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UBC Theses and Dissertations

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 . S c , 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 IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May, 1980 (c) J.S.H. Q u i n t u s P e r e r a , 1980 In presenting th is thesis in par t ia l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the Library shal l make i t f ree ly avai lab le for reference and study. I further agree that permission for extensive copying of th is thesis for scholar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or publ icat ion of th is thesis for f inanc ia l gain shal l not be allowed without my writ ten permission. Department nf Chemistry  The Univers i ty 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 v e r s a t i l e gas phase 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 e m p l o y i n g a PDP 8/e minicomputer t o c o n t r o l t h e s p e c t r o m e t e r f u n c t i o n s and d a t a accumu-l a t i o n i s d e s c r i b e d . F a c i l i t i e s f o r h e a t i n g m a t e r i a l s i n s i d e t h e s p e c t r o m e t e r t o ^10 00°C are c u r r e n t l y a v a i l a b l e , and the advantages o f such are s u i t a b l y d emonstrated. Core l e v e l 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 Group IA m e t a l atoms, sodium, p o t a s s i u m , r u b i d i u m , cesium and the Group I I A me t a l atoms, magnesium, c a l -cium, s t r o n t i u m , and b a r i u m have been o b t a i n e d . These p r o v i d e the f i r s t a c c u r a t e measurements o f t h e core b i n d i n g e n e r g i e s f o r s e v e r a l o f the s e e l e m e n t s . E x p e r i m e n t a l and t h e o r e t i c a l v a l u e s from the l i t e r a t u r e a r e compared w i t h the p r e s e n t r e s u l t s . The f r e e atom b i n d i n g e n e r g i e s are found t o be g r e a t e r than the com-p a r a t i v e 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 . The e x p e r i m e n t a l "phase t r a n s i t i o n s h i f t s " a r e compared w i t h v a r i o u s t h e o r e t i c a l e s t i m a t e s . 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 r e a l s o o b s e r v e d i n the s p e c t r a o f a l l t h e s e atoms. Those 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 are a s s i g n e d t o ns -*- ( n + l ) s t y p e monopole e x c i t a t i o n s u s i n g the e q u i v a l e n t c o r e s a p p r o x i m a t i o n . T h i s a p p r o x i m a t i o n f a i l s t o p r o v i d e a s a t i s f a c t o r y a s s i g n -ment o f the s a t e l l i t e s o b s e r v e d i n the s p e c t r a o f Group I I A atoms. X-ray 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 the h a l o g e n c o r e l e v e l s o f the gaseous t i t a n i u m t e t r a h a l i d e s , T i X ^ ( X = F , C 1 , B r , I ) , a re r e p o r t e d . S a t e l l i t e s a r e o b s e r v e d 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 h a l o g e n c o r e l e v e l s , as w e l l as the t i t a n i u m np l e v e l s . 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 d i s c u s s e d i n some d e t a i l . Gas phase 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 m e t a l a c e t y l a c e t o n a t e s , M ( A c A c ) 2 (M=Co(II), N i ( I I ) , C u ( I I ) ) j have been i n v e s t i g a t e d . The m e t a l 2p, 3s, and 3p core l e v e l s and t h e 0 I s and 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 . S a t e l l i t e s t r u c t u r e i s o b s e r v e d 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 2p, 3s and 3p l e v e l s , and the 0 I s l e v e l s . From a comparison o f the s o l i d phase w i t h t h e p r e s e n t gas phase r e s u l t s , t h e e f f e c t s o f changes 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 the l i g a n d . The r e s u l t s - i v -i n d i c a t e t h a t t h e s a t e l l i t e s seen i n th e s e t r a n s i t i o n m e t a l 3s s p e c t r a , a t b i n d i n g e n e r g i e s 4-6eV h i g h e r than the main peak, a r i s e from m u l t i e l e c t r o n e x c i t a t i r a t h e r than from m u l t i p l e t s p l i t t i n g . - v -TABLE OF CONTENTS Page CHAPTER ONE: INTRODUCTION 1 References 11 CHAPTER TWO: BASIC CONCEPTS OF X-RAY PHOTOELECTRON SPECTROSCOPY 14 2.1 Introduction 14 2.2 N-Electron Wave Functions 15 2.3 Molecular O r b i t a l Calculations For XPS Studies 21 2.4 Koopmans1 Theorem and Binding Energies 25 2.5 Further Binding Energy Calculations.. 2 7 2.6 Configuration Interaction Method .... 29 2.7 Transition 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 Binding Energy S h i f t s 4 3 2.11 Relaxation E f f e c t s on Binding Energy 4 7 2.11.1 Atoms 4 8 2.11.2 Molecules 51 2.11.3 Solids 52 2.11.4 Core Level Binding Energy S h i f t s i n Metals 54 2.12 Multicomponent Structure i n XPS 60 2.12.1 Spin-Orbit S p l i t t i n g 60 2.12.2 M u l t i p l e t S p l i t t i n g 62 2.12.3 Multielectron Excitations .. 69 References 78 - v i -CHAPTER THREE: THE GAS PHASE X-RAY PHOTO-ELECTRON SPECTROMETER; DESIGN AND PERFORMANCE 8 7 3.1 I n t r o d u c t i o n 87 3.2 The S p e c t r o m e t e r 90 3.2.1 The X-ray Source U n i t 9 0 3.2.2 The Gas C e l l s 99 3.2.2.1 The O l d Gas C e l l 100 3.2.2.2 The New High Temperature Gas C e l l 103 3.2.3 The E i n z e l Lens 109 3.2.4 The E l e c t r o n Energy A n a l y s e r and the O p e r a t i n g Mode o f t h e Sp e c t r o m e t e r I l l 3.2.5 H e l m h o l t z C o i l s 114 3.2.6 The Vacuum System 115 3.2.7 The D e t e c t o r System 116 3.2.8 Performance 117 3.3 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 the Gas Phase X-ray Photo-e l e c t r o n S p e c t r o m e t e r 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 C a l i b r a t i o n o f E l e c t r o n S p e c t r a 127 3.5 Data A n a l y s i s 128 R e f e r e n c e s 130 CHAPTER FOUR: X-RAY PHOTOELECTRON SPECTROSCOPY OF GROUP IA AND I I A FREE METAL ATOMS 132 4.1 I n t r o d u c t i o n 132 4.2 E x p e r i m e n t a l 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 B i n d i n g E n e r g i e s 139 4.3.1.1 Sodium 139 4.3.1.2 P o t a s s i u m 144 4.3.1.3 Rubidium 14 7 4.3.1.4 Cesium 151 4.3.1.5 Magnesium 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 Barium 165 4.3.2 Phase T r a n s i t i o n S h i f t s , A E V 170. 4.3.3 M u l t i e l e c t r o n E x c i t a t i o n S a t e l l i t e s 176 4.4 C o n c l u s i o n s 183 Re f e r e n c e s 186 CHAPTER FIVE: X-RAY PHOTOELECTRON SPECTROSCOPY OF TITANIUM TETRAHALIDE VAPORS 191 5.1 I n t r o d u c t i o n 19J. 5.2 E x p e r i m e n t a l 194 5.3 R e s u l t s and D i s c u s s i o n 196 5.4 C o n c l u s i o n 215 Re f e r e n c e s 217 CHAPTER SIX: X-RAY PHOTOELECTRON SPECTROSCOPY OF C o ( I I ) , N i ( I I ) AND C u ( I I ) ACETYLACETONATE VAPORS 221 6.1 I n t r o d u c t i o n 221 6.2 E x p e r i m e n t a l 224 - v i i i -6.3 R e s u l t s and D i s c u s s i o n 226 6.4 C o n c l u s i o n s 259 R e f e r e n c e s 261 CHAPTER SEVEN: SUMMARY AND PROGNOSIS 26 5 R e f e r e n c e s 2 73 APPENDIX: MULTI-CHANNEL SCALING PROGRAM; Sy m b o l i c Program L i s t i n g 276 - i x -LIST OF TABLES Page 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 s used t o o b t a i n the 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 s p e c t r a 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 l e v e l b i n d i n g e n e r g i e s ... 146 4.4 Rubidium 3p l e v e l b i n d i n g e n e r g i e s .... 150 4.5 Cesium 3d l e v e l b i n d i n g e n e r g i e s 153 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 ... 156 4.7 C a l c i u m 2s and 2p l e v e l b i n d i n g e n e r g i e s 160 4.8 S t r o n t i u m 3d l e v e l b i n d i n g e n e r g i e s ... 164 4.9 Barium 3d and 4d l e v e l b i n d i n g e n e r g i e s 168 4.10 E s t i m a t e d v a l u e s o f phase t r a n s i t i o n s h i f t s f o r the group IA and I I A m e t a l s 173 4.11 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 : 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 i n T i X 4 (X=F,Cl,Br ,1) 197 5.2 Halogen c o r e l e v e l b i n d i n g e n e r g i e s i n T i X 4 , H X and X 2 (X=F, C I , B r , I) 198 5.3 S a t e l l i t e s e p a r a t i o n s , A E , a n d t h e 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 4 (X=F,C1,Br,I) .. 205 5.4 S a t e l l i t e s e p a r a t i o n s , A E , a n d t h e 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 h a l o g e n c o r e l e v e l s p e c t r a o f T i X 4 ( F , C I , B r , I) 206 - x -Page Table 6.1 Binding energies of the metal 2p,3s and 3p levels i n MCAcAc)-vapors (M=Co,Ni,Cu) 7 227 6.2 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 spectra of M(AcAc)2 vapors (M=Co,Ni,Cu). 228 6.3 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 spectra of M(AcAc)^ vapors (M=Co,Ni,Cu). 229 6.4 0 Is and C Is binding energies and s a t e l l i t e separations i n acetylacetone and M(AcAc) 9 vapors (M=Co,Ni,Cu) 239 - x i -LIST OF FIGURES Page F i g u r e 3.1 B l o c k diagram o f t h e x - r a y photo-e l e c t r o n s p e c t r o m e t e r 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 tube assembly showing 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 tube assembly 9 3 3.5 The x - r a y tube anode i n d e t a i l 94 3.6 Schematic diagram o f t h e s p e c t r o m e t e r showing the x - r a y tube and t h e o l d gas c e l l 96 3.7 Schematic diagram of 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 3.8 A p r e l i m i n a r y spectrum 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 the new h i g h t e m p e r a t u r e gas c e l l 10 8 3.9 The t h r e e element 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 2 119 3.11 B l o c k diagram o f a microcomputer-c o n t r o l l e d e x p e r i m e n t 121 3.12 Major f u n c t i o n f l o w diagram of t h e 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 I s r e g i o n from atomic sodium 140 4.2 P h o t o e l e c t r o n spectrum o f the p o t a s s i u m 2p r e g i o n from atomic p o t a s s i u m 145 4.3 P h o t o e l e c t r o n spectrum of t h e r u b i d i u m 3p r e g i o n from atomic r u b i d i u m 148 - x i i -Page F i g u r e 4.4 P h o t o e l e c t r o n spectrum of t h e cesium 3d r e g i o n from a t o m i c cesium 152 4.5 P h o t o e l e c t r o n spectrum of t h e magnesium I s r e g i o n from atomic magnesium 155 4.6 P h o t o e l e c t r o n spectrum o f t h e c a l c i u m 2s r e g i o n from atomic c a l c i u m 158 4.7 P h o t o e l e c t r o n spectrum o f t h e c a l c i u m 2p r e g i o n from a t o m i c c a l c i u m 159 4.8 P h o t o e l e c t r o n spectrum o f t h e s t r o n t i u m 3d r e g i o n from atomic s t r o n t i u m 163 4.9 P h o t o e l e c t r o n spectrum of t h e b a r i u m 3d r e g i o n from atomic barium 166 4.10 P h o t o e l e c t r o n spectrum of t h e barium 4d r e g i o n from a t o m i c barium 16 7 5.1 P h o t o e l e c t r o n spectrum 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 f l u o r i d e v apor 200 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 vapor 201 5.3 P h o t o e l e c t r o n spectrum o f 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 b r o m i d e v a p o r 202 5.4 P h o t o e l e c t r o n spectrum of 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 vapor 203 5.5 P h o t o e l e c t r o n spectrum o f 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 vapor 208 5.6 P h o t o e l e c t r o n spectrum of t h e i o d i n e 3d 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 vapor 209 - x i i i *-F i g u r e Page 5.7 V a r i a t i o n o f t h e T i ^V_/2 s a t e l l i t e s e p a r a t i o n s and the T i 2^2/2 and T i 3p b i n d i n g e n e r g i e s w i t h l i g a n d 210 6.1 P h o t o e l e c t r o n spectrum o f the c o b a l t 2p 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 230 6.2 P h o t o e l e c t r o n s pectrum 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 v a p or 2 31 6.3 P h o t o e l e c t r o n s pectrum o f t h e copper 2p r e g i o n from copper a c e t y l a c e t o n a t e v a p or 2 32 6.4 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 6.5 P h o t o e l e c t r o n s pectrum 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 6.6 P h o t o e l e c t r o n s pectrum o f t h e copper 3s r e g i o n from copper a c e t y l a c e t o n a t e vapor 235 6.7 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 6.8 P h o t o e l e c t r o n s pectrum o f t h e n i c k e l 3p 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 v a p or 237 6.9 P h o t o e l e c t r o n spectrum o f t h e copper 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 6.10 P h o t o e l e c t r o n spectrum o f t h e 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 6.11 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 c o b a l t a c e t y l a c e t o n a t e vapor 2 42 6.12 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 v a p or 24 3 6.13 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 - x i v -ACKNOWLEDGEMENTS I would l i k e t o t a k e 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 and P r o f e s s o r C A . McDowell f o r t h e i r s u p p o r t , encouragement and i n t e r e s t t h r o u g h -o u t t h i s work. I am g r a t e f u l t o Dr. M.S.. Banna and p a r t i c u l a r l y t o Dr. B. Wallbank f o r t h e i r h e l p and i n v a l u a b l e c o l l a -b o r a t i o n d u r i n g my f o r m a t i v e days as an x - r a y 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 s t . My v e r y s p e c i a l thanks go t o Dr. N.P.C. Westwood f o r 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 the p a s t y e a r s , and f o r making v e r y u s e f u l comments on t h i s m a n u s c r i p t . I a l s o l i k e t o thank P r o f . A. B r e e , Dr. C. K i r b y , Dr. R. N a k a g a k i , Dr. M. White and Dr. S. White f o r use-f u l d i s c u s s i o n s . I t i s a p l e a s u r e t o acknowledge t h e ma c h i n i n g 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 M c C a f f e r t y and Mr. C e d r i c N e a l e . I am a l s o t h a n k f u l t o Mr. B r i n P o w e l l f o r h i s u s e f u l s u g g e s t i o n s i n d e s i g n i n g the h i g h t e m p e r a t u r e 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 the e v e r h e l p f u l s t a f f i n the e l e c t r o n i c s shop. - XV -I w i s h t o thank Mr. T.D.J. Dunstan and Ms. S. Gamage f o r p r o o f r e a d i n g and Ms. T i l l y S c h r e i n d e r s and Ms. Anna Wong f o r t y p i n g t h i s m a n u s c r i p t . F i n a l l y I would l i k e t o thank t h e U n i v e r s i t y o f B r i t i s h Columbia f o r the g r a n t o f a graduate f e l l o w s h i p w h i c h made t h i s s t u d y 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 Lanka, P e r a d e n i y a Campus f o r the l e a v e o f absence. This thesis i s dedicated to my paven - 1 -CHAPTER ONE INTRODUCTION The fundamental e x p e r i m e n t 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 the sample by a beam o f n e a r l y monoenergetic r a d i a t i o n and then o b s e r v a t i o n o f t h e r e s u l t a n t e m i s s i o n o f p h o t o e l e c t r o n s 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 the p r o c e s s a re d e f i n e d by the E i n s t e i n p h o t o e l e c t r i c r e l a t i o n " ' " , assuming t h a t hv>E^(k) , then hv = E£(k) + E k . n (1.1) where, E ^ ( k ) i s the i o n i z a t i o n energy (or b i n d i n g energy) o f the k-th l e v e l as r e f e r r e d t o t h e vacuum l e v e l and i s the k i n e t i c energy o f such 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 r a d i a t i o n . - 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 p r o c e s 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 energy, d i r e c t i o n o f e m i s s i o n w i t h r e s p e c t t o the specimen and the e x c i t i n g r a d i a t i o n , and, under c e r t a i n s p e c i a l e x p e r i m e n t a l c o n d i t i o n s , i t s s p i n . These t h r e e f e a t u r e s o f e m i t t e d p h o t o e l e c t r o n s l e a d t o t h r e e b a s i c p h o t o e l e c t r o n expe-r i m e n t s . (1) The number d i s t r i b u t i o n o f p h o t o e l e c t r o n s w i t h k i n e t i c energy: T h i s k i n d o f e x p e r i m e n t l e a d s t o an energy d i s t r i b u t i o n c u r v e (EDC) o r a p h o t o e l e c -t r o n spectrum and the i o n i z a t i o n p o t e n t i a l s (IP's) t h u s o b t a i n e d can be equated t o the n e g a t i v e o f the e i g e n v a l u e 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 u s i n g the a p p r o x i m a t i o n commonly known as Koopmans 1 t h e o r e m 2 . (2) The d i s t r i b u t i o n o f p h o t o e l e c t r o n i n t e n s i t y w i t h a n g l e o f e m i s s i o n : These e x p e r i m e n t s i n v o l v e k i n e t i c energy d i s t r i b u t i o n d e t e r m i n a t i o n s a t each o f s e v e r a l a n g l e s o f e m i s s i o n r e l a t i v e t o t h e photon p r o p a g a t i o n d i r e c t i o n o r t o axes f i x e d w i t h r e s p e c t t o the specimen"^' ^. - 3 -(3) The s p i n d i s t r i b u t i o n o f the p h o t o e l e c t r o n i n t e n -s i t y : These measurements r e q u i r e a specimen t h a t has been 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 f i e l d . Under 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 may be e m i t t e d w i t h one o f the two p o s s i b l e s p i n o r i e n t a t i o n s than w i t h the o t h e r , and the r e l a t i v e numbers o f s p i n - u p and spin-down p h o t o e l e c t r o n s are then measured. E x p e r i m e n t a l s t u d i e s o f t y p e s (2) and (3) are l e s s common due 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 the l o n g time r e q u i r e d . S e v e r a l r e v i e w s have appeared 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 such s t u d i e s and 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 . The 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 a n g l e p h o t o e l e c t r o n s t u d i e s and t h i s t e c h n i q u e w i l l be d i s -c u s s e d i n d e t a i l . Two t y p e s o f e x c i t i n g r a d i a t i o n are commonly used 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 . These a r e e i t h e r e s s e n t i a l l y monochromatic beams o f u l t r a v i o l e t r a d i a t i o n p roduced by 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 s o f t x - r a y s o u r c e s . Vacuum u l t r a v i o l e t r a d i a t i o n c o v e r s the energy range from about 5 - 50eV, and t h i s r e s t r i c t s i t s use t o t h e s t u d y o f v a l e n c e l e v e l s . However, the band w i d t h o f such r a d i a t i o n i s u s u a l l y s u f f i c i e n t l y - 4 -narrow t o 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 the 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 (In some s p e c i f i c c a ses ' r o t a t i o n a l s t r u c t u r e may-be p a r t i a l l y r e s o l v e d ) . When thes e t y p e s o f photon s o u r c e s are used 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 s p e c t r o s c o p y which i s known by t h e more common acronyms UPS, UVPES o r s i m p l y PES. When s o f t x - r a y s (^100 - 1500eV) a r e used as t h e e x c i t i n g r a d i a t i o n the t e c h n i q u e i s more commonly r e f e r r e d t o as ESCA ( E l e c t r o n S p e c t r o s c o p y f o r Chemi-c a l A n a l y s i s ) , X-ray PES o r XPS. S o f t x - r a y s are produced i n s t a n d a r d x - r a y tubes and the energy o f t h e x - r a y s produced depends on the anode m a t e r i a l b e i n g used. Mg and A l a r e the most commonly used anode m a t e r i a l s . However, the use o f Na and S i anodes i n x - r a y tubes i s not uncommon"^ '"'"''". A l l f o u r o f t h e s e second row atoms g i v e r i s e t o x - r a y spec-t r a which a r e dominated by a v e r y s t r o n g , u n r e s o l v e d , Ka^-Ka 2 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 2 P . ^ 2 - * l s a n <^ ^l/2^s r e s P e c t ; ' - v e l Y • T n e mean e n e r g i e s o f t h e x - r a y s p r o d u c e d i n such x - r a y tubes are Na Ka, 9 , I , / 1041.OeV 1 0; Mg K a 1 2 , 1253.6eV 1 2; A l Kc^ 2 , 1 4 8 6 . 6 e V 1 3 ; and S i K c ^ 2 , 1739 .5eV i : L. - 5 -When these s o u r c e s are used as e x c i t i n g r a d i a t i o n the p r i m a r y f a c t o r d e t e r m i n i n g the 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 n a t u r a l l i n e w i d t h o f the Ka^ 2 l i n e . The f u l l w i d t h a t h a l f maximum i n t e n s i t y (FWHM) o f the above mentioned source a r e a p p r o x i m a t e l y 0.4eV f o r Na Ka^° 2 , 0.7eV f o r Mg Ka^° 2 , 0.8eV f o r A l K a ^ 3 2 and 1.0 - 1.2eV f o r S i K a j ^ . T h i s makes such r a d i a t i o n l e s s s u i t e d f o r v a l e n c e l e v e l s t u d i e s as the br o a d e x c i t i n g l i n e w i d t h makes i t i m p o s s i b l e t o r e s o l v e t h e v a r i o u s v i b r a t i o n a l l e v e l s o f the i o n produced when a v a l e n c e e l e c t r o n i s e j e c t e d . In a d d i t i o n , t h e i n d i v i d u a l c l o s e l y spaced v a l e n c e l e v e l s t h emselves are o f t e n n o t d i s t i n g u i s h e d . However, t h e a b i l i t y o f t h e s e s o f t x - r a y s t o r e a c h t h e c o r e l e v e l s o f atoms and m o l e c u l e s makes them v e r y u s e f u l i n the stu d y o f i n n e r s h e l l i o n i z a t i o n p r o c e s s e s . A l t h o u g h the n a t u r a l w i d t h o f t h e Kct^ 2 l i n e d e c r e a s e s w i t h the atomic number,the elements below Ne are n o t s u i t a b l e f o r anode m a t e r i a l s as t h e v a l e n c e 2p l e v e l s o f the s e elements a r e broadened by b o n d i n g e f f e c t s , which i n c r e a s e s the n a t u r a l l i n e w i d t h o f the x - r a y s c o r r e s p o n d i n g l y . 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 e x c i t a t i o n s o u r c e s i s the m o n o c h r o m a t i z a t i o n o f Ka^ 2 x - r a d i a t i o n by Bragg r e f l e c t i o n from a s u i t a b l e s i n g l e 14 c r y s t a l . A l t h o u g h t h e l o s s o f i n t e n s i t y d u r i n g such - 6 -monochromatization processes i s considerable, photo-electron peaks as narrow as 0.4eV have been observed 15 with mono chroma t i zed A l Ktx radiation . In f a c t , the l i n e width of 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, that cases have been reported where v i b r a t i o n a l fine structure was resolved i n the core l e v e l spectra of some small molecules^. In addition to these x-ray sources, u l t r a s o f t x-rays produced by the M? t r a n s i t i o n (^P3/2"*"3d5/2^ ^ n the sequential elements yttrium to molybdenum have also been used i n XPS studies. These cover the i n t e r e s t -ing energy range of 100<hv<200eV, and the most frequently used l i n e s of t h i s type are those for Y (hv=132.3eV, FWHM=0.5eV) and Zr(hv=151.4eV, FWHM=0.8eV). These have been used succesfully to study both the valence l e v e l s 10 18 19 and outer core l e v e l s ' ' In some instances, when a higher energy source i s required, i n order to reach the deep l y i n g l e v e l s of a sample, chromium and copper are used occasionally as the 20 x-ray source (Cr Kc^ hv=5414.7eV , FWHM=2.1eV; Cu K a ^ 20 hv=8047.8eV , FWHM=2.6eV). However, the application of these sources i s l i m i t e d by the broad l i n e width of the e x c i t i n g x-ray l i n e s . Another source that has emerged over the l a s t few years i s that of synchrotron r a d i a t i o n . In a syn-chrotron, electrons are constrained to move i n a closed path by a magnetic f i e l d . As they are accelerated by the c e n t r i p e t a l force normal to the d i r e c t i o n of 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 r a d i a t i o n . 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 spectrum 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 wave l e n g t h , X , a t which the r a d i a t i o n i s a l m o s t 100% p o l a r i z e d i n t h e p l a n e o f the o r b i t i n which t h e e l e c -t r o n s 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 about 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 s y n c h r o -t r o n s and phenomena dependent on photon energy and/or p o l a r i z a t i o n are much more e a s i l y s t u d i e d w i t h t h i s 21 r a d i a t i o n than 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 would 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 each atomic o r m o l e c u l a r o r b i t a l . However, the b i n d i n g e n ergy t e r m , E ^ ( k ) , o f eqn.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 d i f f e r e n c e i n t o t a l energy between the i n i t i a l s t a t e , and the f i n a l s t a t e produced by t h e i o n i z a t i o n , i . e . E b ( K ) = E t o t ( N _ 1 , K ) " E t o t ( N ) ( 1 ' 2 ) Here, E ^ o t ( N ) i s t n e t o t a l e nergy o f the ground s t a t e ( b e f o r e i o n i z a t i o n ) and E ^ o t ( N - l , K ) i s the energy o f the K-th ( N - l ) - e l e c t r o n i o n i c s t a t e produced by i o n i z a t i o n , where E^(K) i s the c o r r e s p o n d i n g b i n d i n g energy r e f e r e n c e d t o the vacuum l e v e l . T h e r e f o r e , i f more than one f i n a l s t a t e r e s u l t s from removal o f a c o r e e l e c t r o n , then - 8 -more than one p h o t o e l e c t r o n peak w i l l o c c u r . I n the p h o t o e l e c t r o n spectrum the peak c o r r e s p o n d i n g t o t h e l o w e s t v a l u e o f E^(K) i s h e r e a f t e r r e f e r r e d t o as t h e main peak and 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 v a l u e s are r e f e r r e d t o as s a t e l l i t e peaks. V a r i o u s f i n a l s t a t e e f f e c t s t h a t w i l l r e s u l t i n m u l t i p l e f i n a l s t a t e s (and hence the m u l t i p l e s t r u c t u r e i n the c o r e e l e c t r o n s p e c t r a ) 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 C h a p t e r Two. 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 y i s p r e s e n t l y f i n d i n g a p p l i c a t i o n s i n the s t u d y o f e l e c t r o n i c p r o p e r -14 14 22 t i e s o f a wide range o f m a t e r i a l s ; s o l i d s , vapors ' 23-25 and more r e c e n t l y l i q u i d s . XPS has a l s o been a p p l i e d 2 6 t o m o l e c u l a r beams from hot m e t a l vapors L i q u i d phase XPS h a s , up t o now, been a p p l i e d 2 3 o n l y t o low vapor p r e s s u r e l i q u i d s such as formamide (vapor p r e s s u r e 0.01 - 0.02 t o r r a t room temperature) 25 and e t h y l e n e g l y c o l (Vapor p r e s s u r e ^0.1 t o r r a t room t e m p e r a t u r e ) . A number o f s a m p l i n g t e c h n i q u e s are 25 p r e s e n t l y a v a i l a b l e , i n c l u d i n g the moving w i r e method 23 24 an.d the l i q u i d beam method ' S o l i d samples have been e x t e n s i v e l y s t u d i e d u s i n g XPS. Here the s o l i d i s u s u a l l y a t t a c h e d t o some form o f probe which i s then i n t r o d u c e d i n t o the sample chamber o f the s p e c t r o m e t e r . Powders a r e o f t e n mounted - 9 -by s p r e a d i n g a t h i n l a y e r o n t o double s i d e d ' s c o t c h ' t a p e . An 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 c o n d u c t i n g w i r e mesh. Ma c h i n e a b l e s o l i d s can s i m p l y be c u t , c l e a v e d o r p o l i s h e d i n t o shapes s u i t a b l e f o r mounting i n the specimen p o s i t i o n . F o r s t u d i e s i n v o l v i n g c l e a n s u r f a c e s , samples may be p r e p a r e d by vacuum e v a p o r a t i o n o f the m a t e r i a l o n t o a s u i t a b l e 2 7 2 8 s u b s t r a t e ' . F o r p r e c i s e s u r f a c e s t u d i e s , u l t r a h i g h vacuum f a c i l i t i e s are a n e c e s s i t y , t o a v o i d s u r -f a c e c o n t a m i n a t i o n . D u r i n g t h e s e e x p e r i m e n t s , as the e m i s s i o n o f e l e c t r o n s from any sample c o n s t i t u t e s a n e t l o s s o f n e g a t i v e c h arge, i t i s u s u a l l y n e c e s s a r y t o m i n i m i z e o r c o r r e c t f o r the p o s s i b l e b u i l d i n g - u p o f 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 . I n o r d e r t o reduce such p o t e n t i a l b u i l d - u p , f o r s o l i d s , t h e specimen i s g e n e r a l l y c o n n e c t e d , e l e c t r i c a l l y , t o the sample chamber. The c h a r g i n g p o t e n t i a l , V , produced by an unequal charge d i s t r i b u t i o n , may v a r y w i t h i n the specimen volume p r o d u c i n g a range o f energy l e v e l s h i f t s w i t h r e s p e c t t o the v a l u e s f o r the uncharged s i t u a t i o n . I f r" i s t h e s p a t i a l c o o r d i n a t e o f the e m i s s i o n p o i n t w i t h i n the specimen, eqn. 1.1 can now be r e w r i t t e n as hv=E£(k,r*) + E k . n ( ? ) = E b ( k ) ° + E k i n ( J ) + V c ( ? ) - 10 -where E^(k)° and E^(k,r) are the binding energies i n the absence and presence of charging, respectively. In most cases the r e s u l t of sample charging i s a broadened photoelectron s i g n a l . To correct for such e f f e c t s studies of peak position versus x-ray f l u x can be made. The work described i n t h i s thesis i s p a r t i c u -l a r l y r e l a t e d to the study of atoms and molecules i n the vapor phase. In order to study metal atoms, a high temperature furnace was designed and constructed in t h i s laboratory. The work presented here represents the f i r s t x-ray photoelectron spectroscopic study i n the vapor phase for most of the atoms and molecules reported. Problems involved i n these high temperature gas phase studies and the special advantages of such techniques w i l l be discussed i n the following chapters. - 11 -REFERENCES 1. A. E i n s t e i n , Ann. Phys. 17, 132 (1905) 2. T. Koopmans, P h y s i c a 1, 104 (1934) 3. K. Si e g b a h n , U. G e l i u s , H. Siegbahn, and E. O l s o n , P h y s i c a S c r i p t a 1, 272 (1970) 4. C.S. F a d l e y , and S.A.L. B e r g s t r o m , Phys. L e t t . 35A, 375 (1971) 5. C.R. Brundfe, and A.D. Baker, E d i t o r s , " E l e c t r o n S p e c t r o s -copy - Theory, Techniques and A p p l i c a t i o n s " V o l . 2 (Academic P r e s s , New York,1978) 6. T.A. C a r l s o n , E d i t o r , "X-ray P h o t o e l e c t r o n S p e c t r o s -copy" (Dowden, H u t c h i n s o n & Ross 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 , and H.C. 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Bearden, Rev. Mod. Phys. 3_9_, 78 (1967) 21. K.O. Hodgson, 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 Aug. 21, 1978, p.26 - 13 -22. 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.O. Werme, R. Manne, and Y. Baer, "ESCA, A p p l i e d t o F r e e M o l e c u l e s " ( N o r t h - H o l l a n d P u b l i s h i n g Company, Amsterdam, 1969) 23. H. Siegbahn, and K. Siegbahn, 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, 319 (1973) 24. H. Siegbahn, L. A s p l u n d , P. K e l f v e , K. Hamrin, L. K a r l s s o n , and K. Siegbahn, 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, 1059 (1974) 25. H. F e l l n e r - F e l d e g g , H. Siegbahn, L. A s p l u n d , P. K e l f v e , and K. Si 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. 1_, 421 (1975) 26. Y.S. Khodeyev, H. Siegbahn, K. Hamrin, and K. Siegbahn, Chem. Phys. L e t t . __9, 16 (1973) 27. S.P. Kowalczyk, L. Ley, F.R. McFeely, R.A. P o l l a k , and D.A. S h i r l e y , Phys. Rev. B 8, 3583 (1973) 28. 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) 29. C.S. F a d l e y , G.L. G e f f r o y , S.B.M. Hagstrom, and J.M. H o l l a n d e r , N u c l . I n s t . Methods 6_8, 177 (1969) 30. J.F. M c G i l p , and I.G. Main, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 6, 397 (1975) - 14 -CHAPTER TWO BASIC CONCEPTS OF X-RAY PHOTO-ELECTRON SPECTROSCOPY 2.1 I n t r o d u c t i o n S i n c e the f i r s t o b s e r v a t i o n by Siegbahn and c o - w o r k e r s 1 a t Uppsala U n i v e r s i t y , t h a t c o r e b i n d i n g e n e r g i e s show a d e f i n i t e dependence on c h e m i c a l e n v i -ronment, 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 and 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 i n the XPS l i t e r a -t u r e . S u c c e s s f u l a t t e m p t s are b e i n g 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 such e f f e c t s , as r e v e a l e d by the l a r g e number o f papers t h a t appear i n the j o u r n a l s t h a t d e a l w i t h t h i s s u b j e c t . T h e o r e t i c a l 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 -1—5 6 7 cu s s e d i n d e t a i l i n a number o f books , r e v i e w s ' 8—10 and c o n f e r e n c e p r o c e e d i n g s . Thus, no d e t a i l e d r e v i e w o f the t h e o r y o f XPS w i l l be atte m p t e d h e r e , - 15 -a l t h o u g h some o f the 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 r e p o r t e d i n t h i s t h e s 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 The p r i m a r y aim o f most t h e o r e t i c a l models used i n XPS i s t o i n t e r p r e t the e x p e r i m e n t a l p h o t o e l e c t r o n s p e c t r a u s i n g the now f a m i l i a r eqn. 1.2 (Chapter One), which w i l l be r e w r i t t e n here f o r c o n v e n i e n c e , as E b ( K ) = E t o t ( N - 1 ' K ) " E t o t ( N ) ( 1 ' 2 ) where t ( N - l , K ) i s the t o t a l energy o f t h e K - t h ( N - l ) -e l e c t r o n i o n i c s t a t e c o r r e s p o n d i n g t o the ( N - l ) - e l e c t r o n f i n a l s t a t e wave f u n c t i o n , produced by p h o t o i o n i z a t i o n . 2.2 N - E l e c t r o n Wave F u n c t i o n s In g e n e r a l , 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 w i l l depend upon the s p a t i a l c o o r d i n a t e s , 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 the s p a t i a l c o o r d i n a t e s R , o f the P n u c l e i 'tot = ^ t o t ( r l ' a l ' r 2 ' a 2 - " - r N a N ; W - V { 2 ' 1 ] The relevant Hamiltonian of the N-electron state (in the n o n - r e l a t i v i s t i c limit) can be written - 16 -H tot 2m N 2 E V . i = l i N -E P E 1=1 £=1 r i . N + E 1=1 N E j >i ID p p + E E £=1 m>£ ZzZme ' £m T (2.2) M £=1 £ The f i v e terms on the ri g h t hand side of this expression represent contributions to the t o t a l Hamiltonian from the k i n e t i c energy of electrons, electron-nuclear a t t r a c t i o n , electron-electron repulsion, nuclear-nuclear repulsion and nuclear k i n e t i c energy respectively, where m i s the e l e c t r o n i c mass, i s the charge of the £th nucleus , r . =lr . -£„ I .r . . = I r. - r . I , r „ = I R~ -R I i £ ' i £ 1' i j 1 I j 1 ' £m 1 £ m1 and i s the mass of the £th nucleus. Contributions due to spin-orbit s p l i t t i n g are usually added as an extra term, H , to the t o t a l J so' Hamiltonian i n eqn. 2.2 where H s o = f = 1 S ( r . H i - S i ' <2-3> for atomic o r b i t a l s . Here t;(r^) i s a suitable function of the r a d i a l coordinate r ^ , and £^ and s^ are the one-electron operators for o r b i t a l angular momentum and spin 12 angular momentum respectively . The t o t a l wave function must s a t i s f y the relationship - 17 -H t o t W N ) = E t o t ( N ) W ( N ) ( 2 ' 4 ) 12 13 A c c o r d i n g t o the Born-Oppenheimer a p p r o x i m a t i o n ' the 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 i n t o t h e 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 , v, and a n u c l e a r f u n c t i o n , Y n u c . * t o t ( ? l ' a l " " ? N ' a n ; = ¥ ( ? l ' ° l - - - ? N ' 0 N ) , i f n u c ( S l - - - V (2.5) where V(N) , the e l e c t r o n i c p a r t o f eqn. 2.5, depends o n l y p a r a m e t r i c a l l y on the i n s t a n t a n e o u s s p a t i a l c o o r d i n a t e s o f the P n u c l e i . ^(N) i s a s o l u t i o n t o eqn. 2.4 i n which H t Q t i s r e p l a c e d by H, where i_ 2 2 . . -h p v H = H t o t + F" E - W - ( 2 * 6 ) £ = 1 A The t o t a l energy o f the system, can now be w r i t t e n as ^ = E + E (2.7) t o t nuc - 18 -Here, E i s the e l e c t r o n i c energy and E i s ^ J nuc the energy due to i n t e r n a l nuclear motions which include vibrations, rotations and center-of-mass motions (trans-lations) . Furthermore, i f these d i f f e r e n t modes of nuclear motions are independent, then eqn. 2.7 can be rewritten as E t o t " E + E v i b + E r o t + E t r a n s (2.8) This demands that 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 state must include a complete s p e c i f i c a t i o n of a l l these modes of motion. Vibr a t i o n a l excitations i n the f i n a l state ion give r i s e to v i b r a t i o n a l bands i n UPS studies of molecules in the vapor phase. These have also been observed i n a 14-17 number of high resolution XPS studies . In XPS studies, currently available instrumental resolution does not permit the detection of d i f f e r e n t r o t a t i o n a l excitations i n the f i n a l i o n i c state. The e f f e c t of t r a n s l a t i o n a l motion of an atom or molecule on energies determined by XPS (and UPS) i s two f o l d . (i) Conservation of l i n e a r momentum requires that, for the photoemission process - 19 -? h v + 0 = Pf + Pr ( 2 ' 9 ) where P^ v/ Pf and P r are the photon momentum, pho t o -e l e c t r o n momentum and the r e c o i l momentum o f t h e f i n a l s t a t e i o n r e s p e c t i v e l y . Momentum o f the i n i t i a l s t a t e i s t a k e n t o be 0 (zero) f o r s i m p l i c i t y . The p h o t o e l e c -t r o n s e n c o u n t e r e d i n XPS can be c o n s i d e r e d n o n - r e l a t i v i s t i c , t o 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 h v |£ _5L | P f | (2.10) f o r t he extreme case o f the p h o t o e l e c t r o n s h a v i n g k i n e t i c energy a p p r o x i m a t e l y e q u a l t o the 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 and c are t h e v e l o c i t i e s o f t he 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 . I n g e n e r a l | P^ v| <<|P_:| and P f ^ P r i n d i c a t i n g t h a t the f i n a l s t a t e i o n r e c o i l s i n a d i r e c t i o n o p p o s i t e t o the d i r e c t i o n o f 18 p h o t o e m i s s i o n . The r e c o i l e n e rgy, E r , f o r a g i v e n photon energy and k i n e t i c energy o f p h o t o e l e c t r o n , can be w r i t t e n as E = p 2/2M r * r (2.11) - 20 -where M i s t h e mass o f t h e f i n a l s t a t e i o n . A c c o r d i n g t o a c a l c u l a t i o n by Siegbahn and c o w o r k e r s 1 , o n l y the l i g h t e s t atoms H, He and L i have a s i g n i f i c a n t magnitude o f E , where the r e c o i l e n e r g i e s are 0.9eV and O.leV f o r H and 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 comparison w i t h the a v a i l a b l e XPS i n s t r u -m e n t a l r e s o l u t i o n o f 0.4 - l.OeV. ( i i ) The .thermal t r a n s l a t i o n a l motion o f the e m i t t i n g m o l e c u l e (or atom), i n the gas phase, can i n c r e a s e the peak w i d t h s d e t e r m i n e d by XPS (and UPS) due to D o p p l e r b r o a d e n i n g . I t has been shown t h a t the Doppler 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 m o l e c u l e (or atom) , and i t has been e s t i m a t e d t h a t the Doppler w i d t h i s £ O.lOeV f o r m o l e c u l e s w i t h m o l e c u l a r w e i g h t s ^ 10. F o r a l m o s t a l l c a s e s , the e f f e c t o f t r a n s l a t i o n a l motion on XPS e n e r g i e s , t h r o u g h r e c o i l energy and Doppler b r o a d e n i n g , 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 t o t y p i c a l XPS r e s o l u t i o n o f ^0.4 - l.OeV. - 21 -F o r t h e s e r e a s o n s , u s u a l l y i t i s adequate t o c o n s i d e r q u a n t i t i e s r e l a t i n g o n l y t o e l e c t r o n i c m otion and eqn.1.2 i s now app r o x i m a t e d as (K) = E f ( N - l , K ) - E 1(N) (2.12) 2.3 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 c a r r i e d o u t u s i n g v a r i o u s m o l e c u l a r o r b i t a l a p p r o x i m a t i o n s . A common s t a r t i n g p o i n t f o r such c a l c u l a t i o n s i s the non-r e l a t i v i s t i c H a r t r e e - F o c k (HF) s e l f c o n s i s t e n t f i e l d (SCF) 12 method . In 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 the 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 each o t h e r i n the f i e l d o f t he n u c l e i , and i n d e p e n d e n t l y o f the average d i s t r i b u t i o n o f t h e o t h e r e l e c t r o n s . The HF(SCF) method i s used a t d i f f e r e n t l e v e l s o f e x a c t n e s s i n a p p r o x i m a t i n g N - e l e c t r o n wave f u n c t i o n s . I n the s i m p l e s t form, the wave f u n c t i o n 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 i s app r o x i m a t e d 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 orthonormal 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 the s e one e l e c t r o n o r b i t a l s i n t u r n i s the p r o d u c t o f a s p a t i a l p a r t , <f>^(r) ( i = 1,2, ..,N) , - 22 -and a s p i n p a r t , x-; » which i s e q u a l t o a(m =+—) , o r 1 s 2 3 ( m 3 =~2") • f c a n then be w r i t t e n i n terms o f the a n t i -s y m m e t r i z e r , A, as ¥ * $ = A( <t,lXl, * 2 x 2 ' ••• '* NX N) (2.13) 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 method, each s p a t i a l o r b i t a l , <j>^ , i s assumed t o have a maximum o c c u p a t i o n number o f two and hence o n l y N/2 unique <f>^  s are i n v o l v e d i n d e s c r i b i n g a system w i t h an even number o f e l e c t r o n s ( i n d o u b l y - o c c u p i e d o r b i t a l s ) . The 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 u s i n g the 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 can be used t o determine 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 w e l l as t h e t o t a l energy E c o r r e s p o n d i n g t o t h e s t a t e d e s c r i b e d by $. In a t o m i c u n i t s , t h e H a r t r e e - F o c k e q u a t i o n s i n d i a g o n a l form can be w r i t t e n as P ( l ) * (1) ={-ly 2 - Z + ? m K .]}• .(1) 1 z 1 £=i r m j = l J m s i ' m s j 3 1 = e i * i ( l ) , i = l , 2 , ,N (2.14) - 23 -where, J j and Kj are the Coulomb and exchange operators respectively. These operators are defined such that JV* H (1) = / + / ( 2 ) » — (2) <f>,(l)dT2 (2.15) j x j 12 K-*.(1) = ( 2 ) - i - <J>. (2) * . ( l ) d T o (2.16) -* J r 1 2 3 Thus, the matrix elements of these operators are the two-electron Coulomb integrals J ^ j and exchange integrals K^j: J . . =<•. (1) | J . | * - (1) > = //*. *(1) <t>, * ( 2 ) - ^ - *. (1) 4> . (2)dT,dx I J x j x x j 12 3 (2.17) K. . =<<|>. (1) |K . | <j). (1) > = //*. *(1) * ( 2 ) - ^ - 4>. (2) <(.. ( l ) d x dx„ x j x j x x j 12 (2 .18) 6 i n eqn. 2.14 i s the Kronecker delta which by m . ,m . ^ s i ' s j d e f i n i t i o n i s <X • I X • > = <S = 1 for aa or 66 * i 1 _ m .,m. s i ' s j (2.19) = 0 for a3 or 8 a - 24 -The exchange i n t e r a c t i o n i s o n l y p o s s i b l e between s p i n o r b i t a l s w i t h p a r a l l e l s p i n s ( i . e . cm o r 38) and 6 i n eqn. 2.14 a l l o w s f o r t h i s . Once t h e H a r t r e e -m • /HI s i S j Fock e q u a t i o n s are 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 , t h e o r b i t a l e n e r g i e s e- can be o b t a i n e d from N e i = e i + E < J i j 3=1 J 5 K. . m .,m . i n s i ' S j J (2.20) Here e ? i s the e x p e c t a t i o n v a l u e o f the o n e - e l e c t r o n o p e r a t o r f o r k i n e t i c energy and e l e c t r o n - n u c l e a r a t t r a c t i o n 2 p 2 e?=<*. (1) l-i-V, - I -A" U- (1)> (2.21) 1 1 Z SL=1 r l l 1 Now, t h e t o t a l energy o f the s t a t e a p p r o x i m a t e d by $ i s g i v e n by E = < $ | H | $> N n N N P P 7• zm = I e? + Z I (J---<5 m m K..) + I I (2.22) i = l 1 i = l j > i 1 3 s i ' s j 1 3 1=1 m>l £m - 25 -Here, when a d d i n g the o n e - e l e c t r o n e n e r g i e s t o g e t h e r , f o r the N e l e c t r o n s i n the system, a c o r r e c t i o n i s made w i t h i< j t o a v o i d c o u n t i n g the Coulomb and exchange terms t w i c e . I n u s i n g the H a r t r e e - F o c k method f o r c a l c u l a t i n g b i n d i n g e n e r g i e s , the most a c c u r a t e p r o c e d u r e i s t o compute the d i f f e r e n c e between E f ( N - l , K ) and E"*"(N) c o r r e s p o n d i n g t o the H a r t r e e - F o c k wave f u n c t i o n s ^ ( N - l j K ) and Y 1 ( N ) , r e s p e c t i v e l y . 2.4 Koopmans' Theorem and B i n d i n g E n e r g i e s 20 Koopmans 1 theorem assumes t h a t the i n i t i a l one e l e c t r o n o r b i t a l s , <$>^, making up the d e t e r m i n a n t i*1 (N) are p r e c i s e l y e q u a l t o the f i n a l one e l e c t r o n o r b i t a l s , <}>^, making up t h e f i n a l s t a t e , $ ^ ( N - l , k ) , w i t h a s i n g l e k - s u b s h e l l h o l e . E ^ ( N - l , k ) can now be c a l c u l a t e d u s i n g eqn. 2.22 and the Koopmans 1 b i n d i n g energy o f the k - t h e l e c t r o n can now be c a l c u l a t e d as E ^ ( k ) K T = E f ( N - l , k ) - E 1 ( N ) (2.23) b where E ^ ( N - l , k ) i s the energy o f t h e l o w e s t energy f i n a l i o n i c s t a t e w i t h a h o l e i n the k - t h s u b s h e l l . The b i n d i n g energy o f the - 26 -k-th electron as obtained from egn. 2.23 i s equal to the negative of the o r b i t a l energy and t h i s i s known as 'Koopmans'theorem'. The binding energies calculated using Koopmans' theorem as described here, usually d i f f e r from the actual experimental binding energy values due to a number of reasons. F i r s t l y , i t i s expected that the (N-l) electrons i n the f i n a l state w i l l not have the same s p a t i a l d i s t r i -bution as those i n 4'1(N) due to relaxation or rearrange-ment around the k hole. I t has been shown that, although the o v e r a l l change i n the s p a t i a l form of the passive o r b i t a l s following i o n i z a t i o n i s not large, the r e s u l t i n g change in energy can have a considerable e f f e c t on the 21 calculated binding energies . Secondly, r e l a t i v i s t i c e f f e c t s generally increase core electron binding energies and t h e i r magnitudes depend on the r a t i o of 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 of l i g h t . T h i r d l y , as the i n i t i a l state SCF c a l c u l a t i o n does not include favourable correlation between a given core electron and the other (N-l) electrons, the calculated value of E 1(N) w i l l be too large and hence the binding energy calculated using eqn. 2.12 would be too small. The approximate rel a t i o n s h i p between the Koopmans' binding energy, -e^' and the true binding energy can, therefore, be written as - 27 -E, (k) = -e, -<5E , + 5E , , + 6 E (2.24) b k r e l a x r e l a t c o r r where < S E r e l a x r 6 E r e i a t a n d 5 E C o r r a r e t h e c o r r e c t i o n s t o the Koopmans' b i n d i n g energy due t o o r b i t a l r e l a x a t i o n , r e l a t i v i s t i c 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 o r r e l a t i o n r e s p e c t i v e l y . The most d i r e c t method t o e v a l u a t e 6E , i s t o r e l a x c a r r y o u t SCF H a r t r e e - F o c k c a l c u l a t i o n s f o r t h e i n i t i a l and f i n a l s t a t e s and th e n t o compare t h e E^(k) as c a l c u -l a t e d by the t o t a l energy d i f f e r e n c e method w i t h the Kbopmans * b i n d i n g e n e r g y , - e k - Siegbahn and coworkers" 1" have c a l c u l a t e d a v a l u e o f %2 3eV f o r 6E , f o r Ne I s r e l a x i o n i z a t i o n . 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 , ., ' r e l a t ' 22 ar e u s u a l l y made by u s i n g p e r t u r b a t i o n t h e o r y . D i r e c t 22 t a b u l a t i o n o f t h e s e c o r r e c t i o n s f o r a l l atoms are a v a i l a b l e , and t h i s c o r r e c t i o n f o r C I s i s 0.2eV o u t o f 290eV (0.08%) and i s about 22eV o u t o f 3180eV (^0.69%) f o r Af I s . The c o r r e l a t i o n c o r r e c t i o n , ^ E c o r r / r o r c o r e l e v e l s i n c l o s e d s h e l l systems can 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 o f e l e c t r o n p a i r c o r r e l a t i o n e n e r g i e s e ( i , j ) c a l c u l a t e d >um f o r t h e ground s t a t e o f he s y s t e m 2 3 . The e s t i m a t e d v a l f o r 6 E c o r r ' u s i n 9 t h i s method, f o r Ne I s i s 1.9eV 2 3. ue 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 F o r the a c c u r a t e 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 -t i a l s (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 a c c u r a c y and the b a s i s s e t s used i n the c a l c u l a t i o n s must be l a r g e . They must be a b l e to d e s c r i b e wave f u n c t i o n s c l o s e t o the H a r t r e e - F o c k l i m i t , b o t h f o r the n e u t r a l ground s t a t e and f o r t h e i o n i c s t a t e s . The s i m p l e s t method used t o c a l c u l a t e I P ' s i s Koopmans' theorem and, as d i s c u s s e d b e f o r e , the 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 o f e l e c t r o n i c c o r r e l a t i o n and r e o r g a n i z a t i o n . 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 can be i n c l u d e d by 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 the i n d i v i d u a l i o n i c s t a t e s and the ground s t a t e ; t h i s i s t he so c a l l e d ASCF method. T h i s method has been v e r y s u c c e s s f u l i n the 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 -' . 24 25 n i c r e o r g a n i z a t i o n i s the predominant e f f e c t ' Ab i n i t i o c a l c u l a t i o n s are d e r i v e d from b a s i c p h y s i c a l c o ncepts w i t h o u t r e f e r e n c e t o any e m p i r i c a l d a t a . F o r m o l e c u l e s , t h e ab i n i t i o method i s g e n e r a l l y based on the same fundamental approach as t h a t used 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 , which i s a many c e n t r e problem depending on the number o f atoms i n the m o l e c u l e , can be v e r y e x p e n s i v e i n computer t i m e , b u t i s e x p e c t e d t o g i v e r e l i a b l e v a l u e s . - 29 -S e m i e m p i r i c a l methods such as CNDO (Complete N e g l e c t o f D i f f e r e n t i a l O v erlap) cannot be used to c a l c u l a t 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 because they do n o t c o n s i d e r c o r e 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 c a l c u -l a t e i o n i z a t i o n e n e r g i e s i s t h e m u l t i p l e s c a t t e r i n g 2 6 method w h i c h makes use o f a m u f f i n - t i n p o t e n t i a l A f u r t h e r m o d i f i c a t i o n i s the 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 th e exchange terms o f the H a r t r e e -Fock t o t a l energy are e x p r e s s e d as exchange p o t e n t i a l s t h a t are l o c a l i z e d o r made p r o p o r t i o n a l t o the cube r o o t o f t h e t o t a l e l e c t r o n d e n s i t y . 30-32 Cederbaum and o t h e r s have s u g g e s t e d an a l t e r n a t i v e t o Koopmans' theorem i n v o l v i n g Green's f u n c t i o n s 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 t h e o r y . These c a l c u l a t i o n s i n c l u d e the e f f e c t s o f b oth r e l a x a t i o n energy and c o r r e l a t i o n e f f e c t s , however the d i f f i c u l t y i n p e r f o r m i n g such c o m p u t a tions has r e s t r i c t e d t h i s method t o s i m p l e m o l e c u l e s . 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 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 (CI) method, i n p r i n c i p l e , can be used t o approach the e x a c t wave f u n c t i o n o f the N - e l e c t r o n system t o any degree o f a c c u r a c y . I n - 30 -t h i s method the 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 d e 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 c o n f i g u r a t i o n s . These S l a t e r d e t e r m i n a n t s , $j (N) , i n c l u d e the 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 can be formed by e x c i t i n g e l e c t r o n s from one o r more o f the H a r t r e e - F o c k o r b i t a l s i n t o v i r t u a l o r b i t a l s . Now the e x a c t N - e l e c t r o n wave f u n c t i o n can be w r i t t e n as ¥(N) =1 CA *_, (N) (2.25) The c o e f f i c i e n t s Cj and perhaps a l s o 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>. used t o make up the are o p t i m i z e d by s e e k i n g a minimum i n t o t a l e n e rgy. The c o e f f i c i e n t m u l t i p l y i n g the d e t e r m i n a n t r e p r e s e n t i n g the H a r t r e e - F o c k c o n f i g u r a t i o n w i l l u s u a l l y be the dominant term i n the above e x p a n s i o n , and t h i s c o e f f i -c i e n t u s u a l l y has a v a l u e between 0.9 and 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 C o n f i g u r a t i o n i n t e r a c t i o n i n the i n i t i a l and f i n a l s t a t e s i s f r e q u e n t l y 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 seen i n XPS (and UPS) - 31 -s p e c t r a . T h i s w i l l be d e a l t with i n some d e t a i l i n the s e c t i o n on multi-component s t r u c t u r e , l a t e r i n t h i s chapter. 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 P h o t o e l e c t r o n C r o s s - S e c t i o n s The p h o t o e l e c t r i c c r o s s s e c t i o n , a , i s d e f i n e d as the t r a n s i t i o n p r o b a b i l i t y per u n i t time f o r e x c i t i n g an atom, molecule o r a s o l i d specimen from a s t a t e ^"""(N) to a s t a t e ¥ ^ ( N ) with a u n i t i n c i d e n t photon f l u x . A more convenient q u a n t i t y , however, i s the d i f f e r e n t i a l c r o s s - s e c t i o n f o r e j e c t i o n o f an e l e c t r o n i n a sm a l l s o l i d angle, dfi, w i t h r e s p e c t to some f i x e d a x i s . Such d i f f e r e n t i a l o r t o t a l c r o s s - s e c t i o n s can be c a l c u l a t e d by means o f time dependent p e r t u r b a t i o n theory and are 34 . . d i s c u s s e d elsewhere . For a t r a n s i t i o n from the i n i t i a l s t a t e * (N) to a f i n a l s t a t e * ^ ( N ) c o r r e s p o n d i n g to e l e c t r o n e m i s s i o n , the d i f f e r e n t i a l c r o s s - s e c t i o n , do , can be w r i t t e n as, dfi (2 .26) - 32 -where, e * i s a unit vector i n the direction of p o l a r i -zation and k ^ i s the wave vector of propagation. C, here, i s a combination of fundamental constants, and g^ i s the degeneracy of the i n i t i a l state. Other terms i n the above equation have been defined before. If unpolarized radiation i s used for ex c i t a t i o n , a summation or integration over the various possible, • da orientations of e i s necessary i n deriving g^ -and the summation z i s replaced by £ ^ i n eqn.2.26. i , f i , f , e If the influence of the perturbing radiation on the nuclear co-ordinates i s neglected and the Born-Oppenheimer approximation (eqn. 2.5) i s v a l i d , then eqn. 2 can be rewritten as l^ frfc^ 7 I < v f (N) I Z exp(i.k h v.?.):. V.| T i(N)> | 1 1 / I 1 — JL l < y v i b < P ) l ^ v i b ( P ) > ! 2 (2-27) The squared overlap 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 functions i n th i s expression i s c a l l e d the Franck-Condon factor and t h i s i s largely responsible for the r e l a t i v e i n t e n s i t i e s of the v i b r a t i o n a l bands i n . . 35-37 photoionization t r a n s i t i o n s . As these v i b r a t i o n a l e f f e c t s are observed i n XPS only under special situations only the e l e c t r o n i c aspects are considered further here. - 33 -I f the photon wave length i s much larger than the t y p i c a l dimensions of the system, then by treating exp^k^jr^) as unity i n the integration, eqn. 2.26 can be rewritten as, af= h (hV Z I E ' < ^ ( N ) ! E V. | . I ( N ) > | X 1 f I 1 — J . (2.28) and t h i s i s c a l l e d "the dipole approximation". One form of the matrix element in eqn. 2.2 8 i s F N . ^ F N (N) | Z V. |V (N) > = x- < Y (N) | Z p. | T 1 ( N ) > i=l 1 7 1 i = l x (2.29) There are several le v e l s of accuracy that can be used in the evaluation of matrix elements such as those shown i n eqn. 2.28. In general, the i n i t i a l and f i n a l states i n the matrix element can be described by single determinant Hartree-Fock wave functions for a closed s h e l l system. These can be calculated accurately to include relaxation e f f e c t s , and now the appropriate wave functions can be written as - 34 -l V (N) = A ( ( | ) 1 x 1 / 4> 2 x2 ' •••*' < t )k xk' •••'<f)NxN^ (2.30) f ~ i f f y (N) = A ( * ^ x 1 » + 2 X 2 ' X ' ••*'*NXN) (2.31) The N - e l e c t r o n m a t r i x element f o r a g e n e r a l o n e - e l e c t r o n t r a n s i t i o n o p e r a t o r t depending o n l y on s p a t i a l c o o r d i n a t e s 38 39 can now be w r i t t e n as ' , f ( N ) | E t , | / ( N ) > = m S ^ m ( 1 ) | t | ^ n ( D > D^ml.n) (2.32) < ¥ (N) E t . i = l 1 where the double sum on m and n i s o v e r a l l o c c u p i e d o r b i t a l s and D^1 (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 o v e r l a p d e t e r m i n a n t and i s e q u a l t o the s i g n e d minor formed by removing the m-th row and n - t h column from the NxN d e t e r m i n a n t D"^ 1 whose elements are o v e r l a p s between i n i t i a l - 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 pq element ( D f l ) can be w r i t t e n as < D f i > p q "< • p X p l V q " < 2 ' 3 3 > The p r i m a r y e x c i t a t i o n i s d i s t i n g u i s h e d as b e i n g between <f>k, a g i v e n c o r e o r b i t a l , and <f> f , a h i g h - e n e r g y p h o t o -- 3 5 -e l e c t r o n s t a t e and the 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 < <|> (1) | t|<j>k(l)> have been shown 3 9 4 0 t o be n e g l i g i b l e ' . T h i s l e a d s t o the e x p r e s s i o n An analogous e x p r e s s i o n can a l s o be d e r i v e d by u s i n g the sudden a p p r o x i m a t i o n -2 . 8 Sudden A p p r o x i m a t i o n 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 the p h o t o e m i s s i o n p r o c e s s . The i n i t i a l s t a t e i s r e p r e s e n t e d as an a n t i s y m m e t r i z e d p r o d u c t o f the ' a c t i v e ' k - t h o r b i t a l <l>k(l) from which the p h o t o -e l e c t r o n i s e m i t t e d , and an ( N - l ) - e l e c t r o n r e m a inder V p ( N - l ) r e p r e s e n t i n g t h e r e s t o f t h e e l e c t r o n s : f N „ . < V (N) | Z t . | ¥ (N) > = i = l 1 <*f (1) | t | * k ( l ) > D f l ( f |k) ( 2 . 3 4 ) ^ ( N ) = A(<f»k(l) x k ( D , f R ( N - l ) ) ( 2 . 3 5 ) - 36 -The f i n a l s t a t e , i n the weak c o u p l i n g l i m i t , can, s i m i l a r l y , be w r i t t e n as t h e a n t i s y m m e t r i z e d p r o d u c t o f the continuum o r b i t a l <j>^(l) and the i o n i c wave f u n c t i o n , f f ( N - l ) , V f(N) = A(<f)f (1) x f (1) , * f ( N - l ) ) (2.36) F u r t h e r , i t i s assumed t h a t the p r i m a r y k+f t r a n s i t i o n i s r a p i d o r 'sudden' w i t h r e s p e c t t o the r e l a x a t i o n times o f the p a s s i v e e l e c t r o n s and so the t r a n s i t i o n m a t r i x 34 41 element can now be w r i t t e n as ' f N - -i f f <^ (N) i E t . |^ 1(N)> = < < r ( l ) | t | * . ( l ) > < * r ( N - l ) |Y (N-l)> • i = l 1 R (2.37) The use o f t h i s e x p r e s s i o n i s o f t e n termed the "sudden a p p r o x i m a t i o n " 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 -s e c t i o n s i n t h i s l i m i t are p r o p o r t i o n a l t o |</ (1) |t | cj>k(l) > | 2 M f (N-l) | ¥ R(N-1) > | 2 (2.38) - 37 -and involve a one-electron matrix element and an (N-l)-electron overlap i n t e g r a l between the i o n i c wave function f^(N-l) and the passive-electron remainder T n ( N - l ) . In order for the overlap i n t e g r a l to be non-zero, the symmetry requirements demand that both f^(N-l) and Y R(N-1) must correspond to the same ov e r a l l i r r e d u c i b l e representation and t h i s gives r i s e to the well known 'monopole selection r u l e ' . This w i l l be discussed l a t e r i n t h i s chapter. The simplest approximation for the t r a n s i t i o n matrix element comes from the Koopmans1 theorem or the frozen o r b i t a l f i n a l state in which d>^  = 4 > f o r j^ -k and the said matrix element can then be approximated as <¥ f(N)|z t.|* 1(N)> = <<f>f (1) |t | <|>, (1) > (2.39) i = l 1 K This l a s t method has been used i n the majority of cross-section calculations to date. Configuration i n t e r a c t i o n wave functions can also be used i n the c a l c u l a t i o n of these matrix elements and cross-sections, and these r e s u l t s usually provide a more accurate description of the multielectron processes 42 that often accompany photoionization . It has been shown that the calculated i n t e n s i t i e s can be s i g n i f i c a n t l y - 38 -m o d i f i e d by the 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 i n t h e 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 . F o r c o m p u t a t i o n a l convenience the same s e t o f o r t h o n o r m a l one e l e c t r o n o r b i t a l s 4^, <j>2, ^ M (M>N) u s u a l l y i s used i n making up b o t h the i n i t i a l and f i n a l s t a t e c o n f i g u r a t i o n s . ^ 1(N) = Z C 1 $ X(N) (2.40) j 3 3 / ( N ) = Z C*; $ J ( N ) (2.41) m m m A l l o w a n c e i s made f o r r e l a x a t i o n i n the f i n a l s t a t e by 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 w i t h m i x i n g c o e f f i c i e n t s C^ " and t h a t are o p t i m i z e d f o r b o t h 3 3 * s t a t e s . Now, 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 c o n f i g u r a t i o n s $j(N) and *^(N) i n eqns2.40 and 2.41 can 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 analogous t o eqns. 2.35 and 2.36: 4j(N) = A( ^ ( 1 ) x k ( D , $ j ( N - l ) l (2.42) $ m(N) = A(<j>f (1) x f (1) , *__(N-1)) (2.43) - 39 -I f t he ( N - l ) - e l e c t r o n f a c t o r s i n t h e s e e q u a t i o n s are i n d e x e d i n such a way t h a t ' j ( N - l ) = *^(N-1) f o r j=m (2.44) and t h u s a l s o , < $7(N-1) |$ f (N-l)> = 6 . (2.45) j 1 mv jm 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 can be w r i t t e n as f N " i f f -i < * r ( N ) | l t . | y ( N ) > = <4> r(l) | t | <k ( 1 ) > [ Z ( C . ) * i = l j J -1 (2.46) Only those c o n f i g u r a t i o n s w h i c h have a non-zero c o e f f i c i e n t i n b o t h the i n i t i a l and the f i n a l s t a t e w i l l have a non-zero ( (C?)* Cj ) p r o d u c t and i n the l i m i t i n g case where a s i n g l e c o n f i g u r a t i o n j = l dominates the i n i t i a l s t a t e , t h e square o f t h e m a t r i x element i n eqn. 2.4 7 can be w r i t t e n a s , f N - 2 f 2 |<4<r(N) | Z t . |4' 1(N)>| He,1! (2.47) i = l - 40 -f o r a t r a n s i t i o n t o a g i v e n f i n a l s t a t e . 2.9 Sum R u l e s on Energy and I n t e n s i t y F o l l o w i n g the sudden a p p r o x i m a t i o n , two e x p e r i m e n t a l l y u s e f u l s p e c t r a l sum r u l e s have been . . , ,38,39,41,43 _, ^. .. . , i n t r o d u c e d . The f i r s t sum r u l e p o i n t e d 43 41 o u t by L u n d q v i s t , and Manne and Aberg s t a t e s t h a t the w e i g h t e d average b i n d i n g energy o v e r a l l f i n a l i o n i c s t a t e s Y F(N-1,K) a s s o c i a t e d w i t h a g i v e n p r i m a r y k-*f t r a n s i t i o n i s s i m p l y e q u a l t o the Koopmans' b i n d i n g energy, - e k -e,= I I E, (K) / Z I k K K b K K (2.48) f 2 = Z|<4< ( N - l ,K) | y R ( N - l ) > | E b ( K ) K where I i s the i n t e n s i t y o f the peak p e r t a i n i n g t o K a t r a n s i t i o n 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 energy Ej = )(K) . A n o t h e r p o p u l a r form o f t h i s energy sum r u l e can be d e r i v e d by s u b t r a c t i n g the b i n d i n g energy c o r r e s p o n d i n g t o the l o w e s t energy f i n a l s t a t e , E Q , a s s o c i a t e d w i t h the t r a n s i t i o n k->f, from b o t h s i d e s o f eqn. 2.48, r e s u l t i n g i n o r " £ k - E 0 = I W ^ V / * L K 5 E r e l a x = I \ A K / * K (2.49) where 6E , i s the energy d i f f e r e n c e between the r e l a x 3 Koopmans 1 a p p r o x i m a t i o n e n e r g y , and the a c t u a l f i n a l s t a t e e n e rgy, and i s d e f i n e d by eqn. 2.24. S i n c e a l l the q u a n t i t i e s on the r i g h t hand side o f eqn. 2.49 are 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 f i n d i n g the r e l a x a t i o n energy. However, i n p r a c t i c e t h i s i s u s u a l l y n o t p o s s i b l e because the i n t e n s i t y d i s t r i b u t i o n o v e r the s h a k e o f f continuum (see l a t e r ) i s not e a s i l y e x t r a c t e d 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 r u l e i s t h a t , i n o r d e r f o r r e l a x a t i o n i n the f i n a l s t a t e t o o c c u r i n f o r m i n g the l o w e s t b i n d i n g energy f i n a l s t a t e , e x c i t e d i o n i c s t a t e s c o r r e s p o n d i n g t o b i n d i n g e n e r g i e s - 42 -higher than -e^ must also a r i s e . In other words, i f ( S E r e l a x w e r e z e r o / n o s a t e l l i t e s would be observed and in the case thatSE , i s large, i n p r i n c i p l e , re lax one would observe an intense set of s a t e l l i t e s near the main peak, or weak s a t e l l i t e s far from the main peak or some thing i n between these two extremes. The second sudden approximation sum rule 3 8 39 which was f i r s t pointed out by Fadley ' states that the sum of i n t e n s i t i e s of a l l peaks associated with the states ^(N-l,K) i s given by 2 2 I t o t=El K=CE|<* f(l) |t| * k ( l ) > | |<*f(N-l,K) | ? R(N-1)>| (2.50) K .K where C i s a constant for a given photon energy. This means that the frozen o r b i t a l cross-sections calculated using eqn.2.39 actually represent the cross-sections summed over a l l f i n a l states 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 cross-sections calculated using frozen o r b i t a l s are not d i r e c t l y com-parable to experimental cross-sections observed i n photo-electron experiments. - 43 -2.10 Core Binding Energy S h i f t s Following the observations of Siegbahn and co-workers 1 that core electron binding energies exh i b i t chemically induced s h i f t s , the most widely used aspect of XPS i s the experimental determination of these s h i f t s for elements as a function of chemical environment and subsequent use of t h i s information i n quantitative and q u a l i t a t i v e chemical analysis. The chemical s h i f t between the free atom state, A, and a p a r t i c u l a r mole-cular state, M, for a given element, for the i o n i z a t i o n of the k-th electron can be written as AE^(k) = (EJJ(k)^ - ( E ^ ( k ) ) A (2.51) A large number of models which vary from s t r i c t l y t h e o r e t i c a l , to semiempirical, to purely empirical i n nature have been suggested for the interpretation of ex-perimental results and the advanced prediction of chemical 1 44-63 s h i f t s ' . No attempt w i l l be made to review these models here. However, as no discussion on XPS i s complete without a few words on chemical s h i f t models, a few i n t e -resting points on these w i l l be brought to the attention - 44 -o f the r e a d e r . 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 s h i f t s , must i n g e n e r a l , i n v o l v e the c a l c u l a t i o n o f 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 i n i t i a l s t a t e c a l c u l a t i o n s and two f i n a l s t a t e c a l c u l a t i o n s . So, f o r c a l c u l a t i o n s p e r f o r m e d a t a g i v e n l e v e l o f a c c u r a c y , the p o s s i b l e e r r o r s i n s h i f t s a r e , t h u s , 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 and the most s t r a i g h t f o r w a r d method f o r the c a l c u l a t i o n o f b i n d i n g energy s h i f t s makes use o f a Koopmans' theorem ap p r o a c h . Here i t i s assumed t h a t the r e l a t i v i s t i c , c o r r e l a t i o n and r e l a x a t i o n e f f e c t s on the core b i n d i n g e n e r g i e s remain a p p r o x i m a t e l y the same from one s i t e t o a n o t h e r , f o r a g i v e n element and f o r a g i v e n c o r e l e v e l . Now t h e b i n d i n g energy s h i f t can be eq u a t e d t o the d i f f e r e n c e i n the Koopmans' theorem b i n d i n g e n e r g i e s f o r the two s i t e s . The use o f Koopmans' theorem i n e s t i m a t i n g t h e b i n d i n g energy s h i f t s 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 c a l c u l a t i o n s has produced f a i r l y r e l i a b l e v a l u e s 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 and c o r r e l a t i o n e f f e c t s , as assumed h e r e , can have a p p r o x i m a t e l y t h e same v a l u e when - 45 -g o i n g from one s i t e t o a n o t h e r . However, the same c o u l d be t r u e o n l y t o a much l e s s e r degree i n the case o f r e l a x a t i o n e f f e c t s . T h e r e f o r e , i t i s i m p o r t a n t t o be a b l e 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 t h e s e c h e m i c a l s h i f t c a l c u l a t i o n s . The t r a n s i t i o n s t a t e method, deve-4 7 l o p e d by G o s c i n s k i and co-workers , a l l o w s r e l a x a t i o n e f f e c t s t o second o r d e r i n p e r t u r b a t i o n t h e o r y , and t h e 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 by u s i n g t h i s method have been found v e r y r e l i a b l e ^ . In t h e p o t e n t i a l model used i n the 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 c h e m i c a l s h i f t s by Siegbahn 1 4 8 49 and co-workers , and F a d l e y and co-workers ' , the i n t e r a c t i o n o f a g i v e n c o r e e l e c t r o n w i t h a l l the o t h e r 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 o r a s o l i d i s d i v i d e d i n t o an i n t r a - a t o m i c term and an e x t r a - a t o m i c term. T h i s a l l o w s one t o e x p r e s s a g i v e n b i n d i n g energy as a sum o f two terms, one i n t r a - a t o m i c f r e e i o n term and one e x t r a - a t o m i c p o t e n t i a l : E?J(k) = E^(k,q) + V (2.52) The f i r s t term i s t h e 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 the b i n d i n g energy by the t o t a l p o t e n t i a l due t o a l l o t h e r atoms . 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 systems, w i t h con-1 4 8 4 9 s i d e r a b l e s u c c e s s ' ' . In one v a r i a t i o n o f t h i s 63 51 model Basch and Schwartz have shown t h a t the 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 from one m o l e c u l e t o a n o t h e r i s n e a r l y e q u a l t o (the n e g a t i v e ) s h i f t i n t h e p o t e n t i a l a t the n u c l e u s , -AV . T h i s ' n q u a n t i t y , AV , can be c a l c u l a t e d e a s i l y and r e a s o n a b l y 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 . D a v i s et_ a l used t h i s approach t o p r e d i c t b i n d i n g e n e r g i e s o f a number o f s m a l l m o l e c u l e s and t h e s e 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 v a l u e s . T h i s 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 model) as o n l y t h e ground s t a t e 55 56 p o t e n t i a l s are c o n s i d e r e d ' 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 the c a l c u l a t i o n 5 8 o f b i n d i n g energy s h i f t s D avis and S h i r l e y used a r e l a x a t i o n p o t e n t i a l model, RPM, where the c o r r e c t e d b i n d i n g energy s h i f t i s g i v e n as A E b ( k ) = -AV n - AV R (2.53) - 47 -Here, AV R i s t h e change i n p o t e n t i a l due t o r e l a x a t i o n , and, i n o r d e r t o compute AV t h e y used the ' e q u i v a l e n t i \ 57 c o r e s ' a p p r o x i m a t i o n i n t r o d u c e d by J o l l y . Here i t i s 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 c o m p l e t e l y 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 s h e l l from t h e n u c l e u s . T h i s would a l l o w one to approximate the change i n p o t e n -t i a l a t the n u c l e u s 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 , due t o the r e l a x a t i o n o f o u t e r e l e c t r o n s , t o the change t h a t would o c c u r i f the n u c l e a r charge were i n c r e a s e d by one u n i t . Now, V R i n e q u a t i o n 2.53, i s w r i t t e n i n the RPM a p p r o x i m a t i o n as V D = \ [V (* + 1) - V ] (2.54) R 2 n n 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 e x p e r i m e n t a l v a l u e s and the v a l u e s c a l c u l a t e d f o r AV H are i n f a i r l y good agreement w i t h ab i n i t i o e s t i m a t e s ^ . 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 The r e d u c t i o n i n energy o f the p a s s i v e e l e c t r o n s f o l l o w i n g p h o t o e m i s s i o n l e a d s t o the d e f i n i t i o n o f t h e - 48 -quantity termed relaxation energy, and t h i s i s the major contributor to the difference between the ex-perimentally observed binding energies and the Koopmans'theory based binding energies. The extent of o r b i t a l relaxation upon photoionization varies from atoms to molecules to s o l i d s , and the physical o r i g i n s of the relaxation energy for these systems w i l l be b r i e f l y discussed here. 2.11.1 Atoms Core io n i z a t i o n of an atom results i n a positive hole in the atomic o r b i t a l from which the electron ,is ejected, and t h i s causes the remaining electrons to relax (towards the hole) i n order to minimize the t o t a l energy of the system. The re-laxation energy, 6 E , , due to i o n i z a t i o n from re xax 6 5 o r b i t a l k can be written as the sum of three terms , S E , ( k , n ) = ^ 5 E , (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 of the k-th o r b i t a l and the passive o r b i t a l s respectively. $E_ , _ (n'<n) i s the contribution to the i c XaX relaxation energy due to o r b i t a l s l y i n g deeper than the active s h e l l , n. This term was shown to be ft rr n e g l i g i b l e by Hedin and Johansson by dir e c t calcu-lat i o n s for Na, K and t h e i r ions. The contribution from i n t r a - s h e l l relaxation to the t o t a l relaxation energy i s of intermediate magnitude. This term o r i g i -nates from the fact that the removal of an electron from the s h e l l , n, causes a reduction i n the average e l e c t r o -s t a t i c repulsion between the passive electrons i n that 6 5 shell. Hedin and Johansson calculated a value of 2.9eV for the L s h e l l of sodium and a value of 1.2eV for the M s h e l l of potassium. The outer s h e l l relaxation term i s by far the largest contributor to the t o t a l relaxation energy i n atoms as these outer s h e l l electrons experience an increase in the nuclear charge by approximately one unit. The r e l a t i v e magnitude of this term decreases with increasing n, which i s understandable, and according to Hedin and Johansson's cal c u l a t i o n on potassium, the outer s h e l l relaxation term provides 96 and 82% of the t o t a l relaxation energy for Is and 2s io n i z a t i o n s , respectively. - 50 -A number o f methods are a v a i l a b l e f o r the e s t i m a t i o n o f r e l a x a t i o n energy f o r a t o m s ^ 6 6 The method s u g g e s t e d by S h i r l e y and l a t e r e x t e n -70 s i v e l y used by h i s co-workers i s r e l a t i v e l y s t r a i g h t -f o r w a r d . T h i s method makes use o f t h e p o l a r i z a t i o n p o t e n t i a l approach o f Hedin and J o h a n s s o n ^ 5 , and the e q u i v a l e n t c o r e s a p p r o x i m a t i o n which was f i r s t used 5 7 by J o l l y . E s s e n t i a l f e a t u r e s o f t h i s model can be summarized by the f o l l o w i n g e q u a t i o n s 6 E r e l a x = " e k " E b ( k ) < 2' 5 6> where E^(k) and are the b i n d i n g and o r b i t a l e n e r g i e s o f t h e k - t h o r b i t a l r e s p e c t i v e l y . Now a c c o r d i n g t o the fi 5 Hedin and Johansson p o l a r i z a t i o n p o t e n t i a l model , 6 E r e l a x ( k ) = 1 ^ k^ pJV (2'57> where, V = E (V.(N-1,Z) - V . ( Z ) ) (2.58) j£k 3 Here, V R i s t h e ' r e l a x a t i o n p o t e n t i a l ' f o r t h e i o n i z a t i o n o f the k - t h o r b i t a l . V^(z) r e p r e s e n t s the Coulomb p l u s - 51 -exchange p o t e n t i a l due t o the j - t h o c c u p i e d o r b i t a l and V j ( N - l , j=f=k ,Z ) i s t h e Coulomb p l u s exchange p o t e n -t i a l due t o the j - t h o r b i t a l i n t h e i o n i c s t a t e w i t h a h o l e i n the k - t h o r b i t a l . The use o f t h e e q u i v a l e n t c o r e s a p p r o x i m a t i o n a l l o w s one t o r e p l a c e the h o l e s t a t e i n t e g r a l s i n element Z by t h e c o r r e s p o n d i n g ground s t a t e i n t e g r a l s i n element (Z+l) and t h i s r e s u l t s i n t h e f o l l o w i n g e x p r e s s i o n , 5 E r e l a x = 7 ^ IV " < *k I ^ R I Vz> (2'59> A l t h o u g h , the i n n e r - s h e l l and i n t r a - s h e l l r e l a x a t i o n s a r e 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 a re i n good agreement w i t h b o t h the v a l u e s o b t a i n e d 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 and e x p e r i m e n t . The 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 p r o c e s s e s i s f u r t h e r i l l u s t r a t e d by the ob-s e r v a t i o n s t h a t 6E , (k,n) de c r e a s e s u n i f o r m l y w i t h r e l d x i n c r e a s i n g n and <5 E , (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 and n. 2.11.2 M o l e c u l e s 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 a t o m i c c e n t r e o f a m o l e c u l e can l e a d t o a charge r e d i s t r i b u t i o n - 52 -5 8 66 70 within the molecule. Shirley and co-workers ' ' have sub-divided the relaxation energy for a given core ionization process into two terms; an i n t r a -atomic term which can be treated s i m i l a r to the case of atoms, and an extra-atomic term which includes a l l relaxation processes involving electrons situated on other atomic centres, due to the charge r e d i s t r i b u t i o n caused by p o l a r i z a t i o n of the electrons towards the posit i v e hole. Davis and Shirley have calculated the f i n a l - s t a t e atomic charges using CNDO/2 molecular o r b i -5 6 t a l s i n the RPM approach , for a number of small mole-cules . The relaxation energy for a given core l e v e l i s expected to increase from a free atom to a diatomic molecule and additional ligands would allow further enhancement of 5E , . However, the relaxation energy relax 3 J does not increase i n d e f i n i t e l y with increasing molecular s i z e . For example the experimental binding energy s h i f t for C l s i n the alkane series from CH^ to n-C^H^^ i s 0.32eV 71 and the same s h i f t for n-C gH 1 8 to n - c i 3 H 2 8 1 S 0.08eV 2.11.3 Solids The extent and the nature of relaxation upon core ion i z a t i o n in s o l i d s d i f f e r s from in s u l a t o r s , to semi-- 53 -conductors, to conductors. According to Fadley and 49 co-workers the binding energy associated with the i o n i z a t i o n of an o r b i t a l k at a p a r t i c u l a r s i t e i n a molecular or i o n i c s o l i d can be separated into a l o c a l contribution and a l a t t i c e contribution. The t o t a l relaxation energy for the above process, similarly., can be given as the sum of a l o c a l contribution term and a term due to l a t t i c e p o l a r i z a t i o n , 6 E r e l a x = 6 E r e l a x ( k ' l o c a l ) + 6 E r e l a x <k ^ t i c e ) (2.60) The 6E .. (k,local) term can be treated as discussed 3T6 X 3.X before and for large molecules or ions the t o t a l relaxation energy i s represented, mainly, by t h i s term. Contribution due to l a t t i c e p o l a r i z a t i o n i n molecular l a t t i c e s i s l i t t l e known. However, the 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 of i o n i c c r y s t a l s . 49 Fadley and co-workers were the f i r s t to discuss the p o l a r i z a t i o n energy term for i o n i c l a t t i c e s , based on 72 a model described by Mott and Gurney , and t h e i r r e s u l t s indicate that t h i s term i s of the order of leV or less for a series of potassium s a l t s . The largest values for l a t t i c e p o l a r i z a t i o n i s expected for monovalent, mono-atomic ions. Nothing more w i l l be said here about relaxation e f f e c t s i n s o l i d s . As a part of the work described i n t h i s - 54 -thesis involved the experimental determination of core binding energy s h i f t s between free metal atoms and the standard state, the relaxation e f f e c t s i n the metallic state which are largely responsible for the said 'phase t r a n s i t i o n s h i f t ' w i l l be discussed next i n a separate section. 2.11.4 Core Level Binding Energy Shift s i n Metals The experimentally determined binding energies for conductors have been found to be considerably lower than the calculated values, even a f t e r allowing for 6 6 f i n a l state relaxation, and thus Shirley suggested that the phenomenon of extra-atomic relaxation can be used to explain t h i s difference. According to Shirley and co-workers^' , the t o t a l relaxation energy following core i o n i z a t i o n i n a conductor can be written as, 6 E , (k) = 6 E . . + 6 E ^ (2 .61) relax i n t r a extra where SE. , i s the intra-atomic relaxation term which i n t r a can be treated as i n the case of atoms, and 5 E e x t r a 1 S 6 6 the extra-atomic relaxation. The procedure Shirley - 55 -used t o c a l c u l a t e the r e l a x a t i o n energy i n atoms has 70 been a p p l i e d t o m e t a l s by Ley and co-workers and eqn. 2.59 can now be r e w r i t t e n as r e l a x 2^  y k 1 R | y k Z+l y k 1 R | y k Z' i n t r a (2.62) + 7 ( < * k | V R I V z + l ~ ^ k l ^ K ^ e x t r a where the d i f f e r e n t t erms, by now, are s e l f - e x p l a n a t o r y , I t i s now w e l l known t h a t the e x p e r i m e n t a l core 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 are s y s t e m a t i c a l l y s e -v e r a l eVs l o w e r than t h o s e o f t h e c o r r e s p o n d i n g f r e e 66 70 73—79 atoms ' ' . T h i s core b i n d i n g energy s h i f t (or phase t r a n s i t i o n s h i f t ) , AE^(k,M,A) can be w r i t t e n as A E£(k,M,A)=EjJ(k,A) - E^(k,M) ( 2 ' 6 3 ) where E^(k,A) and E^(k fM) are the vacuum r e f e r e n c e d c o r e b i n d i n g e n e r g i e s f o r the f r e e atom and the condensed phase ( m e t a l l i c s t a t e ) r e s p e c t i v e l y . The q u a n t i t y , AE_J(k,M,A) i s p o s i t i v e 6 6 ' 7 0 ' 7 3 " 7 9 . The phase t r a n s i t i o n s h i f t i s b e l i e v e d t o be caused by a number o f f a c t o r s such as i . S c r e e n i n g o f t h e v a c a n t o r b i t a l v i a e x t r a - a t o m i c r e l a x a t i o n o f the m e t a l v a l e n c e e l e c t r o n s . - 56 -i i . Changes i n the repulsive p o t e n t i a l experienced by the core electrons i n metals. i i i . 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 configuration i n the vapor phase i s x 2 x+1 1 nd (n+1)s as opposed to the nd (n+1)s configuration that represents the s o l i d . Chromium which exhibits 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 series i s an exceptional case where i t has the same ground state configuration i n , both, the free atom and the metal These factors are expected to operate d i f f e r e n -t i a l l y to reduce the inner core l e v e l binding energies more than those for the outer l e v e l s and extra-atomic relaxation i s by far the single largest contributor to the phase t r a n s i t i o n s h i f t 6 6 ' 7 0 ' 7 6 ' 7 8 . Now considering only the extra-atomic relaxation, one can write for AE^(k,M rA), AEb>,M,A)= I ^ k ^ p J V z + l " ^ k l ^ V z W r a ( 2' 6 4 ) 7 8 Shirley and co-workers calculated the phase t r a n s i t i o n s h i f t for the f i r s t t h i r t y elements using t h i s r e l a t i o n -ship, and to evaluate these inte g r a l s they used a theore-t i c a l model based on the assumption that extra-atomic - 57 -relaxation occurs through screening of the hole state by the formation of a semilocalized exciton. Further, they assumed that the exciton state has the symmetry of the lowest unbound state i n the conduction band and that the exciton wave function i s found only i n the neighbour-hood of the hole state. The values calculated for phase t r a n s i t i o n s h i f t s using this model are larger than the experimental values, mainly because the atomic state on which i t i s based should be more l o c a l i z e d than the exciton state. However, t h i s model predicts the trends of binding energy s h i f t s rather accurately, i n d i c a t i n g the v a l i d i t y of the model. 7 6 Recently Beck and Nicolaides estimated the phase t r a n s i t i o n s h i f t s for metals using the above model and e s s e n t i a l l y the same assumptions. Their i n t e r p r e t a t i o n of t h i s model i s as follows. Let the atomic configuration c h a r a c t e r i s t i c of the ni hole state i n the s o l i d be ( n & ) 4 £ + 1 (mI) q(S,L) . (q<4l+2) ' min ^ where ml" i s the valence sub-shell of lowest energy which i s not completely f i l l e d . Now, the free atomic approxi-mation to the e x c i t o n i c state can be written as . (nz) 4 1 + 1 (mji) q + 1(S,L) - 58 -and the binding energy s h i f t can be written as AE^ = E ( . . . ( n j c ) 4 * + 1 . . . ( m D q ( S , L ) . ) -D mm E ( . . . (ru) 4 £ + 1 . . . ( m l ) q + 1 (S , L ) m i n ) (2.65) AE^ i s evaluated from separate ASCF calculations and here i t i s possible to precorrect the binding energies of the two phases i n case there i s a configuration change upon going from free atom to s o l i d . This method gives values which are in good agreement with experiment, and once again the predicted values are higher than the expe-rimental values due to reasons discussed e a r l i e r . o 77 Johansson and Martensson used a Born-Haber cycle to calculate the phase t r a n s i t i o n s h i f t s using available thermochemical data. 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 at a p a r t i c u l a r s i t e of the metal, i s considered equivalent to the creation of an impurity s i t e i n an otherwise perfect c r y s t a l . Then they used the approximation that t h i s f i n a l state i s equivalent to a pure c r y s t a l (Z) i n which an impurity Z+l i s dissolved, and then used ground state thermo-chemical data available for Z and Z+l metals to compute the phase t r a n s i t i o n s h i f t . This method empirically estimates the binding energy s h i f t s referenced to the Fermi l e v e l , and the predicted values are i n reasonable 77 agreement with experiment - 59 -A l l thfree methods mentioned here use the equivalent cores approach to approximate the f i n a l state. The core l e v e l binding energy s h i f t s estimated by using the impu-77 n t y model do not depend on which p a r t i c u l a r inner s h e l l i s ionized because, the Z+l approximation, when used in. the simplest way, does not make any discrimination between the 75 core l e v e l s . This 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 binding energies of rare-gas atoms embedded i n metal f o i l s and these values are 2-5eV 44 lower than those reported for free atoms . As the i n t e r -action between the gas atoms and the host metal atoms i s more of a physical nature, t h i s s h i f t may be i n d i c a t i v e of the degree of extra-atomic relaxation i n the m e t a l l i c state. According to the energy sum rule discussed e a r l i e r i n t h i s chapter (eqn. 2.48, 2.49), o r b i t a l relaxation should r e s u l t i n multicomponent structure i n the XPS spectra. This w i l l be discussed in some d e t a i l i n the next section, however, one i n t e r e s t i n g feature regarding the XPS spectra of metals i s worth some mention here. As described before, core ionization of metals involves a large relaxation energy which means that there must be a f a i r l y large pro-b a b i l i t y for multiple excitation processes. However, no discrete peaks have been observed i n the x-ray photoelectron spectra of metals. This may be due to the fact that i n metals the multiple electron ex c i t a t i o n processes i n v o l -ve the conduction bands, r e s u l t i n g i n a shake up (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 that the relaxation energy i s manifested as a broad background on the high binding energy side of the main peak. 2.12 Multicomponent Structure in XPS The binding energy of an electron for a given i o n i z a t i o n process, as defined by eqn. 1.2, depends on the energies of the i n i t i a l and the f i n a l state. Various i n i t i a l state and f i n a l state e f f e c t s can a l t e r the i n i t i a l state and the f i n a l state t o t a l energies, r e s u l t i n g i n a series of binding energies for a given i o n i z a t i o n process. This leads to multicomponent structure i n u l t r a v i o l e t and x-ray photoelectron spectra. In this section some of these e f f e c t s , as related to XPS w i l l be discussed b r i e f l y . 2.12.1 Spin-Orbit S p l i t t i n g Spin-orbit s p l i t t i n g arises from a coupling of spin 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-turbation which i s readily i d e n t i f i a b l e i n the photoelectron spectra of heavy atom systems. In atoms, spin-orbit s p l i t t i n g - 61 -has been well characterized by r e l a t i v i s t i c s e l f -consistent wave functions. For a closed s h e l l of £>0, two l e v e l s arise with j = Z+?j- and j = z—j where a and j r e f e r to o r b i t a l and t o t a l angular momentum. The j = £—j l e v e l for which the spin-orbit potential i s a t t r a c t i v e , i s more penetrating than the j=£+j l e v e l and as a r e s u l t the former i s of higher binding energy. These two l e v e l s , therefore, lead to two photo-electron l i n e s . The t o t a l i n t e n s i t i e s of a l l photoelectron peaks a r i s i n g from ionization i n a given subshell are pro-portional to the one electron cross section of that subshell m u l t i p l i e d by the occupancy of the subshell. The inten-s i t y r a t i o of the two spin-orbit s p l i t peaks i s approxi-mately equal to the s t a t i s t i c a l r a t i o of l e v e l degeneracies, (2J+1) of the two peaks. Deviations from the s t a t i s t i c a l r a t i o can occur, p a r t i c u l a r l y near the threshold, as the cross sections of the two l e v e l s are not necessarily the same. The two components are separated i n energy by an amount (£+i-)£ according to the Lande i n t e r v a l rule, where i s the appropriate spin-orbit coupling constant. The s p l i t t i n g increases with the nuclear charge, Z, roughly 5 . . . as a function of Z . The spin o r b i t coupling constant 3 depends on the expectation value <l/r > for the subshell and the resultant doublet s p l i t t i n g can be very large for - 62 core l e v e l s . The trend i n doublet separation for sub-s h e l l s of a given p r i n c i p a l quantum number, namely np>nd>nf can also be explained on the basis of a de-crease i n penetration, and therefore a decrease i n <l/r >, with increasing azimuthal quantum number £. 2.12.2 Multiplet S p l i t t i n g When atoms, molecules or s o l i d s with incompletely f i l l e d outer subshell(s) are ionized, the u n f i l l e d s h e l l l e f t behind by photoemission can couple with the p a r t i a l l y f i l l e d outer s h e l l s leading to various possible non-degenerate el e c t r o n i c states. This w i l l lead to multiple peaks i n the photoelectron spectra. These multiplet e f f e c t s can occur for both core and valence emission. Multiplet s p l i t t i n g of core l e v e l spectra have been reported for paramagnetic free m o l e c u l e s 4 4 ' 8 2 and 83 84 systems containing both t r a n s i t i o n metal atoms ' and 85 86 rare earth atoms ' . A few comprehensive reviews on 87 88 multiplet s p l i t t i n g have appeared elsewhere ' , and a simple case w i l l be considered here to i l l u s t r a t e some int e r e s t i n g features of t h i s e f f e c t . Let us consider the following photoemission process, 63 -(n£) q(n' £ ' ) p (filled) (L,S) hv (n'£') p + photoelectron (2.66) where, n£ i s the subshell from which the electron i s emitted and n'£' i s the p a r t i a l l y f i l l e d valence sub-s h e l l . L and S are the t o t a l o r b i t a l and spin angular momenta, and and S^ represent the same i n the (N-l)-electron f i n a l state. The selection rule concerning the one-electron angular momentum of the photoelectron, & p n ' ^ s £p h=£+l and the conservation of t o t a l spin and t o t a l o r b i t a l angular momenta requires that for the f i n a l state ion, AS (2.67) AL = Lf-L=0 • • . , (2.68) The t o t a l i n t e n s i t y of a given f i n a l state w i l l be pro-89 portional to i t s t o t a l degeneracy , so that I ^ ( L f , S f ) - (2S f+l) (2L f+l) (2/69) - 64 -Now, for s o r b i t a l i o n i z a t i o n , AS = S f - S = ± j (.2,70) AL = L f - L = 0 (.2.71) and t h i s w i l l lead to two f i n a l states, corresponding to S f = S ± j , and the in t e n s i t y r a t i o of 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 of 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 separation of the two peaks i s given by Van 9 0 Vleck's theorem , A[E b(ns)] = E f(L,S - j) - E f(L,S + i.) (2.73) A[E b(ns)] = (2S + 1) K n s^ n, £ l for S ^ 0 (2.74) A[E b(ns)] = 0 for S = 0 (2.75) Here K _, 0, i s the ns-n'£* exchange i n t e g r a l which can calculated from - 65 -2 0 0 0 0 a' K n s , n ' £ ' = I F T T oo P n s ( r l ) P n ' £ ' ( r 2 ) P n s ( r 2 ) P n ' J l ' ( r l ) ^ + l d r l d r 2 (2.76) where P (r)/r and P ,„,(r)/r are the r a d i a l wave functions ns n l 8 7 for the respective subshells and e i s the e l e c t r o n i c charge r < and r > are chosen to be the smaller and the larger of r^ and r 2 , respectively. Gaseous paramagnetic molecules such as NO and 0 2 show ©electron core binding energy s p l i t t i n g s analogous to those described by eqns. 2.72 - 2.76, where th e o r e t i c a l estimates of the s p l i t t i n g s from molecular o r b i t a l calculations give 44 values i n good agreement with experiment However, the si t u a t i o n i s less s a t i s f a c t o r y i n the case of systems with t r a n s i t i o n metal atoms. For example, 2 + photoionization of the 3s l e v e l of the Mn ion can lead to two f i n a l states: 3S 3p 6 3d 5 5S (S = 2, L = 0) or 3s 3p 6 3d 5 7S (S = 3, L = 0) A Hartree-Fock ca l c u l a t i o n of the energy s p l i t t i n g between these two f i n a l states, using eqn. 2.74 and 2.76 yi e l d s a - 66 -value of rol3eV°'1. The experimentally observed values 84 for the same s p l i t t i n g reported by Fadley and Shirley for MnF^ and MnO are approximately one h a l f of t h i s predicted value. These discrepancies between the s p l i t t i n g s and i n t e n s i t i e s estimated from free ion calculations and the experimental values obtained for t r a n s i t i o n metal compounds, arise from a number of sources, i . Neglect of the extent of decoupling i n the d o r b i t a l s due to strong f i e l d ligand bonding. i i . Neglect of the extent that the d electrons are delo-c a l i z e d due to the nature of the chemical bond. i i i . Neglect of co r r e l a t i o n e f f e c t s . Bagus and co-workers have shown that c o r r e l a t i o n e f f e c t s make the largest contribution to the observed 91 3 + discrepancy . Their Hartree-Fock c a l c u l a t i o n on Mn f i n a l states, using wave functions with configuration in t e r a c t i o n produced a result which i s in very good agree-ment with experiment, even without including the chemical bonding e f f e c t s . According to these multiconfigurational 7 Hartree-Fock calculations the S multiplet i s e s s e n t i a l l y 5 unchanged by the configuration i n t e r a c t i o n . But, for S, - 67 -configurations which r e s u l t from t r a n s f e r r i n g one 3p electron to the 3S o r b i t a l and another 3p electron to a 3d o r b i t a l (in a l l the d i f f e r e n t ways consistent with the angular momentum of the mu l t i p l e t ) , can mix very strongly with the one-electron configuration, $ 1( 5S) = 3 s 1 ( 2 S ) 3 p 6 ( 1 S ) 3 d 5 ( 6 S ) Here, the terms which r e s u l t from L,S coupling of the subshell to the l e f t are given i n parenthesis. The con-5 figurations which mix strongly with $p ( S) are, $ 2( 5S) = 3 s 2 ( 1 S ) 3 p 4 ( 3 P ) 3 d 6 ( 3 P 1 ) $ 3( 5S) = 3 s 2 ( 1 S ) 3 p 4 ( 3 P ) 3 d 6 ( 3 P 2 ) 5 2 1 4 1 6 5 $ 4 r S ) = 3s^( J-S)3p*( 1D)3d brD) 3 3 6 P-_ and ? 2 represent 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. This configuration mixing w i l l r e s u l t i n at lea s t a f o u r f o l d manifold of states, and the lowest energy 7 component w i l l be moved toward S s i g n i f i c a n t l y . The c a l -7 5 culated separation between S and the lowest energy S 91 component i s 4.7eV which i s i n better agreement with - 68 -the experimental value of 6.5eV for MnF2"*1. The r e l a t i v e i n t e n s i t i e s of the peaks can now be predicted using the sudden approximation r e s u l t of eqn. 2.4 7. However, some of the peaks predicted by the above method may be too weak to be experimentally observed, i n fact 5 2 + only three of the four possible peaks for S of Mn 92 have been observed . These configuration i n t e r a c t i o n calculations also explain the deviation of the experimental 5 7 i n t e n s i t y r a t i o from the r a t i o of 5/7 for S/ S predicted 2 + by simple multiplet theory (eqn. 2.72) for Mn The analysis of m u l t i p l e t - s p l i t structure produced by photoionization of non-s core l e v e l s i s not as s t r a i g h t -forward as that described here for s i o n i z a t i o n of para-magnetic compounds. Coupling of the non-zero o r b i t a l angular momentum and spin of j o r the na o r b i t a l with the p a r t i a l l y f i l l e d valence o r b i t a l ( s ) can occur i n various ways leading to more than two f i n a l states. Here again, the simplest procedure that can be used for 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 multiplet theory For better quantitative descriptions configuration i n t e r -action and chemical e f f e c t s have to be included and these 8 7 9 3 are discussed i n d e t a i l elsewhere ' Extensive s a t e l l i t e structure seen i n paramagnetic t r a n s i t i o n metal compounds can also be produced by electron - 69 -shake up. In fact i t i s believed that most of t h i s structure i s due to shake up and t h i s makes the detection of multiplet structure somewhat ambiguous at times. More w i l l be said about t h i s l a t e r , in the chapter on the x-ray photoelectron spectroscopy of some t r a n s i t i o n metal acetylacetonate vapors. 2.12.3 Multielectron Excitations If an i o n i c state produced by photoionization can be described by a wave function that includes excited con-figurations, then i t i s possible that the ground state may i n t e r a c t with these excited states and there i s a f i n i t e p r o b a b i l i t y that the f i n a l state may end up as one of these excited states. There w i l l be a peak i n the photoelectron spectrum corresponding to each of these excited states, and t h e i r positions and i n t e n s i t i e s with respect to the primary peak are related to the relaxation energy by the energy sum rule discussed i n Section 2.9. There are, i n general, an i n f i n i t e number of excited states associated with the primary state, however, only a few of these have observable i n t e n s i t i e s which can be up to 80% of the i n t e n s i t y of the main peak under favourable conditions. These peaks appearing i n the photo-electron spectrum at higher binding energies than the main (or primary) peak are usually termed co r r e l a t i o n or configu-ration i n t e r a c t i o n s a t e l l i t e s . - 70 -The f i r s t s a t e l l i t e s of t h i s type were observed 94-97 for Ne and Ar by Carlson, Krause and co-workers These s a t e l l i t e s were explained i n terms of two-electron t r a n s i t i o n s . Two types of two-electron t r a n s i t i o n s can occur in a photoemission process (n£) q(n*£') P — ( n O q ~ 1 ( n , £ ' ) P ~ 1 ( n " £ " ) 1 + photoelectron (2.77) (n£) q(n' V ) P — ( n £ ) q ~ 1 ( n , J l , ) p ~ 1 ( e £ " ) + photoelectron (2.78) The f i r s t process involves the t r a n s i t i o n of a second electron into an excited, but bound, state r e s u l t i n g i n a photoelectron peak at a k i n e t i c energy lower than the main l i n e . This process i s known as "shakeup" . The second process involves the exci t a t i o n of a second electron to a continuum state, e£", r e s u l t i n g i n a continuous spectrum on the low k i n e t i c energy side of the main peak. This i s known as "shakeoff". I f i t i s assumed that the i n i t i a l and the f i n a l states are described by a single e l e c t r o n i c configuration, then the shakeup and shakeoff p r o b a b i l i t i e s can be calculated using eqn. 2.38. For a s t r i c t l y two-electron t r a n s i t i o n , i „ i 4>nii / with a l l the other passive o r b i t a l s remaining - 71 -v e r y n e a r l y the same d u r i n g the e x c i t a t i o n p r o c e s s ( i . e . f r o z e n o r b i t a l s ) , the p r o b a b i l i t y , P n,^, ^ n „ £„ 9 8 o f t h e s a i d t r a n s i t i o n can be appro x i m a t e d as Pn'£' + n»£» " N n ' £ ' ^V^'V*'* I ' ' <2-79> where N ,„, i s t h e o c c u p a t i o n number o f t h e n ' A ' sub-n £ ^ s h e l l and R ,„, and R „ n„ are r a d i a l f u n c t i o n s f o r t h e n £ n £ i n i t i a l and f i n a l s t a t e s . The o v e r l a p i n t e g r a l i n eqn. 2.79 w i l l be non-zero o n l y i f £'=£", and t h i s r e s u l t i s o f t e n termed the 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 are a l s o p r e d i c t e d t o f o l l o w a monopole r u l e as i n d i c a t e d by eqn. 2.3 8 A J = A L = A S = A M = A M ^ = A M G = ATT = 0 (2.80) where J i s t h e quantum number f o r L + S* and TT i s t h e o v e r a l l s t a t e p a r i t y . F o r example, t h e 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 2 from the I s l e v e l o f Ne l e a d s t o an i o n i c s t a t e o f S symmetry which when c o u p l e d t o a continuum f u n c t i o n o f p symmetry r e s u l t s i n a -^ P s t a t e i n accordance w i t h the d i p o l e s e l e c t i o n r u l e f o r p h o t o i o n i z a t i o n . A c c o r d i n g 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 o f t h e t y p e s 2p-*np and 2s-*-ns a r e a l l o w e d , as t h e r e s u l t a n t shakeup s t a t e s a re o f the same symmetry as t h a t o f the p r i m a r y s t a t e . A l t h o u g h t h e s e o n e - e l e c t r o n d e s c r i p t i o n s can 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 a c c u -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 s a t i s f a c t o r y i n the case o f p r e d i c t e d i n t e n s i t i e s . A l s o , some s a t e l l i t e s o b s e r v e d e x p e r i m e n t a l l y are much l e s s f a v o u r a b l y d e s c r i b e d by t h i s mechanism. F o r example, i n Ne, the 2p np monopole e x c i t a t i o n accompanying the I s p h o t o e m i s s i o n can l e a d t o 2 5 3 2 two f i n a l i o n i c s t a t e s , 2s 2p np( S) l s ( S) and 2 5 1 2 2s 2p np( S) I s ( S ) , and b o t h o f the s e would have z e r o o v e r l a p w i t h t h e i n i t i a l s t a t e i f the 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 i n i t i a l s t a t e and em p l o y i n g Koopmans' a p p r o x i m a t i o n f o r the f i n a l s t a t e o r b i t a l s . However, two s a t e l l i t e s c o r r e s p o n d i n g t o 2 5 l s 2 s 2p 3p a r e e x p e r i m e n t a l l y o b s e r v e d . In t he case o f A r , the 3s p h o t o e l e c t r o n spectrum shows a br o a d peak s e p a r a t e d by about lOeV from t h e 99 main peak t o the h i g h b i n d i n g energy s i d e , and from o p t i c a l d a t a , i t has been shown t h a t t h i s s e p a r a t i o n 1 6 2 matches the energy d i f f e r e n c e between 3s 3p ( S) and 2 4 1 2 3s 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 and t h i s t r a n s i t i o n cannot be f a v o u r a b l y d e s -c r i b e d u s i n g a s i m p l e s i n g l e c o n f i g u r a t i o n model. - 73 -Spears and co-workers have shown that these two states mix very strongly with each other, thereby making the multielectron t r a n s i t i o n highly probable. These s a t e l l i t e s 9 9 are c a l l e d configuration interaction s a t e l l i t e s , and this d e f i n i t i o n covers shakeup s a t e l l i t e s as a special case where the corresponding t r a n s i t i o n i s a one-electron excitation to a configuration interaction state. Martin and Shirley have reported configuration in t e r a c t i o n calculations for Ne to obtain i n t e n s i t i e s which are in good agreement with experiment. The calcu-lated i n t e n s i t i e s are, in general, lower than the experi-mental values and Martin and Shirley have also shown that, i f configuration interaction i s included in the i n i t i a l state, the calculated values become considerably larger bringing them much closer to the experimental values. This r e s u l t showed that i n i t i a l state configuration i n t e r -action plays a s i g n i f i c a n t role along with f i n a l state configuration interaction in determining the s a t e l l i t e i n t e n s i t i e s . I n i t i a l state configuration interaction has been used to explain the conjugate s a t e l l i t e s observed for mercury 1 0 0. Valence l e v e l i o n i z a t i o n of Hg([core] 6 s 2 (^ S) ) 2 produces the primary i o n i c state [core] 6s( S) as well as 2 the conjugate state [core] 6p,(_..p)-r and these two configu-rations cannot mix with each other. Berkowitz and coworkers - 74 -have shown that the ground s t a t e of Hg i s r e p r e s e n t e d by a mixture o f the two n e a r l y degenerate c o n f i g u r a -2 1 2 1 t i o n s [core]6s ( S) and [core]6p ( S) and t h i s i n i t i a l s t a t e c o n f i g u r a t i o n mixing lea d s t o a non-zero o v e r l a p between the i n i t i a l s t a t e and the conjugate s t a t e . T h i s e x p l a i n s the observed s a t e l l i t e s t r u c t u r e c o r r e s -ponding to the conjugate s t a t e , and s i m i l a r s t r u c t u r e s have a l s o been observed f o r cadmium1*"*1 and lead 1*"* 2 vapors. Strong s a t e l l i t e s have a l s o been observed f o r t r a n s i t i o n metal and r a r e - e a r t h compounds 1^ 3 1 1 1 . Although, these can be co n s i d e r e d as c o r r e l a t i o n s a-t e l l i t e s they are u s u a l l y l a b e l l e d as charge t r a n s f e r s a t e l l i t e s , mainly due to a number of s p e c i f i c e x p e r i -mental o b s e r v a t i o n s . i . The s a t e l l i t e s are absent when the 3d o r b i t a l s are completely f i l l e d 1 ^ . i i . The s a t e l l i t e s may be p r e s e n t when the 3 d o r b i t a l s . 110 are empty i i i . S a t e l l i t e s e p a r a t i o n s and i n t e n s i t i e s o f a given 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 , with the energy s e p a r a t i o n between the s a t e l l i t e and the main l i n e f o l l o w i n g the n e p h e l a u x e t i c s e r i e s i n o c t a -h e d r a l compounds1''"2. - 75 -These observations can be explained f u l l y by a ligand-to-metal charge transfer mechanism which would accompany the photoionization repre-senting an attempt to screen the core hole produced by photoemission. This model was f i r s t put forward by K i m 1 1 3 ' 1 1 4 and more quantitative discussions C , -, J U T 106 , , , , _ 107 were followed by Larsson , and Asada and Sugano The charge transfer process has been shown to obey the monopole selection r u l e . For example, i n octahedral symmetry, the e b •+ type t r a n s i t i o n i s monopole allowed (where the superscripts b and a refer to bonding and antibonding r e s p e c t i v e l y ) . Further, these two o r b i t a l s are represented by a l i n e a r combination of 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 ligand o r b i t a l and being mainly metal 3d type o r b i t a l . The f i n a l state i s considered to be a l i n e a r combination of the 107 two configurations , *, = (core hole) ( e b ) n ( e a ) m 1 g g and $ 9 = (core hole) ( e b ) n _ 1 ( e a ) m + 1 - 76 -where $^  i s the f i n a l state with no change in valence subshell occupations and $ 2 l S t n e f i n a l state r e s u l t i n g from a one-electron ligand^to-metal charge transfer. The l i n e a r combination of these two f i n a l states results in two f i n a l states, 4 = C l l h + C12 $2 A = C21 $1 + C22 $2 This w i l l lead to two photoelectron peaks of which the i n t e n s i t i e s can be calculated by using eqn. 2.4 7. In t h i s model corrections are made due to hole induced covalency and the values calculated for r e l a t i v e inten-s i t i e s , peak positions and widths are in reasonable • , u . _ , .. . 106-107 T. , agreement with the experimental r e s u l t s . It has been suggested that the shortcomings of t h i s model can be remedied by including more than two configurations i n 107 the f i n a l state configuration interaction scheme These charge transfer s a t e l l i t e s in t r a n s i t i o n metal core l e v e l spectra w i l l be further discussed i n Chapters Five and Six. - 77 -The study of s a t e l l i t e structure can obviously help in an understanding of the multielectron pro-cesses accompanying photoioniza tion. 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B 11, 2177 (1975) - 87 -CHAPTER THREE THE GAS PHASE X-RAY PHOTOELECTRON SPECTRO-METER; DESIGN AND PERFORMANCE 3.1 I n t r o d u c t i o n In 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 the e x p e l l e d e l e c t r o n s o r i g i n a t i n g 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 then e n t e r an e l e c t r o n s p e c t r o m e t e r where they are energy a n a l y s e d and s u b s e q u e n t l y d e t e c t e d . The r e s u l t a n t p u l s e s a re counted and s t o r e d i n a s u i t a b l e manner f o r subsequent d a t a a n a l y s i s . A b l o c k diagram o f t h e 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 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 , i l l u s t r a t i n g t h e main components, i s shown i n F i g . 3.1. The b a s i c demands on such an e l e c t r o n s p e c t r o m e t e r 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 s h i f t s 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 s h o u l d B l o c k d i a g r a m o f t h e g a s 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 o m e t e r . F i g . 3.1. B l o c k diagram of t h e 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 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 C h e m i s t r y . - 89 -be as high as possible. However, s e n s i t i v i t y and resolution, as i n many forms of spectroscopy, 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 sort of a compromise has to be reached when designing such a spectrometer. There are additional problems i f the spectro-meter i s to be used i n gas phase studies. In the gas phase, a high pressure i s required i n the region of ionization in order to obtain a reasonable signal strength. At the same time the pressure in the rest of the system has to be s u f f i c i e n t l y low that the ejected electron i s prevented from su 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, before i t reaches the detector. This can be achieved, to a large extent, by employing d i f f e r e n t i a l pumping. Similar low pressure conditions are necessary for e f f e c t i v e operation of the x-ray source. The gas phase x-ray photoelectron spectrometer used i n the work described i n t h i s thesis was con-structed i n the Department of Chemistry at the University of B r i t i s h Columbia. In t h i s chapter the spectrometer w i l l be described in some d e t a i l with special reference to the performance,data acquisition and handling. A b r i e f description of the spectrometer has also appeared elsewhere 1 - 90 -3.2 The Spectrometer 3.2.1 The X-ray Source Unit The x-ray tube used i n t h i s study i s of the hot cathode type, where an anode of a suitable material i s bombarded with electrons produced by thermionic emission from a hot filament to y i e l d x-rays c h a r a c t e r i s t i c of the anode material. The cathode i n this case i s a 'bent h a i r p i n ' of 0.18 mm-diameter tungsten wire, semicircularly bent concentric with the anode (Figs.3.3, 3.4). The filament leads are approximately 0.5 cm apart, t h i s design minimizing current induced magnetic f i e l d s . A support rod i s provided at one end of the filament to prevent d i s t o r t i o n upon heating. An AC current i s used to heat the filament. The anode i s made of a copper tube with the front end sealed. This sealed front end has a l i p which i s uniformly 'pinched' around a 0.3 cm-thick disc of the desired anode material of the highest grade purity (Fig. 3.5). Although, the work described herein employed A l Ka x-rays, we have used Mg, Zr and Y anodes succesfully. This simple design allows s u f f i c i e n t thermal contact between the water-cooled F i g . 3.2. The University of B r i t i s h Columbia,Department of Chemistry,x-ray photoelectron spectrometer. F i g . 3.3. The x-ray tube assembly showing the tungsten filament,filament 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 . F i g . 3 . 4 . The x - r a y tube assembly. F i g . 3.5. The x - r a y t u b e anode i n d e t a i l . - 95 -copper tube and the target material. The laboratory water pressure of 70 p s i was found to be more than enough for cooling the anode under normal operating conditions. The x-ray tube i s maintained at ^2x10 6 t o r r under t y p i c a l operating conditions in order to prevent voltage breakdown, and to increase the filament l i f e t i m e . To maintain t h i s low pressure within the x-ray tube i t i s i s o l a t e d from the neighbouring source chamber (See F i g . 3.6) by using a 0.0025 mm aluminum f o i l window (supplied by A l f a Chemicals). However, when zirconium and yttrium anodes are used, with t h e i r lower energy x-rays, and decreased a b i l i t y to penetrate matter, a 2.5 yg/cm polystyrene f i l m i s employed instead of the aluminum f o i l . A rubber or Viton '0' ring i s used to seal the window to the x-ray tube. An added advan-tage of i s o l a t i n g the x-ray tube from the sample chamber i s that i t prevents the contamination of the anode and the filament by the corrosive gases and hence enhances th e i r respective l i f e t i m e s . To prevent the destruction of the x-ray tube window by overheating, the x-ray tube wall i s water-cooled. The window can also be destroyed by electron bombardment from the filament, but t h i s can be prevented by applying a very high p o s i t i v e p o t e n t i a l to the anode while main-- 96 -g a s i n aluminum windows s t a i n l e s s s t e e l t u b i n g f l a n g e c o o l i n g \ b r a s s f l a n g e 0 - r i n g h e a t e r (boron nitride) h e a t i n g w i r e (chromel) stainless steel tubing s a m p l e stainless steel heat shields g a s c e l l d e m o u n t a b l e b a s e e i n z e l l e n s t o a n a l y z e r F i g . 3.6. Schematic diagram of the spectrometer showing the x-ray tube and the old gas c e l l . - 97 -taining the filament at, or close to, ground p o t e n t i a l . This pos i t i v e p o t e n t i a l also ensures that electrons scattered from the anode are drawn back, and thus cannot s t r i k e the window. Under normal operating conditions the filament i s held at -170V and the t y p i c a l operating power for an aluminum anode i s ^350W (10 kV , 35 mA) . A grounded c y l i n d r i c a l s t a i n l e s s steel s h i e l d between the anode tubing and the filament serves to focus the electron beam from the cathode, onto the target surface (Fig. 3.3). This s h i e l d also ensures that no electrons can reach the back side of the anode. It i s necessary to maintain the anode as clean as possible at a l l times. Most of the anode contamination comes from the tungsten filament i n the form of both tungsten and absorbed impurities i n the filament. This contamination can be minimized by positioning the filament out of d i r e c t sight of the anode, and the stainles s s t e e l s h i e l d which i s used to focus the electrons also doubles as a protective b a r r i e r . The low pressure inside the x-ray tube i s maintained by using a 2 85 i / s e c . 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 to the x-ray tube through a water cooled b a f f l e which prevents backstreaming o i l vapor from contaminating the anode. 98 -The anode high voltage i s i s o l a t e d from the rest of the system by using a "hysol" spacer (Fig. 3.4) and the anode part i s connected to the x-ray tube by using nylon screws. As mentioned i n Chapter One, the primary l i m i t a -tion on instrumental resolution i s the band width of the x-rays. In addition to the x-ray l i n e s characteris-t i c of the anode material, a continuous spectrum depen-dent upon the primary electron energy i s also produced in these x-ray tubes. This continuous spectrum i s normally known as bremsstrahlung. The presence of bremsstrahlung radiation increases the background l e v e l of the photoelectron spectrum. However, the contribution from t h i s continuous spectrum to the background becomes less s i g n i f i c a n t at lower k i n e t i c energies ( i . e . core l e v e l spectra) as the proportion of background from i n e l a s t i c a l l y scattered photoelectrons increases. A more serious problem i s that of x-ray s a t e l l i t e l i n e s . For example, i n Mg and A l , in addition to the predominant Ka, 0 l i n e which, as mentioned e a r l i e r , i s i , z e s s e n t i a l l y an unresolved doublet, other less intense l i n e s are produced by x-ray t r a n s i t i o n s i n multiply ionized anode atoms as well as those t r a n s i t i o n s which involve the valence l e v e l s . In the case of A l (and Mg) there are two s a t e l l i t e s about lOeV to the high energy - 99 -side of the main x-ray l i n e which are produced by tr a n s i t i o n s involving the K hole of a doubly ionized (KL) atom. These are denoted as Ka^ and Ka^ and t h e i r i n t e n s i t i e s are approximately 8% and 4% respectively. In the photoelectron spectra these Ka^ and Ka^ s a t e l l i t e s from strong peaks can i n t e r f e r e and obscure weak peaks and care has to be taken in assigning photoelectron l i n e s produced by such r a d i a t i o n . For example, the Ka-j and Ka^ s a t e l l i t e s of Au 4 f ^ 2 4^7/2 c a n c o m ~ p l e t e l y mask the Au 5p^y 2 l i n e i f A l or Mg Ka radiation i s used to obtain the spectrum. This problem can be solved by using a monochro-2 3 mator ' . However, the increased resolution due to monochromatization i s accompanied by a decreased sensi-t i v i t y as a r e s u l t of the loss of i n t e n s i t y during the process. This loss i n s e n s i t i v i t y can be somewhat 3 minimized by using high power x-ray tubes . These employ rotating anodes i n order to minimize anode over-heating. In the present case a s t a t i s t i c a l method i s used to correct for the x-ray s a t e l l i t e s (see l a t e r ) . 3.2.2 The Gas C e l l s Almost a l l r e a d i l y obtainable gases and v o l a t i l e l i q u i d s have been studied by XPS and UPS. Higher tern-- 100 -peratures are therefore required to generate the free atoms and molecules studied 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 therefore 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 vaporized and unstable gaseous species may be studied. The two 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 sense. 3.2.2.1 The Old Gas C e l l A schematic. diagram of the o l d gas c e l l and a part 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 positioning of the gas c e l l with respect to the x-ray tube. The heater consists of a double threaded boron n i t r i d e cylinder on which chromel wire i s non-inducti-vely wound. This heater i s slipped around the s t a i n -less s t e e l tubing leading to the ion i z a t i o n chamber and so operates outside the vacuum system, thus avoiding destruction of the heating element by the gas under study. The gas c e l l i s e l e c t r i c a l l y i s o l a t e d (see later) from the source chamber by using a perspex ring as a high voltage stand-off. A rubber '0' r i n g - 101 -i s used to seal the gas c e l l to the source chamber and the gas c e l l i s held i n position by four nylon screws. The gas c e l l flange can be a i r or water-cooled to pre-vent overheating of the 'O' ring at gas c e l l tempera-tures i n excess of =400°C. Heat transfer from the ioni z a t i o n chamber to the brass flange i s also minimized by using a thin s t a i n l e s s s t e e l cylinder to connect the two parts. Here, the term ionization chamber refers to the bottom part of the gas c e l l within which the vapor i s exposed to the x-rays. Heat losses from the i o n i z a -tion chamber and from the heater are reduced by means of stainle s s steel shields. Room temperature gases are introduced from the top of the gas c e l l through a st a i n l e s s s t e e l tube as shown in F i g . 3.6, while so l i d s to be vaporized are placed inside a st a i n l e s s s t e e l cup which screws into the top of the io n i z a t i o n chamber. X-rays enter the ion i z a t i o n chamber through a window, having already passed through the x-ray tube window. The function of t h i s second window i s to prevent excessive gas losses from the gas c e l l . I t was found that even the smallest pin hole i n a window can decrease the count rate considerably. Normally, 0.0025 mm Al f o i l i s used as the gas c e l l window material. When Zr Mc and 2 .Y ML, x-rays are used, 2.5 ug/cm polystyrene f i l m can be used. - 102 -The io n i z a t i o n chamber i s made of pure copper and i t i s important to have a l l the surfaces of the inside chamber walls at a constant work function with good conductivity. In p a r t i c u l a r , i t i s desirable to avoid the formation of a non conducting oxide layer, and so the inside wall of the gas c e l l i s p e r i o d i c a l l y coated with benzene soot to prevent deterioration of the copper walls through reaction with the gas under study and to maintain f i e l d homogeneity within the ioni z a t i o n chamber. When polystyrene windows are used, the gas c e l l can only be heated to ^ 100°C. However, when aluminum windows are used i n conjunction with A l Ka x-rays, i t i s possible to achieve temperatures of approximately 500°C or higher with the upper l i m i t set to ^ 570°C (the melting point of the s i l v e r solder used in the construction of the gas c e l l ) . To date the highest temperature at which a species has been studied success-f u l l y using t h i s gas c e l l i s approximately 4 70°C. This was required to study magnesium atoms. Except for the calcium, strontium and barium spectra presented i n the next chapter a l l the other atoms and molecules reported in t h i s thesis were studied using t h i s gas c e l l . This design of the gas c e l l also allows for variable temperature studies since the heater may be removed and - 103 -the cavity f i l l e d with an appropriate refrigerant such as l i q u i d nitrogen or a dry ice-acetone mixture. In order to study transient species a threaded, 0.3 cm-diameter hole i s provided i n the gas c e l l at the l e v e l of the window. A tube made of the appropriate material for the species under study i s inserted into the opening in a d i r e c t i o n perpendicular to the plane of 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 to preserve f i e l d homogeneity, i s located d i r e c t l y opposite the i n l e t f o r sample pumping. In t h i s manner the gas can be fast pumped across the x-ray beam by the 2 85 £/sec d i f f u s i o n pump connected to the source chamber housing the gas c e l l . The sample i n l e t design allows for a short path ( =15 cm) between the ionization region 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 can be used to study a wide range of moderately v o l a t i l e materials i t s upper temperature range i s li m i t e d . To produce vapors of most metals, temperature in excess of 600°C are required, and so another high temperature gas c e l l was designed and constructed. The primary aim was to design a gas c e l l to f i t the e x i s t i n g spectrometer and the best s t a r t i n g point was the old gas c e l l . F i g . 3.7 shows - 104 -1 Stainless steel tubing 9 Boron nitride heater holder 2 Thermocouple 10 Pt wire 3 Heater connection 11 Bayonet fitting 4 Machinable ceramic 12 Removable heat-shield support ring 13 Sample holder (cup) 5 Flange cooling 14 Molybdenum nut 6 Brass flange 15 Demountable cavity 7 Viton 'o' ring 16 C window 8 Boron nitride 17 Window holder support tubing 3.7. A schematic diagram of the new high temperature gas c e l l . - 105 -a s c h e m a t i c r e p r e s e n t a t i o n o f the new h i g h t e m p e r a t u r e gas c e l l . The c r i t i c a l d i m e n s i o n s are unchanged. Only those major changes between t h i s new gas c e l l and t h e o l d gas c e l l w i l l be mentioned h e r e . I n s t e a d o f t h e t u b u l a r boron n i t r i d e h e a t e r i n the o l d gas c e l l , a new h e a t e r was d e s i g n e d . The main 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 w i t h a s p i r a l groove on each 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. T h i s h e a t i n g element i s p l a c e d i n a t h i n w a l l e d boron n i t r i d e cup (See t h e i n s e r t i n F i g . 3.7). These a r e h e l d t o g e t h e r by a r e f r a c t o r y cement ( m e l t i n g p o i n t ^2000°C). A c h r o m e l - a l u m e l thermocouple i s used t o measure the t e m p e r a t u r e . A V i t o n '0' r i n g i s used t o s e a l t h e gas c e l l t o t h e s o u r c e chamber. These '0' r i n g s can w i t h s t a n d a t e m p e r a t u r e o f ^200°C. By d e s i g n i n g the top p a r t o f the gas c e l l t o resemble a vacuum f l a s k , o v e r h e a t i n g o f t h e b r a s s f l a n g e was p r e v e n t e d . The b r a s s f l a n g e was a l s o a i r c o o l e d , and c o u l d be m a i n t a i n e d a t below 100°C, t h e r e b y p r e v e n t i n g d e f o r m a t i o n o f t h e p e r s p e x h i g h v o l t a g e s t a n d - o f f . The e n t i r e gas c e l l , e x c e p t f o r the b r a s s f l a n g e , window h o l d e r and the molybdenum nut which h o l d s t h e sample cup i n p l a c e , i s made o f s t a i n l e s s s t e e l . A l l - 106 -the j o i n t s are welded and the use of screws was avoided as these tend to st i c k at high temperatures. An addi-t i o n a l heat s h i e l d was used to prevent heat loss from the heater and the ionization chamber. To accomodate t h i s additional heat shi e l d , the outer diameter of the i o n i z a t i o n chamber had to be reduced. The ion i z a t i o n chamber i s a detachable cup which i s connected to the rest of the gas c e l l by means of a snug bayonet f i t t i n g which ensures s u f f i c i e n t heat transfer. The rather low melting point of Al (660°C) l i m i t s the use of 0.0025 mm Al f o i l as the window material. 2 2 20 ug/cm and 40 yg/cm C f o i l s were used instead. These carbon f o i l s are prepared by vacuum sublimation of carbon onto 3" x 1" glass s l i d e s , and were supplied 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 holder and, being f r a g i l e are allowed to dry i n the absence of any kind of a disturbance. The window holder i s b a s i c a l l y a copper ring (cross section i s shown i n F i g . 3.7) with copper wires spot welded to form a supporting mesh. These carbon windows are very f r a g i l e by virtue of t h e i r extremely small, ^0.0001 - 0.0002 mm, thickness and hence have to be handled extremely c a r e f u l l y . - 107 -It was found that the e l e c t r i c a l resistance of boron n i t r i d e breaks down at temperatures higher than 700°C, thus making the heater short to the gas c e l l at retarding voltages i n excess of %1000V. This results i n a breakdown of the retarding voltage used to scan the electron energies. This problem was solved by i s o l a t i n g the heater power supply from the main power l i n e using an i s o l a t i o n transformer. The highest temperature achieved by using t h i s gas c e l l was 1100°C. A spectrum of the 3d region of s i l v e r atoms was obtained at t h i s temperature (Fig. 3.8). However, the heating element burnt out before s u f f i c i e n t l y good counting s t a t i s t i c s were achieved. Various types of boron n i t r i d e heaters were t r i e d out, but none of these lasted long enough at 1100°C to produce a good enough spectrum. The gas c e l l has been maintained at ^1025°C for days without burning out the heater, but unfortunately, t h i s temperature i s not high 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 for a gas c e l l of th i s design, the l i m i t i n g factor being the melting point of platinum. The calcium, strontium and barium spectra reported i n t h i s thesis were obtained using t h i s new high temperature gas c e l l . - 108 -3 O o 8 0 i 6 0 -4 0 H 2 0 H 5 0 6 0 7 0 8 0 9 0 1 0 0 C h a n n e l n u m b e r F i g . 3.8. A preliminary spectrum of the Ag 3d region recorded at 1100°C using the new high temperature gas c e l l . E x c i t a t i o n source i s A l Ka x-rays. - 109 -3.2.3 The Ein z e l Lens The electrons leaving the gas c e l l through the opening i n the bottom of the gas c e l l are focused onto the entrance aperture of the analyser by a three-element lens (Fig. 3.9). The c h a r a c t e r i s t i c s of such lenses can 4 be found elsewhere . The three elements are of equal diameter and the r a d i a l axes of these cylinders include the r a d i a l axes of the ex i t hole from the gas c e l l and the entrance hole to the analyser. The top element i s provided with five rows of holes to f a c i l i t a t e pumping, in order to enable the electrons to have a c o l l i s i o n free path through the lens. The middle element i s is o l a t e d from the upper and lower elements by means of 2 mm-diameter sapphire b a l l s . The focusing i s achieved by grounding the two outside elements while applying a posit i v e voltage (be-tween + 150V and + 7 00V; determined empirically for maximum counts and optimum l i n e shapes) to the middle element. Such a lens i s also referred to as 'einzel' or 'unipotential' lens as opposed to an 'asymmetric voltage' lens i n which the three elements are supplied with three d i f f e r e n t voltages. This e i n z e l lens i s made of brass. - 110 -Fi g . 3.9. The three element einzel lens.The holes i n the top element f a c i l i t a t e pumping. - I l l -3.2.4 The Electron Energy Analyser and The Operating Mode of the Spectrometer. Electrons focused by the e i n z e l lens enter a hemispherical e l e c t r o s t a t i c analyser i n which two dimensional point-to-point focusing occurs af t e r 180° deflection i n the f i e l d between the two concentric hemispheres (Fig. 3.1). The electron dispersion pro-perties and focusing action of hemispherical e l e c t r o -5 s t a t i c analysers were f i r s t discussed by Purcell , and i t has subsequently been developed and i t s properties discussed by a number of researchers 6 1 0 . With the analyser set to pass electrons of energy E (eV) along a c i r c u l a r path of radius R where, the pot e n t i a l of the inner hemisphere, V^ n, should be set to R= (R. n + R out )/2 (3.1) V . i n = E Q(3 - 2 R/R.n) (3.2) while that on the outer hemisphere, V out' should be set to V out = E Q(3 - 2R/R o u t) (3.3) - 112 -where R n and R o u t r e f e r to inner and outer hemisphere r a d i i respectively. F o r equal entrance and e x i t hole diameters, w, and for an electron beam entering the analyser with a half angle of 0° then the analyser resolution AEj_/Eo i s given by AE, w = — (3.4) E 2R o where AE^ i s the f u l l width at ha l f maximum (FWHM) of the analyser contribution to a peak in a spectrum. An important implication of Eqn. 3.4 i s that the FWHM of a given peak depends on E Q . The analyser contribution to the FWHM can be kept constant f o r the entire range of k i n e t i c energies of the emitted electrons by preretarding or preaccelerating the electrons to the fixed analyser pass energy, E Q . The values for R. and R . for t h i s spectrometer in out r are 8.25 cm and 12.25 cm respectively, the hemispheres being made of s o l i d brass. These hemispheres are coated with benzene soot, which improves the experimental resolution considerably, and also greatly reduces the background due to scattered electrons. The entrance and ex i t holes are 1.6 mm i n diameter and the instrumental resolution calculated using Eqn. 3.4 i s =0.8%. For a - 113 -pass energy of 50eV the instrumental contribution to the FWHM of a peak i s - 0.4eV. This means that i f a 1 keV electron i s retarded to 50eV i t would produce an absolute energy resolution of 0.4eV, or a percentage resolution of the i n i t i a l k i n e t i c energy of 0.04%. A l -though t h i s resolution can be further improved by decreasing the entrance and e x i t s l i t widths i t can lead to a considerable loss i n s e n s i t i v i t y . The instrumental contribution to the FWHM can be changed by a l t e r i n g the analyser pass energy, E Q . This can be achieved by applying the appropriate voltages to the two hemispheres, which are supplied by a Harrison 6205 B Dual DC Power Supply. The retarding voltage i s applied between the gas c e l l and the upper element of the e i n z e l lens. The retarding voltage i s related to the binding energy of an electron k, E^(k) by the Eqn. Retarding Voltage = x-ray energy - E^(k)-E Q-C (3.5). where C i s a correction which includes the work function of the chamber and the retardation e f f e c t s due to a net pos i t i v e charge i n the cone of i o n i z a t i o n . More w i l l be said about t h i s i n the section on energy c a l i b r a t i o n . - 114 -Spectral scanning i s therefore achieved by varying the retarding voltage and detecting the electrons emitted whilst keeping the voltages on the analyser hemispheres, and hence the pass energy con-stant. 3.2.5 Helmholtz Coils A magnetic f i e l d of 1.OmG can resu l t i n a d i s -persion of about 0.2 mm for a hemispherical e l e c t r o -s t a t i c analyser with a 20 cm-radius and a 1000e.V electron measured with 0.04% resolution 1''" This makes i t important to keep the magnetic f i e l d as low as possible in the region of the source chamber and the analyser. In addition to the earth's magnetic f i e l d of approxi-mately 500 mG, stray f i e l d s caused by certain experimen-t a l arrangements, e.g. a wire wound furnace can be a serious problem. These f i e l d s can be cancelled by using Helmholtz c o i l s , or ferromagnetic shi e l d i n g such as Mu metal. The l a t t e r i s inconvenient due to 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 pairs of Helmholtz c o i l s , four feet square, mounted at ri g h t angles to each other are used. These c o i l s which com-prise 50 turns of 20 gauge insulated copper wire, are - 115 -powered by Lambda regulated DC power supplies (Model LH 122AFM) and may be i n d i v i d u a l l y adjusted to obtain optimum count rates and peak shapes. 3.2.6 The vacuum System Typical gas pressures required i n the ioni z a t i o n -2 chamber are from 10 to 1 t o r r . The pressure i n the rest of the system has to be considerably lower than th i s so that the ejected electrons are detected before under-going c o l l i s i o n s . The normal operating pressure i n the analyser region i s about 5 x 10 t o r r and t h i s low pressure i s maintained 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 analyser entrance s l i t . This i s provided 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 for fast pumping sample gases). Since the source housing communicates with the analyser only through the 1.6 mm-diameter opening, the analyser, as well as the detector, i s spared from attack by corrosive gases. The rather cumbersome task of frequent cleaning of the analyser i s thus avoided. - 116 -The analyser chamber i s pumped by a 1500 l/sec o i l d i f f u s i o n pump. Under normal operating conditions the x-ray tube volume i s i s o l a t e d from the rest of the spectrometer. However the two volumes can be u n i f i e d by opening a valve for rough pumping, thereby eliminating rupture of the delicate x-ray tube window. The pressure in the x-ray tube, source chamber and the analyser housing are monitored by using three separate ionization gauges (NRC 538, i n conjunction with a NRC ion gauge control unit, type 710B). Starting from atmospheric pressure normal operating pressures can usually be obtained in about 90 minutes. 3.2.7 Thfe Detector System The spectrometer geometry i s such that only the electrons ejected i n a d i r e c t i o n 90° to the d i r e c t i o n of the e x c i t i n g radiation can enter the analyser. The energy analysed electrons leave the e x i t hole and s t r i k e the detector which i n t h i s case i s a channel electron m u l t i p l i e r (Mullard B319 AL) operating i n the saturated mode. A voltage of +300V applied to the front end of the channeltron accelerates the electrons, and the signal - 117 -i s amplified across the detector by applying a positi v e voltage of +3.3kV to the output. Pulse counting i s used for data a c q u i s i t i o n and conventional pulse counting equipment i s used for t h i s purpose. The signal from the m u l t i p l i e r i s passed through a modified Varian type pre-amplifier to an amplifier/analyser (Nuclear Enterprises) and a rate meter (Nuclear Enter-prises) . The pulses are counted as a function of re-tarding voltage, repeated scanning i s performed and the data stored i n a Nuclear Chicago multichannel analyser. This was l a t e r replaced by a PDP 8/e computer to allow 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 section on the i n t e r f a c i n g of a PDP 8/e minicomputer to the spectrometer. 3.2.8 Performance The peak width AE^ measured from a spectrum i s made up of a convolution of a number of contributions. Assuming that a l l these components have Gaussian l i n e shapes, the measured half width can be approximated by 12 AE 2 = AE. 2 k + AE 2 'P + AE a 2 (.3.6) - 118 -where AEj, i s the natural width of the l e v e l from which the electron was ejected, and AE and AE are the hal f p a widths of the photon source and the analyser r e s p e c t i -vely . A peak width of 1.2eV can be observed for the Ne Is l e v e l using A l Ka x-rays. The resolution of the instrument i s high enough to distinguish two peaks with a separation of as low as ^ leV under favourable con-ditions 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 multiplet s p l i t t i n g of the 0 Is l e v e l of molecular oxygen can be observed (Fig. 3.10) . At a sample pressure of 0.1 t o r r , about 2000 counts/sec can be obtained for the Ne Is l e v e l . However, more weak s a t e l l i t e peaks produced by multielectron excitations usually take a considerably longer time to produce sa t i s f a c t o r y counting s t a t i s t i c s . It may be possible to improve this s i t u a t i o n by using position sensitive detectors and thereby f u l l y u t i l i s i n g the two dimensional focusing c a p a b i l i t y of the hemispherical analyser1''". 3.3 Interfacing of a PDP 8/e Minicomputer to the Gas Phase X-ray Photoelectron Spectrometer Time averaging with multi-channel scalers (MCS) i s of importance i n x-ray photoelectron spectroscopy where - 119 -+-» C D o 01s • • • • • • • Oxygen • • • • H-ievH • • • • •• • i i • • • • • • • • 1 546 544 542 Binding energy (eV) F i g . 3.10. X-ray photoelectron spectrum of the oxygen Is region from 0 9 obtained with A l Ka X-rays - 1 2 0 -the count rate i s low. Even when the count rate i s comparatively high, additional f l e x i b i l i t y and pre-c i s i o n can be obtained with a d i g i t a l system. The e f f e c t of low frequency noise can be removed by accumulation of data over a period of time, performing multiple scanning where the counts of one p a r t i c u l a r scan are added to the sum of counts from a l l previous scans. When the counting 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 of data may be terminated and the data may be stored d i g i t a l l y for l a t e r use. A p a r t i c u l a r application of a PDP 8/e minicom-puter to t h i s data c o l l e c t i o n technique i s described here. Such a computer i s preferred to conventional multi-channel scalers for a variety of reasons. The data storage capacity may be raised by the addition of extra 4K memory modules, and thereby resolution can be increased. The interface and software may be continually upgraded to provide extra f a c i l i t i e s . The computer i s programmed to control most of the spectrometer functions. A generalized block diagram of a microcomputer controlled experiment i s given i n F i g . 3.11. The interface and software w i l l be b r i e f l y discussed here. Block diagram of a microcomputer-controlled experiment DATA ACQUISITION INTERFACE MONITOR MICROCOMPUTER EXPERIMENT EXPERIMENT CONTROL INTERFACE g. 3.11. Block diagram of a microcomputer-controlled experiment. - 122 -3.3.1 The Interface Pulses from the spectrometer channel m u l t i p l i e r are input to the 12-bit up/down counter. A device code i s assigned to t h i s counter which enables the contents to be transferred to the computer accumu-l a t o r at appropriate times during the scanning routine. The counts are then added to those already stored i n the channel which i s being scanned at that p a r t i c u l a r time. The byte size of the PDP 8/e i s 12 b i t s . This necessi-tates the use of double precision storage and arithmetic. A channel corresponds to a neighbouring pair of 12 b i t bytes. The maximum number of counts that can be accumu-24 lated per channel without causing overflow i s (2 -1) or 16,777,215. In practice t h i s i s never achieved. The spectrometer retarding voltage ramp (analysing energy for electrons) i s controlled through two d i g i t a l to analog converters (DAC) Z and X. The retarding voltage i s produced by a Spellman Super regulated high voltage power supply (Model SRM3P10KD) which i s driven by the appropriate programming voltage from the Z and X DAC's. The Z DAC produces the programming voltage while the X DAC provides the necessary voltage increments. There i s a one to one correspondence between the number of - 123 -voltage increments per scan and the number of channels. The spectrum can be displayed on an oscilloscope (Tektronix Type RM 504) or on a recorder (Nuclear Chi-cago X-Y P l o t t i n g System Model 7590 C(S)), both con-t r o l l e d by two DAC's, X and Y. The X DAC (which also serves to increment the retarding voltage) controls the display i n the x-axis and the Y DAC that i n the y-axis. These two display modes are controlled by d i f f e r e n t software subroutines. In addition, data can be output to a teletype or punched on paper tape. The teletype i s also used to input the spectrometer control commands. 3.3.2 The software Computer programs are most conveniently written in high l e v e l languages such as FORTRAN. However, regardless of how e f f i c i e n t these compilers may be, the code produced almost always occupies more memory than assembler language code, and the very nature of the minicomputers and the small amount of main memory available make the use of such compilers 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 -o f 8K, 12 b i t words. F o r more e f f i c i e n t use o f t h i s r e l a t i v e l y s m a l l memory, t h e e n t i r e c o n t r o l program was w r i t t e n i n Program Assembly Language I I I (PAL I I I ) which was s p e c i a l l y d e v e l o p e d f o r the PDP 8 l i n e o f . . . . 13 computers by t h e D i g i t a l Equipment C o r p o r a t i o n I n d e s i g n i n g the s o f t w a r e f o r m u l t i - c h a n n e l s c a l i n g , the emphasis has been p l a c e d on ease o f o p e r a t i o n o f t h e s p e c t r o m e t e r by u s i n g the t e l e t y p e t o g i v e t h e n e c e s s a r y commands. The c u r r e n t program o c c u p i e s the f i r s t 4K o f t h e memory o f which 15 36 l o c a t i o n s a re pe r m a n e n t l y a l l o -c a t e d f o r d a t a s t o r a g e . A s o f t w a r e f l o w 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 major 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 s o f t w a r e 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 energy r e g i o n s can be scanned 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 are a v a i l a b l e ; A, B, C, D, E, F and G, c o r r e s p o n d i n g t o seven d i f f e r e n t r o u t i n e s . These are as f o l l o w s : Command A: I n i t i a l i z i n g r o u t i n e . The i n i t i a l r e t a r d i n g v o l t a g e , r a t e o f sc a n , r e t a r d i n g v o l t a g e i n c r e m e n t , number o f scans r e q u i r e d and t h e number o f c h a n n e l s f o r MAOOR FUNCTION FLOW DIAGRAM S E T S T A R T I N G V O L T A G E 6ET S C A N S P E E D H A V E A L L S C A N S B E E N C O M P L E T E D J S C A N R E G I O N S A L T E R N A T E L Y 1 H U1 » D I S P L A Y D A T A F i g . 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 s c a l i n g program. - 126 -up to three spectral regions can be input using t h i s routine. Scanning rates of 0.05 sec. to(a maximum of) 4 sec./channel are av a i l a b l e . The largest voltage i n -crement available i s 0.38V and each spectral region can have up to 256 channels. Command B: This enables a routine to pre-check the i n i t i a l and f i n a l voltages for each region. Command C: Scan routine. When more than two regions are requested, two options are available. The second region may be scanned after completing the number of scans required for the f i r s t region or these can be scanned a l t e r n a t e l y . This second option i s useful i n the c a l i b r a t i o n of binding energies. The program i n t r o -duces a pause at the star t of each scan for the purpose of fly-back suppression. The routine can be interrupted by typing any key-board character on the teletype. Command D: Display routine. This allows the accumu-lated data to be displayed. Computer switch r e g i s t e r s 0 - 4 also serve as gain control switches for t h i s routine. Command E: Erase routine. This clears the appropriate storage locations. - 127 -Command F: Three point smooth routine. This d i g i t a l smoothing routine replaces the contents of the i - t h channel, y. by y.' where, However, the use of such smoothing procedures can r e s u l t i n undesirable changes i n peak shapes and therefore should be used with utmost care. Command G: Data transfer routine. The data can be plotted on the x-y recorder, typed on the teletype, or punched on paper tape. The complete symbolic program i s l i s t e d i n the appendix. The number of regions and/or the number of channels can be increased without any d i f f i c u l t y using the presently unused, second 4K block of the memory. 3.4 Calibration of Electron Spectra i-1 (3.7) Eqn. 3.5 i n section 3.2.4 relates the retarding energy to the binding energy of a given electron. This equation can therefore be used to obtain the experimental - 128 -binding energies from the measured retarding voltages. However, the correction factor, C, i n eqn. 3.5 depends on the type of sample and the pressure inside the 14 io n i z a t i o n chamber , which means that C has to be determined for each p a r t i c u l a r experimental condition. This can be achieved by mixing the sample gas with a suitable calibrant gas and then obtaining the photo-electron spectra. The core l e v e l binding energies of noble gases, and a few other more common gases such as N 2 ' °2 a r e a c c u r a t e x Y known1^, and these gases can be used as ca l i b r a n t s , and hence the correction factor C can be calculated. 3.5 Data Analysis I t i s often necessary to correct the data obtained by the methods discussed e a r l i e r i n t h i s chapter for background, and contributions from s a t e l l i t e x-rays. In order to obtain accurate peak positions (binding energies) and areas of c l o s e l y spaced peaks, p a r t i c u l a r l y of multiple peak envelopes, i t i s necessary to separate these into t h e i r component single peaks. For accurate peak deconvolutions i t i s necessary to know the precise peak shapes and background. The peak shapes observed i n x-ray photoelectron spectra are a convolution of several factors such as e x c i t i n g x-ray l i n e shape, analyser l i n e - 129 -shape,possible nonuniform specimen charging, a Lorentzian hole-state l i f e t i m e contribution and 14 Doppler broadening . A number of mathematical methods have been discussed elsewhere for the decon-16 17 volution and smoothing of data ' In t h i s work the spectra were f i t t e d using a 18 least-squares program described by Fadley . Here several basic peak shapes of Gaussian or Lorentzian form are chosen, and an asymptotically constant i n -e l a s t i c t a i l of variable height i s smoothly added to get the best f i t . The e f f e c t of x-ray s a t e l l i t e s are included i n the basic peak shape chosen. The background is considered l i n e a r . A l l the binding energy values reported i n t h i s thesis were reproducible to within O.leV, however, the uncertainty due to voltage measurement i s ±0.2eV. - 130 -REFERENCES 1. M.S. Banna, B. W a l l b a n k , D.C. F r o s t , C A . McDowell, and J.S.H.Q. P e r e r a , J . Chem. Phys. 6_8, 5459 (1978) 2. K. Siegbahn, C N o r d l i n g , A. Fahlman, R. N o r d b e r g , 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: A t o m i c , 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 S p e c t r o s c o p y " , Nova A c t a Regiae Soc. S c i . U p s a l i e n s i s , S e r IV, 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. Siegbahn, 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) 4. 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 ses" ( E l s e v i e r , Amsterdam, 1976) 5. E.M. P u r c e l l , Phys. Rev. 5_4, 818 (1938) 6. J.A. Simpson, Rev. S c i . I n s t . 35_, 1698 (1964) 7. A.M. S k e r b e l e , and E.N. L a s s e t t r e , J . Chem. Phys. 40, 1271 (1964) 8. J.A. Simpson, and C E . K u y a t t , J . A p p l . Phys. 37, 3805 (1966) 9. C E . K u y a t t , and J.A. Simpson, Rev. S c i . I n s t . 38, 103 (1967) 10. H.Z. S a r - E l , Rev. S c i . I n s t . 41, 561 (.1970) 11. T.A. C a r l s o n , " P h o t o e l e c t r o n and Auger S p e c t r o s c o p y " (Plenum P r e s s , New York, 19 75) - 131 -12. A. B a r r i e , "Handbook o f X-ray and U l t r a v i o l e t Photo-e l e c t r o n S p e c t r o s c o p y " D. B r i g g s , E d i t o r (Heyden, London, 19 77) 13. I n t r o d u c t i o n t o Programming" PDP-8 Handbook S e r i e s , D i g i t a l Equipment C o r p o r a t i o n , Maynard, M a s s a c h u s e t t s 14. 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.O. Werme, R. Manne, and Y. B a e r , "ESCA A p p l i e d t o Free M o l e c u l e s " ( N o r t h - H o l l a n d , Amsterdam, 1969) 15. G. Johansson, J . Hedman, A. B e r n d t s s o n , M. K l a s s o n , and 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 . R e l a t . Phenom. 2_, 295 (1973) 16. G.K. Wertheim, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 6_f 239 (1975) 17. H. E b e l , and 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 . R e l a t . Phenom. 5, 799 (1974) 18. C.S. F a d l e y , 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 , B e r k e l e y 19 70 (Lawrence B e r k e l e y L a b o r a t o r y R e p o r t UCRL-19535) - 132 -CHAPTER FOUR X-RAY PHOTOELECTRON SPECTROSCOPY OF GROUP IA AND I I A FREE METAL ATOMS 4.1 I n t r o d u c t i o n The t e c h n i q u e o f 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 a p p l i e d t o gaseous systems p r o v i d e s a d i r e c t , unambiguous measure-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 s p e c i e s 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 v a l e n c e l e v e l s . The e x p e r i m e n t a l s i t u a t i o n w i t h r e g a r d 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 gases have been s t u d i e d . As a r e s u l t , w o r k ers 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 e n e r g i e s 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 t o o b t a i n t h e s e v a l u e s from o t h e r p e r t i n e n t e x p e r i m e n t a l d a t a . The most p o p u l a r o f t h e s e methods i s t o combine x - r a y e m i s s i o n 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 d a t a f o r f r e e atoms. However, as p o i n t e d o u t by S h i r l e y and 8 co- w o r k e r s , such an approach may r e s u l t i n an e s t i m a t e f o r t h e b i n d i n g energy w h i c h i s t o o low because o f - 133 -d i f f e r e n t i a l e x t r a - a t o m i c r e l a x a t i o n i n t h e h o l e s t a t e s i n v o l v e d i n x - r a y e m i s s i o n . 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 i n the s t a n d a r d s t a t e a r e s y s t e m a t i c a l l y s e v e r a l eV lower t h a n t h o s e o f t h e f r e e atoms. The r e d u c t i o n i n b i n d i n g energy f o r t h e i n n e r c o r e l e v e l s a r e e x p e c t e d t o be g r e a t e r t h a n t h a t f o r the 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 l a r g e r t h a n t h o s e o f the c o r r e s p o n d i n g t r a n s i t i o n s i n t h e m e t a l l i c s t a t e , t h u s r e s u l t i n g i n l o w e r v a l u e s f o r e s t i m a t e d f r e e 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 s o l i d s t a t e a re used. S i n c e modern day b i n d i n g energy c a l c u l a t i o n s a r e c a r r i e d o u t a t a g r e a t e r p r e c i s i o n t h a n 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 and more d e s i r a b l e . The p r e s e n t work 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 from t h i s l a b o r a t o r y t o ex t e n d the r e a l m o f x - r a y 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 (XPS) t o atomic s p e c i e s . I n t h i s c h a p t e r t h 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 sodium, p o t a s s i u m , r u b i d i u m , cesium (group I A ) , magnesium, c a l c i u m , s t r o n t i u m and barium (group I I A ) a r e p r e s e n t e d . A p a r t o f the 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 . These r e s u l t s p e r m i t e x a m i n a t i o n o f v a r i o u s p a s t e s t i m a t e s o f c o r e 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 t h e c o r r e s -ponding v a l u e s 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 -l e v e l ) t h e s e 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 q u a n t i t y o f . , , , 4.-4. 4. 11,13-16 c o n s i d e r a b l e c u r r e n t i n t e r e s t . 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 were o b s e r v e d a t h i g h e r b i n d i n g e n e r g i e s t h a n t h e main peak i n most o f t h e c o r e l e v e l s p e c t r a r e p o r t e d h e r e . These w i l l be b r i e f l y d i s c u s s e d i n t h i s c h a p t e r , however, no q u a n t i t a t i v e d i s c u s s i o n w i l l be att e m p t e d h e r e . A s t u d y o f t h e s e s a t e l l i t e s i n c o r e i o n i z a t i o n from t h e s o l i d m e t a l s would be s e v e r e l y hampered by t h e p r e s e n c e o f plasmon s t r u c t u r e s i n t h e r e g i o n o f t h e s a t e l l i t e s . 1 E x p e r i m e n t a l c o n d i t i o n s w i l l be d i s c u s s e d i n t h e n e x t s e c t i o n . The r e s u l t s w i l l be p r e s e n t e d and d i s -c u s s e d i n S e c t i o n 4.3. The c o n c l u s i o n s a r e g i v e n i n S e c t i o n 4.4. 4.2 E x p e r i m e n t a l The s p e c t r o m e t e r used i n t h i s work was d e s c r i b e d i n d e t a i l i n Chapter Three. C a l c i u m , s t r o n t i u m and barium were s t u d i e d i n t h e new h i g h t e m p e r a t u r e gas c e l l w h i l e t h e o t h e r f i v e m e t a l s were s t u d i e d i n t h e o l d gas c e l l (see Chapter T h r e e ) . The t e m p e r a t u r e s used t o o b t a i n t h 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 f o r d i f f e r e n t m e t a l atoms a r e l i s t e d i n T a b l e 4.1. These t e m p e r a t u r e s were - 135 -Tab l e 4.1 Approximate t e m p e r a t u r e s and the gas c e l l window m a t e r i a l used t o o b t a i n the 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 s p e c t r a M e t a l atom Temperature/ C Window Sodium P o t a s s i u m Rubidium Cesium Magnesium C a l c i u m S t r o n t i u m Barium 240 190 145 140 470 690 640 740 Aluminum Aluminum Aluminum Aluminum Aluminum Carbon Aluminum Carbon a Aluminum windows were 0.0025 mm-thick ( s u p p l i e d by A l f a 2 -4 Chemicals) and the carbon windows were 40 ug/cm =2x10 mm-thick ( s u p p l i e d by Yissum Research Development Company, I s r a e l ) - 136 -measured outside the i o n i z a t i o n chamber and therefore do not represent the precise sample temperature, however, t h i s difference i s not expected to exceed 20-30°C. At temperatures above 660°C carbon windows 2 (40 yg/cm ) were used. It was found that a l l three higher temperature metal vapors, calcium, strontium and barium react with the carbon windows. The reaction between carbon and calcium vapor was considerably slower under the experimental conditions and hence did not pose any major problem. However, strontium seemed to react rather vigorously making i t impossible to use carbon windows. For t h i s reason the strontium spectrum reported here was obtained using an aluminum window and hence at less than optimum operating pressures. Although barium did not react as vigorously as strontium, the carbon windows had to be replaced rather frequently. The reaction between the metal atoms and the carbon windows was indicated by a drop i n the count rate. Sodium and potassium were s l i c e d under toluene and then placed i n the gas c e l l sample cup covered with the same l i q u i d for subsequent heating. Ampoules of rubidium and cesium were opened under petroleum ether (boiling range 65-110°C) and were loaded into the gas c e l l with the sample cup f i l l e d with the same solvent. - 137 -In a l l cases the solvents were removed by pumping inside the source chamber before the sample was heated. 99.9% pure magnesium powder was loaded into the spectrometer without any precautions being taken with regard to surface oxidation. The same was done with >99.7% pure calcium f i l i n g s . The strontium sample was prepared by cutting >99.5% pure strontium rod into small pieces. A l l samples studied here are extremely reactive and soon covered with a surface oxide layer. However, t h i s does not constitute a problem since the oxides do not produce a s i g n i f i c a n t vapor pressure under the experimental conditions used to obtain the x-ray photoelectron spectra. Here, barium was found to be a d i f f i c u l t case since, when small amounts of the oxide were present, they tended to form a reddish mass making i t d i f f i c u l t to maintain an optimum pressure inside the i o n i z a t i o n chamber. It has been reported that BaO c r y s t a l s with excess of metal 18 i n the l a t t i c e are deep red. This problem was mini-mized by cleaning the barium pieces i n a glass bead j e t , and then immediately immersing these i n n-hexane. These pieces were then loaded into the gas c e l l under n-hexane and pumped out before heating. This procedure minimized the formation of the said red mass. - 138 -The possible presence of dimers was ruled out on the basis of the vapor pressure data obtained from 19 Nesmeyanov for the temperatures required to produce the operating pressures. The following monomer/dimer r a t i o s are l i s t e d : Na/Na2=71(600K), K/K2=369(550K), Rb/Rb2=482(475K) and Cs/Cs 2=574(450K). There seems to be no similar data on the composition of the a l k a l i n e earth metal vapors. The Hel photoelectron spectra of calcium, strontium and barium have been published by Suzer and co-workers, and these do not show any peaks that can be attributed to dimers. It i s concluded therefore that the dimer concentration i s n e g l i g i b l e i n a l l cases. The spectra were recorded at a minimum of two d i f f e r e n t temperatures (and therefore pressures) to 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 the r e a l photoionization peaks. A l l spectra were least-squares f i t t e d to obtain peak positions, linewidths and areas using the program des-20 cribed by Fadley. C a l i b r a t i o n of the Na Is, Cs 3d, Mg Is and Ba 3d l e v e l s was performed by introducing neon with the vapor under study and scanning the Ne Is l e v e l [870.37(9)eV] 2 1 a l t e r n t i v e l y with the l e v e l of the metal atom. The K 2p lev e l s were s i m i l a r l y c a l i b r a t e d using the C Is l e v e l of methane [290.9(2)eV], 2 2 while - 139 -the Rb 3p, Ca 2s and Ca 2p l e v e l s were referenced 21 using the known Ar 2\?^^ binding energy [248.62(8)eV]. The Ba 4d and the Sr 3d 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 with respect to the known binding energy of the Ne 2s 21 l e v e l [48.47eV], A l l binding energies measured i n t h i s work have an uncertainty of ±0.2eV. 4.3 Results and Discussion 4.3.1 Binding Energies 4.3.1.1 Sodium The sodium Is spectrum i s shown i n F i g . 4.1. Since a l k a l i metal atoms have an unpaired electron i n the valence s h e l l , multiplet s p l i t t i n g should r e s u l t i n two 3 1 l e v e l s S and S a r i s i n g from Is i o n i z a t i o n . The mag-nitude of the multiplet s p l i t t i n g i s obviously small as seen i n the spectrum i n F i g . 4.1. The separation 3 1 between the S and S states (AE) can be calculated using Van Vleck's theorem. (See Section 2.12.2, Chapter 23 2). H i l l i g and co-workers calculated t h i s s p l i t t i n g 24 employing the Hartree-Fock program of Froese-Fischer and obtained a AE of 0.42eV. From deconvolution of t h e i r experimental Auger l i n e s , they obtained a value - 140 -1090 1085 1080 1075 Binding energy (eV) F i g . 4.1. The Is l e v e l of atomic sodium 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 e x c i t a t i o n . - 141 -of 0.26eV for AE. The spectrum i n F i g . 4.1 merely shows an asymmetry on the high binding energy side, however, a least-squares f i t using two Lorentzian peaks with an area r a t i o of 3 to 1 y i e l d s a separation of 0.4(l)eV, which i s i n reasonable agreement with the 23 calculated value of H i l l i g et a_l. For each of the 23 multiplet states, H i l l i g and co-workers calculated a 25 l i n e width of 0.27eV. Banna and Shirley computed an upper l i m i t for the Na K c t , „ emission l i n e from s o l i d sodium of 0.42eV and assuming that the ^2^3 l e v e l s involved 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 value i s primarily 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 has a t o t a l l i n e width of 1.2eV due to additional contributions from the A l Ka e x c i t i n g l i n e (=0.85eV) and the spectrometer resolution (=0.3eV at ^50eV analyser pass energy). Sodium Is binding energies from t h i s work and various other sources are l i s t e d in Table 4.2. The 23 Auger and o p t i c a l value of H i l l i g and co-workers was experimentally obtained by combining the o p t i c a l l y known energy, E [ 2 s 2 2 p 4 ( X D ) 3 s 1 ( D 2 ) ] , of 101.9eV, 2 7 with the 1 2 absolute Auger energy, E [ K L 2 3 L 2 3 ( D) D], both for free sodium atoms. The experimental value 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 value obtained by H i l l i g et a l . 2 3 The 107 9.lev - 142 -Table 4.2 Sodium Is binding energies (eV) Experimental free atom: Is i . This work 10 79.1 i i . Auger + O p t i c a l 3 1078.6 i i i . X-ray emission + o p t i c a l 1079.1 Theoretical free atom: Ref. 9 1078.2 Ref. 26 1079 Ref. 11 1079.3 Experimental standard state* 3 : 10 74.0 Theoretical standard s t a t e c : 1072.8 a. From Ref. 2 3 b. From Ref. 17 c. From Ref. 11 - 143 -value l i s t e d i n Table 4.2 for x-ray emission + o p t i c a l data was taken from the work reported by Kowalczyk and 17 co-workers and i s the r e s u l t of combining x-ray 28 27 emission energies from the s o l i d with o p t i c a l data. The agreement with the x-ray photoelectron value i s excellent and theuse of x-ray energies obtained 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 binding energies l i s t e d i n Table 4.2 are the r e l a t i v i s t i c Hartree-Fock-Slater 9 26 res u l t s of Huang et a_l. and Siegbahn et a 1. .Both these values correspond to the difference i n t o t a l energy between the neutral ground state and the hole state and so the contribution of intra-atomic relaxation i s included. Agreement with experiment i s excellent i n the case of Siegbahn et a_l. but the value of Huang et a l . d i f f e r s by 0.9eV. The ASCF Hartree-Fock c a l c u l a t i o n of Beck and N i c o l a i d e s , 1 1 which includes the corrections for radia t i v e e f f e c t s i s 0.2eV higher than the experimental value; however the two values f a l l within the quoted deviations. 17 Kowalczyk and co-workers have referenced the Na Is binding energy for s o l i d sodium to the vacuum l e v e l and obtained a value of 1074.OeV. The fac t that the vacuum l e v e l referenced standard state binding energies for - 144 -metals i s invariably lower than that for the free atom 14 15 19 30 i s now well 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 discussed i n Section 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 structure due to multielectron e x c i t a t i o n are shown i n F i g . 4.2. The measured binding energies are compared with 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 energies are the average values for the spin multiplets. 28 27 Again the combination of x-ray emission and o p t i c a l data gives binding energies which are i n very good agreement with the experimental free atom binding energies (Table 4.3). The t h e o r e t i c a l values of 26 9 Siegbahn et a l . and Huang et a l . are also i n excellent agreement with experiment. Once again the values calculated by Beck and N i c o l a i d e s 1 1 are s l i g h t l y higher than the d i r e c t experimental r e s u l t . 31 Mansfield obtained a l i m i t to the photoabsorption series 2 p 5 ( 2 P 1 / 2 ) 3 d [ 3 / 2 ] x n s [ 1 ] 1 / 2 3 / 2 of 303.9(2)eV i n potassium vapor. This i s 0.7eV higher than the d i r e c t experimental binding energy of the 2p^y 2 l e v e l . This 31 can be regarded as evidence that Mansfield i s correc i n assigning the photoabsorption series to the above - 145 -F i g . 4.2. The 2p levels of atomic potassium obtained with A l Ka x-rays.The peaks lab e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 146 -Table 4.3 Potassium 2p binding energies (eV) 2 p l / 2 2 p3/2 Experimental free atom: I. This work 303.2 300.5 II . Auger a 303.7(1) 300.9(1) I I I . X-ray emission + o p t i c a l b 303.2(4) 300.5(4) Theoretical free atom : Ref. 9 303.0 300.2 Ref. 26 303 300 Ref. 11 303.7 300.9 Experimental standard s t a t e b : 299.6 296.9 Theoretical standard s t a t e 0 : 29 8.6 295.7 a. From Ref. 4 b. From Ref. 8 c. From Ref. 11 - 147 -configuration rather than the single e x c i t a t i o n series 2p 5 ( 2P 1 /, 2) 4s [ 1/2 ] Q xnd. 4.3.1.3 Rubid ium A spectrum of the rubidium 3p l e v e l s and the accompanying multielectron 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 rather broad, the linewidths obtained by computer f i t t i n g being 3. leV for the 3p^y 2 l i n e and 3. OeV for the 3p^y 2 l i n e . 32 Svensson and co-workers have reported linewidths of 1.80 and 1.48eV for the 3p-jy2 and 3p^y 2 l i n e s of Krypton obtained using monochromatized Al Ka x-rays. The 3pjy 2 l i n e i s broader than the ^2/2 l i n e due to the fact that M-jM^ lSh and M,,M- 0^  type Coster-Kronig t r a n s i t i o n s are energ e t i c a l l y possible for the 3p.jy2 33 34 l e v e l , but not for the 3p^y 2 l e v e l , ' and also additional super Coster-Kronig t r a n s i t i o n s are energetically allowed for the former which are not allowed 32 for the l a t t e r . However, Svensson et aJL. state that the energy l i m i t for the M 2 ^M^ ^ super Coster-Kronig t r a n s i t i o n s l i e s at Z=36(Kr). If t h i s i s the case, then the Rb 3p linewidths one would expect to obtain with monochromatized x-rays would be less than - 148 -Rubidium i i i i i — 260 250 240 Binding energy (eV) F i g . 4.3. The 3p levels of atomic rubidium obtained with A l Ka x-rays.The peaks la b e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 149 -1.5eV. Thus the 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 a r e g r e a t e r t h a n t h o s e t h a t would be e x p e c t e d even when the i n c r e a s e d i n s t r u m e n t a l b r o a d e n i n g o f t h e s p e c t r o m e t e r 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 t h a t c o n f i g u r a t i o n i n t e r a c t i o n r e s o n a n c e s t h r o u g h ^M^ ^M^ 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 be p o s s i b l e beyond Z=36. F u r t h e r e v i d e n c e f o r t h i s s u g g e s t i o n may be o b t a i n e d by comparing t h e o r e t i c a l and e x p e r i m e n t a l b i n d i n g e n e r g i e s f o r the Rb 3p l e v e l s . Rb 3 p ^ y 2 a n d ^V_/2 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 o t h e r s o u r c e s a r e l i s t e d i n 9 T a b l e 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. a r e ^3eV g r e a t e r than the d i r e c t e x p e r i m e n t a l r e s u l t and a s i m i l a r d i s c r e p a n c y between t h e o r y and e x p e r i m e n t was 32 o b s e r v e d f o r k r y p t o n . F o r k r y p t o n i t has been 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. W i t h i n t h e s e 2 c o n f i g u r a t i o n s , a number of 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 each o t h e r and w i t h 3p( P) s t a t e s . The r e s u l t s p r e s e n t e d here s t r o n g l y suggest t h a t s i m i l a r 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 a r e i m p o r t a n t f o r t h e Rb 3p l e v e l s as w e l l . - 150 -Table 4.4 Rubidium 3p binding energies (eV) 3 p l / 2 3 p3/2 Experimental free atom: i . This work 254.3 245.4 i i . X-ray emission + o p t i c a l 3 254.3 245.4 Theoretical free atom: Ref. 9 257.1 247.9 Experimental standard state* 3 : 250 .9 242.0 a. Calculated using x-ray emission values from Ref. 2 8 and o p t i c a l values from Ref. 27 b. Calculated using x-ray emission values from Ref. 28, s o l i d state photoemission values from Ref. 35 and a work function of 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 - r a y emission'' 27 and o p t i c a l v a l u e s 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 e x p e r i m e n t a l r e s u l t as i n t h e case o f sodium and p o t a s s i u m . (Table 4.4) 4.3.1.4 Cesium The cesium 3d l e v e l s a r e shown i n F i g . 4.4 and t h e 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 a r e compared 2 8 w i t h v a l u e s 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 and o p t i c a l 27 r e s u l t s i n T a b l e 4.5. A g a i n t h e r e i s good agreement between 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 e v i d e n c e i n t h i s c a s e t h a t the x - r a y e m i s s i o n + o p t i c a l v a l u e s a r e 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 r e l a x a t i o n i n t h e h o l e s t a t e s i n v o l v e d i n x - r a y e m i s s i o n . However, 2 8 v a l u e s f o r t h e L j N , L ^ M and NjyOj-j- e m i s s i o n l i n e s were used 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 such an i n d i r e c t method a r e p r o b a b l y o a t l e a s t 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 . and Beck and N i c o l a i d e s 1 ' ' " a r e i n e x t r e m e l y good agreement w i t h t h e 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 o b t a i n e d i n t h i s work ( 3 d 3 ^ 2 , 745.8eV; 3&_/2' 7 3 1 • g e V ) ( T a b l e 4.5). - 152 -Fig. 4.4. The 3d levels of atomic cesium obtained with A l Ka x-rays.The peaks la b e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 153 -Table 4.5 Cesiurr, 3d binding energies (eV) 3 d3/2 3 d5/2 Experimental free atom: i . T his work 74 5.8 731.8 i i . X-ray emission + o p t i c a l 3 745.4 731.4 T h e o r e t i c a l free atom: Ref. 9 Ref. 11 745.8 745 .8 731 . 9 732 .0 Experimental standard s t a t e : 742.2 742 . 9 C T h e o r e t i c a l standard s t a t e d : 741.6 a. C a l c u l a t e d using x-ray emission v a l u e s from R e f . 28 ar.d o p t i c a l values from Ref. 27 b. C a l c u l a t e d using x-ray emission values from Ref. 28, s o l i d state photoemission values from Ref. 35 and a work fun c t i o n of 2.1eV from Ref. 36 c. Front Ref. 37. These values are f o r Cs atoms adsorbed on N i , c a l c u l a t e d using a work fu n c t i o n of 1.9eV. 6. Prom Ref. 11 728 .2* 7 2 7 . 9 ' 727.8 - 154 -4.3.1.5 Magnesium The spectrum of the Mg Is l e v e l o b t a i n e d with A l Ka x-rays i s presented i n F i g . 4.5 and the d i r e c t l y measured Is l e v e l b i n d i n g energy i s compared wi t h l i t e r a t u r e v a l u e s i n Table 4.6. There i s good agreement between the d i r e c t experimental measurement (1311.5eV) and the b i n d i n g energy estimated u s i n g v a l u e s from x-ray 28 38 emission and the Mg 2p b i n d i n g energy of Newsom. 39 The Is b i n d i n g energy o b t a i n e d u s i n g Auger data, the Mg 2p b i n d i n g e n e r g y 3 ^ and experimental coulomb i n t e g r a l s 4 0 i s l e v too low. However, the e r r o r quoted 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^ 3 M i and K-M^M^ t r a n s i t i o n s from a higher r e s o l u t i o n Auger spectrum of Mg atoms and the e n e r g i e s of the c o r r e s p o n d i n g f i n a l s t a t e s from o p t i c a l data, to c a l c u l a t e a value of 1311.3(3)eV f o r the Mg Is b i n d i n g energy. T h i s value i s i n good agreement wi t h the experimental XPS value r e p o r t e d i n t h i s work (Table 4.6). 2 6 The t h e o r e t i c a l v a l u e of Siegbahn e t a l . i s i n reasonable agreement w i t h the r e p o r t e d experimental b i n d i n g energy. However Ley and c o - w o r k e r s 1 6 used t h i s t h e o r e t i c a l value and estimated the e f f e c t of e l e c t r o n - 155 -F i g . 4.5. The Is l e v e l of atomic magnesium obtained with A l Ka x-rays.The peaks l a b e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 156 -Table 4.6 Magnesium Is binding energies (eV) Experimental free atom: Is i . This work i i . X-ray emission + o p t i c a l 3 i i i . Auger + o p t i c a l + coulomb integrals 1311.5 1311.2 1310.5(10) Theoretical free atom: Ref. 9 Ref. 26 Ref. 16 1310.6 1312.0 1312.6 Experimental standard state 1306.7 a. Calculated using x-ray emission values from Ref. 2 8 and o p t i c a l values 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.leV 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. The t h e o r e t i c a l r e s u l t o f 9 Huang et_ a l . i s 0.9eV lower t h a n t h e e x p e r i m e n t a l v a l u e . Thus i t seems t h a t i f a s i m i l a r c o r r e l a t i o n 9 c o r r e c t i o n was a p p l i e d t o the 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 exp e r i m e n t might be o b t a i n e d . 4.3.1.6 C a l c i u m The c a l c i u m 2s and 2p l e v e l s and t h e a s s o c i a t e d m u l t i e l e c t r o n e x c i t a t i o n s t a t e l l i t e s a r e shown i n F i g . 4.6 and 4.7 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 o t h e r s o u r c e s i n T a b l e 4.7. I n t h i s s t u d y c a l c i u m e x e m p l i f i e s t h e f i r s t case where t h e b i n d i n g e n e r g i e s e s t i m a t e d u s i n g the 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 d a t a f o r atoms, d i f f e r from t h e d i r e c t e x p e r i -m ental r e s u l t , where t h e former i s lower by 5.0 t o 5.2eV. Alth o u g h , as mentioned e a r l i e r , i t i s e x p e c t e d t h a t t h e 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 e s t i m a t e d u s i n g s o l i d s t a t e x - r a y e m i s s i o n v a l u e s may be somewhat g low, t h e o b s e r v e d d i s c r e p a n c y 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 calcium obtained with A l Ka x-rays.The peak la b e l l e d 'sat' i s due to multielectron e x c i t a t i o n . - 159 -CVJ o in O o 365 355 Binding energy (eV) F i g . 4.7. The 2p l e v e l s of atomic calcium obtained with A l Ka 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 2 s a n d 2 p l e v e l b i n d i n g e n e r g i e s ( e V ) E x p e r i m e n t a l f r e e a t o m : f l 2 p l / 2 2 P 3 / 2 i . T h i s w o r k 4 4 7 . 5 3 5 9 . 6 3 5 6 . 0 i i . A u g e r 3 b ) 3 6 0 . 0 ( 1 ) b ) 3 5 6 . 4 ( 1 ) i i i . X - r a y e m i s s i o n + c ) 3 6 1 . 1 ( 1 ) b ) 3 5 7 . 4 ( 1 ) o p t i c a l * 3 4 4 2 . 5 ( 2 0 ) 3 5 4 . 7 ( 2 0 ) 3 5 1 . 1 ( 2 0 ) T h e o r e t i c a l f r e e a t o m : R e f . 9 4 4 9 . 8 3 6 0 . 5 3 5 6 . 9 E x p e r i m e n t a l s t a n d a r d S t a t e 3 : 4 4 1 ( 1 ) 3 5 3 . 6 ( 5 ) 3 5 0 . 0 ( 5 ) T h e o r e t i c a l s t a n d a r d s t a t e d : 4 4 3 3 5 4 3 5 0 a . F r o m R e f . 4 W h e t h e r b ) o r c ) a r e t h e c o r r e c t v a l u e s d e p e n d s o n t h e a s s i g n m e n t o f A u g e r l i n e s t o f i n a l A u g e r s t a t e s . d . F r o m R e f . 8 - 161 -than what one would have anticipated. Despite the fact that most of the estimated binding energies using t h i s method have shown excellent agreement with the free atom binding energies measured i n t h i s laboratory using XPS, the present discrepancy may be considered a warning that such i n d i r e c t methods should be used only with great care. 4 Mehlhorn and co-workers have given two sets of free atom binding energies for the 2p l e v e l s of calcium (Table 4.7), the correct set of values depending upon the proper assignment of Auger l i n e s to f i n a l Auger states. The two sets of binding energies d i f f e r by 1.0 - 1.leV with the lower energy set only 0.4eV higher than the XPS value measured i n t h i s laboratory. Considering the nature of agreement that has been shown to e x i s t between XPS and Auger Electron Spectroscopy (AES) i n the determination of binding energies, the present r e s u l t suggests that the assignment of the Auger l i n e s to f i n a l Auger states 4 leading to the lower set of values by Mehlhorn et a l . i s correct. Details of t h i s assignment are, however, not available. The t h e o r e t i c a l free atom binding energies from r e l a x e d - o r b i t a l r e l a t i v i s t i c Hartree-Fock-Slater - 162 -calculations by Huang et a_l. are compared with the experimental r e s u l t s i n Table 4.7. The calculated values are 0.9eV higher than the experimental values for the 2p l e v e l s , and the calculated value for the Ca 2s l e v e l i s 2.3eV larger. This difference may be due to the neglect of configuration i n t e r a c t i o n . The i n i t i a l states of the closed s h e l l group IIA atoms are 2 known to possess near degenerate configurations np 2 2 and (n-l)d (for Ba, 4f i s also possible) which can 2 3 mix strongly with the ground state, ns , configuration. 4.3.1.7 Strontium The 3d l e v e l of atomic strontium and the associated s a t e l l i t e structure i s shown i n F i g . 4.8. The experi-mental 3d binding energy i s compared with the l i t e r a t u r e values i n Table 4.8. Core l e v e l binding energies of strontium atoms have been determined previously by 4 Mehlhorn and co-workers, and were repeated i n t h i s laboratory mainly to compare the binding energies measured i n t h i s laboratory with those measured elsewhere using the same technique. As seen i n Table 4.8 the two XPS values d i f f e r by 0.5eV, but f a l l within the quoted errors. As mentioned i n Section 4.2 e a r l i e r i n t h i s - 163 -150 140 Binding energy (eV) F i g . 4.8. The 3d l e v e l of atomic strontium obtained with A l Ka x-rays.The peak labe l l e d 'sat' i s due to multielectron e x c i t a t i o n . - 164 -T a b l e 4 . 8 S t r o n t i u m 3 d b i n d i n g e n e r g i e s ( e V ) E x p e r i m e n t a l f r e e a t o m : 3d i . T h i s w o r k 11. A u g e r i i i . X - r a y e m i s s i o n 1 5 i v . P h o t o a b s o r p t i o n v . O t h e r X P S a 1 4 2 . 6 1 4 2 . 3 (2) ; 1 4 4 . 0 ( 2 ) 1 4 2 . 8 ( 1 1 ) 1 4 2 . 9 1 4 3 . 1 ( 7 ) T h e o r e t i c a l f r e e a t o m : R e f . 1 4 1 . 1 ; 1 4 2 . 8 E x p e r i m e n t a l s t a n d a r d s t a t e e : 1 3 7 . 0 ( 1 0 ) a . F r o m R e f . 4 b . C a l c u l a t e d u s i n g x - r a y e m i s s i o n v a l u e s f r o m R e f . 2 8 a n d 4 p b i n d i n g e n e r g i e s o f f r e e a t o m s f r o m R e f . 4 c . F r o m R e f . 42 d . T h e t w o v a l u e s s h o w n a r e f o r t h e 3 d 5 ^ 2 a n d 3 d3/2 s P i n - o r b i t d o u b l e t . e . F r o m R e f . 4 3, r e f e r e n c e d t o t h e v a c u u m l e v e l u s i n g a w o r k f u n c t i o n o f 2 . 7 ( e V ) f r o m R e f . 44. T h e v a l u e s h o w n i s t h e a v e r a g e b i n d i n g e n e r g y f o r t h e s p i n - o r b i t d o u b l e t 3ds/2 a n d 3d3/2• - 165 -c h a p t e r , t h e 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 b i n d i n g energy 2 8 e s t i m a t e d u s i n g s o l i d s t a t e x - r a y e m i s s i o n r e s u l t s 4 and 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 t h e p r e s e n t r e s u l t , as w e l l as t h a t o b t a i n e d from 42 p h o t o a b s o r p t i o n by M a n s f i e l d and Connerade. 4 Mehlhorn e t a_. have r e p o r t e d a s p i n - o r b i t s p l i t t i n g o f 1.7eV f o r t h e 3d l e v e l from th e Auger spectrum w h i c h i s i n good agreement w i t h t h e t h e o r e t i c a l 9 r e s u l t o f Huang e t a_l. I n t h e XPS spectrum ( F i g . 4.8) t h i s i s seen as an asymmetry on t h e h i g h e r b i n d i n g energy s i d e o f t h e peak. The w e i g h t e d average of the c a l -9 c u l a t e d b i n d i n g energy i s i n good agreement w i t h t h e XPS r e s u l t . 4.3.1.8 Barium The 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 3d and 4s l e v e l s of a tomic b a r i u m a r e shown i n F i g . 4.9 and 4.10 r e s p e c -t i v e l y . The b i n d i n g e n e r g i e s measured i n t h i s work and t h o s e from v a r i o u s o t h e r s o u r c e s a r e c o l l e c t e d i n T a b l e 4 4.9. B i n d i n g energy v a l u e s d e t e r m i n e d by AES and p h o t o -45 a b s o r p t i o n methods f o r the 4d l e v e l s a r e i n good a g r e e -ment w i t h the e x p e r i m e n t a l XPS r e s u l t . However no such - 166 -Barium 3 d5/2 T ' 1 1 r 810 800 790 Binding energy (eV) F i g . 4.9. The 3d levels of atomic barium obtained with A l Ka x-rays.The A l Kq 3 4 x-ray s a t e l l i t e s of the 3 d ^ 2 l i n e are seen next to the 3d,-^2 l i n e « - 167 -"no ' TOO R Binding energy (eV) F i g . 4.10. The 4d leve l s of atomic barium obtained with A l Ka x-rays.The peak la b e l l e d 'sat' i s due to multielectron e x c i t a t i o n . - 168 -T a b l e 4 . 9 B a r i u m 3 d a n d 4 d l e v e l b i n d i n g e n e r g i e s ( e V ) 3 d 3 / 2 3 d 5 / 2 4 d 3 / 2 4 d 5 / 2 E x p e r i m e n t a l f r e e a t o m : i . T h i s w o r k 8 0 3 . 6 7 8 8 . 2 1 0 0 . 9 9 8 . 3 i i . A u g e r a 1 0 1 . 0 ( 1 ) 9 8 . 5 ( 1 ) i i i . X - r a y e m i s s i o n 1 3 8 0 4 . 3 ( 1 1 ) 7 8 9 . 0 ( 1 1 ) 1 0 0 . 7 ( 9 ) 9 8 . 1 ( 9 ) i v . P h o t o a b s o r p t i o n 0 1 0 1 . 0 ( 2 ) 9 8 . 3 ( 2 ) T h e o r e t i c a l f r e e a t o m : R e f . 9 8 0 4 . 6 7 8 9 . 3 1 0 0 . 5 9 7 . 9 E x p e r i m e n t a l s t a n d a r d s t a t e d = 7 9 8 . 6 ( 2 0 ) 7 8 3 . 2 ( 2 0 ) 9 5 . 0 ( 2 0 ) 9 2 . 4 ( 2 0 ) a . F r o m R e f . 4 b . C a l c u l a t 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 f r o m R e f . 2 8 a n d 5 p b i n d i n g e n e r g y o f f r e e a t o m s f r o m R e f . 4 c . F r o m R e f . 4 5 d . F r o m R e f . 4 3 , r e f e r e n c e d t o t h e v a c u u m l e v e l u s i n g a w o r k f u n c t i o n o f 2 . 5 ( e V ) f r o m R e f . 44 - 169 -values are available for the 3d l e v e l s of atomic barium. Of the two spin-orbit s p l i t components of the 4d l i n e , the 4d^^2 component appears i n the x-ray photoelectron spectrum as a shoulder on the high binding energy side of the 4d peak. This can be e a s i l y deconvoluted into two peaks with a separation of 2.6eV. This separation shows excellent agreement with 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 of the 4d l e v e l of Ba calculated by 9 Huang et al_. The 4d spin-orbit s p l i t t i n g observed by 4 45 AES and photoabsorption are 2.5 and 2.7eV respectively. The free atom binding energies estimated using x-ray 2 8 emission data for the s o l i d and the 5p binding energies 4 for the free atoms are i n very good agreement with the experimental XPS values for the 4d l e v e l s , whereas the estimated 3d binding energies are 0.7 to 0.8eV higher than the experimental value. The x-ray emission values reported for Ba have been obtained experimentally using 2 8 43 Ba(N0 3)2 ' and t n e estimation of the free atom binding energies (as well as the standard state binding energies) was c a r r i e d out assuming that these emission values would be maintained i n the metal. Despite the fact that the experimental XPS binding energies of the 3d l e v e l s f a l l within the quoted minimum possible error of the values estimated using these x-ray emission r e s u l t s , as w i l l be - 170 -indicated l a t e r , there i s reason to believe that these estimated values are i n error. 9 The t h e o r e t i c a l l y estimated binding energies for barium free atoms show good agreement with the experi-mental values for the 4d l e v e l s . The binding energies 9 calculated by Huang et a_. are 1.0 to 1.leV higher than the experimental value. 4.3.2 Phase Transition S h i f t s , AE^ It i s now possible to calculate the phase tran-s i t i o n s h i f t , AE^, for the metals discussed so f a r , using the experimental free atom binding energies i n conjunction with the corresponding values i n the s o l i d (referenced to the vacuum l e v e l ) . The free atom binding energies measured i n t h i s work are compared with the appropriate standard state values i n Tables 4.2-4.9. To obtain K 2p binding energies referenced to the vacuum l e v e l for the s o l i d , Shirley and co-workers used x-ray emission values for KCl and a work function of 2.3eV. To the author's knowledge there has been no x-ray photoemission study of potassium metal to give more r e l i a b l e values for the s o l i d state binding energies. g Thus, the values of Shirley e t a_l. were used with the free atom binding energies measured i n t h i s work to - 171 -c a l c u l a t e a AE^ o f 3.6eV. S i m i l a r l y t h e s t a n d a r d s t a t e b i n d i n g e n e r g i e s f o r sodium, magnesium and c a l c i u m were o o b t a i n e d from 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 . The 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 s t a t e 2 8 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 energy 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 the vacuum l e v e l u s i n g 3 6 a work f u n c t i o n o f 2.3eV. When the s o l i d s t a t e v a l u e s d e t e r m i n e d t h i s way a r e combined 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 . The Cs 3d s t a n d a r d 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 t h e same way as t h e Rb 3p l e v e l s w i t h the Cs 5p b i n d i n g 3 5 e n e r g i e s o f Ebbinghaus e_t a l . and a work f u n c t i o n o f 36 v 2.leV b e i n g used. 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. K r i s h n a n e t a l . have d e t e r m i n e d t h e 3d b i n d i n g e n e r g i e s o f ces i u m atoms adsorbed on a n i c k e l (100) s u r f a c e . These v a l u e s o b t a i n e d from x - r a y p h o t o e m i s s i o n and a work 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 i n T a b l e 4.5. However, i t i s t o be noted t h a t t h e s p i n - o r b i t s p l i t t i n g 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 al _ . i s 15.0eV whereas t h e same s p l i t t i n g o b t a i n e d from the 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 atoms and t h e s t a n d a r d s t a t e a r e between 13.8 and 14.0eV. K r i s h n a n 37 e t a_l. r e p o r t a 3 d ^ ^ 2 l e v e l b i n d i n g energy w h i c h shows - 172 -good agreement with both the t h e o r e t i c a l estimation by Beck and N i c o l a i d e s 1 1 and the value obtained using x-ray emission (Table 4.5). The standard state binding energies reported i n Tables 4.8 and 4.9 for strontium and barium are the 43 values reported by Bearden and Burr. These values were calculated from x-ray emission r e s u l t s and re-ferenced to the vacuum l e v e l by using work functions of 44 2.7 and 2.5eV for strontium and barium respectively. The phase t r a n s i t i o n s h i f t s calculated for the group IA and IIA metals using the free atom binding energies measured i n t h i s work, and the t h e o r e t i c a l l y estimated values, are collected i n Table 4.10. The author could not f i n d any t h e o r e t i c a l estimate of core l e v e l binding energies for the standard states of rubidium, strontium and barium. A l l the t h e o r e t i c a l values reported i n Table 4.10 are based on a model f i r s t put forward by S h i r l e y , 2 9 , 4 6 14 Ley and coworkers. (See Section 2.11.4, Chapter Two). In t h i s model i t i s assumed that the hole state produced by core l e v e l i o n i z a t i o n of metals i n the standard state i s screened by the valence electron gas forming a semi-l o c a l i z e d exciton by the dropping down of a conduction band below E^. This 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 s h i f t s , A E ^ , g r o u p I A a n d I I A  m e t a l s , e s t i m a t e d u s i n g t h e f r e e a t o m b i n d i n g e n e r g i e s m e a s u r e d i n t h i s w o r k . A l l s h i f t s a r e i n e V . E b ( e V ) E x p e r i m e n t a l T h e o r e t i c a l N a I s 5 . 1 5 . 3 a 6 . 5 b K 2 p l / 2 3 . 6 3 C 5 . 0 b K 2 p 3 / 2 3 . 6 3 C 5 . 0 b R b 3 p l / 2 3 . 4 R b 3 p 3 / 2 3 . 4 C s 3 d 3 / 2 3 . 6 4 . 2 b C s 3 d 5 / 2 3 . 6 4 . 2 b M g I s 4 . 8 5 . 1 d C a 2 s 6 . 5 7 C C a 2 p l / 2 6 . 0 7 C C a 2 p 3 / 2 6 . 0 7 C S r 3 d ' 5 . 6 B a 3 d 3 / 2 5 . 0 B a 3 d 5 / 2 5 . 0 B a 4 d 3 / 2 5 . 9 B a 4 d 5 / 2 5 . 9 a . F r o m R e f . 1 7 b . F r o m R e f . 1 1 c. F r o m R e f . 8 d . F r o m R e f . 1 6 - 174 -forward by F r i e d e l . **' '**° Beck and Nicolades^"1" use a ASCF method outlined i n Chapter Two to evaluate the phase t r a n s i t i o n s h i f t whereas a l l the other values reported i n Table 4.10 are calculated i n terms of atomic two-electron i n t e g r a l s . ' ^ Both c a l c u l a t i o n procedures make use of the 'equivalent cores' approxi-1129 mation ' and t h i s t h e o r e t i c a l model estimates the core l e v e l binding energy s h i f t due to extra-atomic relaxation. The t h e o r e t i c a l binding energy s h i f t s l i s t e d i n Table 4.10, therefore, represent the estimated values for extra-atomic relaxation. The phase t r a n s i t i o n s h i f t i s caused by a number of factors (Chapter Two) of which extra-atomic relaxation i s the major contributor. The values estimated by Beck and Nicolaides 1''" are larger 8 16 17 than those calculated by Shirley and co-workers. ' ' A l l the t h e o r e t i c a l estimates are larger than the experi-mental values with the exception of the value estimated for K by Shirley et a_. Although, the 'semilocalized exciton' model seems to overestimate the extra-atomic relaxation, the trends of binding energy s h i f t s predicted by t h i s model are i n excellent agreement with experiment. The binding energy s h i f t s predicted for Na Is, Mg Is and Ca 2s agree with the experimental values to within 0.2-0.5eV. - 175 -The binding energy s h i f t s are expected to increase slowly when going from outer core l e v e l s to inner core 8 16 lev e l s ' and t h i s can be seen i n calcium for which the binding energies of three separate lev e l s were measured. However, t h i s trend i s reversed i n barium where the binding energy s h i f t for the 3d l e v e l s i s 0.9eV less than that for the 4d l e v e l s . This may have been caused by the use of incorrect standard state core l e v e l binding energies which were calculated from the 4 3 x-ray emission values for BaCNO^^- As mentioned e a r l i e r , a similar discrepancy i s seen between the experimental XPS free atom binding energies and the values estimated for the 3d l e v e l s of atomic barium using the same set of x-ray emission r e s u l t s where the estimated value i s higher than the experimental one. Such a discrepancy could be caused by met a l l i c barium having d i f f e r e n t x-ray emission r e s u l t s than those for BaCNO-^as the relaxation mechanisms i n the two s o l i d s are not necessarily the same. However, the author could not fi n d an alternate set of x-ray emission values or a d i r e c t x-ray photoemission study of metallic barium. Further discussion of t h i s point, therefore, w i l l not be considered. Direct comparison of the experimental free atom - 176 -binding energies and the binding energy of such atoms adsorbed on various surfaces can be expected to produce d i r e c t information regarding the nature of the adsorbate-substrate interactions. By combining the free atom binding energies of cesium with the binding energies of cesium atoms adsorbed on a ni c k e l (100) surface 37 determined by Krishnan et a l . , binding energy s h i f t s of 2.9eV and 3.9eV can be calculated for the 3d^^ a n d "^5/2 l e v e l s respectively. Unfortunately t h i s s h i f t cannot be discussed i n a meaningful way due to the unexpected difference i n the 3d spin-orbit s p l i t t i n g 37 between t h i s work and the work of Krishnan et a l . . 4.3.3 Multielectron Exc i t a t i o n S a t e l l i t e s In any study of s a t e l l i t e structure on the high binding energy side of the main peaks i t i s important to d i s t i n g u i s h energy loss peaks from peaks due to multielectron 'shakeup' events. However, electron 4 9 50 impact studies of the a l k a l i metal vapors, ' as well as u l t r a v i o l e t photoelectron spectroscopy r e s u l t s ^ 1 show that the most intense t r a n s i t i o n s i n the neutral atoms 49 have energies i n the range l-3eV (2.09eV for Na, 1.6lev for K, 4 9 1.58eV for Rb, 5 0 and 1.41eV for C s 5 0 ) . Of course, i t i s conceivable that the r e l a t i v e i n t e n s i t i e s - 177 -of the energy loss t r a n s i t i o n s may change with the k i n e t i c energy of the e x c i t i n g electron. In the case 50 of potassium, Hertel and Ross established that at ^100eV electron energy, the 1.61eV t r a n s i t i o n i s s t i l l ^100 times greater than any of the others. It seems plausible that the s i t u a t i o n would be more or less the same for the ^1200eV electrons involved i n t h i s x-ray photoelectron study. Similar situations e x i s t for the other metal atoms. In a recent UPS study of group 3 IIA and IIB vapors, Suzer et a_l. reported i n e l a s t i c peaks at energies 2 . 9 , 2.7 and 2.2eV higher than the main peak for calcium, strontium and barium , respectively. 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 i n t e n s i t i e s were observed for a l l these group IA and IIA atoms when spectra were obtained at d i f f e r e n t operating pressures. Inte n s i t i e s of the peaks due to i n e l a s t i c scattering are expected to be pressure dependent. In addition, alternate scans of the Ne Is and Na Is regions i n a mixture of neon gas and sodium vapor gave no evidence for structure ^8eV from the Ne Is peak. Because the k i n e t i c energy of the photoelectrons from the Ne Is and Na Is l e v e l s d i f f e r by only ^200eV, the i n e l a s t i c scattering cross sections should be more or less s i m i l a r . This procedure was repeated with the cesium 3d l e v e l s - 178 -where the k i n e t i c energy from the Ne Is and Cs 3d le v e l s d i f f e r by ^130eV, and the r e s u l t s confirmed that the peaks observed at energies of about 5eV higher than the main l i n e s of the cesium 3d spectrum are indeed due to multielectron e x c i t a t i o n . However, i t i s possible that some structure corresponding to energy loss i s present i n the spectra shown here,but the features l a b e l -led 'sat 1 i n the metal atom spectra are d e f i n i t e l y due to multielectron ex c i t a t i o n . The separation between the s a t e l l i t e s and the main peaks for the d i f f e r e n t atoms are l i s t e d i n Table 4.11. In the one-electron picture and i n the absence of i n i t i a l state and/or f i n a l state configuration i n t e r -action (an obviously oversimplified s i t u a t i o n ) , and i n order to assign the main shakeup t r a n s i t i o n s involved, i t i s useful to consider the el e c t r o n i c states of the 'equivalent core ion' corresponding to the atom under study, with a core' hole. Values for the e x c i t a t i o n 27 energies obtained for the monopole selection 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 equivalent cores approximation are also l i s t e d i n Table 4.11. (For example, to obtain the energy corresponding to the 3s-*4s t r a n s i t i o n i n core ionized sodium, the excitation energy for the same t r a n s i t i o n i n 3s ionized - 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 s a t e l l i t e s : S e p a r a t i o n s  f r o m t h e m a i n l i n e s ( e V ) E q u i v a l e n t c o r e e x c i t a t i o n s E x p e r i m e n t a l n s * ( n + l ) s n s - > ( n + 2 ) s N a I s K 2 p 1 / 2 K 2 p 3 / 2 R b 3 p R b 3 p C s 3 d C s 3 d M g I s C a 2 s C a 2 p C a 2 p S r 3 d B a 4 d 1/2 3 / 2 3 / 2 5 / 2 1/2 3 / 2 8 . 4 6 . 3 6 . 3 6 . 0 6 . 0 5 . 2 ) 5 . 4 6 . 1 , 1 2 . 3 9 . 1 9 . 8 1 0 . 0 1 1 . 0 9 . 7 b 8 . 6 5 6 . 4 7 5 . 9 2 5 . 2 5 3 S 1 1 . 3 2 L S 1 1 . 8 2 S 7 . 2 2 S 7 . 6 0 1 1 . 5 0 8 . 7 6 8 . 0 5 7 . 1 9 14 . 8 9 1 5 . 0 5 a . b . F r o m R e f . 2 7 T h e v a l u e g i v e n h e r e i s t h e s e p a r a t i o n b e t w e e n t h e s a t e l l i t e a n d t h e w e i g h t e d b i n d i n g e n e r g y o f t h e 4 d s p i n - o r b i t d o u b l e t . - 180 -Mg i s sought). The calculated values corresponding to calcium and barium are not l i s t e d i n Table 4.11 as the author could not f i n d the appropriate t r a n s i t i o n energies for S c + and L a + . There i s excellent agreement between the experi-mental values and the ns->-(n+l)s e x c i t a t i o n energies for a l l the a l k a l i metal vapors. Of the a l k a l i n e earth metals the appropriate data are available only for magnesium and strontium. In the case of the Ca 2s, 2p, Sr 3d, and Ba 4d x-ray photoelectron spectra there i s only one s a t e l l i t e peak associated with a given main peak with an energy separation of ^9-lleV, whereas for 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 at 12.3eV i n the magnesium spectrum may be assigned to a 3s->-4s t r a n s i t i o n using the equivalent cores approximation. However the agreement here i s not as good as that obtained for the a l k a l i metal atoms. The s a t e l l i t e at 6.1eV cannot be assigned with any con-fidence to any t r a n s i t i o n using t h i s approximation. However, there i s a 3s-v4p t r a n s i t i o n i n neutral magnesium with an exc i t a t i o n energy of 6.1eV in d i c a t i n g that t h i s peak may be due to energy l o s s . But, as indicated 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 of t h i s peak was observed on changing the operating pressure of - 181 -the magnesium vapor making such an assignment questionable. Comparison of t h i s r e s u l t with the s o l i d state spectra of magnesium i s complicated, because of the presence of surface and bulk plasmons at 16 7.3 and 10.7eV. However, KLL Auger spectra of the 39 free atom do show d i s t i n c t features due to multi-electron e x c i t a t i o n i n the i n i t i a l hole state. Although, the e x c i t a t i o n source and the f i n a l states involved i n the two processes are rather d i f f e r e n t an inter 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 ' for magnesium atoms. 39 Breuckmann and Schmidt observed s a t e l l i t e s i n the Auger spectra of magnesium atoms, with separations 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 basis of Hartree-Fock calculations including configuration i n t e r a c t i o n . These Auger spectra were obtained using a 3.8 keV electron 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 reported to be 0.22 for the 5.5eV s a t e l l i t e and 0.12 for the 11.7eV one. 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 photoelectron spectra obtained i n t h i s work are 0.71 and 0.87 respectively. Although, the counting s t a t i s t i c s of the spectrum shown i n F i g . 4.5 - 182 -a r e not v e r y good, r e s u l t i n g i n r a t h e r l a r g e e r r o r s on t h e above v a l u e s , i t i s o b v i o u s t h a t t h e s a t e l l i t e s here a r e much more i n t e n s e t h a n t h e Auger s a t e l l i t e s 39 r e p o r t e d by Breuckmann and Schmidt. The d i f f e r e n c e 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 r e s p o n s i b l e f o r t h i s d i s c r e p a n c y . The A l Ka r a d i a t i o n i s o n l y ^170eV above t h e t h r e s h o l d energy w h i l e t h e 3.8keV e l e c t r o n s a r e w e l l above the t h r e s h o l d . The 5s->-6s shakeup t r a n s i t i o n energy e s t i m a t e d f o r s t r o n t i u m u s i n g t h e e q u i v a l e n t c o r e s a p p r o x i m a t i o n i s c o n s i d e r a b l y lower t h a n t h e o b s e r v e d v a l u e . A s u i t a b l e e x c i t a t i o n energy f o r t h e 5s->-7s t r a n s i t i o n c o u l d not be found i n t h e l i t e r a t u r e . The f a i l u r e o f t h e e q u i v a l e n t c o r e s a p p r o x i m a t i o n i n t h e case o f t h e a l k a l i n e e a r t h m e t a l s , w h i l e b e i n g so v a l i d f o r t h e 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 t h e breakdown o f the o n e - e l e c t r o n p i c t u r e i n t h e c a s e o f the former. Such breakdowns can be caused by i n i t i a l s t a t e c o n f i g u r a t i o n i n t e r a c t i o n ( I S C I ) , 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 i n t e r a c t i o n (FISCI) and continuum s t a t e c o n f i g u r a t i o n i n t e r a c t i o n . I n t h e group IA elements a F I S C I mechanism i s e x p e c t e d t o be c o m p a r a t i v e l y u n i m p o r t a n t as t h e f i n a l c o r e i o n i z e d i o n i c s t a t e s have o n l y one e l e c t r o n o u t s i d e a c l o s e d s h e l l , whereas - 183 -i n group I I A elements w i t h two e l e c t r o n s i n t h e o u t e r i n c o m p l e t e l y f i l l e d s h e l l and low 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 ISCI and F I S C I . I t i s p o s s i b l e t h a t t h e s e 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 r o l e i n d e t e r m i n i n g t h e s a t e l l i t e s t r u c t u r e i n t h e 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 o f a q u a n t i t a t i v e assignment o f t h e s e 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 ( p o s i t i o n and i n t e n s i t y ) t h e c o n t r i b u t i o n t o s a t e l l i t e s t r u c t u r e t h r o u g h a ' c o n j u g a t e shakeup 1 mechanism may have t o be i n c l u d e d as was found 52 t o be the case w i t h mercury. 4.4 C o n c l u s i o n s The c o r e b i n d i n g e n e r g i e s o f group IA and I I A m e t a l atoms were d e t e r m i n e d u s i n g x - r a y p h o t o e l e c t r o n s p e c t r o s -copy. T h i s work shows t h a t e s t i m a t e s o f c o r e b i n d i n g e n e r g i e s o b t a i n e d from a c o m b i n a t i o n o f s o l i d s t a t e x - r a y e m i s s i o n and o p t i c a l d a t a f o r f r e e atoms can produce r e s u l t s w h i c h , f o r f a v o u r a b l e c a s e s , a r e 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 r e s u l t . However, i n t h e case o f c a l c i u m atoms, the e s t i m a t e d v a l u e i s lower by about 5eV f o r a l l l e v e l s f o r w h i c h the comparisons a r e made, and i n t h e case o f barium - 184 -atoms, although the estimated values agree with the experiment within the quoted errors, the accuracy of the estimation i s rather doubtful. This suggests that although x-ray emission values for the s o l i d , coupled with free atom o p t i c a l values can be used to estimate free atom binding energies reasonably well i n most cases, such i n d i r e c t estimations should be used only with great care. The importance of the phase t r a n s i t i o n s h i f t between the core binding energies i n the s o l i d and vapor i s now well recognized. For example,this binding energy s h i f t may prove useful i n studying adsorbate-substrate i n t e r -actions. The phase t r a n s i t i o n s h i f t s for group IA and IIA metals (except for L i and Be) were estimated using the experimental free atom core l e v e l binding energies measured i n t h i s work. Due to lack of r e l i a b l e x-ray photoemission r e s u l t s , values from i n d i r e c t estimates were used as the standard state binding energies for 3 6 potassium, rubidium, cesium, calcium and barium. Poole reported values for the a l k a l i metal conduction band relaxation energies obtained semiempirically. These values, though much smaller than those reported i n Table 4.10, do show the same trend (Na 2.54eV, K 2.03eV, Rb 2.00eV, and Cs 2.02eV). Theoretical estimates of - 185 -extra-atomic relaxation based on a semi-localized ex-29 46 cit o n model put forward by Shirley, ' Ley and 14 co-workers are a l l , i n general, higher than the experimental values, however, the agreement can be considered good when the s i m p l i c i t y of the above model i s taken into account. This model predicts the trend of the phase t r a n s i t i o n s h i f t s for the elements studied here rather accurately, i n d i c a t i v e of the predominant role played by the extra-atomic relaxation i n determining the phase t r a n s i t i o n s h i f t . As reasonable peak-background r a t i o s were obtained i n t h i s work i t was also possible to study the multi-electron e x c i t a t i o n s a t e l l i t e s associated with 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 state spectra of these species because of the presence of plasmons. It was found that the s a t e l l i t e s could be assigned to a ns-> (n+1) s type shakeup exc i t a t i o n using the equivalent cores approximation for a l k a l i metal atoms. The s a t e l l i t e s found i n a l k a l i n e earth metal atoms could not be assigned unambiguously using a simple one electron picture, where the s i t u a t i o n i s complicated, possibly, by i n i t i a l state and f i n a l i o n i c state configuration i n t e r a c t i o n . - 186 -REFERENCES 1. J.M. Dyke, N.K. Fayad, A. Morris, and I.R. T r i c k l e , J . Phys. B 1_2, 2985 (1979) 2. S. - T. Lee, S. Suzer, E. Matthias, R.A. Rosenberg, and D.A. Shirley, J. Chem. Phys. 6_6 , 2496 (1977) 3. S. Suzer, S. - T. Lee, and D.A. Sh i r l e y , Phys. Rev. A 13, 1842 (1976) 4. W. Mehlhorn, B. Breuckmann, and D. Hausamann, Physica Scripta 16, 177 (1977) 5. Y.S. Khodeyev, H. Siegbahn, K. Hamrin, and K. Siegbahn, Chem. Phys. Lett. 19_, 16 (1973) 6. S. Svensson, N. Martensson, E. B a s i l i e r , P.A. Malmquist, U. Gelius, and K. Siegbahn, J . Electron Spectrosc. Relat. Phenom. 9, 51 (1976) 7. M.S. Banna, D.C. Frost, C A . McDowell, and B. Wallbank, J. Chem. Phys. 6_8, 696 (1978) 8. D.A. Shirley , R.L. Martin, S.P. Kowalczyk, F.R. McFeely, and L. Ley, Phys. Rev. B 15, 544 (1977) 9. K.-N.Huang, M.O. Aoyagi, M.H. Chen, B. Crasemann, and H. Mark, At. Data Nucl. Data Tables 1_8, 243 (1976) 10. P. Albertsen, and P. J^rgensen, J . Chem. Phys. 70_, 3254 (1979) 11. D.R. Beck, and C A . Nicolaides, NATO Adv. Study Inst. Ser., Ser. C (1978) (Pub. 1979) C 46 (Excited States Quantum Chem.) p. 329 - 187 -12. A p a r t o f t h i s work was done i n c o l l a b o r a t i o n w i t h Dr. M.S. Banna and Dr. B. Wallbank, and was p u b l i s h e d i n t h e J o u r n a l o f C h e m i c a l P h y s i c s ; M.S. Banna, B. Wallbank, D.C. F r o s t , C.A. McDowell, and J.S.H.Q. P e r e r a , J . Chem. Phys. 6_8, 5459 (1978) 13. B. Johansson, and N. M a r t e n s s o n , t o be p u b l i s h e d . 14. L. Ley, S.P. Kowalczyk, F.R. McFeely, R.A. P o l l a k , and D.A. S h i r l e y , Phys. Rev. B 8, 2392 (1973) 15. R.E. Watson, M.L. Perlman, and J.F. H e r b s t , Phys. Rev. B 13, 2358 (1976) 16. L. Ley, F.R. M c F e e l y , S.P. K o w a l c z y k , J.G. J e n k i n , a n d D.A. S h i r l e y , Phys. Rev. B 11, 600 (1975) 17. S.P. Kowalczyk, L. Ley, F.R. M c F e e l y , R.A. P o l l a k , and D.A. S h i r l e y , Phys. Rev. B 8_, 3583 (1973) 18. F.A. C o t t o n , and G. W i l k i n s o n , "Advanced I n o r g a n i c C h e m i s t r y " ( I n t e r s c i e n c e , New York, 1972) 19. A.N. Nesmeyanov, "Vapor P r e s s u r e o f t h e C h e m i c a l E l e m e n t s " , e d i t e d by R. Gary ( E l s e v i e r , Amsterdam, 1963) 20. C.S. F a d l e y , 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 , B e r k e l e y , 19 70 (Lawrence B e r k e l e y L a b o r a t o r y R e p o r t UCRL - 19535) 21. G. Johansson, J . Hedman, A. B e r n d t s s o n , M. K l a s s o n , and 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 . R e l a t . Phenom. 2_, 295 (1973) - 188 -22. U. Gelius, S. Svensson, H. Siegbahn, E. B a s i l i e r , A. Faxlav, and K. Siegbahn, Chem. Phys. L e t t . 2_8, 1 (19 74). These authors were able to resolve three v i b r a -t i o n a l components with a separation of 0.4 3eV and r e l a t i v e 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 i o n i z a t i o n p o t e n t i a l was observed at 290.72 (15) . The value quoted here i s a weighted mean of 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 (1974) 24. C. Froese-Fischer, Hartree-Fock Program with Configuration Mixing, University of Waterloo, Ontario, Canada, 196 8 25. M.S. Banna, and D.A. Shirley, J . Electron Spectrosc. Relat. Phenom. 8, 23 (1976) 26. K. Siegbahn, C. Nordling, A. Fahlman, R. Nordberg, K. Hamrin, J. Hedman, G. Johansson, T. Bergmark, S. - E. Karlsson, I. Lindgren, and B.J. Lindberg, "ESCA: Atomic, Molecular and S o l i d State Structure Studied by Means of Electron Spectroscopy", Nova Acta Regiae Soc. S c i . Upsaliensis, Ser IV, V o l . 20 (Almqvist and Wiksells, Stockholm, 1967) 27. C.E. Moore, "Atomic Energy Levels" Natl. Bur. Stand. Ci r c u l a r No. 462 (1949, 1952 and 1958), Vols. 1-3 28. J.A. Bearden, Rev. Mod. Phys. 39_, 78 (1967) 29. D.A. Sh i r l e y , Chem. Phys. Lett. 16_, 220 (1972) 30. P.H. Citrin,and D.R. Hamarmann, Chem. Phys. L e t t . 22, 301 (1973) - 189 -31. M.W.D. Mansfield, 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. Gelius, and K. Siegbahn, Physica Scripta 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, Z. Natureforsch. B 31, 1219 (1976). The binding energies of the 4p levels in Rb and the 5p lev e l s i n Cs have also been reported by R.G. Oswald, and T.A. Ca l l c o t , Phys. Rev. B 4_, 4122 (1971).. The values of Oswald and C a l l c o t t d i f f e r by 0.1 - 0.3eV from those of Ebbinghaus et al_. , but are within the errors quoted by the former. The more recent values of Ebbinghaus et al_. have been used in thi s study. 36. R.T. Poole, Chem. Phys. Lett. 42, 151 (.19 76). 37. N.G. Krishnan, W.N. Delgass, and W.D. Robertson, J . Phys. F 7, 2623 (.1977). 38. G.H. Newsom, Astrophys. J . 166 , 243 (.1971) 39. B. Breuckmann, and V. Schmidt, Z. Phys. 268, 2 35 (19 74). 40. W. Mehlhorn, and W.N. Asaad, Z. Phys. 191, 231 (.1966). 41. B. Breuckmann, J . Phys. B 12_, L609 (.19 791 42. M.W.D. Mansfield, and J . P . Connerade, Proc. Roy. Soc. London A 342, 421 (19 75). 43. J.A. Bearden, and A.F. Burr, Rev. Mod. Phys. 39_. 125 (1967) 44. American Institute of Physics Handbook, 3rd Ed i t i o n , Chap. 9, p. 172 (1972). - 190 -45. D.L. Ederer, T.B. Lucatorto, E.B. Saloman, R.P. Madden, and J. Sugar, J. Phys. B 8, L21 (_1975)_ 46. D.A. Sh i r l e y , Chem. Phys. Lett. 17 f 312 (19 72), 47. J. F r i e d e l , Philos. Mag. 43_, 153 (1952). 48. J. F r i e d e l , Adv. Phys. 3, 446 (1954). 49. I.V. Hertel, and K.J. Ross, J . Phys. B 2, 285 (_1969)_ 50. I.V. Hertel, and K.J. Ross, J . Phys. B 2, 484 (.1969). 51. T.A. Williams, and A.W. Potts, J. Electron Spectrosc. Relat. 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 FIVE X-RAY PHOTOELECTRON SPECTROSCOPY OF TITANIUM TETRAHALIDE VAPORS 5.1 I n t r o d u c t i o n 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 y (XPS) has been used e x t e n s i v e l y t o s t u d y th e p r o p e r t i e s o f s o l i d t r a n s i t i o n m e t a l compounds. A g r e a t d e a l o f t h i s work has been concerned w i t h t h e phenomenon of m u l t i e l e c t r o n e x c i t a t i o n (shakeup) and t h e appearance o f s a t e l l i t e l i n e s i n t h e p h o t o e l e c t r o n s p e c t r a o f the 1 — 16 m e t a l c o r e l i n e s , p a r t i c u l a r l y t h e 2p s h e l l . However, s y s t e m a t i c s t u d i e s i n t h e s o l i d s t a t e / o f t h e sometimes 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 w i t h m u l t i -e l e c t r o n e x c i t a t i o n have been hampered by t h e p r e s e n c e o f l a r g e backgrounds due t o i n e l a s t i c e l e c t r o n c o l l i s i o n s and plasmon e x c i t a t i o n . I t i s , t h e r e f o r e , p o s s i b l e t o e l i m i n a t e the 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 s t u d y i n g t h e compounds i n t h e vapor phase. I n t h i s c h a p t e r a gas phase x - r a y p h o t o e l e c t r o n - 192 -spectroscopic study of the 3d 0 compounds TiX^ (X=F, CI, Br, I) with p a r t i c u l a r emphasis on the structure due to shakeup ex c i t a t i o n w i l l be presented. A complication often encountered i n a study of t h i s kind i s the presence of structure on the metal core l i n e s due to multiplet s p l i t t i n g . However, no such additional complication i s present 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 spectra of 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 interpreted as due to shakeup from the ligand valence o r b i t a l s to the empty 3d o r b i t a l s of the metal ion (e^ -»- e* i n 0^ symmetry) . Similar s a t e l l i t e s i n other t r a n s i t i o n metal ions were explained i n the same way.4 Later experimental work 1^' 1^ on the 3d° systems showed a s a t e l l i t e structure somewhat di f f e r e n t from that known previously as shakeup e x c i t -ations of the type t 2 g t*g also seemed to be present. Molecular o r b i t a l c alculations have shown that high s a t e l l i t e i n t e n s i t i e s may be expected for shakeup 17-21 tr a n s i t i o n s of the ligand-to-metal 3d type. It should also be mentioned that, more recently, ligand-to-metal 4s or 4p shakeup t r a n s i t i o n s have also 22-24 been suggested as the o r i g i n of s a t e l l i t e s , on the - 193 -basis of multiple scattering 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 basis of the agreement between the experimental data and the calculated hole state energy separations for these types of t r a n s i t i o n s . However, 21 i t has been suggested that 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 with any appreciable i n t e n s i t y . From the above discussion i t i s obvious that 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 spectra i s s t i l l an incompletely resolved problem. I t i s hoped that t h i s study of the titanium tetrahalides i n the vapor phase w i l l shed some l i g h t on the problem since the e f f e c t s on the s a t e l l i t e s of changing the ligands without changing the symmetry of the central metal ion ( a l l four compounds are known to 25-28 have tetrahedral symmetry i n the gas phase ) may be examined. Also, the e f f e c t of changing the symmetry without changing the metal ion or ligands may be considered by comparing the gas phase data for TiF^ with that already published for the s o l i d , the structure of which i s thought to be chain-like with the titanium having s i x - f o l d 27 29 30 co-ordination. ' ' A part of t h i s work has appeared elsewhere. 3 1 Experimental d e t a i l s w i l l be discussed i n the next - 194 -section. The r e s u l t s w i l l be presented and discussed in Section 5.3. The conclusions are given i n Section 5.4. 5.2 Experimental The spectrometer used i n t h i s study has been described i n d e t a i l i n Chapter Three. Samples of TiF^, T i C l 4 and TiBr^ were obtained commercially (K and K Laboratories Inc.) and used without further p u r i f i c a t i o n . T i l ^ was prepared by the reaction of hydrogen iodide with 32 titanium tetrachloride i n benzene and the sample obtained was p u r i f i e d by sublimation. A l l four tetrahalides are moisture sen s i t i v e , and so were handled at a l l times i n a dry, i n e r t atmosphere. The tetrachloride and the tetrabromide were introduced into the spectrometer from a glass manifold f i t t e d with a t e f l o n stop-cock, the chloride being mantained at 0°C to help control the vapor pressure and the bromide being studied at room temperature. TiF^ and T i l 4 were placed inside the spectrometer and heated to 'vlOCC and ^75°C, -2 respectively,to obtain a s u f f i c i e n t vapor pressure (^3x10 t o r r ) . Samples were then i r r a d i a t e d with A l Ka x-rays to obtain the photoelectron spectra. - 195 -In the f i r s t few hours aft e r sample loading i t was observed that the r a t i o s of the halogen core l e v e l s to the titanium l e v e l s were much greater than 33 was expected i n d i c a t i n g the presence of the hydrogen halides and/or free halogens. Therefore, the samples were l e f t at the operating conditions for several hours before data were taken to ensure that a l l HX and/or X 2 were removed and that the surfaces of the spectrometer gas c e l l had become 'conditioned'. To further ensure that data obtained for the halogen core l e v e l s were not contaminated with HX or X 2, spectra of the titanium 2p and 3p l e v e l s were taken before the halogen data were obtained thus maintaining a period of at least three days between loading the sample and studying the halogen core l e v e l s . Spectra of hydrogen iodide and molecular iodine were also taken for comparison with T i l ^ . The T i 2p le v e l s were referenced to the N Is l e v e l 34 of N 2 (409.93eV ), which was introduced simultaneously with the gas i n question. The T i 3p, Br 3d and I 4d level s were s i m i l a r l y referenced using the known Ne 2s 34 binding energy (48.47eV ). The F Is and I 3d le v e l s 35 were referenced to the F Is l e v e l of SFg (695. (MeV ) and the C l 2p,Br 3p and I 4s le v e l s to the S 2p.^ 2 l e v e l of SF 6 (180.28eV 3 6). - 196 -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 t o 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 a r e a s u s i n g t h e program 37 d e s c r i b e d by F a d l e y . 5.3 R e s u l t s and D i s c u s s i o n The b i n d i n g e n e r g i e s o f the t i t a n i u m 2p and 3p l e v e l s , and v a r i o u s h a l o g e n l e v e l s a r e summarized i n T a b l e s 5.1 and 5.2 r e s p e c t i v e l y . The s h i f t s o f t h e t i t a n i u m b i n d i n g e n e r g i e s f o r each l e v e l f o l l o w t h e e l e c t r o n e g a t i v i t y t r e n d o f the h a l o g e n s w i t h a l a r g e change between 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 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 and - i o d i d e , as would be e x p e c t e d . The b i n d i n g e n e r g i e s o f c e r t a i n l e v e l s i n the h a l i d e s may be compared w i t h p r e -v i o u s l y p u b l i s h e d d a t a f o r t h e h a l o g e n s , X 2, and t h e 3 8 hydrogen h a l i d e s , HX, ( X = F , C l , B r ) , and the d a t a o b t a i n e d i n the p r e s e n t s t u d y f o r HI and I,,. I t can be seen (Table 5.2) t h a t t h e t e t r a h a l i d e b i n d i n g e n e r g i e s a r e d i f f e r e n t from t h o s e f o r HX and X 2 , i n d i c a t i n g t h a t t h e r e c o r d e d h a l o g e n c o r e l e v e l s p e c t r a a r e not due t o h y d r o l y t i c or d e c o m p o s i t i o n p r o d u c t s and t h u s c o n f i r m i n g t h a t t h e methods used f o r o b t a i n i n g t h e 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 . Comparison of t h e b i n d i n g e n e r g i e s r e p o r t e d here w i t h p r e v i o u s l y p u b l i s h e d - 197 -T a b l e 5 . 1 T i 2 p a n d 3 p 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 ) 2 p l / 2 3 2 P 3 / 2 a b T i F 4 4 7 3 . 8 4 6 8 . 6 4 7 . 5 T i C l 4 4 7 1 . 5 4 6 5 . 4 4 4 . 6 T i B r 4 4 7 0 . 5 4 6 4 . 4 4 3 . 7 T i l 4 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 I s l e v e l o f N 2 ( 4 0 9 . 9 3 e V 3 4 ) b R e f e r e n c e d t o t h e N e 2 s b i n d i n g e n e r g y ( 4 8 . 4 7 e V 3 4 ) T a b l e 5.2 H a l o g e n c o r e b i n d i n g e n e r g i e s (eV) i n T i X 4 , HX and X-, (X=F,C1 ,Br ,1) F I s 692.8 a 693. ft 696.2 b a 2p 1/2 207.7° C l 2p 3/2 Br 3p 1/2 206.6^ 207.2 207.6<T 196.9^ Br 3p 3/2 189. B Br 3d 76.5 U 77.06" 77.101-I 3d 3/2 637.3° I 3d 5/2 625.9° I 4s 193.9^ I 4d 3/2 57.9" I 4< 35, a Referenced to the F Is l e v e l o f SFg (695.04eV ) b From R e f . 38 c Referenced to the S 2 p 3 / 2 l e v e l o f SF g (180.28eV J") d Referenced to the Ne 2s l e v e l (48.47eV 3 4) 36, d5/2 56 57 57 - 199 -d a t a i s p o s s i b l e o n l y f o r t h e C l 2p 3/2 l e v e l o f t i t a n i u m t e t r a c h l o r i d e . A v a n z i n o e t a l . have o b t a i n e d a v a l u e o f 205.77eV f o r t h i s b i n d i n g energy w h i c h i s i n v e r y poor agreement w i t h t h e p r e s e n t v a l u e (206.6eV). I n t h i s l e v e l o f SFg ( C l 2p-S 2p s e p a r a t i o n i s o n l y ^26eV) and 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 o f t h e 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 i s p r e s e n t . However, i t i s not e x p e c t e d t h a t t h i s s h o u l d 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. do n o t r e p o r t t h e method used t o r e f e r e n c e t h e i r spectrum. S p e c t r a o f the T i 2p r e g i o n s o f each 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 . The p h o t o e l e c t r o n l i n e s l a b e l l e d ' s a t ' i n t h e s e F i g u r e s a r e due t o m u l t i -e l e c t r o n (shakeup) e x c i t a t i o n . However, i n any s t u d y o f r a t h e r weak s a t e l l i t e s , the p o s s i b i l i t y of peaks due t o energy l o s s has t o be c o n s i d e r e d . 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 p r e s s u r e s , b u t t h e r e l a t i v e i n t e n s i t i e s o f t h e s e s a t e l l i t e s d i d n o t change s i g n i f i c a n t l y , i n d i c a t i n g t h a t t h e y a r e i n d e e d 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 . To f u r t h e r t e s t t h i s c o n c l u s i o n , t h e N I s x - r a y p h o t o -e l e c t r o n spectrum o f gaseous n i t r o g e n was o b t a i n e d i n the pr e s e n c e o f t i t a n i u m t e t r a c h l o r i d e a t a t y p i c a l o p e r a t i n g p r e s s u r e . The N I s l i n e i n N 2 i s s e p a r a t e d by o n l y ^60eV from t h e T i 2p l i n e s , and i t i s e x p e c t e d t h a t t h e s c a t t e r i n g s t u d y t h e C l 2p 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 - 200 -10-Tif^  2P3/2 • • 8 o S 6 in +-> c ZJ O u 4 A1'2 2 sat. sat. J - 1 / \ if % •*/ \ 1 . s a t / \ V \ 1 V •/ V X »^-^  T » > \ i I I 1 — 4 8 0 470 Binding energy (eV) F i g . 5.1. Photoelectron spectrum of the titanium 2p region from titanium t e t r a f l u o r i d e obtained with A l K a x-rays.The peaks lab e l l e d 'sat' are due to multielectron excitation. - 201 -480 470 Binding energy (eV) F i g . 5.2. Photoelectron spectrum of the titanium 2p region from titanium tetrachloride obtained with A l Ka x-rays.The peaks lab e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 202 -4 8 0 470 Binding energy (eV) F i g . 5.3. 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 tetrabromide o b t a i n e d w i t h A l Ka 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 e x c i t a t i o n . - 2 0 3 -F i g . 4 8 0 470 Binding energy (eV) 5.4. 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 i o d i d e o b t a i n e d with A l Ka x-rays.The peaks l a b e l l e d 'sat' are 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 . - 204 -c r o s s - s e c t i o n o f T i C l 4 o v e r such a s m a l l change i n t h e p h o t o e l e c t r o n k i n e t i c energy i s a p p r o x i m a t e l y c o n s t a n t . Thus any s t r u c t u r e due t o i n e l a s t i c c o l l i s i o n s p r e s e n t i n t h e T i 2p spectrum s h o u l d a l s o be o b s e r v e d i n the N I s spectrum. No 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 energy t h a n t h e N I s peak. T h e r e f o r e , t h e s a t e l l i t e s w i t h t h 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 g i v e n i n T a b l e 5.3 can be a t t r i b u t e d 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 p r o c e s s e s w i t h c e r t a i n t y . 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 s a t e l l i t e s a r e o b s e r v e d on t h e T i 2p 3 /, 2 peaks (at 7-13eV and 2-7eV) w h i l e o n l y one i s o b s e r v e d on t h e ^-"9-^/2 P e a ^ s * I t i s 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 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 2 p ^ y 2 peaks, and t h a t t h e ones w i t h s m a l l e r s e p a r a t i o n s a r e not r e s o l v e d from t h e s a t e l l i t e s w i t h 7-13eV s e p a r a t i o n s from the 2 p 3 ^ 2 peaks ( t h i s second s a t e l l i t e would be e x p e c t e d t o f a l l w i t h i n ^ l e V o f t h e 2 p 3 ^ 2 s a t e l l i t e f o r a l l f o u r t e t r a h a l i d e s ) . S a t e l l i t e s a r e a l s o o b s e r v e d i n t h 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 t h e T i 3p and h a l o g e n c o r e l e v e l s , and have a p p r o x i m a t e l y t h e same s e p a r a t i o n s as t h o s e r e p o r t e d on b o t h o f t h e T i 2p l i n e s but w i t h lower i n t e n s i t i e s . (Table 5.3 and 5.4). The s a t e l l i t e s 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 t h a n the - 205 -T a b l e 5.3 S a t e l l i t e s e p a r a t i o n s , A E , (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 T i 2p and 3p s p e c t r a  o f T i X 4 ( X = F , C l , B r , I ) AE 2 p 1 / 2 ( I ) AE 2 p 3 / 2 ( I ) AE 3 p ( I ) T i F 4 13.9(0.43). 13.0t.19) ,7.1(.12) 13.3(.27) T i F , ( s o l i d ) 3 1 4 . 7 ( . l l ) 4 T i C l 4 9. 8 (0 .41) 9.4 (. 16) ,4. 0 ( .14) 9. 7 (.09) T i B r 4 8.9 (0 .40) 8.5 ( .14) , 3. 3(.06) 9 . 3 (.13) T i l 4 7.3(0 .25) 7.2 (.18) ,2 .1 (.06) - b a From Re f . 8 b A s a t e l l i t e on t h e T i 3p l i n e o f T i l 4 c o u l d n o t be o b s e r v e d b e c a u s e o f i n t e r f e r e n c e f r o m I 4d e l e c t r o n s e x c i t e d by A l K a ^ 4 r a d i a t i o n . Table 5.4 s ^ i i t e separations (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 spectra of TJXQ (X=F,Cl,Br,I) T i F 4 T i C l 4 T i B r 4 T i l , F I s (I) 12.3(.04) a 2 p 1 / 2 ( I ) 10.6(.09) a 2p 3/2(1) 11.2(.04) Br 3 p 1 y 2 ( I ) 9.6(.09) Br 3 p y 2 ( I ) 9.5(.06) Br 3d(I) 8 . K . 0 5 ) 1 0 . 5 ( . 0 3 ) I 3 d 3 / 2 ( I ) 6.6 (.06) I 3(^^(1) 6.5 (.05) I 4 d 3 / 2 ( I ) I 4 d 5 / 2 ( I ) 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 multiple scattering calculations on TiOg and NiFg" 1 8 ' 2 1 predict the 3p s a t e l l i t e s to be ^50-80% as intense as those on the 2p l i n e s , i n reasonable agreement with the data presented here. The spectrum of the I 3d region of T i l ^ i s shown i n Figure 5.6. The bromine core l e v e l s i n T i B r ^ showed similar well-defined s a t e l l i t e s but those observed for the t e t r a f l u o r i d e and tetrachloride were somewhat broader. Vari a t i o n of the T i 2p^y 2 s a t e l l i t e separations, and the T i 2p^y 2 a n c ^ t n e T i ^p binding energies with the ligand i s shown i n F i g . 5.7. It can be seen that t h i s r e s u l t s i n four e s s e n t i a l l y p a r a l l e l l i n e s showing a good c o r r e l a t i o n between ligand electronegativity and s a t e l l i t e separation. Comparison of the spectra of the T i 2p regions of TiF^ i n the s o l i d state with the present data shows that both the s a t e l l i t e separation and i n t e n s i t y are sensitive to changes i n symmetry while the metal ion and ligands remain the same. For a precise assignment of the observed s a t e l l i t e s hole state calculations of the energy separations as well as the i n t e n s i t i e s are required. At the time t h i s project was undertaken no such calculations were available for any of these molecules, but the subsequent publication - 208 -I . I l_J 6 0 5 0 Binding energy (eV) F i g . 5 .5 . Photoelectron spectrum of the titanium 3p region from titanium 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 'sat' i s due to multi-electron e x c i t a t i o n . - 209 -640 630 Binding energy (eV) F i g . 5.6. Photoelectron spectrum of the iodine 3d region from titanium tetraiodide obtained with A l Ka x-rays.The peaks l a b e l l e d 'sat' are due to multielectron e x c i t a t i o n . - 2 1 0 -F Cl Br Ligand F i g . 5.7. Variation of the T i 2p-. s a t e l l i t e separations ( • and 0 ) and the T i 2 p 3 / , (A) arid T i 3p (A) binding energies with ligana.Note,the ordinate only gives r e l a t i v e binding energies. - 211 -31 of these r e s u l t s has led to 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 state and T i 2p core 40 ion state for T i C l ^ . The r e s u l t s of t h i s c a l c u l a t i o n w i l l be discussed l a t e r . In considering 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 4 , TiBr^ and T i l ^ , i t might be thought useful to compare the separation of the s a t e l l i t e s with the ground state o r b i t a l separations. However, the separations of the valence o r b i t a l s can 22-24 change d r a s t i c a l l y on io n i z i n g a core electron. Some information may also be gained by considering the resu l t s of available hole state 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 his calculations that the s a t e l l i t e s are due to ligand-to-metal 3d charge transfer t r a n s i t i o n s of the types t~ -* t„ and/or J j r 2g 2g * e ->- e . He has observed that the i n t e n s i t y of t h i s g g * type of t r a n s i t i o n i s very dependent on the amount of charge transferred from the ligands to the central ion upon i o n i z a t i o n , whether or not the central ion component of the mainly ligand o r b i t a l i s small before i o n i z a t i o n . It i s i n t e r e s t i n g to note that here one has two competing factors since a more covalent ligand has a larger central ion component before i o n i z a t i o n , but leads to more charge being transferred from the ligands to the central ion - 212 -upon i o n i z a t i o n . 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 analogous t o the e -y e and t _ -*- t„ y g g 2g 2g t r a n s i t i o n s i n o c t a h e d r a l symmetry, a r e t 2 •+ t ^ and * e e , r e s p e c t i v e l y . I n t h e o c t a h e d r a l T i (IV) 2— 8 — compounds, T i F , and T i O , ,the most prominent s a t e l l i t e s b b were a s s i g n e d t o t h e e^ -»- e* t r a n s i t i o n a l t h o u g h on t h e 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 i t i s not p o s s i b l e t o r u l e o ut t h e t„ t„ t r a n s i t i o n s . I t i s 2g 2g v e r y t e m p t i n g t o a s s i g n t h e s a t e l l i t e s w i t h t h e 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 as b e i n g due t o t h e t 2 •> t 2 t r a n s i t i o n s and * t h e ones w i t h s m a l l e r s e p a r a t i o n s t o e e . However, 4 -t h e c a l c u l a t i o n s on T i F g s uggest t h a t the two t r a n -s i t i o n s s h o u l d o n l y be s e p a r a t e d by the o r d i n a r y l i g a n d 17 f i e l d s p l i t t i n g of about 3eV , s i n c e t h e lo w e r e^ and t 2 l e v e l s s h o u l d have a p p r o x i m a t e l y t h e same energy. I f t h i s i s the case f o r t h e t e t r a h e d r a l m o l e c u l e s s t u d i e d h e r e , t h e n t h e t 2 and e s a t e l l i t e s s h o u l d o n l y be s e p a r a t e d 41 by a p p r o x i m a t e l y 4/9 o f t h i s , i . e . , ^1.5eV. However, t h e s a t e l l i t e s o b s e r v e d f o r t h e T i 2 p 3 y 2 l e v e l s o f 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, and t h i s makes the assignment o f the two s a t e l l i t e s t o * * t2  t2 a n d e e r a t n e r d o u b t f u l . - 213 -. At t h i s point i t i s i n t e r e s t i n g to consider the 22-24 arguments of Tossell who assigns the s a t e l l i t e s observed i n T i 0 2 , MnF2 and Mnl 2 to be ligand-to-metal 4s or -4p t r a n s i t i o n s on the basis of the hole state energy separations obtained from multiple scattering c a l c u l a t i o n s . In the present case then, one could assign the well separated s a t e l l i t e s to t h i s type of t r a n s i t i o n and the others to the ligand-to-metal 3d * * type (either the t -+ t or e -> e t r a n s i t i o n or both) . 2-In fa c t the multiple scattering c a l c u l a t i o n s on TiF^ * show an e -»• e t r a n s i t i o n energy of 7.6eV which indicates that the 7.1eV separation observed for TiF^ in the present study i s of the r i g h t magnitude for a 40 ligand-to-metal 3d t r a n s i t i o n . T o s s e l l has recently performed SCF Xa MO calc u l a t i o n s on the ground state and the T i 2p core ion state for T i C l ^ and has estimated s a t e l l i t e separations of 3.0 and 4.6eV for ligand-to-* * metal 3d type e e and t 2 t 2 excitations respectively. The weighted average of these separations, 3.7eV, agrees 40 very well with the experimental value of 4.0eV. T o s s e l l has also estimated the energies for two monopole tran-s i t i o n s from the ligand to the C13p-Ti 4s/4p antibonding o r b i t a l s which are at 9.9 and 10.6eV higher binding energy than the main l i n e . Although, these values agree very well - 214 -w i t h the e x p e r i m e n t a l v a l u e o f 9.4eV, Braga and L a r s s o n i n d i c a t e t h a t t h e s e l i g a n d - t o - c o n d u c t i o n band t y p e t r a n s i t i o n s w i l l be v e r y weak. D e s p i t e t h e f a c t t h a t 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 shakeup t r a n s i t i o n s a r e supposed t o be t h e s t r o n g e r m u l t i -17 18 21 e l e c t r o n t r a n s i t i o n s , ' ' i n t h e m o l e c u l e s s t u d i e d h e r e , t h e s a t e l l i t e s w i t h t h e l a r g e r s e p a r a t i o n s a r e t h e more i n t e n s e . So f a r the d i s c u s s i o n has c o n s i d e r e d the d a t a on the b a s i s o f o n e - e l e c t r o n t r a n s i t i o n s . However, M a r t i n 42 and S h i r l e y have suggested t h a t c a l c u l a t i o n s o f e l e c t r o n shakeup p r o b a b i l i t i e s s h o u l d i n c l u d e c o n f i g u -r a t i o n m i x i n g i n b o t h t h e i n i t i a l 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 and a d j a c e n t e l e m e n t s . ' T h e r e f o r e i t may be n e c e s s a r y 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 the c o r e p h o t o e l e c t r o n s p e c t r a o f t i t a n i u m t e t r a h a l i d e s i n o r d e r t o e x p l a i n t h e o b s e r v e d s a t e l l i t e s e p a r a t i o n s and i n t e n s i t i e s . From T a b l e 5.1, i t can be seen 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 w h i l e f o r t h e o t h e r 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 e f f e c t s - 215 -as these would be expected to be only ^O.leV. The usual 9 10 explanation ' for changes i n the spin-orbit separation i n t r a n s i t i o n metal compounds i s multiplet s p l i t t i n g but t h i s cannot be the case here. I t i s possible that i n TiF^ we also have a breakdown of the single p a r t i c l e description of the photoionization process. 5.4 Conclusion In t h i s work i t was shown that s a t e l l i t e structure may be observed on the high binding energy side of core l i n e s i n the gas phase photoelectron spectra of titanium 31 tetrahalides. When t h i s work was f i r s t published hole state c a l c u l a t i o n s were not available for any one of the four tetrahalides, and i t was hoped that these data 40 would stimulate such c a l c u l a t i o n s . Recently, T o s s e l l reported the r e s u l t s of SCF Xa MO c a l c u l a t i o n s of the T i 2p core ion state for T i C l 4 > Using t h i s r e s u l t i t i s now possible to assign the s a t e l l i t e peak at a binding energy of 4.OeV higher than the main l i n e i n the T i 2p3^2 spectrum of T i C l 4 , to ligand-to-metal 3d * * 40 type t r a n s i t i o n s e -> e and ^2 t2 * T o s s e l l also used t h i s SCF Xa r e s u l t to semiempirically estimate the corresponding s a t e l l i t e separations for TiBr„ and - 216 -T i l ^ t o be 2.9 and 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 v a l u e s o f 3.3 and 2.1eV. Based on t h e same c a l c u l a t i o n t h e h i g h e r energy s a t e l l i t e i n t h e T i 2p spectrum o f T i C l ^ can 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 band t y p e 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 ob s e r v e d i n t e n s i t y o f t h i s peak 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 the o n e - e l e c t r o n p i c t u r e . A l t h o u g h i t has been suggested t h a t t h e d i s a g r e e m e n t between t h e s a t e l l i t e i n t e n s i t i e s c a l c u l a t e d u s i n g 8— 2 — Tie- and T i F , c l u s t e r models and t h e e x p e r i m e n t a l o 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 the imp o r t a n c e o f second n e a r e s t n e i g h b o r 18 e f f e c t s i n t h e s o l i d , no such c o n s i d e r a t i o n would have t o be made f o r t h e vapor phase m o l e c u l e s s t u d i e d h e r e . T h e r e f o r e , t h e v a l i d i t y o f the o n e - e l e c t r o n model f o r t h e d i s c u s s i o n o f c o r e 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 s e m o l e c u l e s 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 o f t h e s e d a t a . - 217 -REFERENCES 1. A. Rosencwaig, G.K. Wertheim, and H.J. Guggenheim, Phys. Rev. Lett. 27, 479 (1971) 2. D.C. Frost, A. I s h i t a n i , and C.A. McDowell, Moi. Phys. 24_, 861 (1972) 3. L.J. Matienzo, L.I. Yin, S.O. Grim, and W.E. Swartz, J r . , Inorg. Chem. 12, 2762 (1973) 4. K.S. Kim, J. Electron Spectrosc. Relat. Phenom. 3_' 2 1 7 (1974) 5. B. Wallbank, C.E. Johnson, and I.G. Main, J . Phys. C 6_, L340 (1973) 6. B. Wallbank, C.E. Johnson, and I.G. Main, J. Phys. C 6_, L493 (1973) 7. B. Wallbank, I.G. Main, and C.E. Johnson, J. Electron Spectrosc. Relat. Phenom. 5, 259 (1974) 8. T.A. Carlson, J.C. Carver, L.J. Saethre, F.G. Santibanez, and G.A. Vernon, J. Electron Spectrosc. Relat. Phenom. 5_, 247 (1974) 9. 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Ohno , Physica Scripta 1_4, 148 (.1976) - 221 -CHAPTER SIX X-RAY PHOTOELECTRON SPECTROSCOPY OF Co(II), Ni(II) AND Cu(II) ACETYLACE-TONATE VAPORS 6.1 Introduction The phenomena of multielectron e x c i t a t i o n and multiplet s p l i t t i n g a r i s i n g from core i o n i z a t i o n of t r a n s i t i o n metal compounds have been studied i n considerable d e t a i l with the majority of work c l a s s i f i e d into two main groups:-a) The study of s a t e l l i t e structure as a function of the central metal. ^ b) The study of s a t e l l i t e structure as a function 5-13 of the ligand. Although the s a t e l l i t e structure i s expected to 14 vary with the ligand and the symmetry of the complex very l i t t l e work has been performed on compounds with the same central metal ion and ligand, but with d i f f e r e n t symmetry about the central metal ion. - 222 -Strong s a t e l l i t e s observed i n the inner s h e l l x-ray photoelectron spectra of f i r s t row t r a n s i t i o n metal compounds of octahedral symmetry have been attributed to ligand(L) to metal charge transfer t r a n s i t i o n s of * * the type e^ ->• e^ and/or t 2 g ^2q' depending upon the configuration of the ground state and the nature 2 3 5 9 11 15 of the ligands. ' ' ' ' ' These assignments have been confirmed by self-consistent multiple scattering c a l c u l a t i o n s which predict high i n t e n s i t i e s for shakeup 16 — 21 tr a n s i t i o n s of ligand-to-metal 3d type. However, i t has also been suggested that t r a n s i t i o n s such as ligand-to-metal 4s or 4p o r b i t a l s may be responsible 22-24 for the observed s a t e l l i t e s . This suggestion i s based on SCF-Xa scattered wave MO cal c u l a t i o n s , and no attempt was made to explain the observed i n t e n s i t i e s . 20 Braga and Larsson consider that high r e l a t i v e i n t e n s i t y for s a t e l l i t e peaks cannot be expected for L ->- metal 4s or 4p excitations. The s a t e l l i t e structure seen i n the 3s and 3p core spectra of paramagnetic compounds of f i r s t row tran-s i t i o n metals i s considered to be due mainly to multiplet s p l i t t i n g and configuration i n t e r a c t i o n e f f e c t s . Theoretical assessment of the magnitude of the s p l i t t i n g due to such e f f e c t s has been attempted - 223 -by s e v e r a l w o r k e r s . However, based 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 , argue t h a t f o r N i ( I I ) , and p o s s i b l y a l s o Co ( I I ) s a l t s , t h e s a t e l l i t e s t r u c t u r e i n t h e 3s spectrum a t a s e p a r a t i o n o f 4-7eV a r i s e s from a shakeup mechanism, whereas the 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 t h a t i t cannot be r e s o l v e d e a s i l y . I n t h i s c h a p t e r , a gas phase s t u d y o f some t r a n s i t i o n m e t a l a c e t y l a c e t o n a t e v a p o r s , M(AcAc)2 (M=Co,Ni,Cu), i s r e p o r t e d w i t h s p e c i a l emphasis on t h e s a t e l l i t e s t r u c t u r 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 s p e c t r a . Co(AcAc)2 i s t e t r a m e r i c i n t h e s o l i d phase w i t h t h e Co atom p o s s e s s i n g s i x f o l d c o o r d i n a t i o n . 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 c o o r d i n a t i o n . 2 8 Co i s h i g h s p i n (s=3/2) i n b o t h phases. N i j A c A c ^ / on t h e o t h e r hand, changes b o t h symmetry and s p i n s t a t e when g o i n g i n t o the vapor phase. The s o l i d i s t r i m e r i c and h i g h s p i n w i t h N i showing s i x f o l d c o o r d i n a t i o n . , and t h e d i a m a g n e t i c vapor i s monomeric and square p l a n a r . I n t h e s o l i d s t a t e , Cu(AcAc)2 i s a l m o s t square p l a n a r 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 g o i n g t o the p l a n a r monomeric vapor phase. ' I n b o t h phases, Cu has one u n p a i r e d e l e c t r o n . T h i s s t u d y o f the t r a n s i t i o n m e t a l a c e t y l a c e t o n a t e s 11 12 th u s a f f o r d s a comparison o f s o l i d ' and gas phase - 224 -x-ray photoelectron spectra. I t i s anticipated that t h i s should y i e l d information 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 the observed s a t e l l i t e structure. In addition, the r e l a t i v e roles of exchange s p l i t t i n g and shakeup i n 3s spectra may be examined. In the next section the experimental d e t a i l s are described. The r e s u l t s are discussed i n Section 6.3 and the conclusions are presented i n Section 6.4. This work w i l l appear elsewhere.^ 6.2 Experimental The spectrometer used i n t h i s study has been described i n d e t a i l i n Chapter Three. The Cu, Ni and Co acetylacetonates were prepared by previously established 31 32 methods. ' A l l the compounds were p u r i f i e d by vacuum sublimation. For an optimum count rate a vapor pressure 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. This pressure was produced by heating the sample inside the spectrometer, i n the old high temperature gas c e l l described i n d e t a i l i n Chapter Three. Gas phase Co(AcAc)- spectra were recorded at ^90°C, and the - 225 -spectra of Cu(AcAc) 2 and Ni(AcAc) 2 at ^ 100 and 'vl25°C, respectively. The compounds were i r r a d i a t e d with A l Ka x-rays to obtain the photoelectron spectra. Sample decomposition at the operating temperature was monitored by comparing the r e l a t i v e count rates of 33 metal core lev e l s to those of the 0 Is l e v e l . This comparison showed n e g l i g i b l e decomposition over the period of recording the spectra, as i n previous 31 34 studies. ' At least three separate spectra were recorded for each core l e v e l to make sure that the sometimes weak peaks were reproducible. In addition, the spectra were measured at d i f f e r e n t operating pressures, i n order to be able to detect energy loss structure. There was none detected. The spectra of the C and 0 Is le v e l s of free acetylacetone were also taken for comparison with those of the metal acetylacetonates. Metal 2p le v e l s were referenced to the Is l e v e l of 35 Ne (870.37eV) , and the 3s and 3p spectra were referenced to the Ne 2s l e v e l (48.47eV) 3 5. The C Is lev e l s of acetylacetone and the metal acetylacetonates 3 fi were referenced to the C Is l e v e l of C0 2 (297.5eV), and the 0 Is l e v e l s of these compounds were s i m i l a r l y 3 6 referenced to the 0 i s l e v e l of C0 2 (540.8eV). In a l l cases the reference gas was introduced simultaneously - 226 -into the spectrometer with the sample under i n v e s t i -gation . A l l spectra were least-squares f i t t e d to obtain 37 peak positions, l i n e widths and areas. 6.3 Results and Discussion The 2p, 3s and 3p binding energies of Co, Ni and Cu i n M(AcAc) 2 (M=Co,Ni,Cu) are shown i n Table 6.1. The s a t e l l i t e separations and r e l a t i v e i n t e n s i t i e s are summarized i n Tables 6.2 and 6.3. A l l the binding energy measurements reported i n t h i s work were re-producible to within ±0.1eV. Spectra of the 2p le v e l s of Co, Ni and Cu are shown i n Figs. 6.1 - 6.3 and those of the 3s and 3p l e v e l s i n Figs. 6.4 - 6.6 and 6.7 -6.9 respectively. Binding energies observed for the C Is and 0 ]_s l e v e l s i n the three t r a n s i t i o n metal acetylacetonates and free acetylacetone are l i s t e d i n Table 6.4. The C Is spectrum for Co(AcAc) 2 i s shown i n F i g . 6.10 which i s representative of the C Is spectra of the compounds studied. It can be seen (Table 6.4) that the C Is and 0 Is binding energies observed for the three t r a n s i t i o n metal acetylacetonates are d i f f e r e n t from those of free Table 6 . 1 Binding energies (eV) of metal (M = Co, N i , Cu) 2p, 3s and 3p l e v e l s i n H(AcAc) 2 vapors 2p' 3/2 2p 1/2 3sk 3 P-Co(AcAc) 2 N i ( A c A c ) 2 Cu(AcAc)2 786.5 860.5 940.0 802.0 877.9 960.0 AcAc = acetylacetonate Re Re ferenced to the Ne Is l e v e l (870.37eV) 35 ferenced to the Ne 2s l e v e l (48.47eV) 35 10 8.5 118.2 129 .6 66.4 73.5 84.9, 82.4( The Cu 3p peak could be deconvoluted in t o 2 peaks with a r a t i o 1:2.04 and a separation of 2.5eV between the 3 p 1 / 2 and 3 p 3 / 2 l e v e l s . T a b l e 6 . 2 S a t e l l i t e s e p a r a t i o n s , f l E / ( e V ) a n d 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 2 p s p e c t r a  O f M ( A c A c ) 0 (M = C o , N i , C u ) C o ( A c A c ) . N i ( A c A c ) . C u ( A c A c ) . A E 2 ( I ) P 3 / 2 v a p o r 4 . 2 ( 0 . 5 6 ) 5 . 5 ( 0 . 2 8 ) 5 . 0 ( 0 . 6 9 ) 1 0 . 0 ( 0 . 4 9 ) s o l i d 4 . 8 ( 0 . 6 0 ) ' 4 . 3 ( 0 . 6 2 ) ; 5 . 2 , 9 . 3 C A E . ( I ) 2 p l / 2 v a p o r 5 . 0 ( 0 . 6 0 ) 5 . 9 ( 0 . 2 3 ) 5 . 2 ( 0 . 7 2 ) 9 . 7 ( 0 . 4 8 ) s o l i d 5 . 3 , 9 . 1 1 00 F r o m R e f . 1 1 . H e r e t h e r e l a t i v e i n t e n s i t y i s g i v e n a s t h e r a t i o o f p e a k h e i g h t s ( s a t e l l i t e p e a k t o m a i n p e a k ) F r o m R e f . 12 T a b l e 6.3 S a t e l l i t e s e p a r a t i o n s , A E , 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 3s and 3p  s p e c t r a o f M ( A c A c ) 2 (M = Co,Ni,Cu) A E 3 s ( I ) & E 3 p ( I ) v a p o r s o l i d v a p o r s o l i d C o f A c A c ) , 4.1 (0.39) 4.8 3.0 (0.41) 3.2, 5.2 6.5 (0.09) , N i ( A c A c ) n 4.5 (0.15) 4.4 (0.04) K> C u ( A c A c ) , 4.8 (0.49) 3.3 (0.08) . . ^ 1 4 . 2 a , 8.6 a 7.5 b, 1 5 . 0 b I 10.1 (0.23) 8.7 (0.08) 2 3 . 5 b a D.C. F r o s t , C.A. M c D o w e l l and R.L. T a p p i n g ( u n p u b l i s h e d r e s u l t s ) b From R e f . 13. N o t e , no p e a k s w i t h any d e t e c t a b l e i n t e n s i t y were found a t e n e r g i e s h i g h e r t h a n lOeV from t h e main l i n e i n t h e gas phase s p e c t r a . - 230 -Co(AcAc)2 810 ' 800 790 Binding energy (eV) F i g . 6.1. X-ray photoelectron spectrum of the cobalt 2p region from cobalt (II) acetylacetonate.The peaks lab e l l e d 'sat' are due to multielectron excitation. - 231 -890 ' 880 870 ' 860 Binding energy (eV) F i g . 6.2. X-ray photoelectron spectrum of the nic k e l 2p region from n i c k e l (II) acetylacetonate. The peaks l a b e l l e d 'sat' are due to multi-electron e x c i t a t i o n . - 232 -970 ' 960 ' 950 ' 940 ' Binding energy (eV) F i g . 6.3. X-ray photoelectron spectrum of the copper 2p region from copper (II) acetylacetonate. The peaks l a b e l l e d 'sat' are due to multi-electron e x c i t a t i o n . - 233 -F i g . 6.4. X-ray photoelectron spectrum of the cobalt 3s region from cobalt (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multielectron ex c i t a t i o n . - 234 -125 120 115 ' Binding energy (eV) F i g . 6.5. X-ray photoelectron spectrum of the n i c k e l 3s region from nic k e l (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multi-electron e x c i t a t i o n . - 235 -Cu(AcAc)2 3s 1 . 1 ! 1 1 ' 140 130 Binding energy (eV) X-ray photoelectron spectrum of the copper 3s region from copper ( I I ) acetylacetonate. The peaks l a b e l l e d 'sat' are due to multi-electron excitation. - 236 -Co (Ac Ac )2 3p * 1 • 1 > 1 " — • 75 70 65 Binding energy (eV) F i g . 6.7. X-ray photoelectron spectrum of the cobalt 3p region from cobalt (II) acetylacetonate. The peaks l a b e l l e d 'sat' are due to multi-electron e x c i t a t i o n . - 237 -Ni(AcAc)2 1 , 1 80 70 Binding energy (eV) F i g . 6.8. X-ray photoelectron spectrum of the nic k e l 3p region from n i c k e l (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multi-electron e x c i t a t i o n . - 238 -95 90 85 80 Binding energy (eV) F i g . 6.9. X-ray photoelectron spectrum of the copper 3p region from copper (II) acetylacetonate. The peaks l a b e l l e d 'sat' are due to.multi-electron e x c i t a t i o n . T a b l e 6.4 O I s and C I s b i n d i n g e n e r g i e s (eV) and s a t e l l i t e s e p a r a t i o n s , AE (eV) i n a c e t y l a c e t o n e and M ( A c A c ) 2 v a p o r s (M = C o , N i , C u ) . R e l a t i v e i n t e n s i t y , I , o f the s a t e l l i t e peak i s g i v e n i n p a r e n t h e s e s . C l s a ' b ' C 0 l s d ( F W H M ) e A E Q L G ( I ) A c e t y l a c e t o n e 292.6, 290.4 537.7 (3.15) 3.6 ( . 0 4 ) g 537.3 (1.65) 538.8 ( 1 . 9 5 ) f C o ( A c A c ) , 291.8, 290.0 536.6 (1.8) 4.9 (.08) N i ( A c A c ) 2 292.0, 290.2 536.5 (1.9) 4.8 (.07) C u ( A c A c ) 2 291.8, 290.0 5 36.4 (1.8) 3.8 (.09) I a 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 2 ( 2 9 7 . 5 e V ) 3 6 b The C I s s i g n a l c o u l d be d e c o n v o l u t e d i n t o 2 p e a k s w i t h a r a t i o 1:1.5 ( h i g h b i n d i n g e n e r g y : low b i n d i n g energy) c No s a t e l l i t e s o f d e t e c t a b l e i n t e n s i t y were o b s e r v e d i n t h e C I s s p e c t r a d R e f e r e n c e d t o t h e O I s l e v e l o f C 0 2 ( 5 4 0 . 8 e V ) 3 6 e f g F u l l w i d t h a t h a l f maximum (FWHM) o f th e peak i s g i v e n i n p a r e n t h e s e s . From R e f . 38 See R e f . 39 - 240 -C02 Co(AcAc)2 CIs 300 ' 290~ Binding energy (eV) F i g . 6.10. X-ray photoelectron spectrum of the C Is region from cobalt (II) acetylacetonate. C0 2 was used as the reference gas. - 241 -acetylacetone, in d i c a t i n g that decomposition did not take place and that the methods used for obtaining the M(AcAc)2 (M=Co,Ni,Cu) spectra as outlined i n Sec. 6.2 are s a t i s f a c t o r y . It 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 that the 0 Is l i n e observed for acetylacetone i s very much broader than that observed for the metal acetylace-4 0 tonates (Table 6.4) . The broadening of the 0 Is signal of acetylacetone has been explained i n terms of an equilibrium mixture of keto and enol forms i n the vapor phase. ' ^ In fact the broad 0 Is l i n e of acetylacetone has been deconvoluted into two peaks 3 8 separated by 1.5eV. The reduced f u l l width at half maximum (FWHM) of the 0 Is signal i n the metal acety-lacetonates, compared to that of free acetylacetone, indicates a disappearance of the chemical non-equivalence of the two 0 atoms of the enolic acetylacetonate ligand as a r e s u l t of complex formation. In addition, the 0 i s spectra of a l l these acetylacetonates and free acetylace-tone show an additional peak at 3.5-5.0eV higher binding energies than the main peak (Fig. 6.11-6.13, Table 6.4). This cannot originate from impurities such as ^ 0 (53 9.7 36 36 38 eV) or 0 2 (543.leV). Brown has also reported similar structure i n the 0 Is spectrum of acetylacetone about 3.6eV to higher binding energy than the main l i n e . - 242 -Co (Ac Ac )2 • 1 • 1 ' 1 • 545 540 535 Binding energy (eV) F i g . 6.11. X-ray photoelectron spectrum of the 0 Is region from cobalt (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multi-electron e x c i t a t i o n . - 243 -Ni (AcAc)2 ~" 540 535 Binding energy (eV) F i g . 6.12. X-ray photoelectron spectrum of the 0 Is region from nic k e l (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multi-electron e x c i t a t i o n . - 244 -545 540 535 Binding energy (eV) F i g . 6.13. X-ray photoelectron spectrum of the 0 Is region from copper (II) acetylacetonate. The peak l a b e l l e d 'sat' i s due to multi-electron e x c i t a t i o n . - 245 -In that work the source of t h i s additional l i n e was unknown. This structure was also reported i n the 0 i s spectra of a number of 1,3-dicarbonyl compounds, with the r e l a t i v e i n t e n s i t y and p o s i t i o n dependent on the 3 8 compound investigated. The o r i g i n of t h i s additional structure w i l l be discussed l a t e r . The C Is spectra of acetylacetone and i t s t r a n s i t i o n metal complexes studied i n t h i s work did not show s a t e l l i t e structure at higher binding energies. In a l l of these spectra the C Is l i n e consisted of a doublet (Fig. 6.10) which could be deconvoluted into two peaks with the i n t e n s i t y r a t i o ^1:1.5 (high binding energy peak: low binding energy peak). The high binding energy component of t h i s doublet can be assigned to the carbonyl C atoms. It i s to be noted that the separation of the two components (2.2eV i n acetylacetone) decreases to 1.8eV i n the t r a n s i t i o n metal acetylacetonates (Table 6.4). This decrease i s larg e l y due to a decrease i n the binding energy of the carbonyl carbon atoms upon complex formation. S a t e l l i t e s were observed at higher binding energies than the main l i n e i n the metal 2p, 3s and 3p photoelectron spectra of a l l three complexes(Tables 6.2, 6.3) (Fig. 6.1-6.9). The r e l a t i v e i n t e n s i t y of the peaks did not change with - 246 -pressure, and therefore the additional structure appearing i n these photoelectron spectra can be confidently attributed to 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 of these e f f e c t s w i l l now be discussed. Cu(AcAc)-Cu(AcAc)2 d i f f e r s from the other two acetylaceton-ates studied here,in that i t shows two s a t e l l i t e s for both the 2p^y2 a n (^ ^^1/2 i i n e s ' a n c^ ^ a s approximately the same structure i n both the s o l i d and the vapor phases. S a t e l l i t e structure i s expected to vary with the ligand 14 and the symmetry of the complex. Thus, as shown i n Tables 6.2 and 6.3, the s a t e l l i t e separations observed for Cu(AcAc)2 vapor show a considerable s i m i l a r i t y to those observed for 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 spectra. S a t e l l i t e s present i n the 2p spectra of s o l i d Ni(AcAc)2 and Co(AcAc)2 have been explained 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 . ^ However, Cu(AcAc)2 i s d i f f e r e n t , i n that i t has been suggested that i n the case of 2+ s a t e l l i t e s seen i n Cu spectra, t h i s i s more l i k e l y to be due to a metal-to-ligand charge transfer - 247 -exci t a t i o n , as the core ionized 'ground state' has a completed 3d s h e l l due to an i n f l u x of electrons from 17 42 the ligand. ' This i s despite the fact that the ground state e l e c t r o n i c structure of neutral Cu(II) compounds i s characterized by a vacant spin o r b i t a l which i n D 0, symmetry i s a mainly d o r b i t a l . Larsson"*"8' ^  has suggested that i n core l e v e l spectra of Cu(II) compounds the main peak corresponds c l o s e l y to a d ^ configuration and i t should not show any large multiplet s p l i t t i n g , whereas the s a t e l l i t e which 9 corresponds c l o s e l y to a d configuration should show multiplet s p l i t t i n g . However, the separation between the two 2p s a t e l l i t e s (for both 2p.jy2 a n < ^ 2P3/2^ observed for Cu(AcAc) 2 i n the gas phase i s much too large (^5eV) to be due to multiplet s p l i t t i n g . In the present case . the observed FWHM values for the Cu 2p^^ 2 main l i n e , and the s a t e l l i t e at 5.2eV higher binding energy are 2.4 and 3.9eV respectively with the s a t e l l i t e at 9.7eV 40 having a FWHM of 2.8eV. Despite the fact that the r e l a t i v e valence o r b i t a l energies of 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 electronic spectra and molecular o r b i t a l - 248 -calculations for the neutral molecules i t i s not unreasonable to assign the lower binding energy s a t e l l i t e of both 2p and 3s spectra as due to a metal-to-ligand charge transfer type shakeup t r a n s i t i o n . This assignment supports Larsson's views regarding the o r i g i n of s a t e l l i t e s i n Cu(II) compounds. The large r e l a t i v e broadening of t h i s low binding energy s a t e l l i t e 43 may be explained i n terms of multiplet s p l i t t i n g , also supporting Larsson's views concerning s a t e l l i t e s i n Cu 2p spectra. The s a t e l l i t e peak at 'vlOeV may originate * from a d i f f e r e n t source such as a IT ->- TT t r a n s i t i o n . Further support for these assignments i s provided by the 3s s a t e l l i t e separations being almost i d e n t i c a l to those i n the 2p spectra. Since i t i s now well known that the s a t e l l i t e structure caused by electron shakeup 14 i s not dependent on the exact core electron ejected, one can assign both s a t e l l i t e s seen i n the 3s spectra to shakeup rather than multiplet s p l i t t i n g . Again, the separation between the two s a t e l l i t e s i s too large to be due to multiplet s p l i t t i n g , and the low binding energy s a t e l l i t e has a FWHM of 6.7eV which i s considerably broader 40 than the main peak (FWHM, 3.2eV). Both peaks are broader than the corresponding 2p peaks, mainly due to enhanced 43 co r r e l a t i o n e f f e c t s i n the 3s peak, again consistent with - 249 -Larsson's view that multiplet 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 of Cu(II) compounds. I t may be of s i g n i f i c a n c e to note that the FWHM of the s a t e l l i t e at lO.leV i s 2.9eV i n the 3s spectra compared to that of 2.8eV for the corresponding s a t e l l i t e i n the 2p spectra. This confirms the view that t h i s s a t e l l i t e originates from a d i f f e r e n t mechanism than that of the s a t e l l i t e at ^5eV. The 3p photoelectron spectrum of Cu(AcAc)2 (Figure 6.9) i s remarkably d i f f e r e n t from that of the 2p and 3s l e v e l s . In t h i s work no s a t e l l i t e s of detectable i n t e n s i t y 13 corresponding to those m the s o l i d state at binding energies higher than lOeV were observed. However, a weak peak was observed at 3.3eV higher binding energy than the main l i n e . The main l i n e could be deconvoluted into two components with a r a t i o of 1:2.04 and a separation of 2.5eV. This separation i s comparable to the calculated spin-orbit s p l i t t i n g of 2.8eV between 46 the Cu 3p1^2 a n d 3P3/2 l e v e l s - However the p o s s i b i l i t y that t h i s structure i s due to multiplet s p l i t t i n g cannot be completely excluded as the calculated multiplet structure of the Cu(II) 3p l e v e l indicates that 40% of the t o t a l i n t e n s i t y of a multiplet-derived s a t e l l i t e 18 merges with the main peak. - 250 -Co (AcAc) 2 and Ni.(AcAc.)2 S a t e l l i t e separations observed for Co(AcAc) 2 and Ni(AcAc) 2 vapors are d i f f e r e n t from those reported for 11 12 13 the corresponding s o l i d s . ' ' This strongly demons-trates the dependency of s a t e l l i t e structure on the symmetry of the complex. Both Ni and Co acetylacetonates have s i x - f o l d coordination i n the s o l i d state while, as mentioned before, the two compounds are square planar and tetrahedral respectively, i n the vapor phase. Shakeup t r a n s i t i o n s involve only those o r b i t a l s having the same symmetry since these follow the monopole selection rules. For charge transfer, i n 0^ symmetry, allowed t r a n s i t i o n s are L nt- -> M dt~ 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« Therefore, one would a n t i -cipate d i f f e r e n t s a t e l l i t e structure for compounds of d i f f e r e n t symmetry even when the metal and ligands involved are the same. However, one s i m i l a r i t y between the s o l i d and the vapor phase spectra of Co(AcAc)2 should be noted. 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 be due to the fact that Co i s high spin (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 of t o t a l charge transferred from the ligand to the central metal ion through o r b i t a l s of the correct symmetry, and ( i i ) whether or not the central ion component of the mainly ligand o r b i t a l i s small before i o n i z a t i o n . In diamagnetic complexes covalency of the bonds i s stronger, r e s u l t i n g i n a large central ion component before 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 corres-ponding paramagnetic compounds. For example, Ni(AcAc)^ i n the s o l i d phase (Ni i n a high spin state) shows strong satellites"'"''" whereas i n the gas phase the diamagnetic molecule shows considerably weaker s a t e l l i t e s (Table 6.2) . However, i t i s important to note here, that a compound with incompletely f i l l e d 3d l e v e l s need not be paramagnetic to show strong s a t e l l i t e structure. Carlson et a l . " ^ have reported the presence of strong s a t e l l i t e s i n the 2p photoelectron spectra of cobalt i n K^Co (C204)3 despite the fact that t h i s compound i s known to be d i a -magnetic. The most important requirement for the presence of s a t e l l i t e structure i n the photoelectron spectra of t r a n s i t i o n metal compounds i s an incompletely f i l l e d 3d subshell. This has been confirmed by the presence of s a t e l l i t e s i n Sc(III) and Ti(IV) compounds where the 3d 15 47 subshell i s formally empty ' and the absence of - 252 -s a t e l l i t e s i n Cu(I) compounds where t h e ground s t a t e has a 3d*^ c o n f i g u r a t i o n . I t i s hoped t h a t t h e s e r e s u l t s f o r N i ( A c A c ) 2 vapor w i l l h e l p i n a b e t t e r u n d e r s t a n d i n g 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 comparison between t h e d i a m a g n e t i c N i ( A c A c ) 2 vapor and t h e p a r a -magnetic s o l i d (Table 6.2). 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 e t a l * 1 f o r N i ( S a c S a c ) 2 s o l i d . N i ( S a c S a c ) 2 i s t h e d i s u l f u r analogue o f N i ( A c A c ) 2 and i s d i a m a g n e t i c . I t i s i n t e r e s t i n g t o note here t h a t , a l t h o u g h 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 compounds t h e s a t e l l i t e i n t e n s i t i e s a r e o f t h e same order*"*". (Reported 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 t h e 2 p ^ 2 s a t e l l i t e i n N i ( S a c S a c ) 2 s o l i d a r e 4.4eV and 0.22 r e s p e c t i v e l y and t h e v a l u e s o b t a i n e d i n t h i s work f o r N i ( A c A c ) 2 vapor a r e 5.5eV and 0.28.) Another i m p o r t a n t o b s e r v a t i o n i n t h e case o f t h e N i ( A c A c ) 2 vapor r e s u l t s i s t h e p r e s e n c e o f a s a t e l l i t e i n t h e 3s spectrum. T h i s s a t e l l i t e has 15% o f the i n -t e n s i t y o f t h e main peak (Table 6.3). As N i ( A c A c ) 2 vapor i s known t o be d i a m a g n e t i c , t h i s s t r u c t u r e 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 . T h i s s a t e l l i t e can be a t t r i b u t e d t o a shakeup t r a n s i t i o n . By comparing - 253 -the r e l a t i v e i n t e n s i t y of t h i s s a t e l l i t e peak with the corresponding s a t e l l i t e i n the s o l i d state spectrum, one should be able to get a meaningful answer to the problem of r e l a t i v e roles of shakeup and multiplet s p l i t t i n g i n the 3s spectra of paramagnetic t r a n s i t i o n metal compounds. 48 49 48 Based on atomic calculations ' Carlson et a_l have suggested that the 3s-3p s a t e l l i t e i n t e n s i t y r a t i o i s only one t h i r d that of the 2s-2p s a t e l l i t e i n t e n s i t y . 20 On the other hand, Braga and Larsson, based on a multiple scattering moleclar o r b i t a l treatemnt, have suggested that the s a t e l l i t e i n t e n s i t y r a t i o for 3s-3p lev e l s could be as high as 50-70% that of the 2s-2p l e v e l s . Using t h i s l a t t e r estimate as the upper l i m i t , and from s o l i d state data for the Ni(AcAc)2 2p l e v e l , one would anticipate a s a t e l l i t e i n t e n s i t y of 31-43% for the 3s l e v e l of s o l i d Ni(AcAc) 2. A value i n the same range could be projected by using the observed i n t e n s i t y of 15% for the 3s l e v e l of diamagnetic Ni(AcAc) 2 vapor and the fact that the 2p 3y 2 s a t e l l i t e of the paramagnetic s o l i d i s twice as intense as that of the diamagnetic vapor. For the paramagnetic Co(AcAc) 2 vapor (s=3/2), the observed s a t e l l i t e s are of high i n t e n s i t y for both 3s and - 254 -3p l e v e l s . The separation of 3eV between the main peak of the 3p spectrum and i t s nearest s a t e l l i t e i s too large to be due to spin o r b i t s p l i t t i n g of the 3p subshell. As mentioned i n the introduction, the high binding energy component of the 3s spectra of paramagnetic Ni(II) and Co(II) compounds (at 4-7eV) has been interpreted as 25 19 due to multiplet s p l i t t i n g . Larsson and Braga have recently suggested that the i n t e n s i t y of the high binding energy component of the 3s spectra of paramagnetic Ni(II) and Co (II) compounds belongs to a shakeup s a t e l l i t e , whereas the multiplet s p l i t t i n g of the main l i n e i s so small that i t cannot be resolved e a s i l y . The Co (II) 3s spectrum of Co(AcAc) 2 vapor obtained i n t h i s work w i l l now be discussed i n the l i g h t of these suggestions. The Co 3s spectrum shows a s a t e l l i t e at 4.leV higher binding energy than the main peak, with a r e a l t i v e i n t e n s i t y of 39%. This energy separation i s d i f f e r e n t from that of the 4.8eV observed for s o l i d Co(AcAc) 2 (Table 6.3). For several reasons these r e s u l t s on Co(AcAc)2 indicate that the s a t e l l i t e observed i n the 3s spectrum i s due to shakeup rather than multiplet s p l i t t i n g : (i) The magnitude of the s a t e l l i t e separations i n - 255 -both the 2p^^2 a n < ^ ^s spectra for Co (AcAc) ^  vapor are more or less the.same. This s i m i l a r i t y (but not the precise magnitude) i s common to the s o l i d state r e s u l t s also. The s a t e l l i t e s i n the 2p spectra are known to originate 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 less independent of the o r i g i n a l core hole state, and this,coupled with the observation of similar s a t e l l i t e separations,suggests that the s a t e l l i t e s associated with the 2p and 3s core l i n e s originate from the same mechanism. This statement i s incorrect only i f the multiplet s p l i t t i n g of the 3s l e v e l i s of the same order as that of the shakeup t r a n s i t i o n . However, the following observations more or less exclude t h i s p o s s i b i l i t y . ( i i ) Shakeup t r a n s i t i o n s are more susceptible to changes i n symmetry than multiplet s p l i t t i n g . In the s o l i d phase, Co(AcAc)^ exists as a tetramer and shows octahedral symmetry whereas the monomeric gas phase species i s of tetrahedral symmetry. In both phases Co i s i n a high spin state. Therefore, i f the 3s s a t e l l i t e i s due to multiplet s p l i t t i n g , the separation between the main peak and the s a t e l l i t e should be more or less i d e n t i c a l i n both phases. As mentioned above, the precise magnitude of the s a t e l l i t e separation i s d i f f e r e n t i n the two phases. This difference i n - 256 -s a t e l l i t e separation cannot be due to a change i n spin density at Co when going from the s o l i d to the vapor phase as such changes would be of much smaller magnitude. 7 E a r l i e r work i n t h i s laboratory on CoF 2 and CoF^ confirms t h i s observation. Here the 3s s a t e l l i t e separation changed by only 0.2eV when going from CoF 2 to CoF 3, the number of unpaired electrons increasing from 3 to 4. On the other hand, the observed difference i n s a t e l l i t e separation between the s o l i d and vapor phase 3s spectra could be e a s i l y explained by a shakeup mechanism. ( i i i ) The r e l a t i v e i n t e n s i t y of the Co 3s s a t e l l i t e i n the vapor phase i s 0.39. The value i s d i f f e r e n t from the r a t i o 5:3 expected for the two spin states. Values for the r e l a t i v e i n t e n s i t y of 3s s a t e l l i t e s calculated 25 by V n n i k k a and Ohrn, which include configuration mixing are not i n agreement with t h i s r e s u l t . This i s understandable because these values do not include e f f e c t s due to covalency. This deviation from the 5:3 i n t e n s i t y r a t i o between the main peak and the s a t e l l i t e i n the 3s spectra i s seen i n other Co compounds which 7 were studied previously i n t h i s laboratory. 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 CoF 2, CoCl 2 and CoBr 2 are 0.63, 0.86 and 1.12 respectively. The value for CoF^ i s 0.58. Therefore,in - 257 -the l i g h t of t h i s present work, these r e s u l t s suggest that the s a t e l l i t e s seen i n Co(II) 3s spectra, 4-6eV removed from the main l i n e are due to shakeup rather than due to multiplet s p l i t t i n g . The FWHM of the main peak and the s a t e l l i t e peak i n the 3s spectrum of Co(AcAc) 2 vapor are 3.6 and 4.OeV respectively. The 3s main peak of Co i s broader than that of Cu i n the 3s spectrum of Cu(AcAc) 2. This observation 19 supports the view put forward by Larsson and Braga, who suggested that the multiplet s p l i t t i n g of the 3s spectra of Ni(II) and possibly Co (II) s a l t s i s so small that i t cannot be resolved e a s i l y . However i t i s to be noted that the FWHM of the Co (II) 3s s a t e l l i t e i s less than that of the Cu(II) 3s spectrum, t h i s being the opposite of what one would have expected from gneeral considerations of multiplet s p l i t t i n g . 0 Is The 0 Is spectra of a l l three acetylacetonates studied i n t h i s work show a s a t e l l i t e at binding energies higher than the main peak (Table 6.4). It has been reported 3 8 that acetylacetone also shows a similar structure and th i s i s confirmed by the present work. As stated e a r l i e r , - 258 -t h i s feature has also been observed i n a number of 1,3-dicarbonyl compounds. It i s important to note here that no such s a t e l l i t e s of any appreciable i n t e n s i t y have been reported for 3 ,3-dimethylacetylacetone, where the two methyl groups at the central carbon prevent enolization. The s a t e l l i t e separations i n the 0 i s spectra of the metal acetylacetonates are a l l higher than that of free acetylacetone. These observations suggest the p o s s i b i l i t y that the observed s a t e l l i t e s are due to a shakeup t r a n s i t i o n which i s mainly of L T T + L T T * character. The calculated electronic structure, and observed electronic spectra of acetylacetone and i t s anion indicate the presence of o r b i t a l s of the correct 50 symmetry and energy ordering for 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 considerably on core l e v e l i o n i z a t i o n , the exact nature of the shakeup t r a n s i t i o n could be confirmed only af t e r hole state calculations are ca r r i e d out on these molecules. The p o s s i b i l i t y that 0 Is sate-l l i t e s i n metal acetylacetonates are due to metal to ligand charge transfer remains to be excluded. I f the shakeup t r a n s i t i o n involved 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 explain the enhanced s a t e l l i t e separation i n the 0 Is spectra of metal acetylacetonates compared to that of acetylacetone, since back donation - 259 -of e l e c t r o n s from the metal t o the l i g a n d TT* a n t i -bonding o r b i t a l s i s expected t o d e s t a b i l i z e l i g a n d I T * l e v e l s r e l a t i v e t o bonding TT l e v e l s . Lowering of the c a r b o n y l carbon Is b i n d i n g energy on complex formation i s a l s o noted, i n accord w i t h e x p e c t a t i o n s . 6.4 Concl u s i o n s From the s t u d i e s of the gas phase x-ray photo-e l e c t r o n s p e c t r a , i t was shown t h a t the s a t e l l i t e s t r u c t u r e seen i 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 s depends on the symmetry of the complex. As both N i and Co a c e t y l a c e t o n a t e s undergo a change i n symmetry when going from the s o l i d t o the vapor, the e f f e c t o f change i n symmetry 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 s t u d i e d without changing the c e n t r a l metal atom and/or l i g a n d . At l e a s t i n the case of CuCAcAc^f the second n e a r e s t atom e f f e c t s were found t o be unimportant i n det e r m i n i n g the s a t e l l i t e s t r u c t u r e . Present r e s u l t s s t r o n g l y suggest t h a t the s a t e l l i t e seen i n the 3s s p e c t r a of paramagnetic t r a n s i t i o n metal 2+ 2+ 2+ compounds p a r t i c u l a r l y those of Co , Ni and Cu , a t b i n d i n g e n e r g i e s 4-6eV higher than the main peak are due to 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 . The main - 260 -e f f e c t of multiplet s p l i t t i n g i n these spectra seems to be broadening of the peaks. This broadening i s more predominant 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^ ari 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 that the low binding energy s a t e l l i t e r e s u l t s from a metal-to-ligand charge transfer t r a n s i t i o n as opposed to the ligand-to-metal charge transfer type shakeup mechanism proposed for the s a t e l l i t e s found i n 2p and 3s spectra of Co and Ni acetylacetonates. In the case of the ligand, s a t e l l i t e structure i s seen only i n the 0 Is spectra, and i s possibly due to a L T T + L T T * type shakeup t r a n s i t i o n . Hole state calculations for these molecules are not av a i l a b l e , and t h i s makes i t d i f f i c u l t to assign unambiguously the shakeup peaks to s p e c i f i c shakeup t r a n s i t i o n s . I t i s hoped that t h i s study w i l l stimulate such c a l c u l a t i o n s . - 261 -REFERENCES 1. D.C. Frost, CA. McDowell, and R.L. Tapping, J . Electron Spectrosc. Relat. Phenom. 7, 297 (1975) 2. K.S. Kim, and N. Winograd, Chem. Phys. Lett. 31, 312 (19 75) 3. D.C Frost, CA. McDowell, and B. Wallbank, Chem. Phys. Lett. 4 0 , 189 (1976) 4. J . C Carver, G.K. Schweitzer, and T.A. Carlson, J. Chem. Phys. 57_, 973 (1972) 5. B. Wallbank, I.G. Main, and C E . Johnson, J . Electron Spec-trosc. Relat. Phenom. 5, 259 (1974) 6. M.A. Brisk, and A.D. Baker, J. Electron Spectrosc. Relat. Phenom. 6, 81 (19 75) 7. D.C. Frost, CA. McDowell, and I.S. Woolsey, Moi. Phys. 27, 1473 (1974) 8. D.C. Frost, CA. McDowell, and I.S. Woolsey, Chem. Phys. Lett. 17F 320 (1972) 9. K.S. Kim, J . Electron Spectrosc. Relat. Phenom. 3, 217 (1974) 10. L.J. Matienzo, L.F. Yin, S.O. Grim, and W.E. Swartz, Inorg. Chem. 12, 2762 (1973) 11. T.A. Carlson, J.C. Carver, L.J. Saethre, F.G. Santibanez, and G.A. Vernon, J. Electron Spectrosc. Relat. Phenom. 5_, 247 (1974) 12. D.C. Frost, CA. McDowell, and R.L. Tapping, J. Electron Spectrosc. Relat. Phenom. 6, 347 (1975) - 262 -13. D.C. Frost, A. I s h i t a n i , and CA. McDowell, Moi. Phys. 24, 861 (.1972) 14. M.A. Brisk, and A.D. Baker, J . Electron Spectrosc. Relat. Phenom. 7, 19 7 (.19 75). 15. B. Wallbank, C E . John son, and I. G. Main , J . Phys . C 6 , 340 (1973) 16. S. Asada, and S. Sugano, J . Phys. Soc. Japan 41_, 1291 (1976). 17. S. Larsson, J . Electron Spectrosc. Relat. Phenom. 8_, 171 (.19 76) 18. S. Larsson, Chem. Phys. Lett. £0 , 362 (.1976) 19. S. Larsson, and M. Braga, Chem. Phys. L e t t . 4_8, 596 (1977) 20. M. Braga, and S. Larsson, Int. J . Quantum Chem. Symp. 11, 61 (1977) 21. S. Larsson, Physica S c r i p t a 1£, 378 (.1977). 22. J.A. Tossel, Chem. Phys. 15_, 303 (.1976) 23. J.A. Tossel, J. Electron Spectrosc. Relat. Phenom. 10, 169 (1977) 24. J.A. Tossel, J . Electron Spectrosc. Relat. Phenom. 8_, 1 (1976) 25. E. - K. V i i n i k k a , and Y. Ohrn, Phys. Rev. B 11, 4168 (1975) 26. E. - K. Vi i n i k k a , and S. Larsson, J. Electron Spectrosc. Relat. Phenom. 7, 163 (1975) 27. F.G. Santibanez, and T.A. Carlson, Phys. Rev. B 12, 965 (1975) 28. J.P. Fackler, J r . , Prog. Inorg. Chem. 7, 361 (1966) 29. J.P. Fackler, J r . , M.L. Mittleman, H. Weigold, and CM. Barrow, J. Phys. Chem. 72_, 4631 (1968). - 263 -30. J.S.H.Q. Perera, D.C. Frost, and C.A. McDowell, J. Chem. Phys. 7_2 (19 80). To be published 31. R.G. Charles, and M.A. Pawlikowski, J. Phys. Chem. 62, 440 (1958) 32. J.B. E l l e r n , and R.O. Ragsdale, Inorg. Synth. XI 82 (1968) 33. J.H. Sc o f i e l d , J. Electron Spectrosc. Relat. Phenom. 8_, 129 (1976) 34. M.Z. Gurevich, T.M. Sas, N.E. Lebedeva, V.V. Zelentsov, and B.D. Stepin, Russian J. Inorg. Chem. 17. 556 (.1976). 35. G. Johansson, J . Hedman, A. Berndtsson, M. Klasson, and R. Nilsson. J. Electron Spectrosc. Relat. Phenom. 2_, 295 (1973) 36. K. Siegbahn, C. Nordling, J. Johansson, J. Hedman, P.F. Heden, K. Hamrin, U. Gelius, T. Bergmark, L.O. Werme, R. Manne, and Y. Baer,"ESCA Applied to free molecules" (North Holland, Amsterdam, 1969) 37. C.S. Fadley, Ph.D. thesis, University of C a l i f o r n i a , Berkeley, LBL Report No. 19535 (1970) 38. R.S. Brown, J . Am. Chem. Soc. 9_9 , 5497 (1977) 39. This value was estimated from the results reported i n Ref. 38 40. FWHM values reported here are the values obtained using the 37 curve f i t t i n g program , and include the contributions from the A l Ka ex c i t i n g l i n e (^0.8eV) and the spectrometer resolution (^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. Lett. 32, 401 (1975). 43. S. Larsson, Physica Scripta 16, 381 (1977) 44. F.A. Cotton, C.B. Harris, 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. Nordling, A. Fahlman, R. Nordberg, K. Hamrin, J. Hedman, G. Johansson, T. Bergmark, S. - E . Karlsson, I. Lindgren, and B. Lindberg, Nova Acta Regiae Soc. S c i . Upsaliensis, Ser IV, Vol. 20 (196 7) 47. B. Wallbank, J.S.H.Q. Perera, D.C. Frost, and C.A. McDowell, J. Chem. Phys. 69, 5405 (1978) 48. T.A. Carlson, 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. Nakanishi, H. Morita, and S. Nagakura, B u l l . Chem. Soc. Japan 50, 2255 (1977) CHAPTER SEVEN SUMMARY AND PROGNOSIS The application of electron spectroscopy i n the investigation of the e l e c t r o n i c structure of matter i s now a well established f i e l d of research. Electron spectroscopy has been applied to a l l known physical 1-3 states of matter, however, the study of free atoms and molecules i s p a r t i c u l a r l y rewarding as most of the inherent features of the spectra can be investigated i n the absence of condensed phase e f f e c t s . Then, by comparison of the free atom/molecule r e s u l t s with those obtained for the condensed state, valuable information 3 4 pertaining to condensed phase e f f e c t s can be obtained. ' Gas phase x-ray photoelectron spectroscopy, i n p a r t i c u l a r , i s invaluable as a tool for systematically investigating - 2 6 6 -multielectron e x c i t a t i o n processes accompanying photo-io n i z a t i o n . In the s o l i d state, such studies are occasionally hampered by the presence of large back-grounds caused by i n e l a s t i c scattering, plasmon exci t a t i o n etc. Structure due to i n e l a s t i c c o l l i s i o n s i n the vapor phase spectra can, however, be r e a d i l y i d e n t i f i e d and corrected. The work described i n t h i s thesis has involved the development and operation of a gas phase x-ray photoelectron spectrometer. A high temperature range of upto ^ 1 0 0 0 ° C i s available for vaporizing i n v o l a t i l e s o l i d s and metals, and e f f i c i e n t data a c q u i s i t i o n and manipulation i s handled by a P D P 8 / e minicomputer i n t e r -faced to the spectrometer. This work therefore represents an experimentalist's viewpoint of some important aspects of x-ray photoelectron spectroscopy. More f u l l y quantitative interpretations of these r e s u l t s can now be attempted by f u l l - t i m e theoreticians. For most species, the spectra reported i n t h i s thesis represent the f i r s t x-ray photoelectron spectroscopic study i n the vapor phase. Core l e v e l binding energies of Group IA and IIA free atoms, excepting lithium and beryllium, were determined accurately and the r e s u l t s are reported i n - 267 -Chapter Four. These binding energy values can be used in conjunction with the corresponding standard state binding energies to estimate the 'phase t r a n s i t i o n s h i f t s . ' The free atom binding energies 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 to t e s t the v a l i d i t y of various semi-empirical and t h e o r e t i c a l 5-7 models. The observed values of phase t r a n s i t i o n s h i f t s are lower than those values calculated for extra-6 8 9 atomic relaxation using a semilocalized exciton model. ' ' However, the trendsof these phase t r a n s i t i o n s h i f t s are rather accurately predicted, i n d i c a t i n g the dominant role played by extra-atomic relaxation i n determining these s h i f t s . The d i r e c t l y measured binding energies of Chapter Four are, i n most cases, i n good agreement with those estimated i n d i r e c t l y by combining x-ray emission data for s o l i d s and o p t i c a l r e s u l t s for free atoms. However, for a l l l e v e l s of calcium, t h i s i n d i r e c t method gives values ^5eV lower than the XPS binding energies. Although good agreement i s obtained between the XPS binding energies of barium and values estimated using x-ray emission r e s u l t s and free atom o p t i c a l data, there are indications that the estimates are less than r e l i a b l e . These r e s u l t s , there-fore, strongly suggest that extreme care should be taken in using such i n d i r e c t l y estimated free atom binding energies. - 268 -Multielectron e x c i t a t i o n s a t e l l i t e s were observed in a l l core l e v e l spectra of the free atoms reported i n Chapter Four. In the case of the group IA elements, the observed s a t e l l i t e s can be conveniently assigned to a ns-*(n+l)s type shakeup t r a n s i t i o n , using the 'equivalent cores approximation'. However, the s i t u a t i o n i s less straightforward i n the case of the Group I I A metal atoms. Martin and S h i r l e y ^ have suggested that both i n i t i a l state and f i n a l i o n i c state configuration i n t e r a c t i o n can be important i n determining the s a t e l l i t e structure. The r e s u l t s from the Group I I A metal atoms are strong indications of the incompleteness of the one-electron t r a n s i t i o n description of the shakeup process. X-ray photoelectron spectra of the titanium 2p and 3p le v e l s , and the halogen core l e v e l s from titanium t e t r a -halide vapors, T i X 4 ( X = F , C l , B r , I ) were obtained (Chapter F i v e ) . Two s a t e l l i t e s associated with the T i 2p 3^ 2 l e v e l were observed for a l l four tetrahalides. The s a t e l l i t e at lower binding energies can be assigned to a ligand-to-metal 3d type charge transfer t r a n s i t i o n (either the e+e* or t2-Hr* t r a n s i t i o n , or both). A recent SCF Xa hole state calculation''"''" for 2p ionized T i C l ^ confirms t h i s assignment. This c a l c u l a t i o n has estimated an ex c i t a t i o n energy for 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 agreement w i t h t h e s e p a r a t i o n between t h e h i g h e r energy s a t e l l i t e and the main peak. However, i n t h e o n e - e l e c t r o n p i c t u r e t h e s e t r a n s i t i o n s a r e e x p e c t e d t o be v e r y weak when compared t o l i g a n d - t o - m e t a l 3d t y p e 12 t r a n s i t i o n s d e s p i t e t h e f a c t t h a t t h e former was obs e r v e d t o be t h e s t r o n g e r s a t e l l i t e i n a l l f o u r t e t r a h a l i d e s . F u r t h e r h o l e s t a t e 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 may be o f some use i n e x p l a i n i n g t h e o b s e r v e d i n t e n s i t i e s . New e x p e r i m e n t a l e v i d e n c e was p r e s e n t e d i n Ch a p t e r S i x s t r o n g l y i n d i c a t i n g t h a t t h e s a t e l l i t e s t r u c t u r e seen i n the 3s s p e c t r a o f paramagnetic 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 , N i and Cu , a t b i n d i n g e n e r g i e s 4-6eV h i g h e r than t h e main peak, a r e due 13 t o 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 . T h i s e v i d e n c e came from a st u d y o f t r a n s i t i o n m e t a l a c e t y l -a c e t o n a t e s , M(AcAc)2 ( M = C o ( I I ) , N i ( I I ) , C u ( I I ) ) i n t h e vapor phase. Both N i and Co a c e t y l a c e t o n a t e s undergo a change i n symmetry when g o i n g from t h e s o l i d t o t h e vap o r . I n t h e case o f C o ( I I ) and C u ( I I ) a c e t y l a c e t o n a t e s , t h e s p i n s t a t e s of the m e t a l atoms a r e unchanged when g o i n g from t h e s o l i d t o the v a p o r , whereas f o r N i ( I I ) a c e t y l a c e t o n a t e the s o l i d i s h i g h s p i n , and the vapor i s d i a m a g n e t i c . A l l t h r e e a c e t y l a c e t o n a t e s have been - 270 -previously studied i n the s o l i d state" 1"' 1' x D and comparison of the vapor phase spectra with those i n the s o l i d phase provided information both 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 in symmetry about the metal atom without changing the ligand, and the r e l a t i v e roles 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 3s spectra. The experimental r e s u l t s on Cu(II) acetylacetonate can be explained i n terms of a metal-to-ligand type charge transfer excitation as opposed to the ligand-to-metal charge transfer mechanism proposed for the other t r a n s i t i o n 16 17 metal compounds, an observation supporting 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 metal core l e v e l spectra. The main thesis of t h i s t r e a t i s e has, therefore, been the experimental determination of several core l e v e l binding energies and the associated s a t e l l i t e structure. The present spectrometer has demonstrated a c a p a b i l i t y to e f f e c t i v e l y gather information on such electronic properties of free atoms and molecules. However, further work can, and should be done to improve the performance, s e n s i t i v i t y / and f l e x i b i l i t y of the system. For example, the studies of multielectron e x c i t a t i o n s a t e l l i t e s have shown that for a given core l e v e l these are 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 ' f i n g e r p r i n t ' . However, due t o t h e weak n a t u r e of t h e s e p r o c e s s e s , s e v e r a l m o d i f i c a t i o n s c o u l d be made t o improve t h e d a t a c o l l e c t i o n , t h e r e b y r e d u c i n g the time t o r e c o r d s p e c t r a , and e l i m i n a t i n g problems caused by v o l t a g e d r i f t , 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 tube and gas c e l l windows. 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 t o 48 h r s . t o accumulate. T h i s d e c r e a s e d s e n s i t i v i t y i s caused by t h e s m a l l e r d i a m e t e r o f the e n t r a n c e and e x i t h o l e s o f 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 th e r e s o l v i n g power of t h e s p e c t r o m e t e r (Chapter T h r e e ) . Paramount amongst methods f o r remedying t h i s s i t u a t i o n would be t h e use of a p o s i t i o n s e n s i t i v e m u l t i d e t e c t o r system, i n s t e a d o f t h e s i m p l e c h a n n e l e l e c t r o n m u l t i p l i e r a t 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 c a p i t a l i z e on the 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 m u l t i -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 a r e used i n c o n j u n c t i o n w i t h e l e c t r o n s p e c t r o m e t e r s . * 8 ' * ^ R e c e n t l y 20 H i c k s e t a_l. have d e v e l o p e d an e l e c t r o n s p e c t r o m e t e r employing a c h a r g e - c o u p l e d imaging d e v i c e f o r p o s i t i o n s e n s i t i v e d e t e c t i o n . T h i s i s c l a i m e d t o g i v e a (con-s e r v a t i v e ) improvement o f more th a n a f a c t o r o f 100 i n s e n s i t i v i t y o v e r t h e b e s t e x i s t i n g s p e c t r o m e t e r s . W i t h - 272 -such a multidetector system one would be able to 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 of the minicomputer. Such a modification would be p a r t i c u l a r l y useful i n the study of very high temperature species i . e . >1000°C, which place much more stringent requirements on the spectrometer, necessitating shorter scanning times. Thus, the preliminary spectrum of Ag atoms (Chapter Three) could have been subs t a n t i a l l y improved. Between 1000 and 2000°C, there are several species of high temperature i n t e r e s t , e.g. metal atoms of the f i r s t t r a n s i t i o n s e r i e s . 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 transient and unstable species, where atoms and molecules exist i n unusual bonding situations and where large chemical s h i f t s of core lev e l s may be expected. Such studies would there-fore complement the excellent work that i s being done i n 21 UPS. - 273 -REFERENCES 1. K. Siegbahn, C. Nordling, A. Fahlman, R. Nordberg, K. Hamrin; J. Hedman, G. Johansson, T. Bergmark, S.-E. Karlsson, I. Lindgren, and B. Lindberg, "ESCA: Atomic, Molecular, and S o l i d State Structure Studied by Means of Electron Spectroscopy", Nova Acta Regiae Soc. S c i . Upsaliensis, Ser. IV, Vol.20 (Almqvist and Wiksells, Stockholm, 1967) 2. K. Siegbahn, C. Nordling, G. Johansson, J. Hedman, P. F. Heden, K. Hamrin, U. Gelius, T. Bergmark, L. 0. Werme, R. Mann, and Y. Baer, "ESCA, Applied to Free Molecules" (North-Holland Publishing Company, Amsterdam, 1969) 3. H. Siegbahn, L. Asplund, P. Kelfve, K. Hamrin, L. Karlsson, and K. Siegbahn, J. Electron Spectrosc. Relat. Phenom. 5, 1059 (1974) 4. M. S. Banna, B. Wallbank, D. C. Frost, C. A. McDowell, and J. S. H. Q. Perera, J. Chem. Phys. 68_, 5459 (1978). 5. P. Albertsen, and P. Jo'rgensen, J. Chem. Phys. 70, 3254 (1979) 6. D. R. Beck, and C. A. Nicolaides, NATO Adv. Study Inst. Ser., Ser. C (1978) (Pub. 1979) C46 (Excited States Quantum Chem.) p.329 - 2 74 -B. Johansson, and N. Mortensson, to be published L. Ley, F. R. McFeely, S. P. Kowalczyk, J. G. 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Wallbank, and J . Comer, t o be p u b l i s h e d 21. D. C. F r o s t , S. T. Lee, C. A. McDowell, and N. P. C. Westwood, J . E l e c t r o n S p e c t r o s c . R e l a t . Phenom. 12, 95 (1977) APPENDIX MULTI-CHANNEL SCALING PROGRAM Symbolic Program L i s t i n g / M C S P R O G R A M / M A X I M U M OF 3 R E G I O N S / E A C H N O T E X C E E D I N G 2 5 5 C H A N N E L S / I N I T I A L L I Z E T H E C O M P U T E R /WHEN A I S T Y P E D C O M P U T E R A S K S / F O R I N I T I A L V O L T A G E ( T Y P E I N T H E R E Q U I R E D / R E T A R D I N G V O L T A G E ) , D W E L L T I M E / C U R R E N T I N C R E M E N T , N O . OF S C A N S / A N D N O . OF C H A N N E L S . ( F O R C U H . / I N C . C O M P U T E R T A K E S V A L U E S FROM / 2 - I 6 ; A N Y O T H E R N U M B E R T Y P E D M A K E S / C U R . I N C . T A K E T H E V A L U E OF 4 . ) / T O P R O G R A M D W E L L T I M E / T Y P E I N A N Y N U M B E R FROM 0 T O 7 / A N D T H E C O M P U T E R W I L L S E T T H E / D W E L L T I M E A C C O R D I N G TO T H E / F O L L O W I N G T A B L E . / / N U M B E R T Y P E D : 0 1 2 3 4 / S E C • / C H A N N E L I . 0 5 . 5 1 . 0 1 . 5 2 . 0 2 . / / I N A D D I T I O N / T O T H I S C O M P U T E R T A K E S F O L L O W I N G / I N S T R U C T I O N S . / B i C H E C K I N I T I A L A N D F I N A L V O L T A G E / A F T E R B T Y P E T H E N U M B E R OF T H E R E G I O N / O F I N T E R E S T . C O M P U T E R W I L L S E T T H E / S T A R T I N G V O L T A G E . A N Y K E Y B O A R D C H A R A C T E R / O T H E R T H A N R E T U R N S E T S T H E F I N A L V O L T A G E , / T Y P E ANY C H A R . , B U T CR TO R E S E T . / C A R R I A G E R E T U R N T E R M I N A T E S T H E R O U T I N E . / C : S C A M ROUT I N E : 2 O P T I O N S ; I F 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 / S E C O N D R E G I O N I S S C A N N E D A F T E R / C O M P L E T I N G T H E N U M B E R O F S C A N S / R E Q U I R E D FOR R E G I . I F C R F O L L O W E D / C R E G I O N S A R E S C A N N E D A L T E R N A T E L Y . / A M Y C H A R A C T E R T Y P E D D U H I N G A S C A N / S T O P S T H E R O U T I N E A T T H E E N D O F / T H E S C A N / A F T E R I N T E R R U P T T Y P E C M TO S T A R T / S C A N N I N G A T T H E N E X T S C A N D U E . / S C A N N I N G S T A R T S W I T H 2 B E L L S ; / E N D O F S C A N N I N G 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 S C A N N I N G / S T A R T S W I T H O N E B E L L . . / D : D I S P L A Y ; A F T E R T Y P I N G D / C O M P U T E R W A I T S FOR T H E N U M B E R M / O F T H E R E G I O N T O B E D I S P L A Y E D . ^ / A N Y K E Y B O A R D C H A R . T Y P E D / T E R M I N A T E S T H E R O U T I N E . I / E : C L E A R S T O R A G E L O C A T I O N S / A F T E R E C O M P U T E R W A I T S FOR 7 / T H E R E G I O N N U M B E R . / F : 3 P O I N T S M O O T H I N G OF D A T A / T Y P E T H E N U M B E R O F T H E R E G I O N / O F I N T E R E S T A F T E R F / G l P R I N T OR P L O T D A T A . ' W H E N G I S / T Y P E D T E L E T Y P E P R I N T S " P R I N T " / T Y P E ANY K E Y B O A R D C H A R A C T E R F O L L O W E D / 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 P L O T D A T A T Y P E / R E T U R N F O L L O W E D B Y T H E N U M B E R O F / T H E R E G I O N OF I N T E R E S T . A T T H E E N D O F / P L O T T Y P E R E T U R N TO T E R M I N A T E T H E / R O U T I N E . / A F T E R F OR G T Y P E I N T H E / R E G I O N N U M B E R / J . S . H . O . P E R E R A >50 esse 5 4 5 5 J M P I B B 0 0 5 1 5456 J M P I C C 0 0 5 2 5 4 5 7 J M P I D D 0 0 5 3 5460 J M P 1 EE 0 0 5 4 5461 J M P I FF 0122 0137 0 0 5 S 1245 BB. 1245 0123 0555 c e * 6 4 4 1 4 C C . 4 4 1 4 0124 5200 0 0 5 7 1 0 0 0 DD» 1000 0125 6 2 0 0 e e e c 1 1 3 7 E E , 1 1 3 7 1042 F f , 1 0 4 2 0140 0342 0 0 6 2 1 2 0 0 E E E , 1200 0141 0000 0 e 6 3 1 2 0 5 C U R I N C . 1205 0142 0 0 0 0 0 e e 4 o e c e N U M S C . 0 0143 e » 0 0 0 e 6 5 1 2 2 6 C E T S E T , 1 2 2 6 0144 0ee0 c e t 6 0 0 e e DUELL2, 0 0145 0000 0067 0 0 2 6 O R D E R , 0 0 2 6 0146 0000 0 0 7 0 0 e 0 0 C O U N T 1 , 0 0147 0000 0 e 7 i e z e e O P T I O N , 0 01 50 0000 0 e 7 2 0 3 1 3 I N D E X 1, 0 3 1 3 0151 0000 0 0 7 3 c e e 0 N U M R E G , 0 01 52 0000 ee74 0 0 0 0 REGNO 1, 0 0153 0000 0 0 7 5 0000 O P T 1, 0 01 5 4 0000 • 100 0 1 55 0000 0100 0000 R E G N O , 0 01 5 6 0 H O 0 0 1 0 1 0000 K P S T O , 0 0157 0 0 0 0 0 1 0 2 0000 H P , 0 0l6e 0 0 0 0 0 1 0 3 00e0 L P , 0 0 1 6 1 0 0 0 0 0 i e 4 0341 A L P H A 1, 0 3 4 1 0162 0 0 0 0 0 1 0 5 0330 L I S T I , 0330 0163 0 0 0 0 0106 e e e a N U M S C 1, 0 / N O . S C A N S C O M P L E T E D 0164 6e32 0 1 0 7 0000 0 / I S S T O R E D H E R E 0165 6 0 3 1 0 1 1 0 0000 0 01 66 5165 0111 6 e o e D E C P R T , 6 0 0 0 / U N S I G N E D D E C I M A L P R I N T 01 6 7 6 C 3 6 01 1 2 0 1 0 5 K 105, 0105 01 7 0 6 0 4 6 01 1 3 0000 D W E L L , 0 0 1 7 1 5563 0114 0000 M 5 , 0 0172 0 0 0 0 0 1 1 5 6046 U D P R H T , 6046 / D O U B L E P R . D E C C O N V E R S I O N 0173 6 0 4 1 0116 0724 S P O T . 0724 0174 5173 0117 0000 L P S T O , 0 0175 6 0 4 6 0120 C 2 0 0 R S T A R T , 0200 0176 7 2 0 0 012 1 7520 HM260, 7 520 0177 5 5 7 2 KI37, P P I C K . D T . K6200, • 140 A A L P H A , L I S N , T Y P E , 0 137 0555 5200 6200 0342 0 0 0 0 0 0 0 0 ' 0 / S T O R E F I R S T A N D L A S T / C H A N N E L S H E R E / S T O R E N O . O F S C A N S H E R E / S T O R E C U R . I N C . H E R E / S T O R E D W E L L T I M E H E R E / S T O R E I N I T I A L V O L T A G E / H E R E M 0 0 / S U B R O U T I N E F O R K E Y / B O A R D I N P U T 0 K C C K S F J M P . - 1 K R B T L S J M P I L I S N 0 / S U B R O U T I N E T S F J M P .-I T L S C L A J M P 1 T Y P E 0 2 5 2 3 7 0 3 D C A I S C . 2 0 0 0 2 5 3 1 3 0 2 T A D K 1 4 0 0 0 2 0 0 7 3 0 0 S T A R T , C L A C L L 0 2 5 4 3 7 0 1 D C A I K K I 4 0 0 0 2 0 I 6 0 4 6 T L S 0 2 5 5 1 3 0 0 T A D S T C H A N 0 2 0 2 1 3 2 0 T A D K 2 7 6 0 2 5 6 3 6 7 7 D C A I S T C H A 1 0 2 0 3 6 0 4 6 T L S / T Y P E S > 0 2 5 7 1 1 4 0 A 1 , T A D A A L P H A 0 2 0 4 4 7 2 2 J M S I L L I S N 0 2 6 0 3 3 4 1 D C A A L P H A 0 2 0 5 3 3 1 7 D C A I N S T 0 2 6 1 4 3 3 0 J M S L I S T 0 2 0 6 1 3 17 T A D I N S T G 2 6 2 1 3 1 3 T A D I N D E X 0 2 0 7 1 3 1 6 T A D M H / N E G . C O D E F O R H 0 2 6 3 4 7 2 1 J M S I T T Y P E 0 2 1 0 7 5 1 0 S P A 0 2 6 4 4 3 3 0 J M S L I S T 0 2 1 1 5 2 1 3 J M P . * 2 0 2 6 5 4 6 7 6 J M S I S S I C O N 0 2 1 2 5 2 0 0 J M P S T A R T 0 2 6 6 3 7 1 1 D C A I I B 0 2 1 3 3 3 1 5 D C A C H E C K 0 2 6 7 2 3 11 I S Z I B 0 2 1 4 2 3 1 5 I S Z C H E C K 0 2 7 0 4 3 3 0 J M S L I S T 0 2 1 5 5 2 1 7 J M P . + 2 0 2 7 1 4 5 2 4 J M S I D T 0 2 1 6 5 7 4 0 J M P I G 0 2 7 2 3 7 0 7 D C A I V I 0 2 1 7 2 3 1 5 I S Z C H E C K 0 2 7 3 2 3 0 7 I S Z V I 0 2 2 0 5 2 2 2 J M P . + 2 0 2 7 4 5 6 7 5 J M P I K 4 0 0 0 2 2 1 5 7 2 7 J M P I F 0 2 7 5 0 4 0 0 K 4 0 0 , 0 4 0 0 0 2 2 2 2 3 1 5 I S Z C H E C K / C O N S T A N T S e 2 2 3 5 2 2 5 J M P . + 2 0 2 7 6 6 2 0 0 S S I C O N , 6 2 0 0 0 2 2 4 5 7 2 6 J M P I E 0 2 7 7 0 5 0 5 S T C H A I , 0 5 0 5 C 2 2 5 2 3 1 5 I S Z C H E C K 0 3 0 0 0 1 4 1 S T C H A N , 0 1 4 1 e 2 2 6 5 2 3 0 J M P . + 2 0 3 0 1 0 5 0 6 K K 1 4 0 0 / 0 5 0 6 0 2 2 7 5 7 2 5 J M P I D 0 3 0 2 1 4 0 0 K 1 4 0 0 , 1 4 0 0 0 2 3 0 2 3 1 5 I S Z C H E C K 0 3 0 3 0 5 1 0 S O 0 5 1 0 0 2 3 1 5 2 3 3 J M P . + 2 0 3 0 4 0 1 4 7 S S C , 0 1 4 7 0 2 3 2 5 7 2 4 J M P I C 0 3 0 5 0 5 1 1 C I , 0 5 1 1 0 2 3 3 2 3 1 5 I S Z C H E C K 0 3 0 6 0 1 5 2 C C I , 0 1 5 2 0 2 3 4 5 2 3 6 J M P . * 2 0 3 0 7 0 0 0 0 V I , 0 0 2 3 5 5 7 2 3 J M P I B 0 3 1 0 0 1 5 5 WW I , 0 1 5 5 0 2 3 6 2 3 1 5 I S Z C H E C K 0 3 1 1 0 0 0 0 I D , 0 0 2 3 7 5 2 0 0 J M P S T A R T 0 3 1 2 0 1 6 0 I I B , 0 1 6 0 0 2 4 0 5 2 4 1 J M P A 0 3 1 3 0 0 0 0 I N D E X , 0 0 2 4 1 1 3 1 4 A , T A D K 2 6 1 0 3 1 4 0 2 6 1 K 2 6 1, 0 2 6 1 0 2 4 2 3 3 1 3 D C A I N D E X 0 3 1 5 0 0 0 0 C H E C K , 0 0 2 4 3 1 3 1 2 T A D I I B 0 3 1 6 7 4 7 0 M H , 7 4 7 0 /• 0 2 4 4 3 3 1 1 D C A I B 0 3 1 7 0 0 0 0 I N S T , 0 0 2 4 5 1 3 1 0 T A D V V I 0 3 2 0 0 2 7 6 K 2 7 6 , 0 2 7 6 0 2 4 6 3 3 0 7 D C A V I 0 3 2 1 0 1 7 2 T T Y P E , 0 1 7 2 0 2 4 7 1 3 0 6 T A D C C I 0 3 2 2 0 1 6 3 L L I S N , 0 1 6 3 0 2 5 0 3 7 0 5 D C A I C I 0 3 2 3 0 0 5 0 B , 0 0 5 0 0 2 5 1 1 3 0 4 T A D S S C 0 3 2 4 0 0 5 1 C , 0 0 5 1 / P O I N T E R F O R S T A R T I N G A N D / F I N A L C H A N N E L S T O R A G E / T Y P E S R 1 , R 2 i R 3 / T Y P E S I B = / D E C I M A L T O B I N A R Y C O N V . / D T " - 3 1 0 F O R H 0 3 2 5 0 0 5 2 D» 0 0 5 2 • 4 0 0 0 3 2 6 0 0 5 3 E» 0 0 5 3 0 4 0 0 4 7 1 3 J M S I L L I S T 0 3 2 7 0 0 5 4 ft 0 0 5 4 0 4 0 1 4 4 6 3 J M S I C U R I N C 0 3 3 0 0 0 0 0 L I S T , 0 / S U B R O U T I N E 0 4 0 2 3 7 1 1 D C A I C I I 0 3 3 1 1 7 4 1 T A D I A L P H A 0 4 0 3 2 3 1 1 I S Z C I I 0 3 3 2 4 7 2 1 J M S I T T Y P E 0 4 0 4 4 7 1 3 J M S I L L I S T 0 3 3 3 1 7 4 1 T A D I A L P H A 0 4 0 5 4 7 1 2 J M S I S S S I C O 0 3 3 4 2 3 4 1 I S Z A L P H A 0 4 0 6 3 7 1 0 D C A I S C C 0 3 3 5 7 7 1 0 S P A C L A 0 4 0 7 2 3 1 0 I S Z S C C 0 3 3 6 5 7 3 0 J M P I L I S T 0 4 1 0 4 7 1 3 J M S I L L I S T 0 3 3 7 5 3 3 1 J M P L I S T * 1 0 4 1 1 4 7 12 J M S I S S S I C O 0 3 4 0 0 5 4 0 G , 0 5 4 0 0 4 1 2 3 3 0 7 D C A C H A N 0 3 4 1 0 3 4 2 A L P H A , 0 3 4 2 0 4 1 3 1 3 0 7 T A D C H A N 0 3 4 2 0 2 1 5 0 2 1 5 / C R 0 4 1 4 7 1 0 4 C L L R A L 0 3 4 3 0 2 1 2 0 2 1 2 / L F 0 4 1 5 3 3 0 7 D C A C H A N 0 3 4 4 4 3 2 2 4 3 2 2 / R 0 4 1 6 1 3 0 6 T A D T 1 4 0 0 0 3 4 5 0 2 1 5 0 2 1 5 0 4 1 7 3 7 0 5 D C A I S S T C H A 0 3 4 6 0 2 1 2 0 2 1 2 0 4 2 0 2 3 0 5 I S Z S S T C H A 0 3 4 7 0 3 1 1 0 3 1 1 / 1 0 4 2 1 1 3 0 7 T A D C H A N 0 3 5 0 0 3 0 2 0 3 0 2 /B 0 4 2 2 7 0 0 1 I A C 0 3 5 1 4 2 7 5 4 2 7 5 / = 0 4 2 3 1 3 0 6 T A D T 1 4 0 0 0 3 5 2 0 2 1 5 0 2 1 5 0 4 2 4 3 7 0 5 D C A I S S T C H A 0 3 5 3 0 2 1 2 0 2 1 2 0 4 2 5 1 3 0 4 T A D K I 0 0 0 0 3 5 4 0 3 0 4 0 3 0 4 / D 0 4 2 6 1 3 0 6 T A D T 1 4 0 0 0 3 5 5 0 3 2 4 0 3 2 4 / T 0 4 2 7 3 3 0 6 D C A T 1 4 0 0 0 3 5 6 4 2 7 5 4 2 7 5 / = 0 4 3 0 1 3 0 6 T A D T 1 4 0 0 0 3 5 7 0 2 1 5 0 2 1 5 0 4 3 1 3 3 0 3 D C A M L S T C H 0 3 6 0 0 2 1 2 0 2 1 2 0 4 3 2 1 3 0 3 T A D M L S T C H 0 3 6 1 0 3 0 3 0 3 0 3 / C 0 4 3 3 7 0 4 1 C I A 0 3 6 2 0 3 1 1 0 3 1 1 / I 0 4 3 4 1 7 0 5 T A D I S S T C H A 0 3 6 3 4 2 7 5 4 2 7 5 / = 0 4 3 5 7 7 1 0 SPA C L A C L L 0 3 6 4 0 2 1 5 0 2 1 5 0 4 3 6 5 2 4 3 J M P . + 5 0 3 6 5 0 2 1 2 0 2 1 2 0 4 3 7 4 3 1 6 M S T A K E , J M S R E D O 0 3 6 6 0 3 2 3 0 3 2 3 / S 0 4 4 0 5 6 7 7 J M P I S S T A R T 0 3 6 7 0 3 0 3 0 3 0 3 / C 0 4 4 1 7 0 0 0 NOP 0 3 7 0 4 2 7 5 4 2 7 5 / = 0 4 4 2 7 0 0 0 N O P 0 3 7 1 0 2 1 5 0 2 1 5 0 4 4 3 2 3 0 5 ISZ S S T C H A 0 3 7 2 0 2 1 2 0 2 1 2 0 4 4 4 6 0 3 1 KSF 0 3 7 3 0 3 0 3 0 3 0 3 /c 0 4 4 5 5 2 4 4 J M P . - 1 0 3 7 4 0 3 1 0 0 3 1 0 / H 0 4 4 6 6 0 3 6 KRB 0 3 7 5 4 2 7 5 4 2 7 5 / = 0 4 4 7 3 3 1 4 D C A W A I T 0 3 7 6 0 2 12 0 2 1 2 0 4 5 0 1 3 1 4 T A D W A I T 0 3 7 7 4 2 1 5 4 2 1 5 0 4 5 1 1 2 7 5 T A D M 2 6 4 / C I ' /sc» / C H « 0 0 o 0 4 5 2 7 7 1 0 S P A C L A C L L 0 4 5 3 5 2 5 5 J M P . + 2 e454 5 2 3 7 J M P M S T A K E 0 4 5 5 1 3 1 4 T A D W A I T 0 4 5 6 1 3 0 0 T A D M 2 5 6 0 4 5 7 7 6 4 0 S Z A C L A 0 4 6 0 5 2 6 3 J M P . + 3 e46t 4 7 1 3 J M S I L L I S T 0 4 6 2 5 6 7 7 J M P I S S T A R T 0 4 6 3 1 6 7 6 T A D I I I N D E X C 4 6 4 7 0 4 1 C I A 0 4 6 5 1 3 1 4 T A D W A I T 0 4 6 6 7 7 5 0 S P A S N A C L A e 4 6 7 5 2 3 7 J M P M S T A K E 0 4 7 0 1 3 1 4 T A D W A I T 0 4 7 1 3 6 7 6 D C A I I I N D E X 0 4 7 2 4 7 1 3 J M S I L L I S T 0 4 7 3 5 6 7 4 J M P I A A 1 0 4 7 4 0 2 5 7 A A 1 , 0 2 5 7 0 4 7 5 7 5 1 4 M 2 6 4 , 7 5 1 4 0 4 7 6 0 3 1 3 I I N D E X , 0 3 1 3 0 4 7 7 0 2 0 0 S S T A R T , 0 2 0 0 0 5 0 0 7 5 2 2 M2 5 6 , 7 5 2 2 0 5 0 1 0 1 7 2 T T T Y P E , 0 1 7 2 0 5 0 2 0 1 6 3 L L L I S N , 0 1 6 3 0 5 0 3 0 0 0 0 M L S T C H , 0 0 5 0 4 1 0 0 0 K 1 0 0 0 , 1 0 0 0 0 5 0 5 0 0 0 0 S S T C H A , 0 0 5 0 6 0 0 0 0 T 1 4 0 0 , 0 0 5 0 7 0 0 0 0 C H A N , 0 0 5 1 0 0 0 0 0 s e c 0 0 5 1 1 0 0 0 0 C I I , 0 0 S I 2 6 2 0 0 S S S I C O , 6 2 0 0 0 5 1 3 0 3 3 0 E L I S T , 0 3 3 0 0 5 1 4 0 0 0 0 W A I T , 0 0 5 1 5 0 0 0 0 0 0 5 1 6 0 0 0 0 R E D O , 0 0 5 1 7 7 3 0 0 C L A C L L 0 5 2 0 1 3 3 1 T A D X 0 5 2 1 3 3 3 2 D C A E X I T 0 5 2 2 1 7 3 2 T A D I E X I T 0 5 2 3 4 7 0 1 J M S I T T T Y P E 0 5 2 4 1 7 3 2 T A D I E X I T C 5 2 5 2 3 3 2 I S Z E X I T 0 5 2 6 7 7 1 0 S P A C L A 0 5 2 7 5 7 1 6 J M P I R E D O 0 5 3 0 5 3 2 2 J M P R E D 0 + 4 0 5 3 1 0 5 3 3 X , 0 5 3 3 0 5 3 2 0 0 0 0 E X I T , 0 0 5 3 3 0 2 7 7 0 2 7 7 0 5 3 4 0 2 1 2 0 2 1 2 0 5 3 5 4 2 1 5 4 2 1 5 0 5 3 6 4 0 0 0 4 0 0 0 0 5 3 7 5 0 0 0 C H O I C E , 5 0 0 0 0 5 4 0 4 7 3 7 J M S I C H O I C E 0 5 4 1 1 3 5 2 T A D K 6 0 0 0 5 4 2 3 5 0 4 D C A I A L P H A 1 0 5 4 3 4 5 0 5 J M S I L I S T 1 0 5 4 4 1 1 0 0 T A D R E G N O 0 5 4 5 1 1 1 2 T A D K 1 0 5 0 5 4 6 3 3 5 4 D C A S T 0 5 4 7 1 7 5 4 T A D I S T 0 5 5 0 4 5 1 1 J M S I D E C P R T 0 5 5 1 5 7 5 3 J M P I C O N T 0 5 5 2 0 6 0 0 K 6 0 0 , 0 6 0 0 0 5 5 3 0 6 3 1 C O N T , 0 6 3 1 0 5 5 4 0 0 0 0 S T , 0 0 5 5 5 0 0 0 0 P I C K , 0 / S U B R O U T I N E 0 5 5 6 7 3 0 0 C L A C L L 0 5 5 7 6 0 3 1 K S F 0 5 6 0 5 3 5 7 J M P . - 1 0 5 6 1 6 0 3 6 K R B 0 5 6 2 6 0 4 6 T L S 0 5 6 3 3 1 0 0 D C A R E G N O 0 5 6 4 1 6 7 6 T A D I I I N D E X 0 5 6 5 7 0 4 1 C I A 0 5 6 6 1 1 0 0 T A D R E G N O 0 5 6 7 7 7 5 0 S P A S N A C L A 0 5 7 0 5 3 7 2 J M P . + 2 0 5 7 1 5 2 3 7 J M P M S T A K E 0 5 7 2 1 1 0 0 T A D R E G N O 0 5 7 3 1 1 2 1 T A D M M 2 6 0 0 5 7 4 7 5 5 0 S P A S N A 0 5 7 5 5 2 3 7 J M P M S T A K E 0 5 7 6 3 1 0 0 D C A R E G N O 0 5 7 7 5 7 5 5 J M P I P I C K • 6 0 0 0 6 5 2 1 3 7 5 T A D K 7 7 7 7 0 6 0 0 0 2 1 5 0 2 1 5 0 6 5 3 1 3 7 6 T A D H O L D I 0 6 0 I 0 2 1 2 0 2 12 0 6 5 4 7 1 1 0 C L L R A R 0 6 0 2 0 3 2 3 0 3 2 3 / S 0 6 5 5 4 5 1 1 J M S I D E C P R T 0 6 0 3 0 3 0 3 0 3 0 3 / c 0 6 5 6 1 5 0 1 T A D I H P S T O 0 6 C 4 0 3 0 1 0 3 0 1 / A 0 6 5 7 3 1 0 2 D C A H P 0 6 0 5 0 3 1 6 0 3 1 6 / N 0 6 6 0 1 3 7 0 N X L I N E , T A D K 7 7 I 0 6 0 6 e 3 2 3 0 3 2 3 / S 0 6 6 1 3 5 0 4 D C A I A L P H A 1 0 6 0 7 4 2 7 5 4 2 7 5 /= 0 6 6 2 4 5 0 5 J M S I L I S T I 0 6 1 0 0 2 1 5 0 2 1 5 0 6 6 3 1 5 0 1 T A D I H P S T O 0 6 1 1 0 2 1 2 0 2 12 0 6 6 4 7 0 4 1 C I A 0 6 1 2 0 3 0 4 0 3 0 4 / D 0 6 6 5 1 1 C 2 T A D H P 0 6 1 3 0 3 2 7 0 3 2 7 / V 0 6 6 6 7 1 1 0 C L L R A R 0 6 1 4 0 3 0 5 0 3 0 5 / E 0 6 6 7 4 5 1 1 J M S I D E C P R T 0 6 1 5 0 3 1 4 0 3 1 4 / L 0 6 7 0 7 3 0 7 C L A C L L I A C 0 6 1 6 0 3 1 4 0 3 1 4 / L 0 6 7 1 7 0 0 1 I A C e 6 1 7 4 2 7 5 4 2 7 5 / = 0 6 7 2 7 0 4 1 C I A 0 6 2 0 0 2 1 5 0 2 1 5 0 6 7 3 3 1 1 4 D C A M 5 0 6 2 1 0 2 1 2 0 2 1 2 0 6 7 4 1 1 0 2 R E P E A T , T A D H P 0 6 2 2 0 2 4 3 0 2 4 3 /# 0 6 7 5 7 0 0 1 I A C 0 6 2 3 0 2 4 0 0 2 4 0 / S P A C E 0 6 7 6 3 1 0 3 D C A L P 0 6 2 4 0 3 0 3 0 3 0 3 / C 0 6 7 7 1 3 5 7 T A D K 7 6 0 e 6 2 5 0 3 1 0 0 3 1 0 / H 0 7 0 0 3 5 0 4 D C A I A L P H A 1 0 6 2 6 0 3 0 1 0 3 0 1 / A 0 7 0 1 4 5 0 5 J M S I L I S T I 0 6 2 7 4 2 7 5 4 2 7 5 / = 0 7 0 2 4 5 1 5 J M S I U D P R N T 0 6 3 0 4 0 0 0 4 0 0 0 0 7 0 3 0 1 0 2 0 1 0 2 0 6 3 1 4 5 0 5 J M S I L I S T I 0 7 0 4 4 5 1 6 J M S I S P O T 0 6 3 2 7 0 0 0 N O P 0 7 0 5 1 1 0 1 T A D H P S T O e e 3 3 4 7 7 7 J M S I D T P R N T 0 7 0 6 7 0 0 1 I A C e & 3 4 7 0 4 1 C I A 0 7 0 7 3 1 1 7 D C A L P S T O e635 4 5 1 1 J M S I D E C P R T 0 7 1 0 1 5 1 7 T A D I L P S T O e 6 3 6 4 5 0 5 J M S I L I S T I 0 7 1 1 7 0 4 1 C I A 0 6 3 7 1 1 0 0 T A D R E G N O 0 7 12 1 1 0 3 T A D L P 0 6 4 0 7 1 0 4 C L L R A J - 0 7 1 3 7 6 5 0 S N A C L A 0 6 4 1 1 1 2 2 T A D K 1 3 7 0 7 1 4 5 3 2 2 J M P . + 6 0 6 4 2 3 1 0 1 D C A H P S T O 0 7 1 5 2 1 0 2 I S Z H P e t 4 3 1 1 0 1 T A D H P S T O 0 7 1 6 2 1 0 2 I S Z H P 0 6 4 4 3 3 7 4 D C A H 0 L D 2 0 7 1 7 2 1 1 4 I S Z M 5 0 6 4 5 1 7 7 4 T A D I H 0 L D 2 0 7 2 0 5 2 7 4 J M P R E P E A T 0 6 4 6 7 0 4 1 C I A 0 7 2 1 5 2 6 0 J M P N X L I N E 0 6 4 7 3 3 7 6 D C A H O L D 1 0 7 2 2 4 5 0 5 J M S I L I S T I 0 6 5 0 2 3 7 4 I S Z H 0 L D 2 0 7 2 3 5 5 2 0 J M P I R S T A R T 0 6 5 1 1 7 7 4 T A D I H 0 L D 2 0 7 2 4 0 0 0 0 S S P O T , 0 / : 0 0 to / S U B R O U T I N E F O R D I S P L A Y 0725 7604 LAS 0726 0373 AND K37 1000 0727 7040 CM A 1001 0730 3367 DCA GAIN 1002 07 31 1503 TAD I LP 1003 0732 742 1 MCL 1004 0733 1 502 TAD I HP 1005 0734 2367 ISZ GAIN 1006 0735 7410 SKP 1007 0736 5344 JMP .*6 1010 0737 70 10 RAR 101 1 0740 752 1 SWP 1012 074 1 70 10 RAR 1013 0742 7 52 1 swp 1014 0743 5334 JMP .-7 10 15 0744 7200 CLA 1016 074 5 150 1 TAD I HPSTO 1017 0746 7041 CIA 1020 0747 1 102 TAD HP 102 1 07 50 4465 JMS I GETSET 1022 07 51 6051 6051 /X AXIS 1023 07 52 772 1 CLA SWP 1024 07 53 6061 6061 /Y AXIS 1025 07 54 7000 NOP 1026 07 55 7200 CLA 1027 07 56 5724 JMP I SSPOT 1030 07 57 0760 K760, 0760 1031 0760 0240 0240 1032 0761 4240 4240 1033 07 62 0215 02 1 5 1034 0763 0212 02 12 1035 0764 02 12 02 12 1036 0765 02 12 02 12 1037 0766 42 12 42 12 1040 0767 0000 GAIN, 0 104 1 0770 077 1 K771, 077 1 1042 077 1 0215 02 1 5 1043 0772 4212 42 12 1044 0773 0037 K37, 0037 1045 0774 0000 H0LD2, 0 1046 077 5 7777 K7777, 7777 1047 0776 0000 HOLDI, 0 1050 0777 5232 DTPRNT, 5232 1051 * 1000 4523 JMS I PPICK /DISPLAY ROUTINE 7000 NOP 7000 NOP 7000 NOP 7000 NOP 7000 NOP 7000 NOP 1 100 TAD REGNO 7 104 CLL RAL 1 122 TAD K137 3 10 1 DCA HPSTO 1101 DSPLAY, TAD HPSTO 7001 IAC 3 117 DCA LPSTO 1501 TAD I HPSTO 3102 DCA HP I 102 CONT I, TAD HP 7001 I AC 3103 DCA LP 4516 JMS I SPOT 6031 KSF 5230 JMP .*3 6036 KRB 5520 JMP I RSTART 1 I 03 TAD LP 7041 CIA 1517 TAD I LPSTO 7650 SNA CLA 524 1 JMP .+5 7000 NOP 2 102 ISZ HP 2102 ISZ HP 5220 JMP C0NT1 52 13 JMP DSPLAY 4523 JMS I PPICK /3 POINT SMOOTH ROUTINE 1100 TAD REGNO 7 104 CLL RAL I 122 TAD K137 3101 DCA HPSTO 110 1 TAD HPSTO 7001 I AC 3117 DCA LPSTO 1 0 5 2 1 5 0 1 T A D 1 H P S T O 1 1 2 5 1 5 0 2 T A D I H P 1 0 5 3 3 1 0 2 D C A H P 1 1 2 6 3 3 6 4 D C A S T I 1 0 5 4 1 1 0 2 T A D H P 1 1 2 7 1 5 0 3 T A D I L P 1 0 5 5 7 0 0 1 I A C 1 1 3 0 3 3 6 3 D C A S T 2 1 0 5 6 3 1 0 3 D C A L P 1 1 3 1 1 3 6 2 T A D T H I R D 1 0 5 7 1 5 0 2 T A D I H P 1 1 3 2 3 5 0 2 D C A I H P 1 0 6 0 3 3 6 4 D C A S T I 1 1 3 3 7 5 2 1 S U P 1 0 6 1 1 5 0 3 T A D I L P 1 1 3 4 7 0 1 0 R A R 1 0 6 2 3 3 6 3 D C A S T 2 1 1 3 5 3 5 0 3 D C A I L P 1 0 6 3 7 3 0 7 C 0 N T 2 , C L A C L L I A C R T L 1 1 3 6 5 2 6 3 J M P C 0 N T 2 1 0 6 4 1 1 0 2 T A D H P 1 1 3 7 4 5 2 3 J M S I P P I C K 1 0 6 5 3 3 6 2 D C A T H I R D 1 1 4 0 1 1 0 0 T A D R E G N O 1 0 6 6 1 3 6 2 T A D T H I R D 1 1 4 1 7 1 0 4 C L L R A L 1 0 6 7 7 1 0 1 C L L I A C 1 1 4 2 1 1 2 2 T A D K 1 3 7 1 0 7 0 3 3 6 1 D C A T H I R D 2 1 1 4 3 3 1 0 1 D C A H P S T O 1 0 7 1 1 3 6 1 T A D T H 1 R D 2 1 1 4 4 1 1 0 1 T A D H P S T O 1 0 7 2 7 0 4 1 C I A 1 1 4 5 7 0 0 1 I A C 1 0 7 3 1 5 1 7 T A D I L P S T O 1 1 4 6 3 1 1 7 D C A L P S T O 1 0 7 4 7 6 5 0 S N A C L A 1 1 4 7 1 5 0 1 T A D I H P S T O 1 0 7 5 5 5 2 0 J M P I R S T A R T 1 1 5 0 3 1 0 2 D C A H P 1 0 7 6 7 1 0 0 C L L 1 1 5 1 3 5 0 2 C 0 N T 3 , D C A I H P 1 0 7 7 1 3 6 3 T A D S T 2 / D O U B L E P R E C . A D D 1 1 5 2 1 5 1 7 T A D I L P S T O 1 1 0 0 1 7 6 1 T A D I T H I R D 2 1 1 5 3 7 0 4 1 C I A 1 1 0 1 7 4 2 1 M C L 11 5 4 1 1 0 2 T A D H P 1 1 0 2 7 4 3 0 S Z L 1 1 5 5 7 6 5 0 S N A C L A I 1 0 3 7 3 0 1 C L A C L L I A C 1 1 5 6 5 4 6 2 J M P I E E E 1 1 0 4 1 3 6 4 T A D S T I 1 1 5 7 2 1 0 2 I S Z H P 1 1 0 5 1 7 6 2 T A D I T H I R D 1 1 6 0 5 3 5 1 J M P C 0 N T 3 1 1 0 6 7 0 1 0 R A R 1 1 6 1 0000 T H I R D 2 , 0 1 1 0 7 7 5 2 1 S U P 1 1 6 2 0000 T H I R D , 0 1 1 1 0 7 0 1 0 R A R 1 1 6 3 0000 S T 2 , 0 1 1 1 1 7 1 0 0 C L L 1 1 6 4 0000 S T I , 0 11 1 2 2 1 0 2 I S Z H P 1 1 6 5 0000 H 0 L D 3 , 0 1 1 1 3 2 1 0 2 I S Z H P 1 1 6 6 0 0 0 7 K 7 , 0 0 0 7 1 1 1 4 2 1 0 3 I S Z L P 1 1 6 7 1 1 7 0 K 1 1 7 0 , 1 1 7 0 1 1 1 5 2 1 0 3 I S Z L P 1 1 7 0 7 7 7 0 7 7 7 0 1 1 1 6 1 5 0 3 T A D I L P 1 1 7 1 7 4 4 0 7 4 4 0 / . 5 S E C 1 1 1 7 7 5 2 1 sup 1 1 7 2 7 3 0 0 7 3 0 0 / 1 S E C 1 1 2 0 7 4 3 0 S Z L 1 1 7 3 7 1 6 5 7 1 6 5 / I . 5 S E C 1 1 2 1 7 1 0 1 C L L I A C 1 1 7 4 7 0 7 0 7 0 7 0 / 2 S E C 1 1 2 2 1 5 0 2 T A D I H P 1 1 7 5 7 0 0 2 7 0 0 2 / 2 . 5 S E C 1 1 2 3 7 0 1 0 R A R 1 1 7 6 6 7 2 0 6 7 2 0 / 3 S E C 1 1 2 4 3 3 6 2 D C A T H I R D 1 1 7 7 6 5 7 0 6 5 7 0 / 4 S E C / E R A S E R O U T I N E CO 1 2 0 0 1 1 0 0 * 1 2 0 0 T A D R E G N O 1 2 0 1 1 1 1 2 T A D K 1 0 5 1 2 0 2 3 0 6 4 D C A N U M S C 1 2 0 3 3 4 6 4 D C A I N U M S C 1 2 0 4 5 5 2 0 J M P I R S T A R T 1 2 0 5 0 0 0 0 C U R I N . 0 / S U B R O U T I N E T O C H E C K C U R . I N C . 1 2 0 6 4 7 7 7 J M S I S R 6 2 0 0 1 2 0 7 3 3 7 6 D C A C H E C K 1 12 1 0 1 3 7 6 T A D C H E C K I 1 2 1 1 1 3 7 5 T A D M 2 1 2 1 2 7 5 1 0 S P A 1 2 1 3 5 2 2 2 J M P P U T 4 1 2 1 4 1 3 7 4 T A D M 1 4 1 2 1 5 7 5 4 0 S N A S Z A / I S I T G R E A T E R T H A N 1 6 12 1 6 5 2 2 2 J M P P U T 4 1 2 1 7 7 3 0 0 C L A C L L 1 2 2 0 1 3 7 6 T A D C H E C K 1 1 2 2 1 5 6 0 5 J M P I C U R I N 1 2 2 2 7 3 0 7 P U T 4 , C L A C L L I A C R T L 1 2 2 3 5 6 0 5 J M P I C U R I N 1 2 2 4 7 0 0 0 N O P 1 2 2 5 7 0 0 0 N O P 1 2 2 6 0 0 0 0 B A K E , 0 / S U B R O U T I N E T O C O N T R O L L C U R I N C . 1 2 2 7 7 1 1 0 C L L R A R 1 2 3 0 3 3 7 3 D C A H 0 L D 4 1 2 3 1 1 1 0 0 T A D R E G N O 1 2 3 2 1 3 7 1 T A D K 1 5 1 1 2 3 3 3 3 7 2 D C A H 0 L D 5 1 2 3 4 1 7 7 2 T A D I H 0 L D 5 1 2 3 5 7 0 4 1 C I A 1 2 3 6 3 3 7 2 D C A H O L D S 1 2 3 7 1 3 7 3 T A D H O L D 4 1 2 4 0 2 3 7 2 I S Z H O L D S 1 2 4 1 5 2 3 7 J M P . - 2 1 2 4 2 7 0 0 0 N O P / B Y C H A N G I N G T H I S T O J M S I I N F E R T 1 2 4 3 5 6 2 6 J M P I B A K E / S C A N N I N G C O U L D B E I N V E R T E D . 1 2 4 4 5 1 1 0 I N F E R T , 5 1 1 0 1 2 4 5 4 5 2 3 J M S I P P I C K / R O U T I N E T O C H E C K I N I T I A L A N D 1 2 4 6 1 1 0 0 T A D R E G N O / F I N A L V O L T A G E S O F A 1 2 4 7 1 3 6 7 T A D K 1 5 7 / R E Q U I R E D R E G I O N 1 2 5 0 3 3 7 0 D C A H 0 L D 6 1 2 5 1 1 7 7 0 T A D I H 0 L D 6 12 5 2 7 1 0 4 C L L R A L / 1 2 5 3 1 2 5 4 1 2 5 5 1 2 5 6 1 2 5 7 1 2 6 0 1 2 6 1 1 2 6 2 1 2 6 3 1 2 6 4 1 2 6 5 1 2 6 6 1 2 6 7 1 2 7 0 1 2 7 1 1 2 7 2 1 2 7 3 1 2 7 4 1 2 7 5 1 2 7 6 1 2 7 7 1 3 0 0 1 3 0 1 1 3 0 2 1 3 0 3 1 3 0 4 1 3 0 5 1 3 0 6 1 3 0 7 1 3 1 0 1 3 1 1 1 3 1 2 1 3 1 3 1 3 1 4 1 3 1 5 1 3 1 6 1 3 1 7 1 3 2 0 1 3 2 1 1 3 2 2 1323 1 3 2 4 6 0 7 I 1 3 6 5 3 3 6 6 1 3 6 5 3 3 6 2 7 0 0 0 2 3 6 6 5 2 6 0 2 3 6 2 5 2 6 0 1 1 0 0 7 1 0 4 1 1 2 2 3 1 0 1 1 5 0 1 3 1 0 2 1 1 0 2 7 0 0 1 3 1 0 3 1 1 0 1 7 0 0 1 3 1 1 7 1 5 1 7 7 0 4 1 1 5 0 1 3 0 7 0 7 0 0 0 7 0 0 0 7 0 0 0 6 0 3 1 7 4 1 0 5 3 1 5 4 5 1 6 5 3 1 0 4 5 1 6 1 3 6 5 3 3 6 6 1 3 6 5 3 3 6 2 7 0 0 0 2366 5 3 2 2 6 0 7 1 T A D K 7 6 0 0 D C A D E L A Y 1 T A D K 7 6 0 0 D C A D E L A Y 2 N O P I S Z D E L A Y I J M P . - 2 I S Z D E L A Y 2 J M P . - 4 T A D R E G N O C L L R A L T A D K 1 3 7 D C A H P S T O T A D I H P S T O D C A H P T A D H P I A C D C A L P T A D H P S T O I A C D C A L P S T O T A D I L P S T O C I A T A D I H P S T O D C A C O U N T 1 N O P N O P N O P K S F S K P J M P . * 3 J M S I S P O T J M P . - 4 J M S I S P O T T A D K 7 6 0 0 D C A D E L A Y I T A D K 7 6 0 0 D C A D E L A Y 2 N O P I S Z D E L A Y I J M P . - 2 / S E T S T H E I N I T I A L V O L T A G E / T I M E R F O R D E L A Y 0 0 1 3 2 5 2 3 6 2 I S Z D L L A Y 2 1 3 2 6 5 3 2 2 J M P . - 4 1 3 2 7 1 3 6 5 C 0 N T 4 , T A D K 7 6 0 0 1 3 3 0 3 0 6 6 D C A D W E L L 2 1 3 3 1 7 2 C 0 T I M E R , C L A 1 3 3 2 1 1 1 3 T A D D W E L L 1 3 3 3 3 3 6 3 D C A H 0 L D 7 1 3 3 4 2 3 6 3 I S Z H 0 L D 7 1 3 3 5 5 3 3 7 J M P . + 2 1 3 3 6 5 3 4 3 J M P . * 5 1 3 3 7 7 0 0 0 N O P 1 3 4 0 5 3 4 2 J M P .+2 1 3 4 1 7 3 0 0 N O P 1 3 4 2 5 3 3 4 J M P . - 6 1 3 4 3 2 0 6 6 I S Z D U E L L 2 1 3 4 4 5 3 3 1 J M P T I M E R 1 3 4 5 4 5 1 6 J M S I S P O T 1 3 4 6 7 3 0 5 C L A C L L I A C R A L 1 3 4 7 1 0 7 0 T A D C O U N T 1 1 3 5 0 3 0 7 0 D C A C O U N T 1 1 3 5 1 7 4 3 0 S Z L 13 5 2 5 3 6 0 J M P . + 6 1 3 5 3 2 1 0 2 I S Z H P 1 3 5 4 2 1 0 2 I S Z H P 1 3 5 5 2 1 0 3 I S Z L P 1 3 5 6 2 1 0 3 I S Z L P 1 3 5 7 5 3 2 7 J M P C 0 N T 4 1 3 6 0 5 7 6 4 J M P I K 4 4 0 0 1 3 6 1 7 0 0 0 N O P 1 3 6 2 0 0 0 0 D E L A Y 2 , 0 1 3 6 3 0 0 0 0 H 0 L D 7 , 0 1 3 6 4 4 4 3 0 K 4 4 0 0 , 4 4 0 0 1 3 6 5 7 5 0 0 K 7 6 0 0 , 7 5 0 0 1 3 6 6 0 0 0 0 D E L A Y I , 0 1 3 6 7 0 1 5 7 K 1 5 7 , 0 1 5 7 / P O I N T E R F O R I N I T I A L 1 3 7 0 0 0 0 0 H 0 L D 6 , 0 1 3 7 1 0 1 5 1 K 1 5 1 , 0 1 5 1 1 3 7 2 0 0 G 0 H O L D S , 0 1 3 7 3 0 0 0 0 H 0 L D 4 , 0 1 3 7 4 7 7 6 2 M 1 4 , 7 7 6 2 / G E N A R A T E S - 1 6 1 3 7 5 7 7 7 6 M 2 , 7 7 7 6 1 3 7 6 0 0 0 0 C H E C K 1 , 0 1 3 7 7 6 2 0 0 S R 6 2 0 0 , 6 2 0 0 1 4 0 0 0 0 0 0 / D A T A S T O R A G E L O C A T I O N S F O R R E G I O N #1 2 3 7 7 0 0 0 0 2 4 0 0 0 0 0 0 3 3 7 7 0 0 0 0 3 4 0 0 0 0 0 0 / D A T A S T O R A G E L O C A T I O N S F O R R E G I O N # 2 m . / D A T A S T O R A G E L O C A T I O N S F O R R E G I O N # 3 4 3 7 7 0 0 0 0 • 4 4 0 0 44 52 1373 TAD BELL 4 4 0 0 6030 KCF 44 53 4 172 JMS TYPE 4401 603 1 KSF 44 54 7300 CLA CLL 4402 520 1 JMP .-1 4455 1472 TAD I INDEX 1 4403 6036 KRB 4456 112 1 TAD MM260 4404 3377 DCA H0LD8 44 57 704 1 CIA 440 5 1377 TAD HOLDS 4460 3073 DCA NUMREG 4406 1376 TAD M2 15 4461 3100 C0NT5, DCA REGNO 4407 7640 SZA CLA /IS IT CR 4462 2100 I SZ REGNO 44 10 5775 JMP I ROUTB /NO 4463 4772 GOSCAN, JMS I SCAN 441 1 5520 JMP I RSTART 4464 7300 CLA CLL 4412 7000 NOP 4465 1112 TAD K105 4413 7000 NOP 44 66 1 100 TAD REGNO 4414 7300 CLA CLL /SCAN ROUTINE 4467 3371 DCA H0LD9 4415 603 1 KSF 4470 2771 I SZ I H0LD9 4416 52 1 5 JMP .-1 447 1 7000 NOP 4417 6036 KRB 4472 1 100 TAD REGNO 4420 6046 TLS 4473 1370 TAD K 146 442 1 307 1 DCA OPTION 4474 3367 DCA HOLD10 4422 1 376 TAD M2 1 5 4475 1767 TAD I HOLD10 4423 107 1 TAD OPTION 4476 704 1 CIA 442 4 307 1 DCA OPTION 4477 177 1 TAD I H0LD9 442 5 107 1 TAD OPTION 4500 7700 SMA CLA 4426 1374 TAD M3 1 5 4501 5330 JMP DONE 4427 7640 SZA CLA / I S IT M 4502 6031 KSF /INTERRUPT 4430 5247 JMP GO 4503 5314 JMP RESUME 4431 1074 TAD REGNO 1 /YES, GO TO THE SCAN DUE 4504 6036 KRB 4432 3100 DCA REGNO /AFTER THE INTERRUPTION 4505 7200 CLA 4433 1075 TAD OPTI 4506 1 100 TAD REGNO 4434 307 1 DCA OPTION 4507 3074 DCA REGNO 1 443 5 1472 TAD I INDEX1 4510 107 1 TAD OPTION 4436 1121 TAD MM260 451 1 3075 DCA OPT 1 4437 7041 CIA 4512 5520 JMP I RSTART 4440 3073 DCA NUMREG 4513 7000 NOP 444 1 1373 TAD BELL 4514 107 1 RESUME, TAD OPTION 4442 6041 TSF 451 5 7650 SNA CLA 4443 5242 JMP .- 1 4516 5320 JMP .•2 4444 6046 TLS 4517 5263 JMP GOSCAN 4445 7300 CLA CLL 4520 7200 CLA 4446 5314 JMP RESUME 452 1 1073 TAD NUMREG 4447 7300 GO, CLA CLL /SCANNING STARTS WITH 2 BELLS 4522 1 100 TAD REGNO 44 50 1373 TAD BELL 4523 7700 SMA CLA 44 51 4172 JMS TYPE 4524 52 61 JMP C0NT5 4525 5262 JMP CONTS+1 / UP/DOWN COUNTER CONTROL INSTRUCTIONS 4526 7000 NOP /6141: IF AC 10 IS 1 STOP COUNTER 4527 7000 NOP / IF COUNTER IS STOPPED AND AC 9 IS 4530 107 1 DONE, TAD OPTION / RESET COUNTER 4531 7650 SNA CLA / IF AC 8 IS 1 COUNT UP 4532 5351 JMP DONEl / IF AC 7 IS I COUNT DOWN 4533 1366 TAD K4733 /6 142:IF COUNTER IS STOPPED,READ COUNTER 4534 3504 DCA I ALPHA 1 / IN TO AC SKIP ON OVERFLOW FLAG 4535 4505 JMS I LI STI /6144: RESET COUNTER OVERFLOW FLAG IF IT 4536 1 100 TAD REGNO / HAS BEEN SKIPPED ON.RESET COUNTER 4537 1365 TAD K260 / IF RESET IS ENABLED 454G 4172 JMS TYPE /6146:SKIP ON OVERFLOW FLAG AND RESET 454 1 4505 JMS I LI STI / FLAG. 4542 1073 TAD NUMREG *4600 4543 1 100 TAD REGNO 4600 0000 3SCAN, 0 /SCAN SUBROUTINE 4544 7700 SMA CLA 460 1 7300 CLA CLL 4545 5347 JMP .+2 4602 1 100 TAD REGNO 4546 5262 JMP C0NT5+1 4603 1377 TAD KK157 4547 4 50 5 JMS 1 LIST1 4604 3376 DCA HOLD 11 4550 5520 JMP I RSTART 460 5 1776 TAD I HOLD 11 4551 1073 D0NE1, TAD NUMREG 4606 7 104 CLL RAL 4552 1 100 TAD REGNO 4607 6071 607 1 /SETS INITIAL VOLTAGE 4553 7700 SMA CLA 4610 1375 TAD KK7600 4554 5764 JMP I DON E2 46 1 1 3374 DCA DELAY3 4555 2 1 00 ISZ REGNO 4612 1375 TAD KK7600 4556 1 100 TAD REGNO 46 1 3 3373 DCA DELAY4 4557 1370 TAD K146 4614 7000 NOP /PAUSE 4560 3367 DCA HOLD10 46 15 2374 ISZ DELAY3 4561 177 1 TAD I H0LD9 4616 52 14 JMP .-2 4562 3767 DCA I HOLD10 4617 2373 I SZ DELAY4 4563 5263 JMP GOSCAN 4620 52 14 JMP .-4 4564 4763 D0NE2, 4763 462 1 1 1 00 TAD REGNO 4565 0260 K260, 0260 4622 7 104 CLL RAL 4566 4733 K4733, 4733 4623 1 122 TAD K137 4567 0000 HOLD10, 0 4624 3101 DCA HPSTO 4570 0 146 K 146. 0 146 4625 1 50 1 TAD I HPSTO 457 1 0000 H0LD9, 0 4626 3 102 DCA HP 4572 4600 SCAN, 4600 462 7 1 102 TAD HP 4573 0207 BELL, 0207 4630 700 1 I AC 4574 7700 M 3 1 5, 7700 463 1 3103 DCA LP 457 5 1246 ROUTB, 1246 4632 110 1 TAD HPSTO 4 57 6 7 56 3 M2 1 5, 7563 4633 700 1 I AC 4577 0ee0 H0LD8, 0 4634 3 117 DCA LPSTO 4635 1517 4636 704 1 4637 150 1 4640 3070 4641 4516 4642 1375 4643 3374 4644 1375 4645 3373 4646 7000 4647 2374 4650 5246 4651 2373 4652 5246 4653 4767 CONT6, 4654 3066 4655 3371 4656 1067 4657 6141 4660 742 1 4661 6144 4662 7200 TIMER2, 4663 1113 4664 3374 4665 2374 4666 5270 4667 5274 4670 6146 467 1 5273 4672 2371 4673 5265 4674 2066 4675 5263 4676 7521 4677 6 141 4700. 7 521 4701 6142 4702 5304 4703 2371 4704 7100 4705 1503 4706 3503 4707 7430 TAD I LPSTO 47 10 237 1 ISZ OVRFLO CIA 47 1 1 7300 CLA CLL TAD I HPSTO 47 12 137 1 TAD OVRFLO DCA COUNT 1 47 13 1 502 TAD I H P JMS I SPOT 47 14 3502 DCA I HP TAD KK7600 47 1 5 4516 JMS 1 SPOT DCA DELAY3 47 16 7305 CLA CLL I AC RAL TAD KK7600 47 17 1070 TAD COUNT 1 DCA DELAY4 4720 3070 DCA COUNT I NOP /PAUSE BEFORE SCANNING 472 1 7430 SZL ISZ DELAY3 4722 5600 JMP I SSCAN JMP .-2 4723 2102 ISZ H P ISZ DELAY4 4724 2102 I SZ HP JMP .-4 472 5 2 103 ISZ LP JMS I DTSET 4726 2103 ISZ LP DCA DUELL2 4727 4516 JMS I SPOT DCA OVRFLO 4730 7000 NOP TAD ORDER /DATA WORD FOR COUNTER 4731 5253 JMP C0NT6 6141 4732 7000 NOP MQL 4733 02 15 02 15 /CR 6144 4734 02 12 02 12 /LF CLA 4735 0322 0322 /R TAD DWELL 4736 0305 0305 /E DCA DELAY3 4737 0307 0307 /G ISZ DELAY3 4740 4240 4240 /SPACE JMP .+2 47 4 1 0240 0240 /SPACE JMP .+5 4742 0304 0304 /D 6146 /SKIP ON COUNTER OVERFLOW 4743 0317 0317 /O JMP .+2 4744 0316 03 16 /N ISZ OVRFLO 4745 0305 0305 /E JMP .-6 47 46 02 15 02 1 5 ISZ DWELL 2 47 47 42 12 42 12 JMP TIMER2+1 47 50 02 12 02 12 SWP 47 51 0212 02 12 6141 47 52 02 12 02 12 swp 4753 0212 0212 6142 47 54 0207 0207 /BELL JMP .+2 4755 0207 0207 ISZ OVRFLO 47 56 0207 0207 CLL 47 57 0207 0207 TAD I LP 47 60 4207 4207 DCA I LP 476 1 4000 4000 SZL 4762 7000 NOP K> O 4763 5770 D0NE3, JMP I K6300 5032 1 122 TAD K 137 47 64 7000 NOP 5033 310 1 DCA HPSTO 4765 7000 NOP 5034 110 1 AGAIN, TAD HPSTO 4766 70G0 NOP 50 3 5 700 1 I AC 4767 5242 DTSET, 5242 50 36 3117 DCA LPSTO 4770 6300 K630O, 6300 5037 150 1 TAD I HPSTO 477 I ooco OVRFLO, 0 5040 3 102 DCA HP 4772 0 0 0 0 H0LD12, 0 504 1 1 102 C0NT7, TAD HP 4773 0GG0 DELAY4, 0 5042 700 1 I AC 4774 0 0 0 0 DELAY3, 0 5043 3103 DCA LP 4775 7450 KK7600, 7450 5044 4516 JMS I SPOT 4776 0 0 0 0 H0LD1 1, 0 5045 1 103 TAD LP 4777 0 157 KK157, 0157 5046 704 1 CIA 5047 1517 TAD I LPSTO 50 50 7650 SNA CLA 50 51 5263 JMP FINISH * 5 0 0 0 50 52 2 102 I SZ HP 5 0 0 0 0 0 0 0 PICK2, 0 /PLOT OR PRINT OPTION 50 53 2 102 I SZ HP 5001 1357 TAD K5160 5054 1351 TAD K7745 50B2 3504 DCA I ALPHA 1 5055 3353 DCA C0UNT2 5003 4505 JMS I LISTI 50 56 2352 ISZ C0UNT3 5004 6032 KCC 50 57 52 56 JMP .-1 5005 603 1 KSF 5060 2353 ISZ C0UNT2 5006 5205 JMP .-1 506 1 5256 JMP .-3 5307 6036 KRB 5062 5241 JMP C0NT7 5010 3356 DCA HOLD 15 5063 6032 FINISH, KCC 501 1 1356 TAD H0LD15 5064 603 1 KSF 5012 1355 TAD CRM 5065 5264 JMP .-1 5013 7650 SNA CLA 5066 6036 KRB 5014 52 17 JMP .+3 5067 3356 DCA H0LD15 531 5 4523 JMS I PPICK 5070 1356 TAD H0LD15 50 16 5600 JMP I PICK2 507 1 1355 TAD CRM 50 17 1354 TAD K5170 5072 7650 SNA CLA 5020 3504 DCA I ALPHA 1 5073 5275 JMP .+2 502 1 4505 JMS I LISTI 5074 5234 JMP AGAIN 5022 4523 JMS I PPICK 507 5 1337 TAD K5I40 5023 6032 KCC 5076 3504 DCA I ALPHA 1 5024 603 1 KSF 5077 4505 JMS I LISTI 532 5 5224 JMP .-1 5103 5520 JMP I RSTART 502 6 6036 KRB *51 10 5027 7300 CLA CLL 51 10 0 0 0 0 INVERT, 0 /SUBR0UT1 5030 1 100 TAD REGNO 51 1 1 704 1 CIA 503 1 7 104 CLL RAL 51 12 13 15 TAD KK7777 SI 13 7100 CLL 51 14 57 10 JMP I INVER 5115 7777 KK7777, • 5137 7777 5137 5140 K5140, 5 140 5140 0212 02 12 /LF 5141 e 2 1 5 02 15 /CR 5142 0304 0304 /D 5143 03 17 0317 /O 5144 0316 0316 /N 5145 0305 0305 /E 5146 02 15 02 1 5 5147 42 12 42 12 5150 4000 ,4000 5151 7745 K7745, 7745 5152 0000 COUNTS* 0 51 53 0000 C0UNT2, 0 51 54 5170 K5170, 5170 5155 7563 CRM, 7563 /-CR 51 56 0e00 H0LD15, 0 51 57 5160 K5160, 5160 5160 02 15 02 15 5161 0212 02 12 5162 0320 0320 5163 0322 0322 5164 031 1 031 I 5165 0316 03 16 5166 0324 0324 5167 4240 4240 /"PR 5170 02 15 02 1 5 517 1 02 12 02 12 5172 0320 0320 /P 5173 0314 03 14 /L 5174 0317 03 17 /O 5175 0324 0324 /T 5176 4240 4240 5177 4000 4000 5200 5201 52 02 5203 5204 0000 4525 3227 1227 1226 • 5200 DDT, ID 0 /SUBROUTINE TO SET DWELL TIME JMS I K6200 DCA CHECK2 TAD CHECK2 TAD M7 5205 7540 SMA SZA /IS IT GREATER THAN 7 5206 5215 JMP REDO 1 52 0 7 7300 CLA CLL 52 10 1227 TAD CHECK2 52 1 1 1225 TAD KKI170 5212 3227 DCA CHECK2 52 13 1627 TAD I CHECK2 52 14 5600 JMP I DDT 52 15 7300 REDO 1, CLA CLL 5216 1224 TAD K352 5217 3504 DCA I ALPHA1 5220 5623 JMP I K270 5221 7000 NOP 5222 7000 NOP 5223 0270 K270, 0270 5224 0352 K352, 0352 522 5 1 170 KK1 170, 1 170 5226 777 1 M7, 777 1 5227 0000 CHECK2, 0 5230 0000 *5232 0 52 32 0000 DTPR, 0 /SUBROUTINE DTPRNT 5233 1 100 TAD REGNO 5234 1240 TAD K154 5235 3227 DCA CHECK2 52 3 6 1627 TAD I CHECK2 5237 5632 JMP I DTPR 52 40 0 1 54 KI54, 0 154 524 1 0000 • 5242 0 5242 0000 DDTSET, 0 /SUBROUTINE TO PICK THE CORRECT 5243 1240 TAD K154 5244 1 100 TAD REGNO 52 4 5 3227 DCA CHECK2 5246 1627 TAD I CHECK2 52 47 3113 DCA DWELL 5250 1113 TAD DWELL 5251 5642 JMP I DDTSET /SUBROUTINE FOR UNSIGNED DECIMAL PRINT /COPYRIGHT 197 1 DIGITAL EQUIPMENT CORPORATION /MAYNARD,MASSACHUSETTS. • 6000 6000 0000 DECPR* 0 600 1 3243 DCA VALUE 6002 3244 DCA DIGIT 6003 1235 TAD CNTHZA 6004 3245 DCA CNTRZB 6005 1234 TAD ADDRZA 6006 3213 DCA ARROW 6007 7410 SKP 6010 3243 DCA VALUE 601 1 7 i c e CLL 6012 1243 TAD VALUE 6013 1236 ARROW, TAD TENPWR 6014 7430 SZL 6015 2244 ISZ DIGIT 6016 7430 SZL 6017 52 10 JMP ARROW-3 6020 7200 CLA 6021 1244 TAD DIGIT 6022 1242 TAD KK260 602 3 6041 TSF 6024 5223 JMP .-1 602 5 6046 TLS 602 6 7200 CLA 6027 3244 DCA DIGIT 6030 22 13 ISZ ARROW 6031 2245 ISZ CNTRZB 6032 52 12 JMP ARROW-1 6033 5600 JMP I DECPR 6034 1236 ADDRZA, TAD TENPWR 6035 7774 CNTRZA, -4 6036 6030 TENPWR, - 1750 6037 7634 -0 144 6040 7766 -00 12 604 1 7777 -000 1 6042 0260 K K 2 6 0 , 0260 6043 0000 VALUE, 0 6044 0000 DIGIT, 0 6045 0000 CNTRZB, 0 /SUBROUTINE FOR UNSIGNED DECIMAL PRINT /DOUBLE PRECISION /CALLING SEOUENCEl JMS UDPRN / HIGH ADDR (ADDRESS OF HIGH / ORDER WORD) /COPYRIGHT 1971 DIGITAL EQUIPMENT CORPORATION /MAYNARD, MASSACHUSETTS. • 6046 6046 0000 UDPRN, 0 6047 7300 CLA CLL 60 50 1646 TAD I UDPRN 6051 3361 DCA H0LDI3 60 52 176 1 TAD I H0LD13 60 53 3337 DCA UDGET 60 54 1737 TAD I UDGET 6055 3331 DCA UDHIGH 60 56 2337 I SZ UDGET 60 57 1737 TAD I UDGET 6060 3332 DCA UDLOW 6061 1325 TAD UDLOOP 6062 3330 DCA UDCNT 6063 1326 TAD UDADDR 6064 3340 DCA UDPTR 606 5 2246 ISZ UDPRN 6066 1740 UDARND, TAD I UDPTR 6067 2340 ISZ UDPTR 6070 3333 DCA UDHSUB 6071 1740 TAD I UDPTR 6072 2340 I SZ UDPTR 6e73 3334 DCA UDLSUB 6074 7 100 UDDO, CLL 607 5 1334 TAD UDLSUB 6076 1332 TAD UDLOW 6077 3336 DCA UDTEML 6100 7004 RAL 6101 1333 TAD UDHSUB 6102 133 1 TAD UDHIGH 6103 7420 SNL 6104 5312 JMP UDOUT 6105 2335 ISZ UDBOX 6106 3331 DCA UDHIGH 6107 1336 TAD UDTEML 61 10 3332 DCA UDLOW 6111 5274 JMP UDDO 6112 7200 UDOUT, CLA 61 13 1335 TAD UDBOX 61 14 1 327 TAD UDTWO 6115 6e46 TLS 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 /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 6200 0000 CONV, 0 6201 7300 CLA CLL 6202 3263 DCA H0LD14 6203 1265 TAD M5M 6204 3266 DCA COUNTC 6205 4 163 INPUT, JMS LISN 6206 3264 DCA STORE 6207 1264 TAD STORE 62 10 12 57 TAD MRBOUT 62 1 1 7440 SZA 62 12 52 14 JMP .•2 62 13 5240 JMP RUBOUT 62 14 1260 TAD M260M 62 1 5 7510 SPA 62 16 5244 JMP CHECKC 6217 1261 TAD M27 I 6220 7740 SMA SZA CLA 622 1 5240 JMP RUBOUT 6222 7300 CLA CLL 6223 2266 ISZ COUNTC 6224 5226 JMP .•2 6225 5240 JMP RUBOUT 6226 1263 TAD H0LD14 6227 7106 CLL RTL 62 30 1263 TAD H0LD14 62 3 1 7004 RAL 6232 3263 DCA H0LD14 6233 1264 TAD STORE 62 34 02 62 AND MASK 6235 1263 TAD H0LDI4 6236 3263 DCA H0LD14 62 37 52G5 JMP INPUT 6240 7330 RUBOUT, CLA CLL /IS IT RUBOUT /NO /REINITIATE TO TAKE /A NEW STRING to 624 1 6242 6243 6244 6245 6246 6247 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 127 I 4172 5201 7300 1264 1272 7450 5252 5240 7300 1263 5600 7000 7000 740 1 0117 7767 00 17 0000 0000 7513 eo00 0163 0172 02 12 7563 0000 CH ECHO END. MRBOUT, M260M, M27 I, MASK, H0LD14, STORE* M5M, COUNTO L F . MCR, • 6300 TAD JMS JMP CLA TAD TAD SNA JMP JMP CLA TAD JMP NOP NOP 7401 0117 7767 0017 0 0 7513 0 0163 0172 02 12 7563 0 L F TYPE CONV*1 CLL STORE MCR END RUBOUT CLL H0LD14 I CONV /IS IT THE TERMINATING /CHARACTER 6300 1317 TAD K2 12 6301 4172 JMS TYPE 6302 1 ie0 TAD REGNO 6303 1320 TAD KKK260 6304 4172 JMS TYPE 6305 1316 TAD SPACE 6336 4172 JMS TYPE 6337 1315 TAD K4735 6310 3504 DCA I ALPHA1 631 1 4505 JMS I LI STI 6312 4505 JMS I LI STI 63 13 4505 JMS I LI STI 6314 5520 JMP I RSTART 631 5 4735 K4735, 4735 63 16 0249 SPACE, 0240 63 17 02 12 K2 12, 02 12 6320 0260 KKK260, 0260 A 0 2 4 1 A A L P H A 0 1 4 0 A A l 0 4 7 4 A D D R Z A 6 0 3 4 A G A I N 5 0 3 4 A L P H A 0 3 4 1 A L P H A 1 0 104 ARROW 6 0 1 3 A l 0 2 5 7 B 0 3 2 3 B A K E 1 2 2 6 BB 0 3 5 5 B E L L 4 5 7 3 C 0 3 2 4 CC 0 0 5 6 CCI 0 3 0 6 CHAN 0 5 0 7 C H E C K 0 3 1 5 C H E C K C 6 2 4 4 C H E C K 1 1 3 7 6 C H E C K 2 5 2 2 7 C H O I C E 0 5 3 7 CI 0 3 0 5 CI I 0 5 1 1 C N T R Z A 6 0 3 5 C N T R Z B 6 0 4 5 CONT 0 5 5 3 C O H T I 1 0 2 0 C O N T 2 1 0 6 3 C 0 N T 3 1 1 5 1 C O N T 4 1 3 2 7 CONT 5 4 4 6 1 C 0 N T 6 4 6 5 3 C 0 N T 7 5 0 4 1 CONV 6 2 0 0 C O U N T C 6 2 6 6 C O U N T 1 0 0 7 0 C 0 U N T 2 5 1 5 3 C 0 U N T 3 51 52 CRM 5 1 5 5 C U R I N 1 2 0 5 C U R I N C 0 0 6 3 D 0 3 2 5 DD 0 0 5 7 DDT 5 2 0 0 D D T S E T 5 2 4 2 D E C P R 6 0 0 0 D E C P R T 0 111 D E L A Y 1 1 3 6 6 D E L AY 2 1 3 6 2 D E L AY 3 4 7 7 4 D E L AY 4 4 7 7 3 D I G I T 6 0 4 4 D O N E 4 5 3 0 D 0 N E 1 4 5 5 1 DON E 2 4 5 6 4 DON E 3 4 7 6 3 D S P L A Y 1 0 1 3 DT 0 124 D T P R 5 2 3 2 D T P R N T 0 7 7 7 D T S E T 4 7 6 7 DWELL 0 1 1 3 D W E L L 2 0 0 6 6 E 0 3 2 6 E E 0 0 6 0 E E E 0 0 6 2 END 6 2 5 2 EX I T 0 5 3 2 F 0 3 2 7 F F 0 0 6 1 K K 1 4 0 0 0 3 0 1 F I N I S H 5 0 6 3 K K 1 5 7 4 7 7 7 G 0 3 4 0 K K 2 6 0 6 0 4 2 G A I N 0 7 6 7 K K 7 6 0 0 4 7 7 5 G E T S E T 0 0 6 5 K K 7 7 7 7 5 1 1 5 GO 4 4 4 7 K 1 0 0 0 0 5 0 4 G O S C A N 4 4 6 3 K I 0 5 0 112 H O L D 1 0 7 7 6 K l 1 7 0 1 1 6 7 H O L D 1 0 4 5 6 7 K 1 3 7 0 1 2 2 H O L D 11 4 7 7 6 K I 4 0 0 0 3 0 2 H 0 L D 1 2 4 7 7 2 K 1 4 6 4 5 7 0 H 0 L D 1 3 6 1 6 1 K 1 5 1 1 3 7 1 H 0 L D 1 4 6 2 6 3 K l 54 5 2 4 0 H O L D I 5 5 1 5 6 K J 5 7 1 3 6 7 H 0 L D 2 0 7 7 4 K 2 1 2 63 17 H 0 L D 3 1 1 6 5 K 2 6 0 4 5 6 5 H 0 L D 4 1373 K 2 6 1 0 3 1 4 H 0 L D 5 1372 K 2 7 0 5 2 2 3 H 0 L D 6 1 3 7 0 K 2 7 6 0 3 2 0 H 0 L D 7 1363 K 3 5 2 5 2 2 4 H 0 L D 8 4 5 7 7 K 3 7 0 7 7 3 H 0 L D 9 4 5 7 1 K 4 0 0 0 2 7 5 HP 0 102 K 4 4 0 0 1 3 6 4 H P S T O 0 1 0 1 K 4 7 3 3 4 5 6 6 I B 0 3 1 1 K 4 7 3 5 6 3 1 5 I I B 0 3 1 2 K 5 1 4 0 5 1 3 7 1 I N D E X 0 4 7 6 K 5 1 6 0 5 1 5 7 I N D E X 0 3 1 3 K 5 1 7 0 51 5 4 I N D E X 1 0 0 7 2 K 6 0 0 0 5 5 2 I N F E R T 1 2 4 4 K 6 2 0 0 0 1 2 5 I N P U T 6 2 0 5 K 6 3 0 0 4 7 7 0 I N S T 0 3 1 7 K 7 1 1 6 6 I N V E R T 51 10 K 7 6 0 0 7 5 7 K K K 2 6 0 6 3 2 0 K 7 6 0 0 1 3 6 5 KK1 170 5 2 2 5 K 7 7 1 0 7 7 0 K 7 7 4 5 5 1 5 1 K 7 7 7 7 0 7 7 5 L F 6 2 7 1 L I SN 0 163 L I S T 0 3 3 0 L I S T I 0 1 0 5 L L I SN 0 3 2 2 L L I S T 0 5 1 3 L L L I S N 0 5 0 2 L P 0 103 L P S T O 01 17 MASK 6 2 62 MCR 6 2 7 2 MH 0 3 1 6 M L S T C H 0 5 0 3 M M 2 6 0 0 12 1 MP.BOUT 6 2 5 7 M S T A K E 0 4 3 7 M 14 1 3 7 4 M2 1 3 7 5 M2 15 4 5 7 6 M 2 5 6 0 5 0 0 M2 60M 6 2 6 0 M 2 6 4 0 4 7 5 M27 1 6 2 6 1 M 3 I 5 4 5 7 4 M5 0 114 M5M 6 2 6 5 M7 5 2 2 6 NUMREG 0 0 7 3 NUMSC 0 0 6 4 NUMSC I 0 1 0 6 N X L I N E 0 6 6 0 O P T I O N 0 0 7 1 OPT1 0 0 7 5 O R D E R 0 0 6 7 O V R F L O 4 7 7 1 PI CK 0 5 5 5 PI C K 2 5 0 0 0 P P I C K 0 1 2 3 P U T 4 1 2 2 2 REDO 0 5 1 6 REDO 1 52 15 REGNO 0 100 REGNO 1 0 0 7 4 R E P E A T 0 6 7 4 R E S U M E 4 5 1 4 R O U T B 4 57 5 R S T A R T 0 120 R U B O U T 6 2 4 0 SC 0 3 0 3 SCAN 4 5 7 2 SCC 0 5 1 0 S P A C E 6 3 1 6 S P O T 0 1 1 6 S R 6 2 0 0 1 3 7 7 S S C 0 3 0 4 S S C A N 4 6 0 0 SSI CON 0 2 7 6 S S P O T 0 7 2 4 S S S I C O 0 5 12 S S T A R T 0 4 7 7 S S T C H A 0 5 0 5 ST 0 5 5 4 S T A R T 0 2 0 0 S T C H A N 0 3 0 0 S T C H A 1 0 2 7 7 S T O R E 6 2 6 4 S T I 1 164 S T 2 1 163 TENPWR 6 0 3 6 T H I R D 1 162 T H I R D 2 1161 T I M E R 1331 TI M ER2 4 6 6 2 T T T Y P E 0 5 0 1 T T Y P E 0 3 2 1 T Y P E 0 172 T 1 4 0 0 0 5 0 6 UDADDR 6 1 2 6 UDARND 6 0 6 6 UDBOX 6 1 3 5 U D C N T 6 1 3 0 UDCON 1 6 1 4 1 UDDO 6 0 7 4 U D G E T 6 1 3 7 U D H I G H 6 1 3 1 UDHSUB 6 1 3 3 U D L O O P 6 1 2 5 UDLOW 6 1 3 2 U D L S U B 6 1 3 4 UDOUT 6 1 1 2 UDPRN 6 0 4 6 U D P R N T 0 1 1 5 U D P T R 6 140 U D T E M L 6 136 UDTWO 6 1 2 7 V A L U E 6 0 4 3 U'AI T 0 5 1 4 VI 0 3 0 7 UWI 0 3 10 X 0 5 3 1 

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