  D I S P L A Y  0725 0726 0727 0730 07 31 0732 0733 0734 0735 0736 0737 0740 074 1 0742 0743 0744 074 5 0746 0747 07 50 07 51 07 52 07 53 07 54 07 55 07 56 07 57 0760 0761 07 62 0763 0764 0765 0766 0767 0770 077 1 0772 0773 0774 077 5 0776 0777  7604 0373 7040 3367 1503 742 1 1 502 2367 7410 5344 70 10 752 1 70 10 7 52 1 5334 7200 150 1 7041 1 102 4465 6051 772 1 6061 7000 7200 5724 0760 K760, 0240 4240 0215 0212 02 12 02 12 42 12 0000 GAIN, 077 1 K771, 0215 4212 0037 K37, 0000 H0LD2, 7777 K7777, 0000 HOLDI, 5232 DTPRNT,  LAS AND K37 CM A DCA GAIN TAD I LP MCL TAD I HP ISZ GAIN SKP JMP .*6 RAR SWP RAR swp JMP .-7 CLA TAD I HPSTO CIA TAD HP JMS I GETSET 6051 /X AXIS CLA SWP 6061 /Y AXIS NOP CLA JMP I SSPOT 0760 0240 4240 02 1 5 02 12 02 12 02 12 42 12 0 077 1 02 1 5 42 12 0037 0 7777 0 5232  1000 1001 1002 1003 1004 1005 1006 1007 1010 101 1 1012 1013 1014 10 15 1016 1017 1020 102 1 1022 1023 1024 1025 1026 1027 1030 1031 1032 1033 1034 1035 1036 1037 1040 104 1 1042 1043 1044 1045 1046 1047 1050 1051  * 1000 4523 7000 7000 7000 7000 7000 7000 1 100 7 104 1 122 3 10 1 1101 DSPLAY, 7001 3 117 1501 3102 I 102 CONT I, 7001 3103 4516 6031 5230 6036 5520 1 I 03 7041 1517 7650 524 1 7000 2 102 2102 5220 52 13 4523 1100 7 104 I 122 3101 110 1 7001 3117  JMS I PPICK /DISPLAY ROUTINE NOP NOP NOP NOP NOP NOP TAD REGNO CLL RAL TAD K137 DCA HPSTO TAD HPSTO IAC DCA LPSTO TAD I HPSTO DCA HP TAD HP I AC DCA LP JMS I SPOT KSF JMP .*3 KRB JMP I RSTART TAD LP CIA TAD I LPSTO SNA CLA JMP .+5 NOP ISZ HP ISZ HP JMP C0NT1 JMP DSPLAY JMS I PPICK /3 POINT SMOOTH ROUTINE TAD REGNO CLL RAL TAD K137 DCA HPSTO TAD HPSTO I AC DCA LPSTO  1052  150 1  TAD  1  1125  1502  TAD  I  1053  3102  DCA  HP  1126  3364  DCA  S T I  1 102  TAD  H P  1 127  1 503  1 1 30  3363  1054 1055  7001  1056  3 1 0 3  HPSTO  I AC  1 362  TAD  3502  DCA  S T I  1 133  7 52 1  SUP  1 134  7 0 10  RAR  1 135  3503  1 136  5263  1 1 37  4 52 3  JMS  I  1 140  1 100  TAD  REGNO  TAD  I  1060  3 3 6 4  DCA  HP  1061  1503  TAD  I  1062  3 3 6 3  DCA  S T 2  1063  7 3 0 7  CLA  C L L H P  1064  1 102  TAD  3362  DCA  1066  1362  TAD  1067  7 10 1  CLL  1070  3361  DCA  1071  1361  TAD  L P  ST2  1 132  L P  1 502  1065  I  DCA  1131  DCA  1057  C 0 N T 2 ,  TAD  HP  L P  I AC  R T L  T H I R D  THIRD  DCA JMP  I  HP  I  L P  C0NT2 PPICK  1 141  7 104  CLL  RAL  1 142  1 122  TAD  K 1 3 7  T H I R D 2  1 143  3101  DCA  HPSTO  TH1RD2  1 144  110 1  TAD  HPSTO  1145  700 1  I AC  1 146  3117  T H I R D I AC  1072  704 1  CIA  1073  1517  TAD  I  1074  7 6 5 0  SNA  C L A  1 147  1 501  1075  5520  JMP  I  1 1 50  3102  1076  7 1 0 0  CLL  1151  3 502  1077  1363  TAD  S T 2  1 1 52  1517  1 100  1761  TAD  I  1 1 53  7041  C I A  L P S T O R S T A R T  / D O U B L E  T H I R D 2  P R E C .  ADD  DCA TAD C 0 N T 3 ,  HPSTO  DCA  H P  DCA  I  HP  TAD  I  L P S T O  1101  742 1  MCL  11 5 4  1 102  TAD  7 4 3 0  SZL  1 1 55  7650  SNA  C L A  I 103  730 1  CLA  C L L  1 1 56  5462  JMP  I  1 104  1364  TAD  S T I  1 1 57  2 102  TAD  I  5351  1161  7 52 1  SUP  1162  70  10  RAR  1 163  1111  7 100  CLL  1 164  11 1 2  2 1 0 2  I SZ  1 1 65  0000 0000 0000 0000 0000  H 0 L D 3 ,  0  1113  2102  1 166  0007  K 7 ,  0007  K 1 1 7 0 ,  70  1 107 1110  10  T H I R D  HP  I SZ  H P  JMP T H I R D 2 ,  0  THIRD,  0  S T 2 ,  0  S T I ,  0  E E E  HP  1 160  1106  1114  2 1 0 3  ISZ  L P  1 167  1 170  1115  2  103  I SZ  L P  1 170  7770  7770  I  C0NT3  1 170  1116  1 503  TAD  117 1  7440  7 4 4 0  /.5  1117  7 52 1  sup  1172  7300  7300  /  1 120  7 4 3 0  SZL  1173  7 165  7 1 6 5  / I . 5  112 1  7 10 1  1 174  7070  7 0 7 0  /  CLL  1 122  1 502  TAD  1 123  7 0 1 0  RAR  1 124  3362  DCA  L P  I AC I  HP  T H I R D  CO  H P  RAR  1105  1762  ISZ  R O U T I N E  L P S T O I  1 102  I AC  / E R A S E  SEC 1  2  SEC S E C SEC  1175  7002  7002  / 2 . 5  1 176  6720  6720  /  3  SEC  1177  6570  6570  /  4  SEC  SEC  *  1200  1200  1100  TAD  REGNO  1201  1 1 12  TAD  K  1202  3 0 6 4  DCA  NUMSC  1203  3464  DCA  I  NUMSC  1204  5520  J M P  I  R S T A R T  1205  0 0 0 0  1206  4 7 7 7  J M S  I  S R 6 2 0 0  1207  3 3 7 6  DCA  CHECK 1  12 1 0  1376  TAD  CHECK I  121 1  1375  TAD  M2  1212  7 5 1 0  SPA  1213  5222  J M P  PUT4  1214  1374  TAD  M 14  12 1 5  7 5 4 0  SNA  SZA  12 1 6  5222  J M P  PUT4  1217  7 3 0 0  C L A  C L L  1220  1376  TAD  CHECK 1  122 1  5605  J M P  I  1222  7307  C L A  C L L  1223  5 6 0 5  J M P  I  1224  7 0 0 0  NOP  1225  7 0 0 0  1226  0 0 0 0  1227  7  C U R I N .  P U T 4 ,  105  / S U B R O U T I N E  0  / I S  I AC  0 RAR H 0 L D 4  DCA  1 100  TAD  REGNO  1232  137 1  TAD  K 1 51  1233  3372  DCA  H 0 L D 5  1234  1772  TAD  I  1235  7041  C I A  1236  3372  DCA  HOLDS  1237  1373  TAD  HOLD4  1240  2 3 7 2  I SZ  H O L D S  124 1  5237  J M P  . - 2  1242  7 0 0 0  NOP  1243  5626  J M P  1246  1 1 00  16  RTL  / S U B R O U T I N E  C L L  3 3 7 3  5110  I N C .  CURIN  1230  4 5 2 3  THAN  CUR.  CURIN  123 1  1245  GREATER  CHECK  NOP B A K E ,  110  1244  IT  TO  I N F E R T ,  TO  CONTROLL  CUR  I N C .  H 0 L D 5  /BY I  B A K E  I  P P I C K  CHANGING /SCANNING  T H I S  TO  COULD  J M S  B E  I  I N F E R T  I N V E R T E D .  5110 J M S TAD  REGNO  1247  1367  TAD  K 1 57  1250  3 3 7 0  DCA  H 0 L D 6  1251  1770  TAD  I  12 5 2  7104  C L L  RAL  H 0 L D 6  / R O U T I N E / F I N A L  TO  CHECK  VOLTAGES  / R E Q U I R E D  REGION  OF  I N I T I A L A  AND  /  / S E T S  1253  607 I  607 1  1254  1365  TAD  K 7 6 0 0  1255  3366  DCA  DELAY 1  1256  1365  TAD  K 7 6 0 0  1257  3362  DCA  DELAY2  1260  7 0 0 0  NOP  1261  2 3 6 6  1262  5260  1263 1264  I SZ  DELAY I  J M P  . - 2  2362  ISZ  D E L A Y 2  52  60  JMP  . - 4  1265  1 100  TAD  REGNO  1266  7  C L L  RAL  TAD  K 1 3 7  104  1267  1 122  1270  3101  127 1  1501  1272  3102  DCA  H P S T O  TAD  I  DCA  HP  TAD  HP  / T I M E R  T H E  FOR  I N I T I A L  V O L T A G E  DELAY  H P S T O  1273  1 102  1274  7001  1275  3 1 0 3  1276  1 101  1277  7 0 0 1  I AC  1300  3 1 1 7  DCA  L P S T O  1301  1517  TAD  I  L P S T O  1302  7041  CI  H P S T O  I AC DCA TAD  L P HPSTO 00  A  1303  1501  TAD  I  1304  3 0 7 0  DCA  COUNT 1  1305  7 0 0 0  NOP  1306  7 0 0 0  NOP  1307  7 0 0 0  NOP  1310  603 1  K S F  131 1  7 4 1 0  1312  5 3 1 5  1313  4 5 1 6  J M S  1314  5310  J M P  1315  4 5 1 6  J M S  1316  1365  TAD  1317  3 3 6 6  DCA  DELAY I  1320  1365  TAD  K 7 6 0 0  1321  3362  DCA  D E L A Y 2  1322  7 0 0 0  NOP  1323  2366  ISZ  1324  5322  J M P  SKP JMP  . * 3 I  SPOT . - 4  I  SPOT  K 7 6 0 0  DELAY I . - 2  1325  2362  ISZ  1326  5322  J M P  . - 4  1327  1 365  C 0 N T 4 ,  TAD  K 7 6 0 0  1330  3066  DCA  DWELL2  133 1  72C0  T I M E R ,  C L A  D L L AY 2  1332  1113  TAD  DWELL  1333  3 3 6 3  DCA  H0LD7  1334  2 3 6 3  I S Z  H 0 L D 7  1335  5337  J M P  .+2  1336  5343  J M P  . * 5  1337  7 0 0 0  NOP  1340  5342  J M P  1341  7 3 0 0  NOP  1342  5334  J M P  . - 6  1343  2 0 6 6  I S Z  D U E L L 2  .+2  1344  533 1  J M P  1345  4 5 1 6  J M S  I  1346  7 3 0 5  C L A  C L L  1400  0 0 0 0  T I M E R SPOT I AC  1347  1070  TAD  COUNT 1  1350  3 0 7 0  DCA  COUNT 1  1351  7 4 3 0  SZL  13 5 2  5360  J M P  . + 6  1353  2102  I S Z  HP  1354  2 1 0 2  I S Z  HP  1355  2  103  I S Z  L P  1356  2  103  I SZ  L P  13 5 7  5327  J M P  C 0 N T 4  1360  5764  J M P  136 1  7 0 0 0  1362  0 0 0 0  D E L A Y 2 ,  0  1363  0 0 0 0  H 0 L D 7 ,  0  1364  4430  K 4 4 0 0 ,  4 4 0 0  I  /DATA  STORAGE  L O C A T I O N S  FOR  REGION  #1  / D A T A  STORAGE  L O C A T I O N S  FOR  REGION  #2  /DATA  STORAGE  L O C A T I O N S  FOR  REGION  #3  RAL 2377  0 0 0 0  2400  0 0 0 0  3377  0 0 0 0  3400  0 0 0 0  K 4 4 0 0  NOP  1365  7 5 0 0  K 7 6 0 0 ,  1366  0 0 0 0  DELAY  1367  0 1 57  K 1 57,  1370  0 1 5 7  0000  H 0 L D 6 ,  0  7 5 0 0 I,  137 1  0151  K 1 5 1 ,  0  1372  00G0  H O L D S ,  0 0  1373  0000  H 0 L D 4 ,  1374  7762  M  1375  7 7 7 6  M2,  1376  0 0 0 0  CHECK  1377  6200  S R 6 2 0 0 ,  14,  / P O I N T E R  FOR  151  7762 7 7 7 6 1,  4377  0  0 6 2 0 0  / G E N A R A T E S  - 1 6  I N I T I A L  0 0 0 0  m  .  • 4400 4400  4401 4402 4403 4404 440 5 4406 4407 4 4 10 441 1 4412 4413 4414 4415 4416 4417 4420 442 1 4422 4423 442 4 442 5 4426 4427 4430 4431 4432 4433 4434 443 5 4436 4437 4440 444 1 4442 4443 4444 4445 4446 4447 44 50 44 51  6030 603 1 520 1 6036 3377 1377 1376 7640 5775 5520 7000 7000 7300 603 1 52 1 5 6036 6046 307 1 1 376 107 1 307 1 107 1 1374 7640 5247 1074 3100 1075 307 1 1472 1121 7041 3073 1373 6041 5242 6046 7300 5314 7300 1373 4172  GO,  KCF KSF JMP .-1 KRB DCA H0LD8 TAD HOLDS TAD M2 15 SZA CLA / I S I T CR JMP I ROUTB /NO JMP I RSTART NOP NOP CLA CLL /SCAN R O U T I N E KSF JMP .-1 KRB TLS DCA OPTION TAD M2 1 5 TAD OPTION DCA OPTION TAD OPTION TAD M3 1 5 SZA CLA /IS IT M JMP GO TAD REGNO 1 /YES, GO TO T H E SCAN DUE DCA REGNO / A F T E R T H E INTERRUPTION TAD OPTI DCA OPTION TAD I INDEX1 TAD MM260 CIA DCA NUMREG TAD B E L L TSF JMP .- 1 TLS CLA C L L JMP RESUME CLA C L L /SCANNING STARTS WITH 2 B E L L S TAD B E L L JMS T Y P E  44 52 44 53 44 54 4455 4456 44 57 4460 4461 4462 4463 4464 4465 44 66 4467 4470 447 1 4472 4473 4474 4475 4476 4477 4500 4501 4502 4503 4504 4505 4506 4507 4510 451 1 4512 4513 4514 451 5 4516 4517 4520 452 1 4522 4523 4524  1373 4 172 7300 1472 112 1 704 1 3073 C0NT5, 3100 2100 4772 GOSCAN, 7300 1112 1 100 3371 2771 7000 1 100 1370 3367 1767 704 1 177 1 7700 5330 6031 5314 6036 7200 1 100 3074 107 1 3075 5520 7000 107 1 RESUME, 7650 5320 5263 7200 1073 1 100 7700 52 61  TAD B E L L JMS T Y P E CLA C L L TAD I INDEX 1 TAD MM260 CIA DCA NUMREG DCA REGNO I SZ REGNO JMS I SCAN CLA CLL TAD K 1 0 5 TAD REGNO DCA H0LD9 I SZ I H0LD9 NOP TAD REGNO TAD K 146 DCA HOLD10 TAD I HOLD10 CIA TAD I H0LD9 SMA CLA JMP DONE KSF /INTERRUPT JMP RESUME KRB CLA TAD REGNO DCA REGNO 1 TAD OPTION DCA OPT 1 JMP I RSTART NOP TAD OPTION SNA CLA JMP .•2 JMP GOSCAN CLA TAD NUMREG TAD REGNO SMA CLA JMP C0NT5  4525 4526 4527 4530 4531 4532 4533 4534 4535 4536 4537 454G 454 1 4542 4543 4544 4545 4546 4547 4550 4551 4552 4553 4554 4555 4556 4557 4560 4561 4562 4563 4564 4565 4566 4567 4570 457 1 4572 4573 4574 457 5 4 57 6 4577  5262 7000 7000 107 1 7650 5351 1366 3504 4505 1 100 1365 4172 4505 1073 1 100 7700 5347 5262 4 50 5 5520 1073 1 100 7700 5764 2 1 00 1 100 1370 3367 177 1 3767 5263 4763 0260 4733 0000 0 146 0000 4600 0207 7700 1246 7 56 3 0ee0  DONE,  D0NE1,  D0NE2, K260, K4733, HOLD10, K 146. H0LD9, SCAN, BELL, M 3 1 5, ROUTB, M2 1 5, H0LD8,  JMP CONTS+1 NOP NOP TAD OPTION SNA CLA JMP DONEl TAD K4733 DCA I ALPHA 1 JMS I LI STI TAD REGNO TAD K260 JMS TYPE JMS I LI STI TAD NUMREG TAD REGNO SMA CLA JMP .+2 JMP C0NT5+1 JMS 1 LIST1 JMP I RSTART TAD NUMREG TAD REGNO SMA CLA JMP I DON E2 ISZ REGNO TAD REGNO TAD K146 DCA HOLD10 TAD I H0LD9 DCA I HOLD10 JMP GOSCAN 4763 0260 4733 0 0 146 0 4600 0207 7700 1246 7563 0  4600 460 1 4602 4603 4604 460 5 4606 4607 4610 46 1 1 4612 46 1 3 4614 46 15 4616 4617 4620 462 1 4622 4623 4624 4625 4626 462 7 4630 463 1 4632 4633 4634  0000 7300 1 100 1377 3376 1776 7 104 6071 1375 3374 1375 3373 7000 2374 52 14 2373 52 14 1 1 00 7 104 1 122 3101 1 50 1 3 102 1 102 700 1 3103 110 1 700 1 3 117  / UP/DOWN COUNTER CONTROL INSTRUCTIONS /6141: IF AC 10 IS 1 STOP COUNTER / IF COUNTER IS STOPPED AND AC 9 IS / RESET COUNTER IF AC 8 IS 1 COUNT UP / IF AC 7 IS I COUNT DOWN / /6 142:IF COUNTER IS STOPPED,READ COUNTER / IN TO A C SKIP ON OVERFLOW FLAG /6144: RESET COUNTER OVERFLOW FLAG I F IT HAS BEEN SKIPPED ON.RESET COUNTER / / IF RESET IS ENABLED /6146:SKIP ON OVERFLOW FLAG AND RESET / FLAG. *4600 3SCAN, 0 /SCAN SUBROUTINE CLA CLL TAD REGNO TAD KK157 DCA HOLD 11 TAD I HOLD 11 CLL RAL 607 1 /SETS INITIAL VOLTAGE TAD KK7600 DCA DELAY3 TAD KK7600 DCA DELAY4 NOP /PAUSE ISZ DELAY3 JMP .-2 I SZ DELAY4 JMP .-4 TAD REGNO CLL RAL TAD K137 DCA HPSTO TAD I HPSTO DCA HP TAD HP I AC DCA LP TAD HPSTO I AC DCA LPSTO  4635 4636 4637 4640 4641 4642 4643 4644 4645 4646 4647 4650 4651 4652 4653 4654 4655 4656 4657 4660 4661 4662 4663 4664 4665 4666 4667 4670 467 1 4672 4673 4674 4675 4676 4677 4700. 4701 4702 4703 4704 4705 4706 4707  1517 704 1 150 1 3070 4516 1375 3374 1375 3373 7000 2374 5246 2373 5246 4767 CONT6, 3066 3371 1067 6141 742 1 6144 7200 TIMER2, 1113 3374 2374 5270 5274 6146 5273 2371 5265 2066 5263 7521 6 141 7 521 6142 5304 2371 7100 1503 3503 7430  TAD I LPSTO CIA TAD I HPSTO DCA COUNT 1 JMS I SPOT TAD KK7600 DCA DELAY3 TAD KK7600 DCA DELAY4 NOP /PAUSE BEFORE SCANNING ISZ DELAY3 JMP .-2 ISZ DELAY4 JMP .-4 JMS I DTSET DCA DUELL2 DCA OVRFLO TAD ORDER /DATA WORD FOR COUNTER 6141 MQL 6144 CLA TAD DWELL DCA DELAY3 ISZ DELAY3 JMP .+2 JMP .+5 6146 /SKIP ON COUNTER OVERFLOW JMP .+2 ISZ OVRFLO JMP .-6 ISZ DWELL 2 JMP TIMER2+1 SWP 6141 swp 6142 JMP .+2 ISZ OVRFLO CLL TAD I LP DCA I LP SZL  47 10 237 1 47 1 1 7300 47 12 137 1 47 13 1 502 47 14 3502 47 1 5 4516 47 16 7305 47 17 1070 4720 3070 472 1 7430 4722 5600 4723 2102 4724 2102 472 5 2 103 4726 2103 4727 4516 4730 7000 4731 5253 4732 7000 4733 02 15 4734 02 12 4735 0322 4736 0305 4737 0307 4740 4240 47 4 1 0240 4742 0304 4743 0317 4744 0316 4745 0305 47 46 02 15 47 47 42 12 47 50 02 12 47 51 0212 47 52 02 12 4753 0212 47 54 0207 4755 0207 47 56 0207 47 57 0207 47 60 4207 476 1 4000 4762 7000  ISZ OVRFLO CLA CLL TAD OVRFLO TAD I H P DCA I HP JMS 1 SPOT CLA CLL I AC RAL TAD COUNT 1 DCA COUNT I SZL JMP I SSCAN ISZ H P I SZ HP ISZ LP ISZ LP JMS I SPOT NOP JMP C0NT6 NOP 02 15 /CR 02 12 /LF 0322 /R 0305 /E 0307 /G 4240 /SPACE 0240 /SPACE 0304 /D 0317 /O 03 16 /N 0305 /E 02 1 5 42 12 02 12 02 12 02 12 0212 0207 /BELL 0207 0207 0207 4207 4000 NOP  K>  O  4763 47 64 4765 4766 4767 4770 477 I 4772 4773 4774 4775 4776 4777  5770 7000 7000 70G0 5242 6300 ooco  5000  0000  0000  0GG0 0000  7450 0000 0  157  D0NE3,  DTSET, K630O, OVRFLO, H0LD12, DELAY4, DELAY3, KK7600, H0LD1 1, KK157,  JMP I K6300 NOP NOP NOP 5242 6300 0 0 0  0 7450 0  0157  *5000  1357 5001 50B2 3504 5003 4505 5004 6032 5005 603 1 5205 5006 5307 6036 5010 3356 501 1 1356 5012 1355 5013 7650 52 17 5014 531 5 4523 5600 50 16 50 17 1354 5020 3504 502 1 4505 5022 4523 5023 6032 5024 603 1 5224 532 5 502 6 6036 5027 7300 1 100 5030 503 1 7 104  PICK2,  0 /PLOT OR PRINT OPTION TAD K5160 DCA I ALPHA 1 JMS I L I S T I KCC KSF JMP .-1 KRB DCA HOLD 15 TAD H0LD15 TAD CRM SNA CLA JMP .+3 JMS I PPICK JMP I PICK2 TAD K5170 DCA I ALPHA 1 JMS I L I S T I JMS I PPICK KCC KSF JMP .-1 KRB CLA CLL TAD REGNO CLL RAL  1 122 310 1 110 1 AGAIN, 700 1 3117 150 1 3 102 1 102 C0NT7, 700 1 3103 4516 1 103 704 1 1517 7650 5263 2 102 2 102 1351 3353 2352 52 56 2353 5256 5241 6032 FINISH, 603 1 5264 6036 3356 1356 1355 7650 5275 5234 1337 3504 4505 5520 *51 10 INVERT, 51 10 0 0 0 0 51 1 1 704 1 51 12 13 15  5032 5033 5034 50 3 5 50 36 5037 5040 504 1 5042 5043 5044 5045 5046 5047 50 50 50 51 50 52 50 53 5054 5055 50 56 50 57 5060 506 1 5062 5063 5064 5065 5066 5067 5070 507 1 5072 5073 5074 507 5 5076 5077 5103  TAD K 137 DCA HPSTO TAD HPSTO I AC DCA LPSTO TAD I HPSTO DCA HP TAD HP I AC DCA LP JMS I SPOT TAD LP CIA TAD I LPSTO SNA CLA JMP FINISH I SZ HP I SZ HP TAD K7745 DCA C0UNT2 ISZ C0UNT3 JMP .-1 ISZ C0UNT2 JMP .-3 JMP C0NT7 KCC KSF JMP .-1 KRB DCA H0LD15 TAD H0LD15 TAD CRM SNA CLA JMP .+2 JMP AGAIN TAD K5I40 DCA I ALPHA 1 JMS I L I S T I JMP I RSTART 0 /SUBR0UT1 CIA TAD KK7777  SI 13 51 14 5115  7100 57 10 7777  5137 5140 5141 5142 5143 5144 5145 5146 5147 5150 5151 5152 51 53 51 54 5155 51 56 51 57 5160 5161 5162 5163 5164 5165 5166 5167 5170 517 1 5172 5173 5174 5175 5176 5177  5140 0212  5200 5201 52 02 5203 5204  KK7777, • 5137 K5140,  e215  0304 03 17 0316 0305 02 15 42 12 4000 7745 0000 0000 5170 7563 0e00 5160 02 15 0212 0320 0322 031 1 0316 0324 4240 02 15 02 12 0320 0314 0317 0324 4240 4000 0000  4525 3227 1227 1226  K7745, COUNTS* C0UNT2, K5170, CRM, H0LD15, K5160,  • 5200 DDT,  CLL JMP I INVER 7777 5 140 02 12 /LF 02 15 /CR 0304 /D 0317 /O 0316 /N 0305 /E 02 1 5 42 12 ,4000 7745 0 0 5170 7563 /-CR 0 5160 02 15 02 12 0320 0322 031 I 03 16 0324 4240 /"PR 02 1 5 02 12 0320 /P 03 14 /L 03 17 /O 0324 /T 4240 4000 0 JMS DCA TAD TAD  /SUBROUTINE TO SET DWELL TIME I K6200 CHECK2 CHECK2 M7  ID  5205 5206 52 0 7 52 10 52 1 1 5212 52 13 52 14 52 15 5216 5217 5220 5221 5222 5223 5224 522 5 5226 5227 5230  7540 5215 7300 1227 1225 3227 1627 5600 7300 1224 3504 5623 7000 7000 0270 0352 1 170 777 1 0000 0000  REDO 1,  K270, K352, KK1 170, M7, CHECK2,  *5232 0000 DTPR, 1 100 1240 3227 1627 5632 0 1 54 KI54, 0000 • 5242 5242 0000 DDTSET, 1240 5243 5244 1 100 52 4 5 3227 5246 1627 52 47 3113 5250 1113 5251 5642 52 32 5233 5234 5235 52 3 6 5237 52 40 524 1  SMA SZA /IS IT GREATER THAN 7 JMP REDO 1 CLA CLL TAD CHECK2 TAD KKI170 DCA CHECK2 TAD I CHECK2 JMP I DDT CLA CLL TAD K352 DCA I ALPHA1 JMP I K270 NOP NOP 0270 0352 1 170 777 1 0 0 0 /SUBROUTINE DTPRNT TAD REGNO TAD K154 DCA CHECK2 TAD I CHECK2 JMP I DTPR 0 154 0 0 TAD TAD DCA TAD DCA TAD JMP  /SUBROUTINE TO PICK THE CORRECT K154 REGNO CHECK2 I CHECK2 DWELL DWELL I DDTSET  /SUBROUTINE FOR UNSIGNED DECIMAL PRINT /COPYRIGHT 197 1 DIGITAL EQUIPMENT CORPORATION /MAYNARD,MASSACHUSETTS.  • 6000 6000  0000  600 1 6002 6003 6004 6005 6006 6007  3243 3244 1235 3245 1234 3213 7410 3243 7ice 1243 1236 7430 2244 7430 52 10 7200 1244 1242 6041 5223 6046 7200 3244 22 13 2245 52 12 5600 1236 7774 6030 7634 7766 7777 0260 0000 0000 0000  6010  601 1 6012 6013 6014 6015 6016 6017 6020 6021 6022 602 3 6024 602 5 602 6 6027 6030 6031 6032 6033 6034 6035 6036 6037 6040 604 1 6042 6043 6044 6045  0 DCA VALUE DCA DIGIT TAD CNTHZA DCA CNTRZB TAD ADDRZA DCA ARROW SKP DCA VALUE CLL TAD VALUE ARROW, TAD TENPWR SZL ISZ DIGIT SZL JMP ARROW-3 CLA TAD DIGIT TAD KK260 TSF JMP .-1 TLS CLA DCA DIGIT ISZ ARROW ISZ CNTRZB JMP ARROW-1 JMP I DECPR ADDRZA, TAD TENPWR CNTRZA, -4 TENPWR, - 1750 -0 144 -00 12 -000 1 KK260, 0260 0 VALUE, DIGIT, 0 0 CNTRZB, /SUBROUTINE FOR UNSIGNED DECIMAL PRINT /DOUBLE PRECISION /CALLING SEOUENCEl JMS UDPRN / HIGH ADDR (ADDRESS OF HIGH / ORDER WORD) DECPR*  /COPYRIGHT 1971 DIGITAL EQUIPMENT /MAYNARD, MASSACHUSETTS. • 6046 0 6046 0000 UDPRN, CLA CLL 6047 7300 60 50 1646 TAD I UDPRN DCA H0LDI3 6051 3361 60 52 176 1 TAD I H0LD13 DCA UDGET 60 53 3337 60 54 1737 TAD I UDGET DCA UDHIGH 6055 3331 60 56 2337 I SZ UDGET 60 57 1737 TAD I UDGET DCA UDLOW 6060 3332 6061 1325 TAD UDLOOP 6062 3330 DCA UDCNT 1326 TAD UDADDR 6063 6064 3340 DCA UDPTR ISZ UDPRN 606 5 2246 1740 UDARND, TAD I UDPTR 6066 2340 6067 ISZ UDPTR 6070 DCA UDHSUB 3333 6071 1740 TAD I UDPTR 6072 2340 I SZ UDPTR 3334 DCA UDLSUB 6e73 6074 7 100 UDDO, CLL 1334 607 5 TAD UDLSUB 6076 TAD UDLOW 1332 6077 3336 DCA UDTEML 7004 6100 RAL 6101 1333 TAD UDHSUB 6102 TAD UDHIGH 133 1 SNL 6103 7420 6104 JMP UDOUT 5312 6105 2335 ISZ UDBOX 6106 3331 DCA UDHIGH 6107 1336 TAD UDTEML DCA UDLOW 61 10 3332 5274 6111 JMP UDDO 6112 7200 UDOUT, CLA TAD UDBOX 61 13 1335 TAD UDTWO 61 14 1 327 TLS 6115 6e46  CORPORATION  6116 61 17 6120 6121 6122 6123 6124 6125 6126 J127 6130 6131 6132 6133 6134 6135 6136 6137 6140 6141 6142 6143 6144 6145 6146 6147 61 50 6151 6152 6153 6154 61 55 61 56 6157 6160 6161  6041 5316 7300 3335 2330 5266 5646 7770 6141 0260 0000 0000 0000 0000 0000 0000 0000 0000 0000 3166 4600 7413 6700 7747 4540 7775 4360 7777 6030 7777 7634 7777 7766 7777 7777 0000  UDLOOP, UDADDR, UDTVO, UDCNT, UDHIGH, UDLOW, UDHSUB, UDL3UB, UDBOX, UDTEML, UDGET, UDPTR, UDCON1*  HOLD 13,  TSF JMP .-1 CLA CLL DCA UDBOX ISZ UDCNT JMP UDARND JMP I UDPRN - 10 UDCONI 0260 0 0 0 0 0 0 0 0 0 3 166 4600 7413 6700 7747 4540 7775 4360 7777 6030 7777 7634 7777 7766 7777 7777 0  /SUBROUTINE CONV /CONVERTS A STRING OF 4 DECIMAL /NUMBERS TO BINARY.RETURNS WITH /BINARY EQUIVALENT IN AC.MAXIMUM /NUMBER CORRECTLY CONVERTED IS 409 5  6200 6201 6202 6203 6204 6205 6206 6207 62 10 62 1 1 62 12 62 13  0000 7300 3263 1265 3266 4 163 3264 1264 12 57 7440 52 14 5240  62 14 62 1 5 62 16 6217 6220 622 1 6222 6223 6224 6225 6226 6227 62 30 62 3 1 6232 6233 62 34 6235 6236 62 37 6240  1260 7510 5244 1261 7740 5240 7300 2266 5226 5240 1263 7106 1263 7004 3263 1264 02 62 1263 3263 52G5 7330  /TELETYPE CHARACTERS OTHER THAN /DELETE. CR AND 0 TO 9 ARE NEGLECTED /CR TERMINATES SUBROUTINE.DELETE TYPES /LF CALLING CORRECT STRING.STRINGS WITH /MORE THAN 4 CHARACTERS DISCARDED /ANY ILLEGAL CHARACTER REINITIALLIZE /THE SUBROUTINE CALLING FOR THE /CORRECTED STRING. • 6200 CONV, 0 CLA CLL DCA H0LD14 TAD M5M DCA COUNTC INPUT, JMS LISN DCA STORE TAD STORE TAD MRBOUT SZA /IS IT RUBOUT JMP .•2 /NO JMP RUBOUT /REINITIATE TO TAKE /A NEW STRING TAD M260M SPA JMP CHECKC TAD M27 I SMA SZA CLA JMP RUBOUT CLA CLL ISZ COUNTC JMP .•2 JMP RUBOUT TAD H0LD14 CLL RTL TAD H0LD14 RAL DCA H0LD14 TAD STORE AND MASK TAD H0LDI4 DCA H0LD14 JMP INPUT RUBOUT, CLA CLL  to  624 1 6242 6243 6244 6245 6246 6247  127 I 4172 5201 7300 1264 1272 7450  6250 6251 6252 6253 62 54 62 55 62 56 62 57 62 60 626 1 62 62 6263 6264 6265 6266 6267 6270 627 1 6272 6273  5252 5240 7300 END. 1263 5600 7000 7000 740 1 MRBOUT, 0117 M260M, 7767 M27 I, 00 17 MASK, 0000 H0LD14, 0000 STORE* 7513 M5M, eo00 COUNTO 0163 0172 02 12 L F . 7563 MCR, 0000 • 6300 1317 4172 1 ie0 1320 4172 1316 4172 1315 3504 4505 4505 4505 5520 4735 K4735, 0249 SPACE, 02 12 K2 12, 0260 KKK260,  6300 6301 6302 6303 6304 6305 6336 6337 6310 631 1 6312 63 13 6314 631 5 63 16 63 17 6320  CH ECHO  TAD JMS JMP CLA TAD TAD SNA  L F  TYPE CONV*1 CLL STORE MCR  JMP END JMP RUBOUT CLA CLL TAD H0LD14 JMP I CONV NOP NOP 7401 0117 7767 0017 0 0 7513 0 0163 0172 02 12 7563 0 TAD K2 12 JMS TYPE TAD REGNO TAD KKK260 JMS TYPE TAD SPACE JMS TYPE TAD K4735 DCA I ALPHA1 JMS I LI STI JMS I LI STI JMS I LI STI JMP I RSTART 4735 0240 02 12 0260  /IS IT THE TERMINATING /CHARACTER  A  024 1  COUNTC  6266  FF  0061  KK1400  AALPHA  0  COUNT 1  0070  FINISH  5063  KK157  4777  AAl  0474  C0UNT2  5153  G  0340  KK260  6042  ADDRZA  6034  C0UNT3  51 5 2  GAIN  0767  KK7600  4775  AGAIN  5034  CRM  5155  GETSET  0065  KK7777  5115  ALPHA  034 1  CURIN  1205  GO  4447  K1000  0504  ALPHA 1  0  CURINC  0063  GOSCAN  4463  K I 0 5  0  ARROW  6013  D  0325  HOLD 1  0776  K l  Al  0257  DD  0057  HOLD10  4567  K137  B  0323  DDT  5200  H O L D 11  4776  K I 4 0 0  0302  DDTSET  5242  H0LD12  4772  K146  4570  BAKE  140  104  1226  170  0301  112  1 167 0122  BB  0355  DECPR  6000  H0LD13  6161  K151  1371  BELL  4573  DECPRT  0  H0LD14  6263  K l  5240  C  0324  DELAY 1  1366  HOLD I 5  5156  KJ57  CC  0056  DEL AY 2  1362  H0LD2  0774  K212  63  CCI  0306  DEL AY 3  4774  H0LD3  1 165  K260  4565 0314  111  54  1367 17  CHAN  0  DEL AY 4  4773  H0LD4  1373  K261  CHECK  0315  DIGIT  6044  H0LD5  1372  K270  5223  CHECK C  6244  DONE  4530  H0LD6  1370  K276  0320  507  CHECK 1  1376  D0NE1  4551  H0LD7  1363  K352  5224  CHECK 2  5227  DON E 2  4564  H0LD8  4577  K37  0773  CHOICE  0537  DON E 3  4763  H0LD9  457 1  K400  0275  CI  0305  DSPLAY  1013  HP  0 102  K4400  1364  CI I  051 1  DT  0  HPSTO  0101  K4733  4566  124  CNTRZA  6035  DTPR  5232  IB  031 1  K4735  6315  CNTRZB  6045  DTPRNT  0777  IIB  0312  K5140  5137  CONT  0553  DTSET  4767  1INDEX  0476  K5160  5157  1020  DWELL  0  INDEX  0313  K5170  51 5 4 0 552  COHTI  113  CONT2  1063  DWELL2  0066  INDEX1  0072  K600  C0NT3  1151  E  0326  INFERT  1244  K6200  0  CONT4  1327  EE  0060  INPUT  6205  K6300  4770  CONT 5  446 1  EEE  0062  INST  0317  K7  C0NT6  4653  END  6252  INVERT  51  K760  C0NT7  504 1  EX I T  0532  KKK260  6320  K7600  CONV  6200  F  0327  KK1  5225  K77 1  170  10  125  1 166 0757 1365 0770  K7745  5151  ORDER  0067  TENPWR  K7777  0775  OVRFLO  477 1  THIRD  1 162  L F  627 1  PI CK  0555  THIRD2  1161  PI  5000  TIMER  0123  TI M ER2  4662  163  CK2  LI  SN  0  LI  ST  0330  PPICK  LI  STI  0  6036  1331  PUT4  1222  TTTYPE  050 1  0322  REDO  0516  TTYPE  032 1  L L I S T  0513  REDO 1  52  TYPE  0  L L L I S N  0502  REGNO  0  T1400  0506  LP  0  LLI  SN  105  15  100  172  REGNO 1  0074  UDADDR  6126  LPSTO  01  17  REPEAT  0674  UDARND  6066  MASK  62 62  RESUME  4514  UDBOX  6135  MCR  6272  ROUTB  4 57 5  UDCNT  6130  MH  0316  RSTART  0  UDCON 1  614 1  MLSTCH  0503  RUBOUT  6240  UDDO  6074  MM260  0 12 1  SC  0303  UDGET  6137  MP.BOUT  6257  SCAN  4572  UDHIGH  6131  MSTAKE  0437  SCC  0510  UDHSUB  6133  103  120  M 14  1374  SPACE  6316  UDLOOP  6  M2  1375  SPOT  0116  UDLOW  6132  125  M2 15  4576  SR6200  UDLSUB  6134  M256  0500  SSC  0304  UDOUT  6112  M2 6 0 M  6260  SSCAN  4600  UDPRN  6046  M264  0475  SSI  0276  UDPRNT  0  115  M27 1  6261  SSPOT  0724  UDPTR  6  140  M3I5  4574  SSSICO  05  UDTEML  6  136  M5  0  114  SSTART  0477  UDTWO  6127  M5M  6265  SSTCHA  0505  VALUE  6043  M7  5226  ST  0554  U'AI T  0514  NUMREG  0073  START  0200  VI  0307  NUMSC  0064  STCHAN  0300  UWI  03  NUMSC I  0106  STCHA1  0277  X  0531  NXLINE  0660  STORE  6264  OPTION  007 1  STI  1 164  OPT1  0075  ST2  1 163  CON  1377  12  10  

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