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Matrix isolation - I.R. studies: oxygen-fluorine discharges and the photolysis of cis-thionylimide Tchir, Peter Oryst 1972

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MATRIX ISOLATION - I.R. STUDIES: OXYGEN-FLUORINE DISCHARGES AND THE PHOTOLYSIS OF CIS-THIONYLIMIDE by PETER ORYST TCHIR B. S c . ( H o n s . ) , U n i v e r s i t y o f A l b e r t a , 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department o f 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 t h e r e q u i r e d s t a n d a r d . THE UNIVERSITY OF BRITISH COLUMBIA May, 1972 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of CApArt ' i f f The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8 , Canada i i ABSTRACT Oxygen-f1uorides: A t t e m p t s have been made a t i d e n t i f y i n g O^F^ i n the c o n d e n s a t e o f oxygen f l u o r i n e d i s c h a r g e s u s i n g i . r . s p e c t r o s -copy. 2^^ 2' ^2^2 ' ^2 ' ^ a n C ' 3^ n a v e been o b s e r v e d and numer-ous o v e r t o n e s and c o m b i n a t i o n s have been measured and a s s i g n e d f o r the f i r s t t i m e . No e v i d e n c e c o u l d be found f o r t h e p r e s e n c e o f an s p e c i e s s u g g e s t i n g t h a t "O^^" i s a c t u a1' v a m i x t u r e o f Q^^z and (0 2F) 2. The c o n f i r m a t i o n o f the p r e v i o u s l y r e p o r t e d s p e c t r u m o f s o l i d ®2^2 k e e n m a c ^ e a n c* a c a r e f u l a n a l y s i s o f the normal c o o r d -i n a t e c a l c u l a t i o n s has r e s u l t e d i n a p r e f e r e n c e f o r a f o r c e f i e l d °2 f o r 0_Fo w i t h f =7.1^  aJ/A i n c o n t r a s t t o the p r e v i o u s l y r e p o r t e d 2 2. oo °2 c a l c u l a t i o n s w h i c h found f = 10.25 aJ/A . oo c ? s-HNSQ: The s p e c t r a o f cis-HNSO and i t s i s o t o p i c homologs c o n t a i n -15 3** ing N, D and S have been o b t a i n e d i n A r and m a t r i c e s . A f o r c e f i e l d w i t h 11 p a r a m e t e r s ( c o n t a i n i n g 3 i n t e r a c t i o n c o n s t a n t s ) has been c a l c u l a t e d from t h e 29 o b s e r v e d f r e q u e n c i e s . The u.v. and vacuum u.v. p h o t o l y s i s o f cis-HNSO has been c a r r i e d o u t i n Ar m a t r i c e s w i t h the i d e n t i f i c a t i o n o f 6 new s p e c i e s from t h e i r i . r . s p e c t r a . Complete s p e c t r a have been o b s e r v e d f o r cis-HOSN and trans-HSNO, f o u r modes f o r trans-HNSO, two modes f o r SNO and one mode f o r cis-HSNO and NSO. U s i n g i s o t o p i c s u b s t i t u t i o n , a s s i g n m e n t s have been made i n a l l c a s e s and a p p r o x i m a t e f o r c e f i e l d s i i i have been o b t a i n e d f o r cis-HOSN, trans-HSNO and trans-HNSO u s i n g guessed s t r u c t u r e s . The f o l l o w i n g r e a c t i o n scheme has been d e t e r -mined from k i n e t i c s t u d i e s . u.v. u.v. u.v. cis-HNSO f a S t > cis-HOSN s l ° W > cis-HSNO + trans-HSNO S l ° W » SNO cis-HNSO A > 3 0 0 0 A » trans-HNSO cis-HNSO 1 2 1 6 A » NSO i v TABLE OF CONTENTS Page A b s t r a c t T a b l e o f C o n t e n t s ! v L i s t o f T a b l e s x L i s t o f F i g u r e s x ' ' ' Acknowledgement x v i i CHAPTER I A. BACKGROUND: INFRARED SPECTROSCOPY AND MATRIX ISOLATION 1 1. I.R. S p e c t r o s c o p y 1 2. M a t r i x I s o l a t i o n : The Method 3 3. M a t r i x I s o l a t i o n : E f f e c t on I.R. S p e c t r a . . . . 5 (a) M a t r i x S h i f t s 7 (b) R o t a t i o n 8 (c) A g g r e g a t i o n 9 (d) M u l t i p l e S i t e S p l i t t i n g 12 1». U n s t a b l e S p e c i e s 14 (a) S t a b l i z a t i o n 14 (b) Methods o f P r o d u c t i o n 16 ( i ) D i s c h a r g e and P y r o l y s i s 17 ( i i ) D i r e c t R e a c t i o n 18 ( i i i ) P h o t o l y s i s 18 (c) Charged S p e c i e s 19 V Page B. EXPERIMENTAL APPARATUS . . . 21 1. Gas H a n d l i n g Systems 21 (a) G l a s s 21 (b) M e t a l 21 2. Sample D e p o s i t i o n L i n e s . . . . . 2h 3. The H e l i u m C r y o s t a t 27 k. P h o t o l y s i s Lamps 27 (a) E x t e r n a l 27 (b) I n t e r n a l 30 5. Microwave D i s c h a r g e Equipment . . . . . 31 6. I.R. S p e c t r o p h o t o m e t e r 31 C. DISCUSSION ON THE CALCULATION OF FORCE CONSTANTS . . . 37 1 . B a s i c Theory 37 2. L e a s t Squares R e f i n e m e n t o f F o r c e C o n s t a n t s . . . 3- A p p r o x i m a t i o n s and E r r o r s E s t i m a t e s hS (a) Harmonic O s c i l l a t o r hS (b) M o d i f i e d F o r c e F i e l d s . hi (c) E r r o r E s t i m a t e s 50 k. Use i n I d e n t i f y i n g Unknown S p e c i e s 52 BIBLIOGRAPHY: CHAPTER I . . . . . 53 CHAPTER II - THE OXYGEN FLUORIDES A. BACKGROUND 56 B. 0 2F 2: DIOXYGEN DIFLUORIDE 59 v i Page 1. I n t r o d u c t i o n : P r e p a r a t i o n and S t r u c t u r e . . . . 59 2. I . r . and Raman s p e c t r a 62 (a) Background 62 (b) R e s u l t s 66 3. Normal C o o r d i n a t e A n a l y s i s 70 (a) P r e v i o u s Work 70 (b) P r e s e n t C a l c u l a t i o n s 74 (c) D i s c u s s i o n 84 C. 0 3F 2: OZONE FLUORIDE 91 1. R e p o r t e d P r e p a r a t i o n 91 2. Review o f S p e c t r a l E v i d e n c e 91 (a) V i s i b l e Spectrum 91 (b) E l e c t r o n P a r a m a g n e t i c Resonance Spectrum. . 93 (c) Mass S p e c t r o s c o p y 93 (d) N u c l e a r M a g n e t i c Resonance Spectrum . . . . 94 (e) I n f r a r e d Spectrum 95 3. 0 2/F 2 D i s c h a r g e s 96 (a) E x p e r i m e n t a l 96 (b) R e s u l t s 96 ( i ) M a t r i x E x p e r i m e n t s . . . . . 97 ( i i ) 0 2/F 2 Only 110 BIBLIOGRAPHY: CHAPTER II 119 v i i Page CHAPTER I I I - cis-HNSO: MATRIX I.R. STUDIES AND FORCE FIELD A. BACKGROUND 122 1 . P r e p a r a t i o n 122 2. I n f r a r d Spectrum 123 3. Microwave Spectrum and S t r u c t u r e 125 A. U l t r a v i o l e t S pectrum 125 5. Reasons f o r I n t e r e s t 127 B. MATRIX I.R. SPECTRA 130 1 . I n t r o d u c t i o n 130 2. E x p e r i m e n t a l '31 3. R e s u l t s 131 3*» (a) Sample I s o l a t i o n and S A b s o r p t i o n s . . . 131 (b) Fermi Resonance o f and 2v,- 137 (c) M a t r i x S p l i t t i n g 1^2 (d) M a t r i x S h i f t s : A r and N 2 \lik C. FORCE FIELD 1^8 D. THERMODYNAMIC FUNCTIONS 155 BIBLIOGRAPHY: CHAPTER I I I 157 CHAPTER IV - THE PHOTOLYSIS OF cis-HNSO A. INTRODUCTION 158 B. IDENTIFICATION OF MOLECULES: GENERAL 160 1. G r o u p i n g o f A b s o r p t i o n s 160 2. S p e c t r a , S t r u c t u r e s , A s s i g n m e n t s and N.C.A. . . . 161 v i i i Page 3. A R e a c t i o n Mechanism . . . . . 162 C. IDENTIFICATION OF MOLECULES: RESULTS 164 1. trans-HNSO '67 (a) S p e c t r a l67 (b) N.C.A 172 (c) D i s c u s s i o n '74 2. cis-HOSN '79 (a) S p e c t r a ' 7 9 (b) N.C.A ' 84 (c) Thermodynamic F u n c t i o n s 190 (d) D i s c u s s i o n 19 ' 3. HSNO - c i s and t r a n s ' 94 (a) S p e c t r a '94 (b) N.C.A 203 (c) D i s c u s s i o n 206 k. SNO: A R a d i c a l 207 (a) S p e c t r a 207 (b) N.C.A 210 (c) D i s c u s s i o n 210 5. The 1195 cm" 1 D o u b l e t , NSO 212 D. REACTIONS 215 1. P r o d u c t s 215 2. R e a c t i o n 1 218 i x Page (a) O b s e r v a t i o n s 218 (b) D i s c u s s i o n 219 3. R e a c t i o n 2 222 (a) O b s e r v a t i o n s 222 (b) D i s c u s s i o n 223 A. R e a c t i o n 3 2 2 5 5. HNSO: c i s - t r a n s Isomerism 226 6. NSO: P r o d u c t i o n and P h o t o l y s i s 226 7. C o n c l u s i o n s 227 BIBLIOGRAPHY: CHAPTER IV 228 APPENDIX I 229 X LIST OF TABLES T a b l e Page (1 8) 2-1 M a t r i x i . r . a b s o r p t i o n s o f 0»F„ from S p r a t l e y v . . . 63 2-2 S o l i d O^F^ '" r* a ^ ) S o r P t ' o n s f r o m Loos e t a l ^ 1 ^ . . . . 64 2-3 I . r . a b s o r p t i o n s o f 02^2 ' n t ^ e c o n < ^ e n s a t e f r o m ®2^2 d i s c h a r g e s 67 2-4 F o r c e f i e l d found by Loos e t a l ^ 1 5 ^ f o r 0 ^ 71 2-5 I n t e r n a l and symmetry c o o r d i n a t e d e f i n i t i o n s f o r ' ^ 2-6 A s y m metric modes: symmetry c o o r d i n a t e f o r c e c o n s t a n t s , s o l i d O^F^ f r e q u e n c i e s and p o t e n t i a l energy d i s t r i b u t i o n 79 2-7 Symmetric modes: symmetry f o r c e c o n s t a n t s , s o l i d f r e q u e n c i e s and p o t e n t i a l e nergy d i s t r i b u t u i o n 81 2-8 F o r c e c o n s t a n t s from t h e i . r . f r e q u e n c i e s o f s o l i d O2F2 82 2-9 B e s t f o r c e f i e l d f o r O^F^ - m a t r i x f r e q u e n c i e s . C a l c u l a t e d and o b s e r v e d f r e q u e n c i e s and P.E.D 85 2-10 F o r c e c o n s t a n t s f o r O^F 86 2-11 I . r . a b s o r p t i o n s a s s i g n e d t o o x y g e n - f l u o r i d e s i n an a rgon m a t r i x . From Q^/F^/tKr d i s c h a r g e s 102 2-12 A b s o r p t i o n s a s s i g n e d t o i m p u r i t i e s i n a rgon m a t r i c e s . From 0^/F^/Ar d i s c h a r g e s 103 2-13 Weak, u n a s s i g n e d a b s o r p t i o n s i n a rgon m a t r i c e s . From ° 2 / F 2 / A r d i s c h a r 9 e s 1 0 i* 2-14 0_/F 9 d i s c h a r g e . L i s t o f oxygen f l u o r i d e a b s o r p t i o n s . . 113 X? T a b l e Page 2 - 15 O-j/^o d i s c h a r g e . L i s t o f i m p u r i t i e s 11 h 3 - l I.r. f r e q u e n c i e s and a s s i g n m e n t s f o r cis-HNSO and cis-DNSO i n the gas phase ( R i c h e r t ^ ) 12^ 3 - 2 Cis-HNSO dimer a b s o r p t i o n s and a s s i g n m e n t s 138 3 - 3 A s t u d y o f Fermi r e s o n a n c e i n cis-HNSO. S e p a r a t i o n s o f u n p e r t u r b e d and 2v<- ( c a l . ) l e v e l s 140 3 - A M a t r i x s h i f t s f o r cis-HNSO i n ar g o n and n i t r o g e n . . . . 1^5 3 - 5 Comparison o f m a t r i x s h i f t s f o r HNSO and DNSO i n ar g o n . 1^6 3 - 6 Observed f r e q u e n c i e s f o r s e v e r a l i s o t o p e s o f cis-HNSO i n a r gon m a t r i c e s 1^9 3~7 F o r c e f i e l d f o r cis-HNSO i n c l u d i n g l e a s t s q u a r e s e r r o r e s t i m a t e s 151 3 - 8 P o t e n t i a l energy d i s t r i b u t i o n and a s s i g n m e n t r e s u l t i n g f rom f o r c e f i e l d i n t a b l e 3~7 152 3 -9 C a l c u l a t e d f r e q u e n c i e s and t h e i r e r r o r s f o r cis-HNSO . . 153 3 - 1 0 Thermodynamic f u n c t i o n s f o r HNSO c a l c u l a t e d from v i b r a -t i o n a l f r e q u e n c i e s , cal/mole°K 156 k~] S e t s o f a b s o r p t i o n s produced on t h e p h o t o l y s i s o f cis-HNSO 166 h-2 Observed a b s o r p t i o n f r e q u e n c i e s (cm o f trans-HNSO i n an argon m a t r i x 171 *»-3 Comparison o f c i s - t r a n s f r e q u e n c y s h i f t s f o r HNSO and HONO 173 k-h F o r c e f i e l d f o r trans-HNSO 175 x i i Tab 1e Page 4-5 C a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s from o b s e r v e d f r e q u e n c i e s (A) f o r trans-HNSO 176 4-6 P o t e n t i a l energy d i s t r i b u t i o n and a s s i g n m e n t s f o r ' trans-HNSO 177 4-7 I . r . a b s o r p t i o n s and a s s i g n m e n t s f o r cis-HOSN i n an argon m a t r i x 183 4-8 Comparison o f the f i t o f the c i s and t r a n s forms o f HOSN t o t h e o b s e r v e d t o r s i o n a l f r e q u e n c i e s 187 4-9 F o r c e f i e l d f o r cis-HOSN 188 4-10 C a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s from o b s e r v e d f r e q u e n c i e s (A) f o r cis-HOSN 189 4-11 P o t e n t i a l energy d i s t r i b u t u i o n and a s s i g n m e n t s f o r cis-HOSN 190 4-12 The p r i n c i p l e moments o f i n e r t i a and thermodynamic f u n c t i o n s (cal/mole°K) f o r cis-HOSN 192 4-13 Observed a b s o r p t i o n s and p o s s i b l e a s s i g n m e n t s f o r HSNO 197 4-14 F o r c e f i e l d f o r trans-HSNO 204 4-15 Observed f r e q u e n c i e s , c a l c u l a t e d f r e q u e n c i e s , p o t e n t i a l e n ergy d i s t r i b u t i o n and a s s i g n m e n t f o r trans-HNSO . . . 205 4-16 Observed f r e q u e n c i e s and a s s i g n m e n t s f o r t h e r a d i c a l SNO 211 x i i i LIST OF FIGURES F i g u r e Page 1 - 1 The a b s o r p t i o n o f A s C l ^ i n an a rgon m a t r i x 35 37 (M/R = 5 0 0 ) showing s p l i t t i n g r e s u l t i n g from CI -CI i s o t o p e s 6 1 - 2 The a s y m m e t r i c s t r e t c h , v^, o f ozone (produced by d i s c h a r g e o f 0 2 / A r m i x t u r e s ) showing t h e n a r r o w i n g o f peaks on d i l u t i o n II 1 - 3 The a s y m m e t r i c s t r e t c h e s o f s e v e r a l bent t r i a t o m i c m o l e c u l e s showing c h a r a c t e r i s t i c argon m a t r i x s p l i t t i n g 1 3 1 - 4 G l a s s vacuum s y s t e m 2 3 1 - 5 Spray on a s s e m b l y , c r y o s t a t t a i l s e c t i o n and p h o t o l y s i s a p p a r a t u s 2 6 1 - 6 L i q u i d h e l i u m c r y o s t a t w i t h i . r . s p e c t r o s c o p y - m a t r i x i s o l a t i o n t a i l a ssembly 2 9 1 - 7 Vacuum u l t r a v i o l e t p h o t o l y s i s lamp and mounting assembly 3 3 1 - 8 E v e n s o n - B r o i d a microwave c a v i t y , t y p e 5 3 5 1 - 9 B l o c k d i a g r a m o f main p e r t u r b a t i o n c y c l e f o l l o w e d by computer ( t a k e n from r e f e r e n c e 3 3 ) 4 3 2 - 1 The o v e r l a p p i n g a b s o r p t i o n s o f FN0 2(symmetric NO s t r e t c h ) and 0 2 F 2 ( 0 - 0 s t r e t c h ) a t 1 3 0 5 cm 1 6 9 2 - 2 I n t e r n a l c o o r d i n a t e s f o r 0 2 F 2 7 6 2 ~ 3 ( a ) F o r c e c o n s t a n t - bond o r d e r c o r r e l a t i o n s f o r s e v e r a l 0 - 0 bonds 8 7 x i v F i g u r e Page 2-3(b)Bond l e n g t h - bond o r d e r c o r r e l a t i o n f o r s e v e r a l 0-0 bonds 88 2-4 V i s i b l e a b s o r p t i o n s p e c t r a o f s e v e r a l oxygen f l u o r i d e s ( r e f e r e n c e 26) 92 2-5 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d Y^/Q^/kr = 4/1/50 98 2-6 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d V^/Q^/kr = 1/4/50 99 2-7 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d Y^/O^hr = 1/2/200 100 2-8 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d O^/Ar = 1/200 . . . 101 2-9 Hi g h r e s o l u t i o n s p e c t r u m o f F^/O^/Ar d i s c h a r g e 106 2-10 Hi g h r e s o l u t i o n s p e c t r u m o f O^/Ar d i s c h a r g e showing o f ozone 106 2-11 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d ®2^2 = . . . . 112 2- 12 Spectrum o f c o n d e n s a t e o f d i s c h a r g e d ®2^2 ~ f o l l o w i n g warming t o 77°K 117 3 - l The s t r u c t u r e o f c i s - t h i o n y l i m i d e o b t a i n e d by K i r c h h o f f ^ 126 3 -2 P o s s i b l e p o t e n t i a l e nergy c u r v e s f o r c i s - t h i o n y l i m i d e p r o p o s e d by A l l e g r e t t i ^ 128 3~3 The i n f r a r e d s p e c t r u m o f cis-HNSO i n argon m a t r i c e s . . 133 3 -4 The h i g h r e s o l u t i o n s p e c t r u m o f o f cis-HNSO showing 34 both t h e S i s o t o p i c s p l i t t i n g and the 2v^ o v e r t o n e t o low f r e q u e n c y ' 134 3 -5 The Fermi r e s o n a n c e d o u b l e t o f and 2v^ o f c i s - H ^ N S O 139 3-6 V j and o f cis-HNSO and o f SO^ showing m a t r i x s p l i t t i n g s 143 XV F i g u r e Page 4-1 Spectrum f o l l o w i n g t he vacuum u.v. p h o t o l y s i s o f cis-HNSO i n an ar g o n m a t r i x (M/R = 800) 159 4-2 Growth c u r v e s o f t h r e e d i f f e r e n t groups o f peaks u s i n g Hg lamp p h o t o l y s i s , A = 673 cm 1 , B = 1597 cm C = 1523 cm" 1 . 165 4-3 The f o u r o b s e r v e d a b s o r p t i o n s o f trans-HNSO: p r o d u c t i o n o w i t h p h o t o l y s i s u s i n g X>3000 A and d i s a p p e a r a n c e u s i n g A>2000 A 168 4-4 Spectrum f o l l o w i n g t he 1 mi n u t e Hg lamp p h o t o l y s i s o f cis-HNSO i n argon (M/R = 400) 180 4-5 C o r r e l a t i o n o f NS bond l e n g t h w i t h NS s t r e t c h i n g f r e q u e n c y . . . . . 185 4-6 Spectrum f o l l o w i n g the 4 2 m i n u t e Hg lamp p h o t o l y s i s o f cis-HNSO i n argon (M/R = 400) 196 4-7 Comparison o f 1596 cm ' and 1570 cm ' a b s o r p t i o n i n t e n s i t i e s (a) Hg lamp p h o t o l y s i s (b) hydrogen r e s o n a n c e lamp p h o t o l -y s i s w i t h s p r a y - o n 198 4-8 S p e c t r a o f t h e NO s t r e t c h i n g r e g i o n f o r DSNO and HS^NO 199 4-9 The h i g h r e s o l u t i o n s p e c t r a o f s e v e r a l trans-HSNO a b s o r p -t i o n s showing s p l i t t i n g s 201 4-10 The h i g h r e s o l u t i o n s p e c t r a o f the NO s t r e t c h and SNO bend o f SNO. 209 XV I F i g u r e Page 4-11 The SO s t r e t c h i n g mode o f NSO produced by vacuum u.v. p h o t o l y s i s o f cis-HNSO. (a) shows the d i s a p p e a r a n c e o f t h e a b s o r p t i o n f o l l o w i n g Hg lamp p h o t o l y s i s 2 1 3 4-12 I n t e n s i t y o f a b s o r p t i o n s as a f u n c t i o n o f p h o t o l y s i s t i m e , X > 2 0 0 0 A 2 1 6 4 - 1 3 I n t e n s i t y o f a b s o r p t i o n s as a f u n c t i o n o f p h o t o l y s i s o t i m e , X > 3 0 0 0 A 2 1 7 4-14 L o g a r i t h m i c p l o t o f t h e d i s a p p e a r a n c e o f cis-HNSO on p h o t o l y s i s , A > 2 0 0 0 A 2 2 1 ACKNOWLEDGEMENT I wiAh to zxptiQAA my Ainczn.z&t appfizdation to Vn,. R.V. Spiatlzy ^on. IvU guidance, and zncoufiagzmznt a i we££ a6 ki6 fisiizndAhip throughout thz duration o& thiA uio/ik. kti>o, I am dzzpZy indebted to thz many othzn. pzoptz mho hztpzd in ziXkzn. tixz KZi>zah,oh on. thz pn.zpan.ation o£ thz manuA oxi.pt. - 1 -CHAPTER I A. BACKGROUND: INFRARED SPECTROSCOPY AND MATRIX ISOLATION 1. I.R. SPECTROSCOPY The s t u d y o f the a b s o r p t i o n o f l i g h t by m o l e c u l e s i n t h e i n f r a r e d r e g i o n o f the s p e c t r u m was begun b e f o r e the t u r n o f t h e c e n t u r y . In 1912 i t was shown by N i e l s B j e r r u m t h a t i n f r a r e d a b s o r p -t i o n by m o l e c u l e s was due t o the up t a k e o f r o t a t i o n a l and v i b r a t i o n a l e nergy i n d e f i n i t e q u a n t a ^ . S i n c e t h a t t i m e , w i t h the development o f t h e o r y and improvement o f equipment, i . r . s p e c t r o s c o p y has become one o f the c h e m i s t ' s main t o o l s f o r the s t u d y o f m o l e c u l a r s t r u c t u r e . In i . r . s p e c t r o s c o p y t h e most i n f o r m a t i o n can be o b t a i n e d (2) from the gas phase s t u d y o f s m a l l m o l e c u l e s . T r a n s i t i o n s a r e o b s e r v e d between t h e r o t a t i o n a l e n ergy l e v e l s o f one v i b r a t i o n a l s t a t e and s i m i l a r l e v e l s i n a h i g h e r s t a t e . The r e s u l t i s a s e t o f a b s o r p -t i o n s i n t h e i n f r a r e d c o r r e s p o n d i n g t o v i b r a t i o n a l t r a n s i t i o n s upon w h i c h a r e su p e r i m p o s e d t h e i r p a r t i c u l a r r o t a t i o n a l f i n e s t r u c t u r e s . From t h i s r o t a t i o n a l s t r u c t u r e t h e moments o f i n e r t i a o f t h e m o l e c u l e i n i t s v a r i o u s v i b r a t i o n a l s t a t e s can be c a l c u l a t e d and from t h e s e i t i s p o s s i b l e t o d e t e r m i n e the bond l e n g t h s and bond a n g l e s i n the mole-c u l e . B e f o r e t h i s can be done, the shape o f the m o l e c u l e must be d e t e r m i n e d and a s t u d y o f t h e v i b r a t i o n a l s p e c t r u m a i d s i n t h i s as w e l l . The k i n e t i c energy o f v i b r a t i o n depends upon t h e masses o f the bonded atoms w h i l e the p o t e n t i a l e n ergy depends upon t h e s t r e n g t h - 2 -o f the bonds. As a r e s u l t , v i b r a t i o n a l s p e c t r a can be used t o d e t e r -mine th e t y p e s o f bonds i n the m o l e c u l e . As w e l l , knowledge o f w h i c h v i b r a t i o n a l - r o t a t i o n a l t r a n s i t i o n s a r e o b s e r v e d can o f t e n a l l o w the c h o i c e between s e v e r a l p o s s i b l e s t r u c t u r e s on the b a s i s o f symmetry. T h i s i n f o r m a t i o n i s o f t e n enough t o f i x the shape o f a s m a l l m o l e c u l e and a l l o w f o r a n a l y s i s o f t h e r o t a t i o n a l s t r u c t u r e . Then, knowing the a c c u r a t e s t r u c t u r e s and v i b r a t i o n a l e n e r g i e s , f o r c e c o n s t a n t s ^ can be c a l c u l a t e d f o r the m o l e c u l e t o g i v e a d i r e c t measure o f bond s t r e n g t h . The c a l c u l a t i o n o f f o r c e c o n s t a n t s i s d i s c u s s e d i n s e c t i o n C o f t h i s c h a p t e r . For l a r g e r m o l e c u l e s t h e r o t a t i o n a l s t r u c t u r e becomes so c l o s e l y spaced as t o p r e v e n t r e s o l u t i o n . As a r e s u l t , the a c c u r a t e s t r u c t u r e c a n n o t be d e t e r m i n e d a l t h o u g h the band c o n t o u r s r e s u l t i n g from t h e r o t a t i o n can s t i l l g i v e some i n f o r m a t i o n about the symmetry of a v i b r a t i o n a l mode. The o n l y i n f o r m a t i o n o b t a i n e d i s then l i m i t e d t o t h e v i b r a t i o n s o f t h e m o l e c u l e . T h i s , as b e f o r e , can s t i l l be a n a l y s e d t o h e l p d e t e r m i n e t h e s t r u c t u r e o r c a l c u l a t e f o r c e c o n s t a n t s i f the s t r u c t u r e i s known by some o t h e r means. Some compounds, however, do not have s u f f i c i e n t vapour p r e s s u r e t o be s t u d i e d by i . r . s p e c t r o s c o p y i n the gas phase. These compounds must then be s t u d i e d as pure l i q u i d s , s o l u t i o n s o r s o l i d s . The i n t e r a c t i o n s between m o l e c u l e s i n l i q u i d s o r s o l i d s tend t o s h i f t and broaden v i b r a t i o n a l t r a n s i t i o n s and p r e v e n t r e s o l u t i o n o f c l o s e l y s p a ced bands. S i m i l a r l y , i n the gas phase, c l o s e l y spaced c o n t o u r s - 3 -can a l s o p r e v e n t r e s o l u t i o n . Thus i n t h e s e c a s e s s m a l l s p l i t t i n g s r e s u l t i n g from d i f f e r e n t i s o t o p e s c a n n o t be r e s o l v e d . As w e l l , n e a r l y d e g e n e r a t e v i b r a t i o n s w i l l o v e r l a p p r e v e n t i n g an a c c u r a t e d e t e r m i n a t i o n o f t h e i r p o s i t i o n s . To overcome t h e s e d i f f i c u l t i e s and a l s o t o a l l o w s t u d y o f u n s t a b l e s p e c i e s , the method o f m a t r i x i s o l a t i o n has been adapt e d t o i n f r a r e d s p e c t r o s c o p y . 2 . MATRIX ISOLATION: THE METHOD M a t r i x i s o l a t i o n i s the entrapment o f i n d i v i d u a l m o l e c u l e s i n a r i g i d , i n e r t l a t t i c e a t v e r y low t e m p e r a t u r e s . Th]s i s done by r a p i d l y f r e e z i n g d i l u t e gas m i x t u r e s o f t h e m o l e c u l e (R) and the m a t r i x m a t e r i a l (M). The m a t r i x must be r i g i d , i . e . t h e i s o l a t e d m o l e c u l e must be u n a b l e t o d i f f u s e , r o t a t e o r c h e m i c a l l y r e a r r a n g e . A l s o the m a t r i x must be i n e r t i n b o t h a p h y s i c a l and c h e m i c a l sense - i t must be u n r e a c t i v e so t h a t b o t h s t a b l e and u n s t a b l e s p e c i e s can be i s o l a t e d and i t cannot i n t e r a c t s t r o n g l y w i t h the m o l e c u l e so t h a t the shape, v i b r a t i o n s and e l e c t r o n i c s t a t e s o f t h e m o l e c u l e a r e not s i g n i f i c a n t -l y e f f e c t e d . Y e t t h e i n t e r a c t i o n must be s t r o n g enough t o p r e v e n t r o t a t i o n , i n t e r n a l r o t a t i o n o r c h e m i c a l rearrangement o f t h e m o l e c u l e . The m o l e c u l e i s i s o l a t e d when i t i s s u r r o u n d e d by m a t r i x m a t e r i a l and hence does not i n t e r a c t w i t h o t h e r m o l e c u l e s . However, i f t he m a t r i x i s not r i g i d , d i f f u s i o n w i l l cause m o l e c u l e s t o a s s o c -i a t e w i t h each o t h e r and d e s t r o y the i s o l a t i o n . T h e r e f o r e , the temp-e r a t u r e must be low enough t o p r e v e n t n o n - r i g i d i t y . A l s o , i f the - 4 -m a t r i x i s not i n h i g h enough e x c e s s i n the o r i g i n a l gas m i x t u r e , some m o l e c u l e s w i l l l i k e l y a s s o c i a t e on f r e e z i n g and i s o l a t i o n w i l l not be a c h i e v e d . The s t r o n g e r the i n t e r a c t i o n s between m o l e c u l e s , the h i g h e r the d i l u t i o n r e q u i r e d t o a c h i e v e i s o l a t i o n . D i l u t i o n i s u s u a l l y d e s c r i b e d as a mole r a t i o o f m a t r i x t o m o l e c u l e , M/R, and common v a l u e s o f M/R a r e from 50 t o 5000. Groups o f two o r more m o l e c u l e s t r a p p e d n e x t t o each o t h e r so t h a t they i n t e r a c t ( i . e . a r e not i s o l a t e d ) a r e c a l l e d a g g r e g a t e s . The main reason f o r u s i n g m a t r i x i s o l a t i o n i s t h a t i t a l l o w s the s t u d y o f i n d i v i d u a l m o l e c u l e s . Most p r o p e r t i e s o f the m o l e c u l e s i n t he m a t r i x a r e v e r y n e a r l y the same as i n t h e gas s i n c e s t r o n g i n -t e r a c t i o n s w h i c h a r e found i n l i q u i d s and s o l i d s a r e e l i m i n a t e d . A l s o the i s o l a t i o n a t low t e m p e r a t u r e s a l l o w s f o r t h e s t a b i l i z a t i o n o f r e a c t i v e s p e c i e s w h i c h a r e d i f f i c u l t t o s t u d y under normal c o n d i t i o n s . T h i s was the p r i m a r y purpose f o r the i n t r o d u c t i o n o f the t e c h n i q u e . The method a l s o a l l o w s t h e s t u d y o f i n t e r a c t i o n s . By c o n t r o l l i n g t he e x t e n t o f a s s o c i a t i o n s o l u t e - s o l u t e i n t e r a c t i o n s such as hy d r o g e n -bonding can be l o o k e d a t w h i l e s o l u t e - s o l v e n t i n t e r a c t i o n s s i m i l a r t o th o s e i n l i q u i d s o l u t i o n s can be measured f o r i s o l a t e d m o l e c u l e s . A f t e r i s o l a t i o n m o l e c u l e s a r e s t u d i e d i n the m a t r i x by some form o f s p e c t r o s c o p y . A l t h o u g h the method was o r i g i n a l l y d e v e l o p e d f o r use w i t h i n f r a red s p e c t r o s c o p y , i t has become commonly a d a p t e d to u l t r a v i o l e t and e l e c t r o n p a r a m a g n e t i c r e s o n a n c e s p e c t r o s c o p y . In t h i s work o n l y i t s use w i t h i . r . w i l l be f u r t h e r d i s c u s s e d . F i r s t - 5 -the c h a r a c t e r i s t i c s o f m a t r i x i . r . s p e c t r a w i l l be d e s c r i b e d and then the e x p e r i m e n t a l t e c h n i q u e wi 1 1 be o u t l i n e d w i t h a d e t a i l e d d e s c r i p -t i o n o f t h e n e c e s s a r y a p p a r a t u s . 3. MATRIX ISOLATION: EFFECT ON I.R. SPECTRA Because m o l e c u l e s v i b r a t e but u s u a l l y do not r o t a t e when t r a p p e d i n a m a t r i x , o n l y one a b s o r p t i o n i s o b s e r v e d i n the i . r . f o r most v i b r a t i o n a l t r a n s i t i o n s . The t r a n s i t i o n s g i v e v e r y s h a r p a b s o r p -t i o n peaks because the i n t e r a c t i o n s between the m o l e c u l e and the m a t r i x a r e weak, a l l o w i n g the r e s o l u t i o n o f a b s o r p t i o n s s e p a r a t e d by o n l y 1 o r 2 cm '. Thus i s o t o p i c s p l i t t i n g s o f o n l y a few cm 1 can be d e t e r m i n e d , o v e r c o m i n g a major p r o b l e m e n c o u n t e r e d i n the s p e c t r a o f l a r g e m o l e c u l e s . For example, f i g u r e 1-1 shows the h i g h r e s o l u t i o n s p e c t r u m o f the 35 37 a b s o r p t i o n o f A s C l ^ i n w h i c h the s p l i t t i n g s r e s u l t i n g from CI and CI (4) i n t h e i r n a t u r a l abundance a r e r e s o l v e d . These s p l i t t i n g s have not been o b s e r v e d i n the gas phase. As w e l l , because a l l t h e i n t e n s i t y o f a t r a n s i t i o n i s i n one s h a r p a b s o r p t i o n peak, the peak i s e a s i l y d e t e c t e d and o n l y v e r y s m a l l amounts o f sample a r e needed. As a r e s u l t o f t h e s e a d v a n t a g e s , the use o f m a t r i x i s o l a t i o n w i t h i . r . s p e c t r o s c o p y i s v e r y p o p u l a r . However, m a t r i x i . r . s p e c t r a have s e v e r a l o t h e r i m p o r t a n t c h a r a c t e r i s t i c s w h i c h must be c o n s i d e r e d . I . r . a b s o r p t i o n s i n the m a t r i x show s m a l l s h i f t s from the gas phase f r e q u e n c i e s , some s m a l l m o l e c u l e s show h i n d e r e d r o t a t i o n i n the m a t r i x w i t h a r e s u l t i n g - 6 -W c m " ' ) 4 0 0 3 9 0 3 8 0 _j | i _ F i g u r e 1-1. The a b s o r p t i o n o f A s C l ^ in an a rgon m a t r i x (M/R= 5 0 0 ) showing s p l i t t i n g r e s u l t i n g form C 1 3 5 - C 1 3 7 i s o t o p e s . - 7 -s p l i t t i n g o f a b s o r p t i o n s , a g g r e g a t i o n may a l s o cause s p l i t t i n g o r b r o a d e n i n g o f peaks and some l a t t i c e s a l l o w t r a p p i n g i n s e v e r a l i n -e q u i v a l e n t m a t r i x s i t e s w i t h f u r t h e r s p l i t t i n g p o s s i b l e , (a) M a t r i x S h i f t s : Because o f the i n t e r a c t i o n o f the m o l e c u l e w i t h the m a t r i x , v i b r a t i o n a l a b s o r p t i o n s a r e s l i g h t l y s h i f t e d f r o m t h e i r gas phase v a l u e s . These , s h i f t s , w h i c h may be t o h i g h e r o r lower f r e q u e n c y , a r e s m a l l , u s u a l l y l e s s than 20 cm \ They a r e found t o depend on the m a t r i x m a t e r i a l and v a r y f o r d i f f e r e n t modes o f a g i v e n m o l e c u l e . V i b r a t i o n a l modes i n v o l v i n g h y d r o g e n , because t h e y have l a r g e r a m p l i t u d e s , a r e the most s t r o n g l y e f f e c t e d and sometimes have s h i f t s l a r g e r than 20 cm \ P i m e n t e l and C h a r l e s ^ l i s t s h i f t s f o r s e v e r a l m o l e c u l e s i n and Ar m a t r i c e s . (5) P i m e n t e l and C h a r l e s a l s o draw c o r r e l a t i o n s between t h e s h i f t s o f d i f f e r e n t v i b r a t i o n a l modes and the s i z e o f b o t h the mole-c u l e and t h e l a t t i c e s i t e . These c o r r e l a t i o n s a l l o w f o r a model, s i m i l a r t o t h a t used i n s o l u t e - s o l v e n t i n t e r a c t i o n s t u d i e s i n l i q u i d s , w h i c h s u c c e s s f u l l y a c c o u n t s f o r the d i r e c t i o n o f m a t r i x s h i f t s on the b a s i s o f the " t i g h t n e s s " o f the m a t r i x cage. Barnes and H a l l a m ^ , i n t h e i r r e v i e w on m a t r i x i s o l a t i o n and i . r . s p e c t r o s c o p y , summarize o t h e r a t t e m p t s t o c a l c u l a t e s h i f t s by e s t i m a t i n g m o l e c u l e - m a t r i x i n -t e r a c t i o n s . They show t h a t t he i n t e r a c t i o n p o t e n t i a l e n e r g y may be e x p r e s s e d as a sum o f e l e c t r o s t a t i c , i n d u c t i v e , d i s p e r s i v e and r e p u l -s i v e t erms. However, i n n o n - p o l a r m a t r i c e s the e l e c t r o s t a t i c term i s z e r o . The s h i f t can then be g i v e n by - 8 -Av = A v . , + A v , . + A v i nd d i s rep A t t e m p t s a t c a l c u l a t i n g the terms u s i n g v a r i o u s methods a r e o u t l i n e d in the r e v i e w ^ . U n f o r t u n a t e l y not enough e x p e r i m e n t a l d a t a i s y e t a v a i l a b l e to show how a c c u r a t e the a t t e m p t s o f c a l c u l a t i n g t h e s e i n t e r a c t i o n s a r e . However, because the se s h i f t s a r e s m a l l , they cau se l i t t l e d i f f i c u l t y and f o r c e c o n s t a n t s c a l c u l a t e d f rom m a t r i x f r e q u e n c i e s a r e v e r y near t he ga.s phase v a l u e s . A l s o , the a c c u r a c y o f m a t r i x f o r c e c o n s t a n t s i s p a r t i a l l y a r e s u l t o f the f a c t t h a t changes in v i b r a t i o n a l f r e q u e n c y upon i s o t o p i c s u b s t i t u t i o n a r e v e r y n e a r l y the same in the m a t r i x as in the gas . I s o t o p i c s u b s t i t u t i o n i n f o r m a t i o n i s the most impor t an t s o u r c e o f d a t a f o r the c a l c u l a t i o n o f f o r c e c o n s t a n t s . (b) Rota t i o n : A l t h o u g h l a r g e m o l e c u l e s a r e h e l d f i x e d in a m a t r i x , many sma l l m o l e c u l e s p o s s e s s n e a r l y f r e e r o t a t i o n in c a v i t i e s o f s u f f i c i e n t s i z e ^ ' ^ . Because o f the low t e m p e r a t u r e , o n l y the f i r s t and second r o t a t i o n a l l e v e l s have s u f f i c i e n t p o p u l a t i o n t o g i v e o b -s e r v a b l e a b s o r p t i o n s . As a r e s u l t , f o r d i a t o m i c s the R ( 0 ) peak i s the s t r o n g e s t w h i l e the R O ) and P ( l ) a b s o r p t i o n s a r e seen but a r e weak. However, on warming the m a t r i x s l i g h t l y , but s t i l l k e e p i n g i t a t a t e m p e r a t u r e a t wh i ch i t i s r i g i d , the i n t e n s i t y o f the P ( l ) and R(l). peaks i n c r e a s e s w i t h r e s p e c t t o R ( 0 ) and a d d i t i o n a l weak peaks a p p e a r . On c o o l i n g the o r i g i n a l i n t e n s i t i e s r e t u r n - the r e v e r s i b i l -i t y b e i n g c h a r a c t e r i s t i c o f p o p u l a t i o n c h a n g e s . - 9 -For d i a t o m i c s t he i n t e r p r e t a t i o n o f m a t r i x s p e c t r a f o l l o w s t h a t o f the gas phase s p e c t r a w i t h o n l y s m a l l d e c r e a s e s i n the " r o t a -t i o n a l c o n s t a n t s " w h i l e f o r l a r g e r m o l e c u l e s t h e s i t u a t i o n i s more complex. For example, o f t e n t h e r o t a t i o n a l s t r u c t u r e i s o n l y seen i n c e r t a i n v i b r a t i o n a l modes s u g g e s t i n g t h a t r o t a t i o n i s a l l o w e d about c e r t a i n axes but r e s t r i c t e d about o t h e r s . A l s o , f o r l a r g e r m o l e c u l e s , p r o b a b l y because t h e r o t a t i o n i s so s t r o n g l y h i n d e r e d , the s e p a r a t i o n s o f r o t a t i o n a l bands a r e much s m a l l e r than i n gas phase s p e c t r a . However, p e r t u r b a t i o n c a l c u l a t i o n s o f b a r r i e r s t o r o t a t i o n r e s u l t i n g from i n t e r a c t i o n s w i t h t he m a t r i x have not been v e r y s u c c e s s f u l i n p r o v i d i n g a good agreement w i t h e x p e r i m e n t nor i n p r o v i d i n g a model f o r the u n d e r s t a n d i n g o f r o t a t i o n and n o n - r o t a t i o n i n a m a t r i x ^ , A model i n v o l v i n g c o u p l i n g o f r o t a t i o n and t r a n s l a -t i o n w i t h i n the cage has been more s u c c e s s f u l but few c a l c u l a t i o n s have been m a d e ^ . The i m p o r t a n t f e a t u r e t h a t i d e n t i f i e s r o t a t i o n i n a m a t r i x i s t he r e v e r s i b l e t e m p e r a t u r e dependence o f the i n t e n s i t i e s o f a mul-t i p l e t a b s o r p t i o n . O t h e r causes o f s p l i t t i n g s o f a b s o r p t i o n s d i s c u s s e d below, do not show t h i s t e m p e r a t u r e s e n s i t i v i t y . (c) A q q r e g a t i o n : When m o l e c u l e s a g g r e g a t e , i n t e r a c t i o n s between them cause s h i f t s o f v i b r a t i o n a l energy l e v e l s . As a r e s u l t , a g g r e g a t e s cause b r o a d e n i n g and s h i f t i n g o f a b s o r p t i o n s i n t h e i . r . The e x t e n t o f b r o a d e n i n g and s h i f t i n g o f l e v e l s depends on the s t r e n g t h o f t h e i n t e r a c t i o n . When the m o l e c u l e s a r e p o l a r , s t r o n g d i p o l e i n t e r a c t i o n s - 10 -and thus l a r g e s h i f t s o c c u r w h i l e f o r n o n - p o l a r m o l e c u l e s c o u p l i n g i s o n l y t h r o u g h weak i n d u c t i v e and d i s p e r s i v e f o r c e s so t h a t o n l y b r o a d e n i n g o f a b s o r p t i o n s i s o b s e r v e d . V i b r a t i o n a l modes i n v o l v i n g hydrogen show l a r g e s h i f t s on hydrogen bonding - s i m i l a r t o s h i f t s o b s e r v e d i n s o l u t i o n s p e c t r a (see r e f e r e n c e 7). For example, the complex s p e c t r u m o f H^O i n a N^ m a t r i x has been i n t e r p r e t e d on the (8) b a s i s o f a g g r e g a t i o n w h i l e i n t h i s work, hydrogen b o n d i n g was o b s e r v e d i n t h e s p e c t r u m o f cis-HNSO i n an argon m a t r i x ( c h a p t e r 3). Because a g g r e g a t i o n depends on the c o n c e n t r a t i o n o f sample, a d e m o n s t r a t i o n o f c o n c e n t r a t i o n dependence i s n e c e s s a r y t o show t h a t a peak s p l i t t i n g i s due t o a g g r e g a t i o n . In t h i s way i . r . s p e c -t r o s c o p y a c t s as a good measure o f i s o l a t i o n i n the m a t r i x . U n l e s s i n t e r a c t i o n s a r e t o be s p e c i f i c a l l y s t u d i e d , i . r . a l l o w s a c h o i c e o f M/R such t h a t a g g r e g a t i o n e f f e c t s a r e not a p r o b l e m . For n o n - p o l a r m o l e c u l e s v a l u e s o f M/R o f s e v e r a l hundred a r e s t a t i s t i c a l l y a dequate f o r i s o l a t i o n o f more than 30% o f the m o l e c u l e s . For p o l a r m o l e c u l e s v a l u e s o f 1000 o r more a r e o f t e n n e c e s s a r y . B e s i d e s n e a r e s t n e i g h b o u r i n t e r a c t i o n s i n a g g r e g a t e s , mol-e c u l e s can have weak, l o n g range i n t e r a c t i o n s when s e p a r a t e d by s e v -e r a l c a g e s . The e f f e c t s o f t h e s e i n t e r a c t i o n s a r e s m a l l and show up o n l y as s l i g h t b r o a d e n i n g s o f the a b s o r p t i o n p e a k s . T h i s e f f e c t can be seen i n f i g u r e 1-2 w h i c h shows a c o m p a r i s o n o f t h e s h a r p n e s s o f the a b s o r p t i o n o f ozone produced by d i s c h a r g e o f 0^ i n A r a t M/R = 50 and 200. In t h e M/R = 50 sample the d o u b l e t c o u l d not be - i i -F i g u r e 1-2. The a s y m m e t r i c s t r e t c h , v^ , o f ozone (p roduced by d i s c h a r g e o f O^/Ar m i x t u r e s ) showing the n a r r o w i n g o f peaks on d i l u t i o n . - 12 -w e l l r e s o l v e d because o f b r o a d e n i n g . To r e s o l v e a b s o r p t i o n s s e p a r -a t e d by l e s s than 2 cm ' o f t e n r e q u i r e s e x t r e m e l y h i g h d i l u t i o n . ( d ) M u l t i p l e S i t e S p l i t t i n g : S p l i t t i n g s t h a t do not show t e m p e r a t u r e o r c o n c e n t r a t i o n dependence ( i . e . a r e not due t o r o t a t i o n o r a g g r e g a -t i o n ) a r e a l s o o b s e r v e d . I t i s b e l i e v e d t h a t t h e s e s p l i t t i n g s r e s u l t f rom i s o l a t i o n o f the m o l e c u l e i n d i f f e r e n t s i t e s w i t h i n the m a t r i x ^ ' ^ T h i s r e s u l t s i n d i f f e r e n t e n v i r o n m e n t s and so s l i g h t l y d i f f e r e n t v i b r a -t i o n a l f r e q u e n c i e s . The s i t e s a r e d e s c r i b e d as s u b s t i t u t i o n a l o r i n t e r s t i t i a l . However, no means f o r a c t u a l l y d e t e r m i n i n g the d i f f e r -e n t s i t e s has been found and thus t h e h y p o t h e s i s has not been s u b s t a n t -i a t e d . J u s t as m a t r i x s h i f t s a r e d i f f e r e n t f o r t h e d i f f e r e n t v i b -r a t i o n a l modes o f a m o l e c u l e , so a r e the m a t r i x s i t e s p l i t t i n g s . I t i s found t h a t f o r a s e r i e s o f s i m i l a r m o l e c u l e s a p a r t i c u l a r a b s o r p -t i o n peak w i l l c o n s i s t e n t l y show t h e same s t r u c t u r e . In f i g u r e 1-3 a r e shown t h e a s y m m e t r i c s t r e t c h i n g a b s o r p t i o n o f s e v e r a l bent t r i -a t o m i c m o l e c u l e s . In a l l c a s e s the s i m i l a r d o u b l e t c h a r a c t e r a s s i g n e d t o m a t r i x s i t e s p l i t t i n g i s p r e s e n t . These s p l i t t i n g s f o r bent t r i -a t o m i c s a r e among the l a r g e s t o b s e r v e d - s t i l l a l l a r e l e s s than 8 cm '. In most c a s e s s p l i t t i n g s a t t r i b u t e d t o m u l t i p l e s i t e s a r e o n l y 1 o r -1 2 cm S i n c e t h e s e s p l i t t i n g s a r e g e n e r a l l y s m a l l , the u n c e r t a i n t y i n f o r c e c o n s t a n t s d e t e r m i n e d from s p l i t a b s o r p t i o n s i s no g r e a t e r than t h a t a l r e a d y a s s o c i a t e d w i t h the m a t r i x s h i f t s . In p r a c t i c e , - 1 3 -1/ ( c m - 1 ) 1050 lOOO 1650 1600 8 5 0 8 0 0 1400 1300 1200 1150 ft / N f o 3 N 0 2 1 O F 2 s o 2 05IM F i g u r e 1 - 3 - The a s ymmet r i c s t r e t c h e s o f s e v e r a l bent t r i a t o m i c m o l e c u l e s showing c h a r a c t e r i s t i c a rgon m a t r i x s p l i t t i n g . - 14 -the most i n t e n s e peak o f the m u l t i p l e t i s r e p o r t e d as the v i b r a t i o n a l f r e q u e n c y and used i n c a l c u l a t i o n s . T h i s peak i s u s u a l l y the s h a r p e r o f the two and i f doubt e x i s t s as t o whether the s p l i t t i n g r e s u l t s f r o m m u l t i p l e s i t e s o r a g g r e g a t i o n s , t h i s method g u a r a n t e e s t h a t the a b s o r p -t i o n o f the i s o l a t e d , r a t h e r than a g g r e g a t e d , m o l e c u l e i s u s e d . 4. UNSTABLE SPECIES As i s p o i n t e d out by Barnes and Hal l a m ^ m a t r i x i s o l a t i o n was o r i g i n a l l y d e v e l o p e d f o r the s t u d y o f f r e e r a d i c a l s . S i n c e t h e n , i t s use has been e x t e n d e d t o many o t h e r m o l e c u l e s w h i c h a r e d i f f i c u l t t o s t u d y under normal c o n d i t i o n s e i t h e r because o f t h e i r r e a c t i v i t y o r t h e i r t endency t o decompose. Examples o f m a t r i x s t u d i e s on f r e e r a d i c a l s as w e l l as o t h e r u n s t a b l e s p e c i e s such as n o b l e gas compounds and h i g h t e m p e r a t u r e s p e c i e s (such as metal o x i d e s and h a l i d e s ) a r e g i v e n i n r e f e r e n c e 6. T h e r e f o r e , t h i s s e c t i o n c o n t a i n s o n l y a b r i e f d i s c u s s i o n o f the r e a s o n s why t h e m a t r i x i s o l a t i o n t e c h n i q u e i s o f such v a l u e i n s t u d y i n g u n s t a b l e compounds and a d e s c r i p t i o n o f com-mon methods f o r t h e i r p r o d u c t i o n . ( a ) S t a b l i z a t i o n : R a d i c a l s a r e m o l e c u l e s t h a t p o s s e s s u n p a i r e d e l e c -t r o n s . A l t h o u g h some r a d i c a l s such as NO a r e q u i t e s t a b l e , most a r e h i g h l y r e a c t i v e because o f the tendency t o p a i r e l e c t r o n s . When p r o -duced i n the gas phase, f r e e r a d i c a l s a r e u s u a l l y v e r y s h o r t l i v e d , q u i c k l y r e c o m b i n i n g w i t h each o t h e r o r o t h e r f r a g m e n t s o r m o l e c u l e s i n the gas u n t i l , a f t e r a v e r y s h o r t p e r i o d , none o f the f r e e r a d i c a l - 15 -d e s i r e d f o r s t u d y r e m a i n s . T h i s i s an i m p o s s i b l e s i t u a t i o n f o r i . r . s p e c t r o s c o p y where s e n s i t i v i t y i s low, d e t e c t o r s respond s l o w l y and scan t i m e s a r e l o n g . U n f o r t u n a t e l y , u l t r a v i o l e t s p e c t r o s c o p y , w h i c h i s g e n e r a l l y used t o s t u d y r a d i c a l s i n the gas phase, does not always p r o v i d e a l l the v i b r a t i o n a l i n f o r m a t i o n about the r a d i c a l . However, i f t h e r e a c t i v e r a d i c a l can be i s o l a t e d i n an i n e r t m a t r i x , i t w i l l not be a b l e t o r e a c t and as a r e s u l t i t w i l l be s t a b l i z e d f o r as l o n g as the low t e m p e r a t u r e i s m a i n t a i n e d . Thus s t u d y by i . r . i s p o s s i b l e . A n o t h e r type o f u n s t a b l e s p e c i e s i s one t h a t tends t o d i s -s o c i a t e a t normal t e m p e r a t u e s . T h i s o c c u r s i n a m o l e c u l e w i t h a s h a l l -ow p o t e n t i a l w e l l w h i c h a l l o w s v e r y low v i b r a t i o n a l e n e r g i e s t o l e a d t o bond f r a c t u r e . S u f f i c i e n t t h e r m a l energy i s r e a d i l y a v a i l a b l e a t room t e m p e r a t u r e o r lower t o cause d i s s o c i a t i o n o f t h e s e m o l e c u l e s . In a m a t r i x a t k°K o r 20°K t h i s i s not so. At such low t e m p e r a t u r e s o n l y the ground v i b r a t i o n a l s t a t e w i l l be p o p u l a t e d and t h i s w i l l o f t e n be a s t a b l e l e v e l . A n o t h e r f a c t o r h i n d e r i n g d i s s o c i a t i o n i s the s t e r i c p r e s e n c e o f t h e m a t r i x atoms and t h e i r a s s o c i a t e d p o t e n t i a l . That i s , as a bond becomes v e r y l o n g , the i n t e r a c t i o n w i t h the m a t r i x w i l l s t a r t t o p r e v e n t i t s f u r t h e r i n c r e a s e and thus p r e v e n t d i s s o c i a t i o n . The m a t r i x has i n e f f e c t deepened the p o t e n t i a l w e l l and thus s t a b l -i z e d t h e u n s t a b l e s p e c i e s . I t i s g e n e r a l l y a c c e p t e d t h a t f o r d i s -s o c i a t i o n t o o c c u r i n a m a t r i x s u f f i c i e n t e n e r g y must be s u p p l i e d above the normal d i s s o c i a t i o n e nergy t o cause a fragment o f the d i s -s o c i a t i o n t o escape t h e cage o f m a t r i x atoms s u r r o u n d i n g the m o l e c u l e . - 16 -L a r g e f r a g m e n t s have not been o b s e r v e d t o escape and o n l y hydrogen and f l u o r i n e atoms, p r o b a b l y because o f t h e i r s m a l l s i z e , a r e ex-p e c t e d t o d i f f u s e away from t h e p a r e n t . B e s i d e s t h e s e two, CO has been r e p o r t e d t o escape the cage on p h o t o l y s i s o f metal c a r b o n y l s (q) i s o l a t e d i n a m a t r i x M o l e c u l e s t h a t r e a r r a n g e t o more s t a b l e isomers a r e a t h i r d t y p e o f u n s t a b l e s p e c i e s s t u d i e d i n m a t r i c e s . P r i m a r i l y t h e s e r e a c t i o n s a r e c i s - t r a n s i s o m e r i z a t i o n s o r hydrogen t r a n s f e r from one p a r t o f a m o l e c u l e t o a n o t h e r . The p r e s e n c e o f a n o n - s p h e r i c a l cage can r e a d i l y r e s t r i c t both such r e a c t i o n s and as b e f o r e , t h e low temp-e r a t u r e s used do not p r o v i d e f o r enough energy t o overcome even s m a l l a c t i v a t i o n e n e r g i e s . S e v e r a l examples o f t h i s t y p e o f s t a b l i z a t i o n a r e g i v e n i n t h e f o l l o w i n g s e c t i o n a l o n g w i t h examples o f r a d i c a l s t a b l i z a t i o n and d i s s o c i a t i o n s t a b l i z a t i o n . ( b )Methods o f P r o d u c t i o n : The methods f o r the p r o d u c t i o n and e n t r a p -ment o f - u n s t a b l e s p e c i e s f a l l i n t o two c a t e g o r i e s . In the f i r s t the u n s t a b l e s p e c i e s i s g e n e r a t e d i n t h e gas phase and then t r a p p e d by r a p i d f r e e z i n g b e f o r e i t can r e a c t o r decompose. In the second c a t -e g o r y the d e s i r e d m o l e c u l e o r r a d i c a l i s g e n e r a t e d i n the m a t r i x from a s t a b l e m o l e c u l e w h i c h has p r e v i o u s l y been i s o l a t e d . The t e c h n i q u e s a r e t h o s e c o n v e n t i o n a l l y used t o produce f r e e r a d i c a l s and u n s t a b l e m o l e c u l e s - glow d i s c h a r g e , p y r o l y s i s , d i r e c t c h e m i c a l r e a c t i o n and p h o t o l y s i s . The f i r s t t h r e e f a l l i n t o t h e gas phase c a t e g o r y o f p r o d u c t i o n w h i l e the l a s t one i s used most o f t e n w i t h a l r e a d y i s o l a t e d - 17 -m o l e c u l e s . ( i ) D i s c h a r g e and P y r o l y s i s - In the u s u a l m a t r i x e x p e r i -ment th e gas m i x t u r e p a s s e s t h r o u g h an o r i f i c e and i s f r o z e n on a c o l d C s l window. I f j u s t b e f o r e the o r i f i c e i s mounted a microwave c a v i t y o f the t y p e shown i n s e c t i o n B-5 o f t h i s c h a p t e r , t h e gas m i x t u r e can be d i s c h a r g e d . I f i n s t e a d a h e a t i n g c o i l i s mounted on the tube the r e s u l t i s a c e l l f o r t h e p y r o l y s i s o f t h e gas m i x t u r e . In b oth c a s e s the a p p a r a t u s c o n s t i t u t e s a f l o w s y s t e m and i f r e l a -t i v e l y h i g h d i l u t i o n i n the m a t r i x gas i s used some o f t h e u n s t a b l e s p e c i e s produced s u r v i v e l o n g enough t o t r a v e l t o t h e window, t h e r e t o be i s o l a t e d i n t h e m a t r i x f o r s t u d y . These methods, however, a r e not v e r y s e l e c t i v e . In a d i s -c h a r g e , because o f t h e h i g h e n e r g i e s , m o l e c u l e s a r e n e a r l y c o m p l e t e l y decomposed t o atoms so t h a t the u n s t a b l e m o l e c u l e s a r e o f t e n i n t e r -m e d i a t e s i n t h e r e c o m b i n a t i o n o f the atoms. As a r e s u l t , many p o s s -i b l e s p e c i e s can be p r o d u c e d . P y r o l y s i s i n v o l v e s lower e n e r g i e s and i s thus somewhat more s e l e c t i v e i n w h i c h bonds i t i s a b l e t o b r e a k . T h i s r e s u l t s i n the p r o d u c t i o n o f fewer s p e c i e s . But b o t h methods can y i e l d complex i . r . s p e c t r a from t h e numerous s t a b l e and u n s t a b l e s p e c i e s t h a t can be formed and t r a p p e d . The p r o b l e m o f i d e n t i f y i n g t h e p r o d u c t s and o f making v i b r a t i o n a l a s s i g n m e n t s can be q u i t e i n -v o l v e d . An example o f the s u c c e s s f u l use o f a d i s c h a r g e i s the work by N e l s o n and P i m e n t a l ^ ^ i n w h i c h XeCl„ was produced by - 18 -d i s c h a r g i n g i n an e x c e s s o f Xe. Because o f the low r e a c t i v i t y o f xenon, o n l y one i . r . a b s o r p t i o n , the a s y m m e t r i c s t r e t c h o f X e C ^ , was o b s e r v e d , w h i l e i n the work f o r t h i s t h e s i s the d i s c h a r g e o f 0^ and F^ m i x t u r e s r e s u l t e d i n v e r y complex s p e c t r a (see c h a p t e r I I ) . An example o f the use o f p y r o l y s i s i s S n e l s o n ' s ^ ' ^ i s o l a t i o n o f the methyl r a d i c a l i n an argo.n m a t r i x . ( i i ) D i r e c t R e a c t i o n - In d i r e c t r e a c t i o n , two s p r a y on l i n e s a r e employed, one f o r each r e a c t i v e s p e c i e s . The gases a r e then s i m u l t a n e o u s l y f r o z e n w i t h e x c e s s m a t r i x m a t e r i a l . The r e a c t i o n can o c c u r i n the gas phase as the gases mix b e f o r e becoming f r o z e n o r a f t e r f r e e z i n g i f two r e a c t i n g m o l e c u l e s a r e t r a p p e d n e x t t o each o t h e r i n t h e m a t r i x . The r e s u l t i n g p r o d u c t s o r t r a p p e d i n t e r m e d i a t e s , w h i c h may be s t a b l e o r u n s t a b l e , can then be s t u d i e d u s i n g i . r . An (12 13) example o f t h i s t e c h n i q u e i s the work by Andrews and P i m e n t e l ' i n w h i c h methyl h a l i d e s were c o d e p o s i t e d w i t h l i t h i u m atoms i n an a t t e m p t t o produce and i s o l a t e the methyl r a d i c a l . However, as was p o i n t e d out 1 a t e r ^ ' 1 ' ' ^ p r o b a b l y what was o b s e r v e d was a c t u a l l y a new m o l e c u l a r s p e c i e s , a methyl a l k a l i h a l i d e . ( i i i ) P h o t o l y s i s - P h o t o l y s i s has been the most common method f o r p r o d u c t i o n o f u n s t a b l e s p e c i e s i n m a t r i c e s . The method has g r e a t s e l e c t i v i t y s i n c e o n l y d i s s o c i a t i o n s i n w h i c h a H o r F atom i s s e p a r a t e d from the p a r e n t and r e a r r a n g e m e n t s can o c c u r e a s i l y . T h i s s e l e c t i v i t y i s f u r t h e r i n c r e a s e d by the use o f d i f f e r e n t p h o t o l -y s i s e n e r g i e s by e i t h e r e m p l o y i n g f i l t e r s w i t h s t a n d a r d u.v. lamps 19 -o r by g o i n g t o t h e h i g h e r energy o u t p u t o f vacuum u.v. r e s o n a n c e lamps. The re a r r a n g e m e n t s can be s i m p l e c i s - t r a n s i s o m e r i z a t i o n i n v o l v i n g i n t e r n a l r o t a t i o n as i n n i t r o u s a c i d so c a r e f u l l y s t u d i e d (15) by H a l l and P i m e n t e l o r more c o m p l i c a t e d t y p e s such as the pho-t o l y s i s o f i s o c y a n i c a c i d (HNCO) by J a c o x and M i l l i g a n ^ ' ^ t o g i v e HOCN. The r e a c t i o n s i n v o l v i n g t he s e p a r a t i o n o f atoms a r e o f two t y p e s . In t h e f i r s t t he d e s i r e d p r o d u c t i s t h e r a d i c a l l e f t b e h i n d when a H o r F atom i s removed by p h o t o l y s i s . In t h e second t y p e the d e s i r e d p r o d u c t i s produced by t h e r e a c t i o n o f a d i f f u s i n g H o r F atom w i t h a n o t h e r m o l e c u l e i s o l a t e d i n t h e m a t r i x . In t h i s c a s e the p h o t o l y s i s i s o n l y f o r the p r o d u c t i o n o f the atom and does not d i r e c t -l y p r o d u c e t h e u n s t a b l e p r o d u c t s t u d i e d . R e f e r e n c e 6 l i s t s numerous examples o f b o t h t y p e s . S i F ^ ^ produced from the p h o t o l y s i s o f (18) S i H ^ F ^ and O^F produced from the p h o t o l y s i s o f F^ i n a m a t r i x c o n t a i n i n g 0^ a r e f u r t h e r examples o f t h e f i r s t and second t y p e s o f p h o t o l y s i s r e s p e c t i v e l y . In s e c t i o n B-k o f t h i s c h a p t e r t h e equipment and t e c h n i q u e s f o r p h o t o l y s i s o f m a t r i c e s i s d e s c r i b e d i n d e t a i l . C h a p t e r 5 c o n t a i n s a d e t a i l e d a p p l i c a t i o n o f the t e c h n i q u e . (c) Charged S p e c i e s : In the l a s t two y e a r s s e v e r a l r e p o r t s o f the (19-21) o b s e r v a t i o n o f io n s i n m a t r i c e s have been made . The p r o d u c -t i o n o f t h e s e i o n s has been by vacuum u.v. p h o t o l y s i s , by e l e c t r o n bombardment and by microwave d i s c h a r g e . The b e l i e f t h a t the peaks - 20 -o b s e r v e d were due t o i o n s was s u p p o r t e d by the f a c t t h a t t h e i r i n t e n -s i t i e s i n c r e a s e d on t h e a d d i t i o n t o the m a t r i x o f a p h o t o e l e c t r o n s o u r c e such as sodium atoms. The ions so f a r i d e n t i f i e d i n a m a t r i x a r e C~ ^ 1 8 ^ , N0~ ^ 1 9 ^ and CC1*, HCC1* and H C C l " ^ 2 0 ^ . As w e l l , i t was found t h a t N0^ i o n s produced w i t h vacuum u.v. p h o t o l y s i s c o u l d (19) be i o n i z e d t o by p h o t o l y s i s w i t h near u.v. l i g h t How the i s o l a t e d i o n i s s t a b l i z e d i n t h e m a t r i x i s not (19) w e l l u n d e r s t o o d , but s t u d i e s w i t h NO^ and v a r i o u s a l k a l i m e t a l s showed NO^ peaks w h i c h depended on t h e a l k a l i metal used as w e l l as a s i n g l e peak t h a t d i d n o t . The f o r m e r were a s s i g n e d t o i o n p a i r s o f the form UO^ N a + and the l a t t e r t o t h e i s o l a t e d NO^ i o n . At p r e s e n t o n l y t h e s e few i o n s have been s t u d i e d i n a m a t r i x . I t i s v e r y l i k e l y t h a t f u r t h e r s t u d y w i l l r e s u l t i n a b e t t e r u n d e r s t a n d i n g o f how the m a t r i x s t a b l i z e s the i o n as w e l l as v a l u a b l e i n f o r m a t i o n about i o n i c i n t e r a c t i o n s p a r t i c u l a r l y i n c a s e s where t h e a n i o n and c a t i o n a r e s e p a r a t e d by v a r i o u s d i s t a n c e s w i t h i n t h e m a t r i x . - 21 -B. EXPERIMENTAL APPARATUS 1. GAS HANDLING SYSTEMS (a) G l a s s : For most o f t h e work i n t h i s t h e s i s gas samples were p r e p a r e d i n a g l a s s vacuum sy s t e m e q u i p p e d w i t h an o i l (Dow-Corning 704 o i l ) d i f f u s i o n pump. A d i a g r a m i s shown i n f i g u r e 1-4. P r e s s -u r e s f r o m 1 cm t o 76 cm o f Hg were read u s i n g a C r o s b y - A s h t o n low vacuum gauge (#AS0-10894). P r e s s u r e s from 1 t o r r t o 40 t o r r were read on an o i l (D.C. 704 o i l ) manometer. P r e s s u r e s from 1 u t o 1 t o r r were measured on a Veeco t h e r m o c o u p l e gauge (DV-l-M) and -6 -3 p r e s s u r e s from 10 t o r r t o 10 t o r r w i t h a Veeco d i s c h a r g e gauge (DG2-11) both u s i n g a Veeco gauge c o n t r o l (DG2-2T). M a t r i x gases were i n t r o d u c e d from a m a n i f o l d o f gas c y l i n d e r s v i a a c o p p e r l i n e . R e a c t i o n s and gas m i x i n g s were done i n both f i x e d and p o r t a b l e g l a s s b u l b s o f 2 and 5 l i t r e s . The system was c o n n e c t e d t o t h e c r y o s t a t t h r o u g h a g l a s s l i n e f i t t e d w i t h b a l l j o i n t s t o a l l o w movement. Gas f l o w was c o n -t r o l l e d by a Whitey m i c r o m e t e r v a l v e (22RS4) and the f l o w r a t e was m o n i t o r e d by measuring the p r e s s u r e w i t h the t h e r m o c o u p l e gauge f o l l o w i n g the v a l v e . T y p i c a l f l o w r a t e s were 2 m i l l i m o l e s t o t a l sample per hour w i t h t y p i c a l p r e s s u r e s o f 150 m i c r o n s . The p r e s s u r e f o r the d e s i r e d f l o w was dependent on the r e s i s t a n c e t o gas f l o w and t h e r e f o r e had t o be d e t e r m i n e d f o r each sample d e p o s i t i o n l i n e . (b) Meta 1: For work i n v o l v i n g f l u o r i n e a metal vacuum sy s t e m was used. The main f e a t u r e s were b r a s s s t o r a g e b u l b s , s t a i n l e s s s t e e l - 22 -F i g u r e 1-4. G l a s s Vacuum Sy s tem. 1. to c r y o s t a t 2. d i s c h a r g e gauge 3. t he rmocoup le gauge 4. m i c r o m e t e r v a l v e 5. s t o r a g e b u l b s 6. l i n e to gas c y l i n d e r m a n i f o l d 7. p o r t a b l e b u l b 8. C ro sby gauge 9. o i l manometer 10. o i l d i f f u s i o n pump 1 I . r o t a r y pump F i g u r e 1 - 4 . G l a s s vacuum s y s t e m . - 2k -q u a r t e r i n c h t u b i n g , s i l v e r s o l d e r e d c o n n e c t i o n s , Whitey s t a i n l e s s s t e e l v a l v e s (IRS4-316), and a sodium c h l o r i d e t r a p t o remove from t h e pump o u t . P r e s s u r e s were measured w i t h a Veeco t h e r m o c o u p l e gauge and C r o s b y - A s h t o n gauge as i n d i c a t e d above. F o r low vacuum the system was e q u i p p e d w i t h i t s own pump. For h i g h vacuum i t was con-n e c t e d t o t h e g l a s s s y s t e m f o r pumping t h r o u g h the d i f f u s i o n pump. The sample p a s s e d t h r o u g h a Whi t e y m i c r o m e t e r v a l v e (22RS4) and f l e x i b l e s t a i n l e s s s t e e l b e l l o w s t u b i n g w h i c h c o n n e c t e d t o the c r y o s t a t . Flow r a t e s were m o n i t o r e d by changes i n p r e s s u r e on t h e Crosby gauge. 2. SAMPLE DEPOSITION LINES Spray on l i n e s were c o n n e c t e d t o t h e c r y o s t a t t h r o u g h a Kovar s e a l w h i c h was b l a c k waxed i n t o a s l e e v e a t t a c h e d t o a p l a t e mounted on the c r y o s t a t u s i n g an 0 - r i n g f o r a vacuum s e a l . D i s c h a r g e s t were s u s t a i n e d i n t h e s e tubes by p l a c i n g a microwave c a v i t y immediate-l y b e f o r e t h e c r y o s t a t . When d i s c h a r g e s were used t h e l i n e s were made o f q u a r t z t o p r e v e n t m e l t i n g o f t h e l i n e . The l i n e s were about 8 mm in d i a m e t e r c o n s t r i c t e d t o 2 mm a t the end t o p r o v i d e b e t t e r d i r e c t -i o n o f the beam towards t h e c o l d window. A s p r a y on l i n e , microwave c a v i t y p o s i t i o n and mounting assembly a r e i l l u s t r a t e d i n f i g u r e 1-5. When f l u o r i n e was u s e d , the s p r a y on l i n e was 1/4" l u c a l o x tube ( G e n e r a l E l e c t r i c ) mounted as above. L u c a l o x i s a p o l y c r y s t a l -l i n e a l u m i n a c e r a m i c w h i c h i s c h e m i c a l l y r e s i s t a n t t o f l u o r i n e , m e l t s - 2 5 -F i g u r e 1 - 5 . Spray on a s s e m b l y , c r y o s t a t t a i l s e c t i o n and p h o t o l y s i s a p p a r a t u s . 1. s p r a y on l i n e and d i s c h a r g e 2. c r y o s t a t t a i l s e c t i o n 3 . p h o t o l y s i s a l i g n m e n t 4. sample in 5. q u a r t z d i s c h a r g e tube 6. microwave c a v i t y 7. kovar s e a l 8. i n n e r g l a s s sp ray on l i n e 9. mount ing s l e e v e 1 0 . C s l windows 11. q u a r t z window 12. f i l t e r 1 3 - w a t e r in q u a r t z c e l l 14. q u a r t z f o c u s i n g l en s 15- p h o t o l y s i s lamp F i g u r e 1-5. S p r a y - o n a s s e m b l y , c r y o s t a t t a i l s e c t i o n and p h o t o l y s i s a p p a r a t u s . - 27 -a t v e r y h i g h t e m p e r a t u r e s (2040°C) and t r a n s m i t s microwave energy thus a l l o w i n g d i s c h a r g e . 3. THE HELIUM CRYOSTAT The c r y o s t a t used was an A ndonian MHD-3L-15N modular l i q u i d h e l i u m dewar e q u i p p e d w i t h i . r . - m a t r i x i s o l a t i o n o p t i o n s . The dewar i s i l l u s t r a t e d i n f i g u r e 1-6. The vacuum shroud was pumped t h r o u g h the top t o 10 ^ t o r r o r l e s s . The sample l i n e s were mounted as above. On t h e o t h e r t h r e e s i d e s o f the t a i l were mounted, u s i n g 0 - r i n g s , two C s l windows f o r s p e c t r a t a k i n g and a q u a r t z w i n -dow f o r u.v. p h o t o l y s i s . The i n n e r C s l window was mounted on the c o pper t a i l s e c t i o n u s i n g i n d i u m g a s k e t s f o r maximum therma l conduc-t i v i t y . A g o l d - c o b a l t vs c o n s t a n t a n t h e r m o c o u p l e w i t h r e f e r e n c e a t l i q u i d n i t r o g e n t e m p e r a t u r e was mounted i n the C s l window t o m o n i t o r the t e m p e r a t u r e . The dewar was mounted so t h a t t h e o u t s i d e o f the t a i l s e c t i o n remained f i x e d w h i l e the upper p o r t i o n a t t a c h e d t o t h e window c o u l d be r o t a t e d 360° on 0 - r i n g s e a l s . T h i s a l l o w e d p o s i t i o n i n g o f the window f o r s p r a y on, s p e c t r a t a k i n g and p h o t o l y s i s . The whole assembly was mounted on r a i l s t o a l l o w movement i n and o u t o f the sample compart-ment o f t h e s p e c t r o m e t e r . 4. PHOTOLYSIS LAMPS (a) E x t e r n a 1: Near u l t r a v i o l e t p h o t o l y s i s was done u s i n g PEK 100 - 28 -F i g u r e 1-6. L i q u i d h e l i u m c r y o s t a t w i t h i . r . s p e c t r o s c o p y -m a t r i x i s o l a t i o n t a i l a s s e m b l y . 1. c o o l a n t r e s e r v o i r s and vacuum sh roud 2. t a i l s e c t i o n 3. e v a c u a t i o n p o r t 4. l i q u i d he l iurn 5- 1 iqu id n i t r o g e n 6. o - r i n g s e a l s f o r r o t a t i o n o f t a i l 7. c o l d s h i e l d (77°K) 8. C s l windows - 29 -F i g u r e 1-6. L i q u i d h e l i u m c r y o s t a t w i t h i . r . s p e c t r o s c o p y -m a t r i x i s o l a t i o n t a i l a s s e m b l y . - 30 -w a t t medium p r e s s u r e mercury (112-2118) and PEK 75 w a t t xenon (X75-1280) a r c s w i t h a PEK model AO 1 power s u p p l y . P h o t o l y s i s was t h r o u g h the q u a r t z window o f the c r y o s t a t u s i n g a q u a r t z l e n s f o r f o c u s i n g . A q u a r t z c e l l c o n t a i n i n g w a t e r was p l a c e d between t h e lamp and t h e dewar t o m i n i m i z e heat i n p u t t o the C s l window. F i l t e r s f o r the s e l -e c t i o n o f p h o t o l y s i s e nergy c o u l d be p l a c e d i n the l i g h t beam. The o f i l t e r s used were a C o r n i n g #3 _ 73 w i t h o p t i c a l c u t o f f a t 4000 A and o a C o r n i n g #0-54 w i t h c u t o f f a t 3000 A. The a l i g n m e n t o f the o p t i c s i s shown i n f i g u r e 1-5-o The o u t p u t o f the mercury lamp was s t r o n g e s t a t 2537 A, o o o 2652 A, 3130 A and 365O A w i t h good i n t e n s i t y i n the w h ole u l t r a v i o l e t o r e g i o n above 2000 A. The xenon lamp showed a more c o n t i n u o u s o u t p u t o w i t h v e r y l i t t l e i n t e n s i t y below 3000 A. (b) I n t e r n a l : For vacuum u l t r a v i o l e t p h o t o l y s i s a lamp b u i l t by J.K.B. (22) B i s h o p based on a d e s i g n by D a v i s and Braun was used. The s y s t e m c o n s i s t e d o f l a r g e r e s e r v o i r b u l b s f o r t h e gases u s e d , a W h i t e y m i c r o -meter v a l v e (22RS4) t o c o n t r o l gas f l o w , a Veeco t h e r m o c o u p l e gauge (DV-l-M) t o m o n i t o r f l o w r a t e and p r e s s u r e , a f l o w t h r o u g h s y s t e m w i t h q u a r t z s e c t i o n f o r microwave d i s c h a r g e , a L i F window e p o x i e d t o t h e end o f t h i s tube t o a l l o w t r a n s m i t t a n c e o f vacuum u.v. l i g h t and a pump out l i n e t o m a i n t a i n a c o n s t a n t f l o w . The lamp was mounted on the t a i l s e c t i o n o f t h e dewar u s i n g a Veeco t y p e C Q u i c k Vacuum Coup-l i n g (#3100-311) and was a n g l e d and o f f s e t t o a l l o w p o s i t i o n i n g o f a d e p o s i t i o n l i n e f o r s i m u l t a n e o u s s p r a y on and p h o t o l y s i s . The lamp - 31 -u n i t and mounting assembly a r e shown i n f i g u r e 1-7-The gas used was a 10% m i x t u r e o f i n He w h i c h p r o v i d e d 0 (22) good i n t e n s i t y o f the 1216 A a t o m i c hydrogen (Lyman - a) l i n e when d i s c h a r g e d . Under t h e s e c o n d i t i o n s the u n i t i s a hydrogen resonance lamp. Output a t o t h e r w a v e l e n g t h s was low when d i s c h a r g e (22) p r e s s u r e s were kep t a t t h e i r u s u a l 0.5 _ 1.0 t o r r When u s i n g the vacuum u.v. lamp i t has been found t h a t s i m u l t a n e o u s s p r a y on and p h o t o l y s i s i s n e c e s s a r y t o maximize y i e l d o f p h o t o l y s i s p r o d u c t s ( e . g . r e f e r e n c e 2 3 ) . T h i s need r e s u l t s be-o cause the 1216 A r a d i a t i o n does not p e n e t r a t e v e r y d e e p l y i n t o t h e m a t r i x . By s i m u l t a n e o u s p h o t o l y s i s each l a y e r o f sample i s i r r a d i -a t e d as i t i s d e p o s i t e d . 5. MICROWAVE DISCHARGE EQUIPMENT A S c i n t i 1 I o n i c s I n c o r p o r a t e d HV15A microwave (2450 MHz) g e n e r a t o r u s u a l l y o p e r a t e d a t 70 w a t t s power was used w i t h an Evenson-(24) B r o i d a c a v i t y , t y p e 5 , t h r o u g h w h i c h the d i s c h a r g e tube was p a s s e d . F i g u r e 1-8 shows the c a v i t y used. The c a v i t y and d i s c h a r g e tube were c o o l e d by f o r c e d a i r d u r i n g o p e r a t i o n . A d j u s t m e n t o f t h e t u n i n g s t u b was r e q u i r e d t o m i n i m i z e t h e r e v e r s e power i n the g e n e r a t o r . 6. INFRARED SPECTROPHOTOMETER A l l s p e c t r a were r e c o r d e d on a P e r k i n - E l m e r 225 S p e c t r o -photometer w i t h C s l o p t i c s w h i c h a l l o w e d use from 200 cm 1 t o 5000 cm - 3 2 -F i g u r e 1 - 7 - Vacuum u l t r a v i o l e t p h o t o l y s i s lamp and mount ing a s s e m b l y . 1 . mount i ng un i t 2 . lamp 3 - 3 / 4 " c o u p l i n g f o r lamp 4 . 1 / 4 " c o u p l i n g f o r s p ray on l i n e 5. L i F wi ndow 6 . pump ou t 1 i n e 7 . microwave c a v i t y 8. q u a r t z d i s c h a r g e tube 9. gas f l o w - i n - 3k -F i g u r e 1-8. E v e n s o n - B r o i d a microwave c a v i t y , t ype 5. 1. t u n i n g s t u b 2. c o n n e c t o r to microwave power c a b l e 3. removab le cap k. o p e n i n g f o r d i s c h a r g e tube 5. a i r i n l e t f o r c o o l i n g 6. f i n e t u n i n g s t u b ( t e f l o n ) - 35 -1-8. E v e n s o n - B r o i d a microwave c a v i t y , t y p e 5-- 36 -The s p e c t r o m e t e r was purged o f w a t e r vapour w i t h a P e r k i n - E l m e r a i r p u r g i n g u n i t c o n t a i n i n g s i l i c a g e l l beads ("K-C-drying beads", K a l i -Chemie A G ) . R e s o l u t i o n a t t a i n e d was b e t t e r than 0.5 cm ' a t a l l wave-l e n g t h s . In g e n e r a l , f r e q u e n c y a c c u r a c y was ± 2 cm ' on r a p i d s u r v e y scans and ± 0.5 cm ' under h i g h r e s o l u t i o n c o n d i t i o n s . C a l i b r a t i o n was made u s i n g a t m o s p h e r i c w a t e r vapour and c a r b o n d i o x i d e w i t h the i n s t r u m e n t on s i n g l e beam o p e r a t i o n . - 37 -C. DISCUSSION ON THE CALCULATION OF FORCE CONSTANTS 1. BASIC THEORY (3) I t i s w e l l known t h a t the v i b r a t i o n a l p r o b l e m can be f o r m u l a t e d i n terms o f i n t e r n a l c o o r d i n a t e s - bond s t r e t c h e s , a n g l e bends and t o r s i o n s - u s i n g the W i l s o n FG - m a t r i x method. The f o r m u l a t i o n i n v o l v e s the harmonic o s c i l l a t o r a p p r o x i m a t i o n i n w h i c h the p o t e n t i a l e n e r g y i s e x p r e s s e d as a f u n c t i o n o f the s q u a r e o f t h e i n t e r n a l c o o r d i n a t e s : 2V = RF R . (1-1) F i s t h e m a t r i x o f Hooke's law c o n s t a n t s known as t h e v a l e n c e f o r c e f i e l d and R i s t h e column v e c t o r o f i n t e r n a l c o o r d i n a t e s . R* i s t h e t r a n s p o s e o f R . The k i n e t i c e n e r g y has i t s u s u a l e x p r e s s i o n as a f u n c t i o n o f t h e masses and t h e s q u a r e o f t h e v e l o c i t i e s , 2 T - R ' G - , R 0-2) where G i s a m a t r i x i n v o l v i n g t h e i n v e r s e masses g i v e n by G = B M 1 B' . (1-3) M i s t h e d i a g o n a l m a t r i x o f the a t o m i c masses and B i s t h e non-sq u a r e m a t r i x g i v i n g t h e t r a n s f o r m a t i o n from t h e 3N (N b e i n g t h e num-ber o f atoms i n the m o l e c u l e ) c a r t e s i a n d i s p l a c e m e n t c o o r d i n a t e s t o the 3N-6 i n t e r n a l c o o r d i n a t e s : (1-4) R = B x and B 9 R . i 3 x , ( ' " 5 ) ' J The energy e i g e n v a l u e e q u a t i o n then c o n s i s t s o f the c l a s s i c a l - 38 -hami1 t o n i a n o p e r a t o r G F , the v i b r a t i o n a l e i g e n v e c t o r s and t h e e i g e n v a l u e s X^: G F L = L A . (1-6) A i s the d i a g o n a l m a t r i x o f e i g e n v a l u e s r e l a t e d t o the o b s e r v e d f r e q u e n c i e s , v, , by , 2 2 2 o and L i s the m a t r i x g i v i n g t h e t r a n s f o r m a t i o n f r o m normal c o o r d i n a t e s , Q , i n w h i c h t h e v i b r a t i o n a l e n ergy c o n t a i n s no c r o s s t e r m s , t o i n -t e r n a l c o o r d i n a t e s , R , i n w h i c h F i s e x p r e s s e d : R - L Q (1-8) and L- . 1 J 9 R . (1-9) The m a t r i x G can be o b t a i n e d from t h e known geometry o f (3) t h e m o l e c u l e and so i f F i s known t h e v i b r a t i o n a l f r e q u e n c i e s can be o b t a i n e d by s o l u t i o n o f the s e c u l a r d e t e r m i n a n t |G F - X k E I = 0 (1-10) where E i s the u n i t m a t r i x . However, the u s u a l c a s e i n s p e c t r o s c o p y i n v o l v e s the r e v e r s e p r o b l e m : o b s e r v i n g t h e f r e q u e n c i e s w h i c h y i e l d t he e i g e n v a l u e s and then c a l c u l a t i n g from t h e s e the f o r c e c o n s t a n t s as p a r a m e t e r s . The m a t h e m a t i c a l problems i n v o l v e d i n t h i s c a l c u l a t i o n and some o f the a t t e m p t s t o overcome them a r e d i s c u s s e d i n the next s e c t i o n . F i r s t , however, the reaso n s f o r i n t e r e s t i n the f o r c e con-s t a n t s s h o u l d be p o i n t e d o u t . R e f e r e n c e s 2 and 3 d i s c u s s f u l l y t he l a r g e amount o f i n f o r -- 39 -mat i o n t h a t can be o b t a i n e d from i . r . s p e c t r a . Of pri m e i n t e r e s t a r e t h e f o r c e c o n s t a n t s and t h e i r r e l a t i o n s h i p t o c h e m i c a l b o n d i n g . A v e r y i m p o r t a n t r e a s o n f o r f o r m u l a t i n g t h e v i b r a t i o n a l p r o b l e m i n terms o f i n t e r n a l c o o r d i n a t e s i s the r e s u l t i n g c o n s i s t e n c y w i t h t he c h e m i s t ' s n o t i o n o f bonds. The d i a g o n a l e l e m e n t s o f the f o r c e c o n -s t a n t m a t r i x , f . . , which, appear i n the p o t e n t i a l e nergy e x p r e s s i o n i n terms such as f . . r f (,-.,) where r . i s the change i n t h e l e n g t h o f bond i , r e p r e s e n t a f o r c e r e s i s t i n g t h i s change i n bond l e n g t h . T h i s f o r c e depends on the s t r e n g t h o f the bond and as a r e s u l t f o r c e c o n s t a n t s show t r e n d s , a l o n g w i t h bond l e n g t h s and bond o r d e r s , w h i c h a r e r e l a t e d t o bond s t r e n g t h . Thus f o r c e c o n s t a n t s , w h i c h g i v e a p h y s i c a l p i c t u r e o f the f o r c e f i e l d w i t h i n t he m o l e c u l e as w e l l as the n a t u r e o f t h e mot i o n o f the atoms on v i b r a t i o n , a l s o p r o v i d e a n o t h e r c r i t e r i o n f o r the s t u d y o f b o n d i n g . I t i s f o r t h i s r e a s o n t h a t t h e y a r e o f i n t e r e s t t o t he c h e m i s t . Note on Uni t s : The f o r c e c o n s t a n t a p p e ars i n t h e p o t e n t i a l e n e r g y e x p r e s s i o n i n terms such as f..R.R. where R. and R. a r e i n t e r n a l I J i j i j c o o r d i n a t e s . The u n i t s o f the f o r c e c o n s t a n t must be energy p e r c o -o r d i n a t e s q u a r e d . When R. and Rj a r e b o t h bond s t r e t c h e s , f o r c e con-5 2 s t a n t s a r e u s u a l l y i n the o r d e r o f 10 ergs/cm . I t has been common o p r a c t i c e t o e x p r e s s t h e s e c o n s t a n t s as m i l l i d y n e s / A s i n c e i n t h e s e u n i t s t he f o r c e c o n s t a n t i s i n the o r d e r o f u n i t y . F o r bends the - ko -f o r c e c o n s t a n t s a r e about 10 e r g s / r a d i a n and f o r b e n d - s t r e t c h -3 ° i n t e r a c t i o n s they a r e near 10 e r g s / r a d i a n A. I t has a l s o been common t o d i v i d e the bend c o n s t a n t s by an a p p r o p r i a t e bond l e n g t h s q u a r e d and b e n d - s t r e t c h c o n s t a n t s by s i m p l y an a p p r o p r i a t e bond l e n g t h . T h i s b r o u g h t b o t h c o n s t a n t s t o v a l u e s o f the o r d e r o f one o m i l l i d y n e / A a t the expense o f c h a n g i n g the c o n s t a n t by the bond l e n g t h f a c t o r . However, u s i n g the M.K.S. sys t e m o f u n i t s , i t i s p o s s i b l e t o s i m p l i f y c a l c u l a t i o n s . When the energy i s e x p r e s s e d i n a t o J o u l e s and the bond l e n g t h s i n Angstroms the s t r e t c h c o n s t a n t s have the form aJ/A (=mdyn/A) w h i l e b e n d - s t r e t c h c o n s t a n t s a r e i n aJ/A rad -3 ° 2 - 1 1 (= 10 e r g s / r a d A) and bend c o n s t a n t s a r e i n a J / r a d (= 10 e r g s / 2 rad ) . T h i s change l e a v e s a l l t h e c o n s t a n t s i n the m e a n i n g f u l e n e r g y / c o o r d i n a t e s q u a r e d u n i t s , o f t h e o r d e r o f u n i t y and unchanged by some a r b i t r a r y bond l e n g t h f a c t o r . T h e r e f o r e , i n t h i s t h e s i s a l l f o r c e c o n s t a n t s c a l c u l a t e d w i l l be e x p r e s s e d i n t h e s e c o n v e n i e n t " n a t u r a l un i t s " . 2. LEAST SQUARES REFINEMENT OF FORCE CONSTANTS In g e n e r a l t h e f o r c e c o n s t a n t p r o b l e m i s i n s o l u b l e s i n c e the f o r c e c o n s t a n t m a t r i x c o n t a i n s n ( n + l ) / 2 e l e m e n t s w h i l e the num-ber o f f r e q u e n c i e s o b s e r v e d i s a t most n. T h i s means t h a t an i n f i n -i t e number o f s o l u t i o n s can be found t o f i t the d a t a and a t t e m p t s t o s e l e c t the t r u e s o l u t i o n from t h i s i n f i n i t e s e t a r e c o n s i s t e n t l y - 41 -(25) based on f a l s e l o g i c . To s o l v e t h e p r o b l e m t h e n , more d a t a i s needed, and t h e r e f o r e r e l a t i o n s h i p s between f o r c e c o n s t a n t s and o t h e r (26) o b s e r v a b l e s have been a n a l y s e d . Meal and P o l o have shown the c o r r e l a t i o n between C o r i o l i s c o u p l i n g c o n s t a n t s , o b t a i n e d from h i g h r e s o l u t i o n gas phase i . r . s p e c t r o s c o p y , and f o r c e c o n s t a n t s . K i v e l s o n (27) and W i l s o n have d e v e l o p e d a second i m p o r t a n t r e l a t i o n s h i p w i t h f u r t h e r d a t a , the c e n t r i f u g a l d i s t o r t i o n c o n s t a n t s w h i c h a r e o b t a i n e d (28) from microwave s p e c t r o s c o p y . Of l e s s v a l u e , C y v i n has d e m o n s t r a t e d a r e l a t i o n s h i p between f o r c e c o n s t a n t s and the mean s q u a r e a m p l i t u d e s (29) o f e l e c t r o n d i f f r a c t i o n w h i l e H e r s c h b a c h and L a u r i e have e s t a b l i s h e d y e t a n o t h e r w i t h i n e r t i a l d e f e c t s w h i c h a r e a l s o o b t a i n e d by microwave s t u d i e s . Whenever t h i s i n f o r m a t i o n i s a v a i l a b l e , i t s use i n d e t e r m i n -ing the t r u e f o r c e f i e l d a c c u r a t e l y has been shown t o be v e r y v a l u a b l e ^ ^ However, p r o b a b l y the most i m p o r t a n t s o u r c e o f e x t r a d a t a comes from t h e f a c t t h a t t h e f o r c e c o n s t a n t m a t r i x i s i n v a r i a n t t o i s o t o p i c s u b s t i t u -t i o n . I s o t o p i c s u b s t i t u t i o n d o e s , however, cause a change i n the G m a t r i x and thus a change i n the o b s e r v e d f r e q u e n c i e s . As a r e s u l t a second s e t o f f r e q u e n c i e s i s a v a i l a b l e f o r the c a l c u l a t i o n o f F F u r t h e r i s o t o p i c s u b s t i t u t i o n y i e l d s f u r t h e r d a t a . W i t h t h e development o f h i g h s p e e d , h i g h s t o r a g e c o m p u t e r s , t h e p r e f e r r e d method f o r f o r c e c o n s t a n t c a l c u l a t i o n s when e x t r a d a t a i s a v a i l a b l e has become l e a s t s q u a r e s f i t t i n g . In l e a s t s q u a r e s an i n i t i a l a p p r o x i m a t e f o r c e f i e l d i s r e f i n e d by an i t e r a t i v e p r o c e d u r e so as t o g i v e an a c c u r a t e f i t o f t h e t o t a l d a t a . The p r o c e d u r e i s - kl -(31 32) (30) w e l l o u t l i n e d i n papers by M i l l s ' , A l d o u s and M i l l s , Overend ( 3 3 ) ( 3 4 ) and S c h e r e r and S c h a c h t s c h n e i d e r . The b l o c k d i a g r a m i n f i g u r e 1-9, t a k e n from r e f e r e n c e 3 3 , i l l u s t r a t e s the c y c l e f o l l o w e d by the computer program, i n c l u d i n g t h e i n p u t d a t a r e q u i r e d and the normal e q u a t i o n s o f l e a s t s q u a r e s t h a t have t o be s o l v e d . The p r o c e d u r e i s as f o l l o w s . An a p p r o x i m a t e f o r c e f i e l d i s used t o c a l c u l a t e a s e t o f e i g e n v a l u e s w h i c h a r e compared w i t h t h e o b s e r v e d e i g e n v a l u e s t o g i v e a s e t o f e r r o r s . Under the c o n d i t i o n o f s m a l l d i s p l a c e m e n t s t h e s e e r r o r s a r e r e l a t e d t o c o r r e c t i o n s i n the f o r c e c o n s t a n t s by t h e l i n e a r e q u a t i o n AX = J A F (1-12) where J i s the J a c o b i a n m a t r i x whose terms a r e t h e f i r s t d e r i v a t i v e s J . . = i J '8Ai ( 1 - 1 3 ) F. c o n s t a n t (31) M i l l s has shown t h r o u g h t h e use o f p e r t u r b a t i o n t h e o r y t h a t t h e s e d e r i v a t i v e s can be e x p r e s s e d i n terms o f the e i g e n v e c t o r s , L q , o b t a i n e d from the s e c u l a r e q u a t i o n . Thus, 3F, , o k i o i l k l The e l e m e n t s o f F a r e o b t a i n e d from the m u l t i p l i c a t i o n o f the t r a n s -f o r m a t i o n m a t r i x Z and t h e column v e c t o r o f f o r c e c o n s t a n t s % such t h a t F k . " ? Z k l J * J ( , " 1 5 ) The use o f Z and $ s i m p l i f i e s t he l e a s t s q u a r e s e q u a t i o n when - i.3 -i n CF1 F-Z$ L f-F i g u r e 1-9. B l o c k d i a g r a m o f main p e r t u r b a t i o n c y c l e f o l l o w e d by computer ( t a k e n from r e f e r e n c e 33). - -e l e m e n t s o f t h e F m a t r i x a r e not i n d e p e n d e n t . The l i n e a r e q u a t i o n can then be w r i t t e n as AX = J Z A $ (1-16) The c o n d i t i o n t h a t the sum o f the w e i g h t e d s q u a r e s o f the e r r o r s i n the e i g e n v a l u e s , AX, be m i n i m i z e d i s then imposed. T h i s r e s u l t s i n t h e normal e q u a t i o n s (J Z ) ' P AX = ( J Z ) ' P ( J Z ) A$ (1-17) where P i s a d i a g o n a l m a t r i x o f w e i g h t i n g e l e m e n t s such t h a t a l a r g e r e f l e c t s a l a r g e c o n f i d e n c e i n t h e o b s e r v a t i o n o f X^ w h i l e a s m a l l P^ r e f l e c t s a l a r g e u n c e r t a i n t y i n the o b s e r v e d X^. The recommended method, w h i c h i s f o l l o w e d i n c a l c u l a t i o n s i n t h i s t h e s i s , i s t o s e t P, = -|- • Note t h a t o n l y r e l a t i v e w e i g h t s a r e r e q u i r e d s i n c e a c o n s t a n t k X|< term i n P would s i m p l y c a n c e l . The s o l u t i o n o f t h i s e q u a t i o n r e s u l t s i n a new s e t o f f o r c e c o n s t a n t s , $ , w h i c h i s then r e c y c l e d u n t i l t h e v e c t o r o f c o r r e c t i o n s , A$ , has a l l i t s e l e m e n t s s m a l l e r than a p r e v -i o u s l y s p e c i f i e d v a l u e . At t h i s p o i n t s e 1 f - c o n s i s t a n c y has been reached and t h e r e f i n e m e n t has g i v e n f o r c e c o n s t a n t s as a c c u r a t e as t h e l i m i t a t i o n s o f the o b s e r v e d d a t a w i l l a l l o w . I t can be seen t h a t the d i m e n s i o n o f <5> i s d e t e r m i n e d by the number o f f o r c e c o n s t a n t s t o be c a l c u l a t e d w h i l e the J Z m a t r i x has d i m e n s i o n s o f the number o f o b s e r v a t i o n s by the number o f f o r c e con-s t a n t s . Thus when more d a t a i s a v a i l a b l e , the a d d i t i o n o f more rows to the j Z m a t r i x c o n v e n i e n t l y a l l o w s f o r i t s use. The e x p r e s s i o n f o r the J a c o b i a n o f the o b s e r v e d f r e q u e n c i e s w i t h r e s p e c t t o a f o r c e c o n -- ks -s t a n t i s g i v e n i n e q u a t i o n 1-14. S i m i l a r e x p r e s s i o n s have been dev-c o n s t a n t s and c e n t r i f u g a l d i s t o r t i o n c o n s t a n t s . The c o m b i n a t i o n o f normal e q u a t i o n s r e s u l t i n g from t h e s e new forms o f d a t a s t i l l s i m p l y r e q u i r e s t h e a d d i t i o n o f more rows t o the normal e q u a t i o n s (eq. 1-17). However, i n t h e c a l c u l a t i o n s done f o r t h i s t h e s i s o n l y i s o t o p i c f r e q u e n c i e s were a v a i l a b l e as a d d i t i o n a l d a t a . The s i z e o f the m o l e c u l e s and t h e i r low symmetry r e s u l t e d i n the c a l c u l a t i o n s b e i n g u n d e r d e t e r m i n e d even when numerous i s o t o p i c s u b s t i t u t i o n s were a v a i l a b l e . As a r e s u l t , a p p r o x i m a t i o n s were n e c e s s a r y i n t h e c a l c u -l a t i o n o f the f o r c e f i e l d s . 3. APPROXIMATIONS AND ERROR ESTIMATES (a) Harmonic O s c i l l a t o r : The harmonic o s c i l l a t o r f o r m a l i s m g i v e n above c o n s t i t u t e s t h e main a p p r o x i m a t i o n used i n v i b r a t i o n a l a n a l y s i s . T h i s means t h a t t h e T a y l o r s e r i e s e x p a n s i o n o f t h e p o t e n t i a l e n e r g y as a f u n c t i o n o f d i s p l a c e m e n t from t h e e q u i l i b r i u m c o n f i g u r a t i o n i s t e r m i n a t e d f o l l o w i n g t h e q u a d r a t i c term. Thus a l l h i g h e r terms a r e a p p r o x i m a t e d t o z e r o , even though i t has been found t h a t c u b i c and q u a r t i c terms do i n f a c t make m e a s u r a b l e c o n t r i b u t i o n s - g e n e r a l l y i n a combined t o t a l o f about 2 per c e n t . -The s o l u t i o n o f t h e S c h r o d i n g e r e q u a t i o n f o r the s i m p l e harmonic o s c i l l a t o r e l o p e d by M i l l s (3D u s i n g p e r t u r b a t i o n t h e o r y f o r C o r i o l i s c o u p l i n g 2 2 dx hi (E - ~K X 2 ) i> = 0 (1-18) - hb -g i v e s the quantum m e c h a n i c a l energy e x p r e s s i o n : E = a) (v + 1/2) (1-19) e where w i s a c o n s t a n t i n wave number u n i t s and v i s the v i b r a t i o n a l e quantum number. For d i a t o m i c m o l e c u l e s t h i s e n ergy e x p r e s s i o n i s u s u a l l y c o r r e c t e d f o r a n h a r m o n i c i t y ( i . e . h i g h e r terms i n the p o t e n -t i a l e nergy e x p r e s s i o n ) by the a d d i t i o n o f a second term such t h a t E = ai (v + 1/2) - u x (v + 1 / 2 ) 2 (1-20) e e e where u) x i s a m o l e c u l a r c o n s t a n t a l s o i n cm \ e e For a p o l y a t o m i c m o l e c u l e t h i s becomes 3N-6 3N-6 3N-6 g . q E = E w . (v. + f 4 + E E X (v. + f 4 ( v . + ^ i ) (1-21) 1=1 i=l J = i J J where X „ i s the anharmonic energy term and g. i s the d e g e n e r a c y o f the i ^ v i b r a t i o n a l mode. I f o n l y the fundamental f r e q u e n c i e s , v . , ( i . e . Av.=l) a r e o b s e r v e d , o n l y E can be o b t a i n e d , but i f enough o v e r t o n e s and c o m b i n a t i o n bands can be s e e n , then the O J . ' S and X..'s i i j can a l s o be c a l c u l a t e d . The f o r m e r a r e the " h a r m o n i c f r e q u e n c i e s " and i n f a c t s h o u l d be used r a t h e r than the o b s e r v e d f r e q u e n c i e s , v . , f o r t h e d e t e r m i n a t i o n o f the e i g e n v a l u e s and t h u s the " harmonic f o r c e c o n s t a n t s " i n the FG - m a t r i x c a l c u l a t i o n s . The X..'s a r e the "an-' J (35) harmonic c o r r e c t i o n s " and have been shown by N i e l s o n t o be com-p l i c a t e d f u n c t i o n s o f the C o r i o l i s c o e f f i c i e n t s as w e l l as the c u b i c and q u a r t i c c o e f f i c i e n t s i n the p o t e n t i a l e nergy e x p r e s s i o n ( i . e . the c u b i c and q u a r t i c f o r c e c o n s t a n t s ) . W i t h the i n a v a i 1 a b i 1 i t y o f s u f f i c i e n t d a t a e x c e p t f o r o n l y - 47 -a v e r y few s m a l l m o l e c u l e s ( e . g . see r e f e r e n c e 36) both the w.'s and X..'s a r e i n d e t e r m i n a t e . As a r e s u l t , t h e o b s e r v e d f r e q u e n c i e s U must be used f o r the c a l c u l a t i o n o f f o r c e c o n s t a n t s . T h i s means t h a t i n r e a l i t y o n l y a p p r o x i m a t e h a r m o n i c f o r c e c o n s t a n t s a r e c a l -c u l a t e d s i n c e o n l y a p p r o x i m a t i o n s t o the harmonic f r e q u e n c i e s a r e used. A n o t h e r way t o l o o k a t i t i s t o c o n s i d e r the f o r c e c o n s t a n t s s i m p l y as f i t t i n g p a r a m e t e r s g i v i n g t h e b e s t f i t o f t h e o b s e r v e d d a t a t o a q u a d r a t i c p o t e n t i a l e n e r g y e x p r e s s i o n r a t h e r than as a c c u r a t e l y measured p h y s i c a l p r o p e r t i e s o f t h e m o l e c u l e . However, as mentioned b e f o r e , the a n h a r m o n i c i t y i s s m a l l , c e r t a i n l y l e s s than 5 p e r c e n t , so t h a t the c a l c u l a t e d p a r a m e t e r s a r e f a i r l y good a p p r o x i m a t i o n s t o the a c t u a l harmonic f o r c e c o n s t a n t s . To the c h e m i s t they a r e a l m o s t a l w a y s a l l t h a t i s n e c e s s a r y . I f enough o b s e r v e d d a t a i s a v a i l a b l e t o c a l c u l a t e a s e t o f p a r a m e t e r s under t h e a p p r o x i m a t i o n o f i g n o r i n g a n h a r m o n i c i t y , i t i s u s u a l l y found t h a t t h e i r a c c u r a c y i s good enough f o r c o m p a r i s o n s o f bonds w i t h i n a s e r i e s o f m o l e c u l e s , and t h i s i s what u s u a l l y i s o f c h e m i c a l i n t e r e s t . (b) M o d i f i e d F o r c e F i e l d s : Even w i t h the harmonic o s c i l l a t o r a p p r o x i -m a t i o n , t h e number o f f o r c e c o n s t a n t s i s s t i l l n ( n + l ) / 2 w h i c h i s u s u a l -l y more than can be d e t e r m i n e d from a v a i l a b l e d a t a . T h i s may be because fewer than n ( n + l ) / 2 p i e c e s o f o b s e r v e d d a t a a r e a v a i l a b l e o r because some o f the f o r c e c o n s t a n t s a r e found t o be i n s e n s i t i v e t o t h e d a t a . The m o d i f i c a t i o n o f a f o r c e f i e l d i s then an a p p r o x i m a t i o n by w h i c h the number o f p a r a m e t e r s i s reduced by u s i n g i n t u i t i v e r e l a t i o n s h i p s - 48 -between f o r c e c o n s t a n t s o r more commonly by s i m p l y s e t t i n g f o r c e c o n s t a n t s t h a t a r e i n s e n s i t i v e t o the d a t a t o z e r o . The l a t t e r t e c h -n i q u e i s the one t h a t must be f o l l o w e d f o r m o l e c u l e s v/hose b o n d i n g i s not s i m p l e enough o r not w e l l enough u n d e r s t o o d t o y i e l d t o i n t u i t i o n . Such i s the cas e w i t h m o l e c u l e s f o r w h i c h f o r c e f i e l d c a l c u l a t i o n s a r e a t t e m p t e d i n t h i s t h e s i s , . A method t h a t was found p a r t i c u l a r l y u s e f u l i n t h e s e c a l c u -l a t i o n s was f i r s t t o d e t e r m i n e an a p p r o x i m a t e f o r c e f i e l d by s e t t i n g a l l t h e o f f - d i a g o n a l e l e m e n t s o f t h e F m a t r i x , the s o - c a l l e d i n t e r -a c t i o n c o n s t a n t s , t o z e r o . In many c a s e s , when o n l y one s e t o f f r e -q u e n c i e s i s a v a i l a b l e t h i s i s the b e s t a p p r o x i m a t i o n t h a t can be made. Here, however, because o f the use o f numerous i s o t o p e s , some o f t h e i n t e r a c t i o n c o n s t a n t s were a l s o d e t e r m i n a b l e . What was done was t o i n t r o d u c e s e l e c t e d o f f - d i a g o n a l e l e m e n t s e i t h e r i n d i v i d u a l l y o r i n c o m b i n a t i o n s and then t o examine the new c a l c u l a t i o n s w i t h r e s p e c t 3X t o the v a l u e s o f the J a c o b i a n s (-77=-) , the e r r o r s i n the l e a s t s q u a r e s or f o r c e c o n s t a n t s c a l c u l a t e d by t h e method d e s c r i b e d i n the f o l l o w i n g s e c t i o n , t h e e r r o r s i n the c a l c u l a t e d f r e q u e n c i e s and the n a t u r e o f the e i g e n v e c t o r s and t h e p o t e n t i a l e nergy d i s t r i b u t i o n (P.E.D.= a c o m p a r i s o n o f c a l c u l a t i o n s showed t h a t a f o r c e c o n s t a n t had l i t t l e e f f e c t on the c a l c u l a t i o n and p o s s -e s s e d a l a r g e e r r o r ( e r r o r s o f g r e a t e r than 20 per c e n t were s u s p e c t ) , then i t was c o n s i d e r e d i n d e t e r m i n a t e and f i x e d a t z e r o . In t h i s way the f o r c e c o n s t a n t s found i m p o r t a n t i n f i t t i n g a l l t h e o b s e r v e d d a t a - k3 -t o t h e m o d i f i e d h a r m o n i c o s c i l l a t o r p o t e n t i a l e nergy e x p r e s s i o n were c a l c u l a t e d . T h i s f o r c e f i e l d was then t a k e n t o be the b e s t a p p r o x i -m a t i o n t o t h e t r u e harmonic f o r c e f i e l d t h a t c o u l d be d e t e r m i n e d from the a v a i l a b l e d a t a . As i s p o i n t e d o u t above, the e x p r e s s i o n f o r t h e J a c o b i a n o f t h e e i g e n v a l u e s w i t h r e s p e c t t o f o r c e c o n s t a n t s i s 8 A I = L..L.. (1-14) 9FT. J 1 K ' J K Remembering t h a t L , t h e e i g e n v e c t o r m a t r i x g i v e s the t r a n s f o r m a t i o n R = L Q (1-8) then t h e e l e m e n t s o f L can be w r i t t e n L J . " I 5 J - ( , - 9 ) I t can be seen t h a t i f t h e i n t e r n a l c o o r d i n a t e R. makes a l a r g e con-t r i b u t i o n t o the normal c o o r d i n a t e Q., the n . may be l a r g e enough so t h a t t h e J a c o b i a n , L..L. ., i s s i g n i f i c a n t . In t h a t c a s e , the j i k i 3 ' l a r g e J a c o b i a n r e s u l t s i n the f o r c e c o n s t a n t , F j ^ * b e i n g d e t e r m i n a b l e by l e a s t s q u a r e s . Thus i f normal modes have l a r g e c o n t r i b u t i o n s from s e v e r a l i n t e r n a l c o o r d i n a t e s , as i n the c a s e o f near d e g e n e r a t e v i b r a -t i o n s o f the same symmetry, i t i s found t h a t the o f f - d i a g o n a l c o n s t a n t s c o n n e c t i n g t h e s e i n t e r n a l c o o r d i n a t e s a r e d e t e r m i n a t e i f enough d a t a i s a v a i l a b l e . B u t , i f not enough d a t a i s a v a i l a b l e t o c a l c u l a t e a l l the i m p o r t a n t d i a g o n a l and o f f - d i a g o n a l c o n s t a n t s , s e t t i n g some t o z e r o w i l l n ot h e l p because l a r g e e r r o r s w i l l r e s u l t . An example o f such a s i t u a t i o n i s seen i n c h a p t e r I I I i n the c a l c u l a t i o n s i n v o l v i n g t he - 50 -1250, 1080, 900 and kk$ cm v i b r a t i o n s o f cis-HNSO. The o p p o s i t e s i t u a t i o n can a l s o o c c u r . Normal modes t h a t a r e e n e r g e t i c a l l y s e p a r a t e d from o t h e r modes o f the same symmetry a r e u s u a l l y composed, a l m o s t e x c l u s i v e l y , o f o n l y one i n t e r n a l co-o r d i n a t e . Examples a r e the hydrogen s t r e t c h e s w h i c h a r e u s u a l l y 1500 cm ' away f r o m other, modes and have o n l y a few per c e n t con-t r i b u t i o n f rom o t h e r i n t e r n a l c o o r d i n a t e s . In t h e s e c a s e s a l l L.., •J i / j , a r e s m a l l so t h a t the e i g e n v a l u e s a r e o n l y dependent upon the one d i a g o n a l f o r c e c o n s t a n t , the o f f - d i a g o n a l e l e m e n t s i n t h e same column and row i n the F m a t r i x b e i n g i n d e t e r m i n a t e . These o f f - d i a g o n a l e l e m e n t s must be h e l d f i x e d a t some v a l u e , g e n e r a l l y t a k e n t o be z e r o . T h i s , however, does not l e a d t o l a r g e e r r o r s s i n c e t h e s e i n t e r a c t i o n c o n s t a n t s have v e r y l i t t l e e f f e c t upon the c a l c u l a t i o n . Thus, i n t h e s e c a s e s t h e d i a g o n a l f o r c e c o n s t a n t can be d e t e r m i n e d a c c u r a t e l y w i t h v e r y l i t t l e d a t a w h i l e t h e o f f - d i a g -o n a l f o r c e c o n s t a n t s c a n n o t be d e t e r m i n e d w i t h much c o n f i d e n c e even w i t h a l a r g e number o f i s o t o p i c f r e q u e n c i e s . An example o f t h i s s i t u a t i o n i s the hydrogen s t r e t c h o f cis-HNSO i n the c a l c u l a t i o n s found i n c h a p t e r I I I . (c) E r r o r E s t i m a t e s : The method o f l e a s t s q u a r e s has b u i l t i n t o i t a method o f e s t i m a t i n g t h e e r r o r o f the c a l c u l a t e d f o r c e c o n s t a n t s based upon t h e d i f f e r e n c e i n c a l c u l a t e d and o b s e r v e d f r e q u e n c i e s . (38) I t can be shown t h a t the moment m a t r i x f o r t h e f o r c e c o n s t a n t e s t i m a t e s i s g i v e n by - 51 -_ i AA. P A X M ( F ) = [ ( J Z ) ' P ( J Z ) ] n- m • - (1-22) where AX i s the column v e c t o r o f d i f f e r e n c e s between o b s e r v e d and c a l c u l a t e d e i g e n v a l u e s , n i s the number o f o b s e r v e d f r e q u e n c i e s , m i s the number o f f o r c e c o n s t a n t s and n-m i s known as the number o f degrees o f freedom o f the l e a s t s q u a r e s f i t . The term A X 1 P A X n-m i s t he u n b i a s e d e s t i m a t e o f t h e v a r i a n c e o f an o b s e r v a t i o n o f u n i t 2 w e i g h t and i s g i v e n t h e symbol a . The d i a g o n a l terms o f M(F) g i v e the s t a t i s t i c a l v a r i a n c e o f t h e c a l c u l a t e d f o r c e c o n s t a n t s . The s q u a r e r o o t s o f t h e s e d i a g -o n a l e l e m e n t s then g i v e an e s t i m a t e i n the e r r o r o f the c o n s t a n t s . The o f f - d i a g o n a l terms o f t h i s m a t r i x g i v e the c o r r e l a t i o n between the e r r o r s i n the f o r c e c o n s t a n t s . These e r r o r s l i s t e d w i t h t h e f o r c e c o n s t a n t s i n t h i s t h e s i s a r e o f a s t a t i s t i c a l n a t u r e and not o f a p h y s i c a l n a t u r e . That i s , they r e f l e c t the a c c u r a c y o f t h e f i t o f the d a t a t o t h e chosen model, but not n e c e s s a r i l y t h e a c c u r a c y o f t h e model. For example, the e r r o r s found f o r the d i a g o n a l f o r c e c o n s t a n t s a r e o f t e n s m a l l e r than the ex-p e c t e d a n h a r m o n i c i t y . The major use o f t h e e r r o r s i s the c o m p a r i s o n between v a r i o u s c a l c u l a t i o n s t o see the e f f e c t o f u s i n g d i f f e r e n t i n -t e r a c t i o n c o n s t a n t s . I m p o r t a n t , d e t e r m i n a t e i n t e r a c t i o n c o n s t a n t s have low e r r o r s and do not i n t r o d u c e l a r g e e r r o r s i n t o the d i a g o n a l c o n s t a n t s . - 52 -Note, t h a t i f a d d i n g a n o t h e r f o r c e c o n s t a n t does not improve the f i t much, then t h e e r r o r w i l l i n c r e a s e because o f the d e c r e a s e i n n-m. k. USE IN IDENTIFYING UNKNOWN SPECIES The c a l c u l a t i o n o f f o r c e c o n s t a n t s can sometimes a i d i n the i d e n t i f i c a t i o n by i . r . s p e c t r o s c o p y o f an unknown s p e c i e s such as might be i s o l a t e d i n a m a t r i x . The method e n t a i l s the i n v e n t i n g o f a model - i n c l u d i n g v a l u e s o f bond l e n g t h s and a n g l e s - f o r each o f the p o s s i b l e c h o i c e s f o r the unknown a b s o r b e r . The f o r c e f i e l d s f o r each model a r e then compared t o t h e models a b i l i t y t o r e p r o d u c e i s o t o p i c s h i f t s and t o the r e a s o n a b l e n e s s o f f o r c e c o n s t a n t s o b t a i n e d . However, w h i l e some p o s s i b i l i t i e s may be e l i m i n a t e d , t h e method i s u s u a l l y not d e f i n i t e i n s e l e c t i n g t h e c o r r e c t s p e c i e s but o n l y i n p r o v i d i n g c o r r o b o r a t i v e e v i d e n c e . The main d i f f i c u l t y i s t h a t sometimes not enough i n t e n s i t y can be o b t a i n e d from a m a t r i x i s o l a t e d u n s t a b l e s p e c i e s t o see a l l i t s t r a n s i t i o n s . In such c a s e s c a l c u l a t i o n s r e q u i r e the f i x i n g o f some c o n s t a n t s and h o p i n g t h a t the m i s s i n g f r e q u e n c i e s a r e not i n a r e g i o n o f the s p e c t r a where a l a r g e amount o f m i x i n g w i l l o c c u r . A l s o , s i n c e the s t r u c t u r a l p a r a m e t e r s a r e e s t i m a t e d , t h e c a l c u l a t i o n must be f u r t h e r s u s p e c t . However, d e s p i t e the many d i f f i c u l t i e s t he method i s u s e f u l . - 53 -BIBLIOGRAPHY: CHAPTER I 1. W.J. Moore; " P h y s i c a l C h e m i s t r y " , P r e n t i c e - H a l l , 1962 2. G. H e r z b e r g ; " I n f r a r e d and Raman S p e c t r a " , D. Van N o s t r a n d , 1945 3. E.B. W i l s o n , J.C. D e c i u s and P.C. C r o s s ; " M o l e c u l a r V i b r a t i o n s " , M c G r a w - H i l l , 1955 4. B.A. M o n t p e l l i e r ; B.Sc. T h e s i s , U.B.C., 1970 5. G.C. P i m e n t e l and S.W. C h a r l e s ; Pure Appl . Chem., ]_, 111 (1963) 6. A . J . Barnes and H.E. H a l l a m ; Q u a r t . Rev., 2J_, 392 (1969) 7. G.C. P i m e n t e l and A.L. M c C l e l l a n ; "The Hydrogen Bond", Freeman, I960 8. M. Van T h i e l , E.D. Be c h e r , G.C. P i m e n t e l ; J . Chem. P h y s . , 27_, 486 (1957) 9- M.A. Graham, M. P o l i a k o f f and J . J . T u r n e r ; J . Chem. Soc. A., 1971, 2939 10. L.Y. N e l s o n and G.C. P i m e n t e l ; I n o r g . Chem., 6_, 1758 (1967) 11. A. S n e l s o n ; J . o f Phys. Chem., 74 , 537 (1970) 12. W.L.S. Andrews and G.C. P i m e n t e l ; J . Chem. P h y s . , 4 4 , 2527 (1966) 13. W.L.S. Andrews and G.C. P i m e n t e l ; J . Chem. P h y s . , 4 7 , 2637 (1967) 14. L.Y. Tan and G.C. P i m e n t e l ; J . Chem. P h y s . , 48 , 5202 (1968) 15. R.T. H a l l and G.C. P i m e n t e l ; J . Chem. Phys . , 3§_, 1889 (1963) 16. M.E. J a c o x and D.E. M i l l i g a n ; J . Chem. P h y s . , 4 0 , 2457 (1964) 17. D.E. M i l l i g a n and M.E. J a c o x ; J . Chem. Phys . , 4 9 , 4269 (1968) 18. R.D. S p r a t l e y , J . J . T u r n e r , G.C. P i m e n t e l ; J . Chem. P h y s . , 4 4 , - 54 -2063 (1966) 19. M.E. J a c o x and D.E. M i l l i g a n ; J . Chem. P h y s . , 5J_, 1952 (1969) 2 0 . M.E. J a c o x and D.E. M i l l i g a n ; J . Chem. P h y s . , 52_, 3864 (1970) 2 1 . M.E. J a c o x and D.E. M i l l i g a n ; J . Chem. Phys . , 54, 3935 (1971) 22 . D. D a v i s and W. Braun; AppJ . Opt., ]_, 2071 (1968) 2 3 . D.E. M i l l i g a n and M.E. J a c o x ; J . Chem. Phys . , 49_, 4269 (1968) 24 . F.C. F e h s e n f e l d , K.M. Evenson and H.P. B r o i d a ; Rev. S c i . I n s t r . , 36, 294 (1965) 25 . B.S. A v e r b u k h , L.S. Mayants, G.B. S h a l t u p e r ; J . M o l . S p e c t r y . , 30 , 310 (1969) 26. J.H. Meal and S.R. P o l o ; J . Chem. Phys . , 2 4 , 1119 ( 1 9 5 6 ) ; 24 , 1126 (1956) 27 . D. K i v e l s o n and E.B. W i l s o n ; J . Chem. Phys . , 2]_, 1229 (1953) 28 . S . J . C y v i n ; " M o l e c u l a r V i b r a t i o n s and Mean Square A m p l i t u d e s " , E l s e v i e r , I968 2 9 . D.R. Herschbach and W. L a u r i e ; J . Chem. Phys . , 4 0 , 3142 (1964) 30 . J . A l d o u s and I.M. M i l l s ; S p e c t r o c h i m . A c t a , J_8, 1073 ( 1 9 6 2 ) ; 19, 1567 (1963) 3 1 . I.M. M i l l s ; J . M o l . S p e c t r y . , 5_, 334 (I960) 32. I.M. M i l l s ; S p e c t r o c h i m . A c t a , J j [ , 35 ( i 9 6 0 ) 33. J - Overend and J.R. S c h e r e r ; J . Chem. P h y s . , 32_, 1289 (I960) 34. J.H. S c h a c h t s c h n e i d e r ; S h e l l Development Co., Tech. R e p o r t #263 _ 62 35. H.H. N i e l s o n ; Rev. o f Mod. P h y s i c s , 2_3, 90 (1951) 36. M.A. P a r i s e a u , I. S u z u k i , J . Overend; J . Chem. Phys . , 4_2, 2335 (1965) - 55 -|. S u z u k i ; J . Mol . S p e c t r y . , 2_5, 477 (1968) 37 . I.M. M i l l s ; S p e c t r o c h i m . A c t a , J9_, 1585 (1963) 38 . W.C. H a m i l t o n ; " S t a t i s t i c s i n P h y s i c a l S c i e n c e " , R o n a l d P r e s s , 1964 - 56 -CHAPTER I I THE OXYGEN FLUORIDES A. BACKGROUND In t h e l a s t f i f t e e n y e a r s , w i t h the development o f a dequate h a n d l i n g t e c h n i q u e s , i n o r g a n i c f l u o r i n e compounds have become a v e r y a c t i v e f i e l d o f c h e m i c a l r e s e a r c h . Many new compounds have been p r e -pared t h r o u g h i n g e n i o u s methods and o f t h e s e , a c o n s i d e r a b l e number have had t h e i r s t r u c t u r e d e t e r m i n e d t h r o u g h v a r i o u s s p e c t r o s c o p i c t e c h -n i q u e s . I n f r a r e d and Raman s p e c t r o s c o p y , used t o s t u d y v i b r a t i o n s o f m o l e c u l e s , have p r o b a b l y been t h e most w i d e l y used t e c h n i q u e s , l a r g e l y because o f t h e i r a v a i l a b i l i t y and t h e l a r g e amount o f i n f o r m a t i o n o b t a i n a b l e from them. One s m a l l but v e r y i n t e r e s t i n g group o f f l u o r i n e compounds t h a t has been q u i t e i n t e n s e l y s t u d i e d s p e c t r o s c o p i c a 1 l y i s t h a t o f the oxygen f l u o r i d e s . Reviews on the p r e p a r a t i o n s and c h e m i c a l p r o p e r t i e s .(3) by S t r e n g ^ and on p h y s i c a l a s p e c t s by T u r n e r ^ p r o v i d e a t h o r o u g h background t o t h i s group o f compounds. A more r e c e n t a r t i c l e by T u r n e r r e v i e w s the work up t o I 9 6 8 and t h e r e f o r e b r i n g s t h i n g s a l m o s t up t o d a t e . C o n s i d e r i n g t h e s e p a p e r s , o n l y a b r i e f m e ntion o f t h e s e compounds and some o f t h e i r more i n t e r e s t i n g p r o p e r t i e s need be made h e r e . The compounds t o be c o n s i d e r e d a r e 0 F 2 , O^^.-O^, 0 ^ F 2 > «0F, O^F^ 0 ^ 2 and 0 ^ 2 " 0 F 2 i s a f a i r l y s t a b l e m o l e c u l e whose s t r u c t u r e has been - 57 -d e t e r m i n e d by microwave s p e c t r o s c o p y and whose f o r c e f i e l d i s w e l l (3) e s t a b l i s h e d from v i b r a t i o n a l s p e c t r o s c o p y . S i m i l a r l y , ^^2' w n 1 c n i s p r e p a r e d by e l e c t r i c a l d i s c h a r g e o f oxygen and f l u o r i n e a t low t e m p e r a t u r e s has had i t s s t r u c t u r e d e t e r m i n e d by microwave s p e c t r o s -copy. However, because o f low l y i n g t r a n s i t i o n s , low i n t e n s i t y t r a n -s i t i o n s , l a c k o f f l u o r i n e i s o t o p i c d a t a and the m o l e c u l e s i n s t a b i l i t y w h i c h p r e v e n t s both gas phase and l a r g e q u a n t i t y m a t r i x i . r . s t u d y , the v i b r a t i o n s o f t h e m o l e c u l e and i t s f o r c e f i e l d have not been s a t -i s f a c t o r i l y e x p l a i n e d . A s e c t i o n d i s c u s s i n g r e c e n t s p e c t r a and f o r c e c o n s t a n t c a l c u l a t i o n s f o r O^F^ i s found l a t e r i n t h i s c h a p t e r . The o t h e r two m o l e c u l e s w h i c h have been d e f i n i t e l y i d e n t i -f i e d a r e r a d i c a l s . They a r e u n s t a b l e and have o n l y been i s o l a t e d i n (5) i n e r t gas m a t r i c e s . A r k e l l e t a l p r o duced 'OF by the p h o t o l y s i s o f OF^ i n a m a t r i x and d e t e r m i n e d i t s v i b r a t i o n a l f r e q u e n c y . A r k e l l and S p r a t l e y e t a l ^ b o t h produced t h e r a d i c a l 'O^F by the p h o t o l y s i s o f and F^ i n m a t r i c e s and s t u d i e d i t s i n f r a r e d s p e c t r u m and d e t e r -mined i t s f o r c e c o n s t a n t s . As w e l l , the e l e c t r o n p a r a m a g n e t i c s p e c t r a has been o b t a i n e d o f a s a n ' m P u r ' t y i n ®2^2^^ ' The r e m a i n i n g oxygen f l u o r i d e s , whose r a t h e r ambiguous p r e -p a r a t i o n s u s i n g e l e c t r i c d i s c h a r g e s have been r e p o r t e d , a r e 0 ^ 2 a n c ' 0 ^ 2 ^ , O i , ^ ^ a n c ' ^ 3 ^ 2 ^ ^ ' N ° s P e c t r a ' e v i d e n c e has been seen f o r any o f t h e s e s p e c i e s e x c e p t f o r the i d e n t i f i c a t i o n o f peaks i n t h e m a t r i x s p e c t r u m o f •C^F w i t h the dimer (-C^F^, i . e . 0^F 2* From t h i s d a t a the e x i s t e n c e o f t h i s m o l e c u l e i s o n l y supposed and l i t t l e can be - 58 -s a i d o f the n a t u r e o f t h e b o n d i n g between the 'G^*7 m o n o m e r s - The l a r g e number o f a t t e m p t s t h a t have been made a t s t u d y i n g s P e c ~ t r o s c o p i c a l l y have a l s o been u n s u c c e s s f u l r a i s i n g d oubts o f i t s e x i s t e n c e and r e p o r t e d p r e p a r a t i o n ^ ^ , and as a r e s u l t , t h e e x i s -t e n c e o f a n c ' ^6^2 a S w e ' ^ ' A t t e m p t s i n t h i s l a b o r a t o r y t o o b t a i n O^f^ by way o f microwave d i s c h a r g e o f 0^ and m i x t u r e s f o l l o w e d by f r e e z i n g b o t h w i t h and w i t h o u t a m a t r i x and u s i n g i . r . s p e c t r o s c o p y f o r d e t e c t i o n a r e d e s c r i b e d i n the l a s t p a r t o f t h i s c h a p t e r . - 59 -B. 0 2F 2: DI OXYGEN DIFLUORIDE 1. INTRODUCTION: PREPARATION AND STRUCTURE The m o l e c u l e ^2^2' ^ ' r s t P r e P a r e d by R u f f and M e n z e l ^ ' ^ i n 1933, i s produced by p a s s i n g an e l e c t r i c a l d i s c h a r g e t h r o u g h a low p r e s s u r e m i x t u r e o f 02 and F 2 i n a v e s s e l immersed i n a l i q u i d n i t r o g e n b a t h . The red c r y s t a l s o f 0 2 F 2 c o l l e c t on the c o l d w a l l s o f t h e r e a c t i o n v e s s e l . However, owing t o i t s i n s t a b i l i t y a t h i g h e r t e m p e r a t u r e s , l i t t l e was known about i t s s t r u c t u r e u n t i l 1962 when (12) J a c k s o n was a b l e t o o b t a i n i t s microwave s p e c t r u m u s i n g a con-t i n u o u s f l o w s y s t e m i n a microwave c e l l c o o l e d w i t h d r y i c e . I t was t h i s d e t e r m i n a t i o n t h a t s t i r r e d t h e i n t e r e s t i n 0 2F 2 o f bot h e x p e r i -m e n t a l i s t s and t h e o r e t i c i a n s . J a c k s o n found the s t r u c t u r e o f u 2 r " 2 t o be s i m i l a r t o t h a t o o o f H 20 2 w i t h r(0-0) = 1.217 ± 0.003 A, r(F-O) = 1.575 ± 0.003 A, <(00F) = 109° 30' ± 30' and t h e d i h e d r a l a n g l e = 87° 30' ± 30'. F Of i n t e r e s t a r e t h e s h o r t 0-0 bond and the l o n g OF bonds. By com-o o p a r i s o n , the 00 bond i n 0 2 H 2 i s 1.48 A and i n 0 2 > 1.21 A. Thus t h i s bond i n ®2^2 ' s m u c n m o r e l i k e the d o u b l e bond i n m o l e c u l a r oxygen - 60 -r a t h e r than the s i n g l e bond i n hydrogen p e r o x i d e . As w e l l , the OF o bond i s l o n g e r than the OF s i n g l e bond (1.41 A) found i n 0 . W i t h t h i s s t r u c t u r a l d e t e r m i n a t i o n i t became i m p o r t a n t t o e x p l a i n the bond l e n g t h s w i t h i n the framework o f known bonding t h e o r y . J a c k s o n ' s o r i g i n a l e x p l a n a t i o n was i n terms o f a ty p e bond-in g o f f l u o r i n e p o r b i t a l s w i t h the s i n g l y o c c u p i e d TT" o r b i t a l s o f 0^. S i n c e f l u o r i n e i s v e r y e l e c t r o n e g a t i v e , i t would d o n a t e v e r y l i t t l e e l e c t r o n d e n s i t y t o t h e IT" m o l e c u l a r o r b i t a l and t h e r e f o r e change t h e n a t u r e o f the 0-0 bond o n l y s l i g h t l y f r o m 0^. Hydrogen on the o t h e r -hand, b e i n g much l e s s e l e c t r o n e g a t i v e , would c o n t r i b u t e much more e l e c t r o n d e n s i t y t o the a n t i b o n d i n g o r b i t a l and thus weaken t h e 0-0 bond t o e s s e n t i a l l y a pure s i n g l e bond. T h i s w o u l d thus e x p l a i n the d i f f e r e n c e i n 0-0 bond l e n g t h s i n ^2^2 a n c ' ^2^2' S i m i l a r l y , t he 0-F bond would be e x p e c t e d t o be weaker i n ^2^2 t n a n ' n ^ 2 a n < ^ t n u s t n e (13) d i f f e r e n c e i n t h i s bond l e n g t h . S p r a t l e y and P i m e n t e l f u r t h e r c o n s i d e r e d t h i s b o n d i ng model f o r ^ -^2 a n C ' '®2^ a n C ' e x t e n d e d ' f c t o the a n a l o g o u s NO system. Two r e c e n t 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 have tended t o (14) s u p p o r t t h i s s i m p l e model. P e d e r s e n , u s i n g the s e m i - e m p i r i c a l method CND0/II, found t h a t the oxygen P^ and P^ o r b i t a l s w h i c h form the TT" a n t i b o n d i n g o r b i t a l i n 0^ have s u b s t a n t i a l l y l ower e l e c t r o n d e n s i t y i n ®2^2 than i n ^2^2' t n u s c o n f i r m i n g J a c k s o n ' s model. T h i s e l e c t r o n d e n s i t y r e s u l t s i n a l a r g e r 0-0 bond o r d e r i n ^ 2 ^ 2 - U s i n g - 61 -the e x t e n d e d H u c k e l a p p r o x i m a t i o n L o o s , G o e t s c h e l and C a m p a n i l e ^ " ^ found t h a t f o r "O^F the s i m p l e model c o r r e l a t e d w e l l w i t h t h e i r c a l -c u l a t i o n s , but t h a t the more complex bonding i n ^2^2' r e s u 1 1 i n g from the a v a i l a b i l i t y o f more f l u o r i n e p o r b i t a l s , made i t no l o n g e r p o s s i b l e t o d e s c r i b e t h e b o n d i n g s i m p l y i n terms o f p-Tr" a bonds. T h e i r c a l c u l a -t e d r e l a t i v e bond o r d e r s o f 0.40 and 0.41 f o r 0 ^ and 'O^F and 0.18 f o r $2^2 a 9 r e e w ' t n t n e bond l e n g t h d a t a . T u r n e r and H a r c o u r t ^ ^ however q u e s t i o n the s i m p l e p i c t u r e f o r ®2^2 s ' n c e t n e f l u o r i n e - o x y g e n a o r b i t a l would have t o i n t e r a c t w i t h the IT o r b i t a l as w e l l as the TT" o r b i t a l o f t h e oxygens s i n c e f o r the s y s t e m F00 they b o t h b e l o n g t o the same i r r e d u c i b l e r e p r e s e n t a t i o n . In f a c t , they f e e l t h a t t h e d e l o c a 1 i z a t i o n o f t h e TT o r b i t a l i n t o t h r e e c e n -t e r s i s t h e r e a s o n f o r t h e s h o r t 0-0 bond and l o n g 0-F bond. In the c a s e o f no such d e l o c a l i z a t i o n w i l l o c c u r . Because hydrogen i s l e s s e l e c t r o n e g a t i v e than f l u o r i n e i t w i l l not a t t r a c t t h e e l e c t r o n d e n s i t y as w e l l and because the and °"Q^* o r b i t a l s l i e f u r t h e r away i n e n e r g y from t h e oxygen TT o r b i t a l than do t h e Ogp and OQ^' o r b i t a l s they w i l l not i n t e r a c t w i t h the TT bond as s t r o n g l y . The b o n d i n g i n ^ 2 ^ 2 must then be d e s c r i b e d i n terms o f l o c a l i z e d OH a bonds o n l y . T u r n e r and H a r c o u r t ' s i n t e r p r e t a t i o n o f t h e i r c a l c u l a t i o n s u b s t a n t i a t e s t h i s v i e w . In any c a s e , t h e i r c a l c u l a t e d bond o r d e r s a r e c o n s i s t e n t w i t h the bond l e n g t h s i n O^F^ and 0 2 H 2 . The r e m a i n i n g i m p o r t a n t s p e c t r a l e v i d e n c e on 0 ^ 2 ' S ' t S ^ ' u o r -i n e -19 n u c l e a r m a g n e t i c r e s o n a n c e s p e c t r u m . Nebgen, Metz and R o s e ^ ^ - 62 -found t h a t the f l u o r i n e i s c o n s i d e r a b l y l e s s s h i e l d e d i n t n a n i n o r OF^. A l t h o u g h they do not a t t e m p t a mechanism f o r t h i s a n t i s h i e l d i n g , they s u g g e s t i t i s r e l a t e d t o the l o n g OF bond and p o s s i b l y t o the o v e r l a p o f t h e f l u o r i n e p o r b i t a l s w i t h the 0^ TT" o r b i t a l . More s p e c t r o s c o p i c d a t a would be u s e f u l i n a i d i n g under-s t a n d i n g o f the b o n d i n g . In p a r t i c u l a r the i . r . s p e c t r u m and r e s u l t -i n g f o r c e c o n s t a n t s would p r o v i d e a n o t h e r c o r r e l a t i o n w i t h o t h e r mol-e c u l e s t o complement the bond l e n g t h d a t a and bond o r d e r c a l c u l a t i o n s . 2. I.R. AND RAMAN SPECTRA (a) Background: In t a b l e 2-1 a r e found t h e i n f r a r e d a b s o r p t i o n f r e -(1 8) q u e n c i e s o b s e r v e d by S p r a t l e y f o r O^F^ ' s o ' a t e d ' n a n a r 9 o n m a t r i x . The ®2^2 W a S P r ° d u c e d by p h o t o l y s i s o f 0^ and F^ i n the argon m a t r i x . S i m i l a r v a l u e s were o b t a i n e d i n t h i s l a b o r a t o r y from m a t r i c e s p r oduced by a microwave d i s c h a r g e o f 0^/F^/kr m i x t u r e s f o l l o w e d by f r e e z i n g a t 4°K (See s e c t i o n l l - C - 1 ) . S p r a t l e y ' s a s s i g n m e n t s a r e g i v e n but no normal c o o r d i n a t e a n a l y s i s was a t t e m p t e d by him w i t h such a s h o r t a g e o f d a t a . A l s o shown i n t a b l e 2-1, a s s i g n e d t o the t o r s i o n , i s the (12) low f r e q u e n c y t r a n s i t i o n e s t i m a t e d by J a c k s o n from microwave d a t a . A n o t h e r a b s o r p t i o n e s t i m a t e d by J a c k s o n a t 250 ± 20 cm 1 was not found i n the i . r . and was c o n s i d e r e d s p u r i o u s by S p r a t l e y . More r e c e n t l y Loos e t a l ^ " * ' ^ have o b t a i n e d the s o l i d phase i . r . s p e c t r a o f ^2^2 a t 77°K« T a b l e 2-2 shows t h e i r v a l u e s and - 63 -(18) T a b l e 2 -1 . M a t r i x i . r . a b s o r p t i o n s o f 0 ^ from S p r a t l e y \ , 6 o l 8 o t e n t a t i ve ass i gnment 624.2 614.5 596.6 OF s t r . 612.0 596.6 586.4 OF s t r . 461.9 455-7 449.1 OOF bend 368.1 ? 360.5 OOF bend "160 ± 10 t o r s i o n " E s t i m a t e d by J a c k s o n from microwave s p e c t r u m . - 64 T a b l e 2-2. S o l i d O^F^ '* r' a b s o r P t i o n s from Loos e t a l ^ ' " ^ 0^ 0^  a s s i g n m e n t 1306 1239 00 s t r . 621 595 OF sym. s t r . 615 586 OF asym. s t r . 457 444 OOF asym. bend 369 362 OOF sym. bend 205 t o r s i o n - 65 -a s s i g n m e n t s . A g a i n , as i n S p r a t l e y ' s work the a s s i g n m e n t s appear t o be l a r g e l y i n t u i t i v e . However, the a s s i g n m e n t o f symmetry shown i n t a b l e 2-2 and used i n Loos e t a l ' s ^ * ^ normal c o o r d i n a t e a n a l y s i s has been proven t o be i n c o r r e c t by G a r d i n e r e t a l i n t h e i r Raman s p e c t r a o f O^F^ both i n t h e s o l i d and i n CCIF^ s o l u t i o n . They found the band o f 630 cm ' t o be a n t i - s y m m e t r i c w h i l e the one a t 6l4 cm ' t o be s y m m e t r i c . Then, f o l l o w i n g S p r a t l e y , G a r d i n e r e t a l chose t o c a l l t h e s e the OF s t r e t c h i n g modes w h i l e c a l l i n g t he a b s o r p t i o n a t 468 cm ' the a n t i - s y m m e t r i c bend and the a b s o r p t i o n a t 377 cm ' the sym m e t r i c bend. They a l s o o b s e r v e d an a b s o r p t i o n a t 195 cm ' i n the Raman s p e c t r u m o f 02^2 ' n ^ C I F ^ w h i c h they a s s i g n e d t o the t o r s i o n as compared t o Loos e t a l ' s s o l i d v a l u e o f 205 cm ' f o r the t o r s i o n . C o n s i d e r i n g t h e i n t e r e s t i n t h e 0-0 bond, the 0-0 s t r e t c h -i n g mode s h o u l d be o f p r i m a r y i n t e r e s t . Loos e t a l ' s v a l u e s f o r the s o l i d a r e g i v e n i n t a b l e 2-2 w h i l e peaks a t about 40 cm ' above t h e s e were a s s i g n e d by them t o t h e c o m b i n a t i o n o f v w i t h a l a t t i c e mode. 3 ' oo S i m i l a r l y G a r d i n e r e t a l found an a b s o r p t i o n i n the Raman s p e c t r u m o f s o l i d a t 1^ 70 cm ' w h i c h they a s s i g n e d t o VQQ as w e l l as peaks a t 1305 cm ^ and 1339 cm t h e l a t t e r a s s i g n e d t o V q o+ l a t t i c e . However, t h e i r i . r . m a t r i x s p e c t r a o f O^F^ ' n argon showed s e v e r a l peaks i n t h e 1200-1300 cm ' r e g i o n . C o n s i d e r i n g t h e c o n c e n t r a t i o n dependence o f t h e s e peaks G a r d i n e r e t a l chose t o a s s i g n them t o the 0-0 s t r e t c h as f o l l o w s : 1290 cm t r i m e r and p o l y m e r ; 1274 cm di m e r ; 1257 cm \ monomer. I f t h i s a s s i g n m e n t i s c o r r e c t , then t h e - 66 -1257 cm a b s o r p t i o n would be the one t o use i n f o r c e c o n s t a n t c a l -c u l a t i o n s s i n c e i t would most c l o s e l y a p p r o x i m a t e the gas phase f r e q u e n c y . (A weak a b s o r p t i o n a t 1260 cm 1 found i n t h i s l a b o r a t o r y f o l l o w i n g a d i s c h a r g e o f C-2:F2:Ar = 1:2:200 c o u l d p o s s i b l y be t h i s same peak. However, s i n c e i t can a l s o be a s s i g n e d t o ^0, i t c a n n o t be used w i t h much c o n f i d e n c e . F i g u r e 2-7 shows the s p e c t r u m c o n t a i n -i n g t h i s a b s o r p t i o n . ) (b) R e s u l t s : P r i o r t o the p u b l i c a t i o n o f the above r e s u l t s , work i n t h i s l a b was c a r r i e d o u t t o s t u d y t h e p r o d u c t s o f o x y g e n - f l u o r i n e d i s c h a r g e s by t r a p p i n g t h e s e p r o d u c t s on c o l d C s l windows i m m e d i a t e l y f o l l o w i n g the d i s c h a r g e . The c o n d e n s a t e was then s t u d i e d u s i n g i . r . s p e c t r o s c o p y . 2^^ 2 W 3 S ° n e °^ ^ & P r o c ' u c t s r e a d i l y i d e n t i f i e d f r o m i t s known i . r . s p e c t r u m . T a b l e 2-3 l i s t s t h e a b s o r p t i o n s t h a t were found i n t h e s e e x p e r i m e n t s t h a t c o u l d be a s s i g n e d t o f u n d a m e n t a l s , o v e r t o n e s and c o m b i n a t i o n s o f t h e ®2^2 m o ' e c u ' e ' n a n e a r s o l i d t y p e e n v i r o n m e n t . These e x p e r i m e n t s a r e f u r t h e r d i s c u s s e d i n s e c t i o n C-2-b o f t h i s c h a p t e r and f i g u r e 2-11 found i n t h a t s e c t i o n g i v e s the s p e c t r u m from w h i c h t h e v a l u e s i n t a b l e 2-3 a r e t a k e n . U n f o r t u n a t e l y due t o the c o m p l e x i t y o f the s p e c t r u m r e s u l t -i n g from t h e numerous oxygen f l u o r i n e compounds and s e v e r a l i m p u r i t i e s , the r e g i o n o f t h e 0-0 s t r e t c h o f O2F2 was not r e a d i l y i n t e r p r e t e d . A broad a b s o r p t i o n t h a t a p p ears r e g u l a r l y w i t h maximum a t 1305 cm ' does not show i n t e n s i t y c o r r e l a t i o n s w i t h the known peaks o f ^2^2' b u t r a t h e r w i t h s e v e r a l i m p u r i t y bands w h i c h a r e most p r o b a b l y a t t r i b u t a b l e - 67 -T a b l e 2-3. I.R. a b s o r p t i o n s o f O^F^ i n the c o n d e n s a t e from 0 / F 0 d i s c h a r g e s v(cm ^) ass ignment comment (1905) V l + V 2 ' V l + V 5 1760 V v 6 1665 v l + v 3 (1510) v l + v 4 13^0 v.+ l a t t i c e 1305 v, (00) 1220 2 v2' v2 + v5' 2 v 1070 v 5 + v 6 , v 2 + v 6 985 V5+V3 975 V2 + V 3 727 2 V3 655 V v 4 620 v,- (OF, asym) 611 v 2 (OF, sym) 568 V4 + V 3 458 (OOF, asym) 370 (OOF, sym) 400 2v4 [205] ( t o r s i o n ) o b s c u r e d by F 2C0 o b s c u r e d by O^F^ f o l l o w i n g Loos e t a l from Loos e t a l (15) - 68 t o n i t r y l f l u o r i d e , NO^F. G a r d i n e r e t a]^^ a l s o s u g g e s t i n t h e i r work t h a t the 1305 cm 1 a b s o r p t i o n i n the m a t r i x i s due t o NO^F. However, t h e s p e c t r a p u b l i s h e d by Loos e t a l ^ ' " ^ do not show a b s o r p -t i o n s a t 1800 cm \ 800 cm ' and 540 cm o t h e r s t r o n g a b s o r p t i o n s i n t he NO^F s p e c t r u m . As a r e s u l t , they a s s i g n e d t h e i r 1305 cm ' peak t o the 0-0 s t r e t c h o f 0^. I t was f o u n d , however, t h a t i n t h i s work the s t r o n g 1305 cm 1 peak p o s s e s s e d two s h o u l d e r s t o low f r e q u e n c y as seen i n f i g u r e 2-1. S i n c e o t h e r a b s o r p t i o n s i n the s p e c t r u m a r e q u i t e s y m m e t r i c , t h e s e s h o u l d e r s must r e s u l t from a m o l e c u l e o t h e r than NO^F. Of t h e s e two pe a k s , 1290 cm 1 and 1270 cm ', i t i s t e m p t i n g t o a s s i g n the f o r m e r t o s u p p o r t G a r d i n e r e t a l ' s v a l u e o f 1290 cm 1 f o r the m a t r i x a b s o r p t i o n o f 0 2F 2 t r ' m e r a r ) d polymer w h i l e a s s i g n i n g t h e l a t t e r t o t h e + v 2 (815 + 460 = 1275 cm mode o f 0 F 2 -F u r t h e r e v i d e n c e c o n c e r n i n g t h i s a s s i g n m e n t , however, i s o b t a i n e d by s t u d y i n g t h e weak a b s o r p t i o n s a t 1760 cm 1 and 1665 cm ' i n f i g u r e 2-11. When t h e s e a r e a s s i g n e d t o the + (1290 + 458 = 1748 cm" 1) and V j + (1290 + 370 = 1660 cm ') c o m b i n a t i o n s o f °2F2' i t can be seen t h a t 1290 cm ' g i v e s v a l u e s o f c o m b i n a t i o n s t h a t a r e too low. I t i s then n e c e s s a r y t h a t t h e 0-0 s t r e t c h i n g f r e q u e n c y i n the s o l i d be t h e 1305 cm 1 peak as r e p o r t e d by Loos e t a l ^ 1 ^ , but t h a t the p r e s e n c e o f the N0 2F a b s o r p t i o n i n the same r e g i o n p r e v e n t s a more a c c u r a t e d i r e c t d e t e r m i n a t i o n . The a b s o r p t i o n a t 1305 cm 1 has as a r e s u l t been a s s i g n e d t o both m o l e c u l e s . - 69 -v ( cm - 1 ) 1400 1300 1200 J 1 L 0.1 O c o n \_ o (0 n < 0.5-O: F = 3 : 2 2 2 F i g u r e 2-1. The o v e r l a p p i n g a b s o r p t i o n s o f FNO^(symmetric NO s t r e t c h ) and 0 2 F 2 (00 s t r e t c h ) a t 1305 cm"'. - 70 -The d i s c h a r g e s t u d i e s g i v e f u r t h e r e v i d e n c e r e g a r d i n g the t o r s i o n a l mode, v^, as w e l l . A l t h o u g h n o t h i n g c o u l d be seen a t 205 cm w h i c h i s a t t h e l i m i t o f the s p e c t r a l r e g i o n o f t h e s p e c t r o -m e t e r , a b s o r p t i o n s a t 655 cm \ 568 cm ' and 400 cm ' ( f i g u r e 2-11) have been a s s i g n e d t o v ^ v ^ (458 + 205 = 663 cm~'), v^+v (205 + 370 = 575 cm ') and 2v^ (2 x 20.5 = 410 cm ') . These a r e c o n s i s t e n t w i t h the v a l u e o f 205 cm ' r e p o r t e d by Loos e t a l ^ " ^ f o r t h e t o r s i o n a l mode o f ^2^2 ' n t' 1 6 s°l'd- Thus , w i t h a change i n a s s i g n m e n t o f and Vj., t h i s work c o n f i r m s the s o l i d phase s p e c t r u m o b t a i n e d by Loos e t a l f o r O^F^. The s p e c t r a i n b o t h the s o l i d and m a t r i x a r e now known w i t h some c o n f i d e n c e and i n t u i t i v e a s s i g n m e n t s have been made. How-e v e r , a f o r c e f i e l d must be c a l c u l a t e d t o c o n f i r m t h e a s s i g n m e n t and t o l e a r n more about t h e m o l e c u l e and i t s v i b r a t i o n s . The n e x t s e c t i o n o u t l i n e s t h e c a l c u l a t i o n o f a f o r c e f i e l d f o r ^2^2' 3. NORMAL COORDINATE ANALYSIS (a) P r e v i o u s Work: F o l l o w i n g t h e i r d e t e r m i n a t i o n o f t h e c o m p l e t e 16 18 s p e c t r u m o f s o l i d ^2^2 a n c * P a r t ' a ' s p e c t r u m o f s o l i d ^2^2' *- o o s e t a l ^ ^ a t t e m p t e d t h e f i r s t f o r c e f i e l d c a l c u l a t i o n on d i o x y g e n d i f l u o r i d e . T a b l e 2-h g i v e s the f o r c e c o n s t a n t s t h a t they c a l c u l a -(21) t e d . However, o u r a t t e m p t s , and t h o s e o f o t h e r s , t o d u p l i c a t e t h e s e c a l c u l a t i o n s have been u n s u c c e s s f u l . F o r t h i s r e a s o n , and o t h e r s , i t i s f e l t t h a t t h e i r a p p r o x i m a t e f o r c e f i e l d i s h i g h l y - 71 -T a b l e 2-4. F o r c e f i e l d found by Loos e t a l ^ 5 ^ f o r 0 ^ c o n s t a n t mdyne/A k r 1.50 ± 0.07 k D 10.25 ± 0.11 K k 1.19 ± 0.02 a k 0.472 ± 0.022 x k_ 1.27 ± 0.06 Rr k D 1-71 ± 0.06 Ra k 0.141 ± 0.015 r a - 72 -q u e s t i o n a b l e . F i r s t , d i s c r e p a n c i e s o c c u r i n u n i t s . Loos e t a l l i s t o t h e i r f o r c e c o n s t a n t s , s t a t i n g them t o be i n u n i t s o f mdynes/A. At the same time they s t a t e t h a t the f o r c e c o n s t a n t s o f S p r a t l e y e t a l ^ o f o r t h e r a d i c a l a r e a ' s o ' n mdynes/A. However, t h i s i s not t r u e , f o r S p r a t l e y ' s bend f o r c e c o n s t a n t s a r e l i s t e d i n t h e i r n a t u r a l u n i t s 2 o f e r g s / r a d . T h i s r a i s e s the q u e s t i o n as t o whether Loos e t a l have made th e same e r r o r r e g a r d i n g u n i t s i n t h e i r own f o r c e c o n s t a n t s . T h i s would i n t r o d u c e a f a c t o r o f ( r R ) 1 / 2 (where r i s the OF bond l e n g t h and R i s the 0-0 bond l e n g t h ) f o r the b e n d - s t r e t c h i n t e r a c t i o n con-s t a n t s and rR f o r the b e n d i n g c o n s t a n t s . At t h e same t i m e , i t cannot be c e r t a i n what f a c t o r was used by Loos e t a l t o a d j u s t the u n i t s o f the t o r s i o n a l f o r c e c o n s t a n t s . The n e x t p r o b l e m w i t h t h e s e f o r c e c o n s t a n t s i s w h e t h e r they a r e i n f a c t i n t e r n a l c o o r d i n a t e f o r c e c o n s t a n t s o r f o r c e c o n s t a n t s f o r t h e o b v i o u s symmetry c o o r d i n a t e s . [ I t s h o u l d be m entioned h e r e t h a t the symmetry c o o r d i n a t e s used by Loos e t a l a r e o f the form Sj = r ] + r 2 r a t h e r than the n o r m a l i z e d f o r m Sj = ( r ^ + r ^ ) . ] A t one p o i n t they s t a t e , " T h i s f o r c e f i e l d , c o n s i s t i n g o f seven f o r c e con-s t a n t s e x p r e s s e d i n terms o f i n t e r n a l c o o r d i n a t e s " . However, below t h e i r t a b l e o f c o n s t a n t s they s t a t e , "k , k„, k and k a r e the ' r R a T d i a g o n a l f o r c e c o n s t a n t s c o r r e s p o n d i n g t o the symmetry c o o r d i n a t e s d e f i n e d i n t a b l e I I I , k,, , k and k a r e o f f - d i a q o n a l f o r c e cons-Rr r a r a a t a n t s i n the F m a t r i x w h i c h r e p r e s e n t i n t e r a c t i o n s o f the symmetry c o o r d i n a t e s i n d i c a t e d " . The c o o r d i n a t e s R, r , a and T a r e t h o s e - 73 -d e f i n e d i n f i g u r e 2-2. The problems t h a t t h i s u n c e r t a i n t y l e a d s t o a r e : s h o u l d the i n t e r a c t i o n c o n s t a n t s k_ and k n be d i v i d e d by 2 Rr Ra t o t r a n s f o r m them t o i n t e r n a l c o o r d i n a t e s o r a r e they a l r e a d y i n i n t e r n a l c o o r d i n a t e s ; t h e r e s h o u l d be two k 's f ° r symmetry c o o r -d i n a t e s o r f o r i n t e r n a l c o o r d i n a t e s but o n l y one i s l i s t e d w i t h no i n d i c a t i o n o f w h i c h ; and o f c o u r s e i n symmetry c o o r d i n a t e s b o t h k r and k^ would have two v a l u e s , one f o r the s y m m e t r i c and one f o r the a s y m m e t r i c c o o r d i n a t e , u n l e s s t h e a p p r o x i a m t i o n i s made t h a t k and k a r e z e r o . These problems a r e not answered i n the body o f t h e aa p a p e r . The n e x t p r o b l e m l i e s i n Loos e t a l ' s i n t e r p r e t a t i o n o f t h e i r c a l c u l a t i o n s . They found t h a t the c a l c u l a t i o n c o u l d c o n v e r g e t o two s e t s o f f o r c e c o n s t a n t s , t h e s e t l i s t e d i n t a b l e 2-k and a o s e t i n w h i c h " k D - 7-0 mdynes/A". They chose the f i r s t s e t on t h e f e e l i n g t h a t the s i m i l a r i t y o f the 0-0 bond t o 0^  r e q u i r e d a h i g h f o r c e c o n s t a n t and t h a t the low o b s e r v e d f r e q u e n c y i s a r e s u l t o f the l a r g e k^ r and k i n t e r a c t i o n c o n s t a n t s . They i n f a c t imposed l a r g e i n t e r a c t i o n c o n s t a n t s on ^2^2 w ' t n o u t a n v p r e c e d e n t f o r such h i g h v a l u e s . The o t h e r weakness i n i n t e r p r e t a t i o n i n v o l v e s t h e l a r g e m i x i n g o f the bends, OF s t r e t c h e s and t h e t o r s i o n i n the c a l -c u l a t e d normal c o o r d i n a t e s but o n l y s m a l l m i x i n g o f the 0-0 s t r e t c h . T h i s would s u g g e s t t h e i m p o r t a n c e o f t h e k and k and the l a c k o f i m p o r t a n c e o f k ^ and k ^ . From e x p e r i e n c e g a i n e d i n t h e s e and o t h e r c a l c u l a t i o n s i t i s f e l t t h a t the m i x i n g s h o u l d cause k^ r and - Ik -k„ t o be i n d e t e r m i n a t e from the a v a i l a b l e d a t a and c r e a t e the need Ra f o r k and k i n the l e a s t s q u a r e s f i t t i n g . But Loos e t a l c a l c u -O T rx ^ 3 l a t e d k ^ and k^ r where l i t t l e m i x i n g o c c u r s and i g n o r e any i n t e r a c -t i o n o f the OOF bends and OF s t r e t c h e s w i t h t h e t o r s i o n even though t h e r e i s c o n s i d e r a b l e m i x i n g o f t h e s e i n t e r n a l c o o r d i n a t e s i n the e i g e n v e c t o r s . T h e i r p r o c e d u r e i s not c o n s i s t e n t w i t h o u r e x p e r i e n c e . B e s i d e s t h e s e i n c o n s i s t e n c i e s , Loos e t a l made t h e i r c a l -c u l a t i o n s u s i n g i n a c c u r a t e d a t a . T h e i r use o f s o l i d f r e q u e n c i e s s h o u l d l e a d t o d i f f e r e n c e s i n f o r c e c o n s t a n t s from t h e gas phase m o l e c u l a r c o n s t a n t s . Thus the m a t r i x v a l u e s o f G a r d i n e r e t a\^^ s h o u l d be used. T h i s e r r o r w o u l d be s m a l l f o r a l l f r e q u e n c i e s ex-c e p t t h e 0-0 s t r e t c h where a l a r g e d i f f e r e n c e i s o b s e r v e d between m a t r i x and s o l i d f r e q u e n c i e s . The o t h e r e r r o r i n the d a t a i s the i n c o r r e c t symmetry a s s i g n m e n t o f t h e 621 cm 1 and 615 cm 1 a b s o r p -t i o n as m entioned above. T h i s , however, would p r o b a b l y l e a d t o o n l y s m a l l e r r o r s i n t h e c a l c u l a t e d c o n s t a n t s s i n c e the peaks a r e 1 8 b o t h c l o s e t o g e t h e r and show s i m i l a r s h i f t s on 0 s u b s t i t u t i o n . (b) P r e s e n t C a l c u l a t i o n s : Many a t t e m p t s have been made by us t o a c h i e v e a more m e a n i n g f u l f o r c e f i e l d f o r ^>2^2 t n a n t n a t s u p p l i e d by Loos e t a l ^ " ^ . The i n i t i a l a t t e m p t s were made w i t h o u t the use o f symmetry c o o r d i n a t e s so t h a t t h e unsymmetrica11y s u b s t i t u t e d 16 18 0 0 d a t a o f S p r a t l e y c o u l d be used. The e x t r a d a t a , however, d i d not l e a d t o b e t t e r r e s u l t s . In f a c t , the p r o b l e m e n c o u n t e r e d by Loos e t a l o f c o n v e r g e n c e t o s e v e r a l s e t s o f f o r c e c o n s t a n t s - 75 -c o u l d not be s o l v e d and i t was not f e l t j u s t i f i e d t o choose one o r a n o t h e r as they had done. The p r o b l e m seems t o be t h a t the a v a i l a b l e v i b r a t i o n a l d a t a i s not s u f f i c i e n t t o f i x a f o r c e f i e l d i n a m o l e c u l e where such mixed normal c o o r d i n a t e s a r e p r e s e n t . To c a l c u l a t e a f o r c e f i e l d t h e n , the use o f f u r t h e r a p p r o x i m a t i o n s appeared n e c e s s a r y . To more c a r e f u l l y f o l l o w t h e c a l c u l a t i o n and see w h i c h a p p r o x i m a t i o n s were n e c e s s a r y t h e p r o b l e m was f o r m u l a t e d i n symmetry c o o r d i n a t e s i n the f o l l o w i n g way. The i n t e r n a l c o o r d i n a t e s ( R ) a r e d e f i n e d i n f i g u r e 2-2 and the symmetry c o o r d i n a t e s (S) a r e o u t l i n e d i n t a b l e 2-5. They a r e r e l a t e d by the t r a n s f o r m a t i o n S = U R (2-1) where U i s a u n i t a r y m a t r i x . The s y m m e t r i z e d F and G m a t r i c e s f o r (22) ^2^2 C a n k £ c a ' c u l a t e ^ from the r e l a t i o n s h i p s and ^ = U ' F U (j = U ' G U (2-2) (2-3) Thus, F = f R f R r sym. f f f Rr Ra Ra RT f f ' f r r r a r a r x f * f f r r a r a rx f f f a aa ax f f a ax f X - 76 -F i g u r e 2-2. I n t e r n a l c o o r d i n a t e s f o r 0 oF T a b l e 2-5. I n t e r n a l and symmetry c o o r d i n a t e d e f i n i t i o n s f o r 0 2F 2 I n t e r n a l , Symmetry, R 00 bond S l = R sym. r l OF bond S2 _ J_ ~SZ (r,+r 2 ) sym. r2 S5 _ \_ ( r , - r 2 ) asym. °1 OOF a n g l e S3 1 (a,+a2) sym. °2 S6 1 = ^ (aj-a 2) asym. T d i h e d r a l a n g l e = T sym. - 77 -and 3-12 22 sym. 13 23 "33 \k 2k :3k kk '55 sym '56 r66 From the t r a n s f o r m a t i o n i t i s found t h a t F M = f R F . 2 = ^ f R r F . 3 = / ? f R a F , 4 = f R x F 2 2 = f r + f r r F 2 3 = f r a + f r a ^ f r X F 3 3 = f a + f a a F 3 4 = ^ f a x F ^ = f x f o r the s y m m e t r i c b l o c k and F = f - f 55 r r r 56 r a r a fab a aa f o r the a s y m m e t r i c b l o c k . The same e q u a l i t i e s h o l d between the and m a t r i x e l e m e n t s . - 78 -A f t e r s y m m e t r i z a t i o n one can see t h a t the a s y m m e t r i c modes p r o v i d e a two by two p r o b l e m w i t h o n l y t h r e e f o r c e c o n s t a n t s - F^^» Fj.£ and Fg^- There a r e two as y m m e t r i c modes whose a s s i g n m e n t has been made u s i n g Raman s p e c t r o s c o p y . For '^0 and ^0 t h e r e a r e then f o u r o b s e r v e d f r e q u e n c i e s but s i n c e t h e s e a r e r e l a t e d by t h e p r o d u c t r u l e , o n l y t h r e e a r e i n d e p e n d e n t . However, t h i s i s s u f f i -c i e n t d a t a t o c a l c u l a t e t h r e e f o r c e c o n s t a n t s . The f o u r f r e q u e n c i e s i n t he s o l i d ^ - * ^ were then f i t t e d w i t h the t h r e e c o n s t a n t s u s i n g t h e l e a s t s q u a r e s program d e s c r i b e d e a r l i e r . The f o r c e c o n s t a n t s so o b t a i n e d and t h e c a l c u l a t e d f r e q u e n c i e s and p o t e n t i a l e n e r g y d i s t r i -b u t i o n (and thus a s s i g n m e n t ) a r e g i v e n i n t a b l e 2-6. However, b e f o r e p r o c e e d i n g t o the s y m m e t r i c p a r t o f t h e p r o b l e m i n w h i c h e i g h t f o r c e c o n s t a n t s must be d e t e r m i n e d f r o m seven f r e q u e n c i e s , some a p p r o x i m a t i o n s must be made. C o n s i d e r i n g t h e mole-c u l e , i t might be e x p e c t e d t h a t r^ and ct^ would not i n t e r a c t s t r o n g l y w i t h e i t h e r r ^ o r a^. U s i n g t h i s , t he t h r e e i n t e r a c t i o n c o n s t a n t s , f , f and f ' , can be s e t e q u a l t o z e r o . In symmetry c o o r d i n a t e s r r act r a t h i s means t h a t F„„=Fr. =f , F =F, ,=f and F 0_=F r.,=f . In the f i t t i n g 22 55 r 33 66 a 23 56 r a o f t h e symm e t r i c f r e q u n c i e s , t h e s e f o r c e c o n s t a n t s c o u l d then be h e l d f i x e d t o the v a l u e s d e t e r m i n e d i n t h e a s y m m e t r i c c a l c u l a t i o n . A t t e m p t s t o f i t t h e s y m m e t r i c s o l i d phase f r e q u e n c i e s ^ ^ w i t h o n l y the d i a g o n a l e l e m e n t s F^ and F ^ h o l d i n g ^22' 3^3 anc* F23 f i x e d r e s u l t e d i n c o n v e r g e n c e but a poor f i t o f the low f r e q u e n c y modes. As a r e s u l t , t he b e n d - t o r s i o n i n t e r a c t i o n c o n s t a n t was - 79 -T a b l e 2-6. A s y m m e t r i c modes: symmetry c o o r d i n a t e f o r c e c o n s t a n t s , s o l i d ^2^2 f r e q u e n c i e s and p o t e n t i a l e n e r g y d i s t r i b u t i o n F c c = 1.62 ± 0.09 a J / A 2 F 6 6 = 1-12 ± 0.06 a J / r a d 2 O F, c = 0.122 ± 0.011 aJ/A rad f r e q u e n c y PED obs. ca 1 . F55 F66 ass ignment , 6 0 F °2 F2 621 621 .5 0.60 0.50 OF s t r . 457 457.6 0.41 0.51 OOF bend , 8 0 F 2 2 595 594.5 0.64 0.46 444 443.3 0.37 0.55 Average f r e q u e n c y e r r o r : 0.6 cm (0.11%) - 80 -a l l o w e d t o e n t e r the c a l c u l a t i o n and a f a i r l y good f i t o f f r e q u e n c i e s was o b t a i n e d . A t t e m p t s t o i n t r o d u c e F ^ . a 0-0 s t r e t c h - OF s t r e t c h i n t e r a c t i o n , were u n s u c c e s s f u l w i t h the p e r t u r b a t i o n d i v e r g i n g and r e s u l t i n g l a r g e e r r o r s i n F j ^ . S i n c e t h e f i t w i t h o u t t h i s i n t e r a c -t i o n was f a i r l y good, i t was d e c i d e d t h a t t h i s c o n s t a n t i s i n d e t e r -m i n a t e and s m a l l and t h a t i t s a p p r o x i m a t i o n t o z e r o i s j u s t i f i e d . The r e s u l t s f o r the s y m m e t r i c modes o f s o l i d Q^^z a r e 9 ' v e n ' n t a b ' e 2-1. From the v a l u e s o f t h e f o r c e c o n s t a n t s i n symmetry c o o r d i n a t e s i n t a b l e 2-6 and t a b l e 2-7 and u s i n g the a p p r o x i m a t i o n s made above, v a l u e s o f t h e f o r c e c o n s t a n t s i n i n t e r n a l c o o r d i n a t e s a r e g i v e n i n t a b l e 2-8 f o r t h e s o l i d 02^2 ^ r e c l u e n c ' e s • The s o l i d f r e q u e n c i e s o f Loos e t a l ^ " ^ were used because they c o n s t i t u t e the most c o m p l e t e s e t o f d a t a . The f o r c e f i e l d i n t a b l e 2-8 was then e n t e r e d i n t o t h e (18) unsymmetrized p r o b l e m u s i n g the more a c c u r a t e m a t r i x d a t a o f S p r a t l e y and G a r d i n e r e t a l . The v a l u e f o r v was t a k e n a t 1257 cm ' f o r oo ^ U 2 F 2 and u s i n g the s h i f t o b s e r v e d i n t h e s o l i d , t h e v a l u e o f 1193 cm ' 18 was e s t i m a t e d f o r ®2^2' ^ e v a ^ u e u s e d f o r t h e t o r s i o n was the 205 cm ' o b s e r v e d i n t h e s o l i d . The mixed f r e q u e n c i e s were i n c l u d e d as e x t r a d a t a . The a t t e m p t a t r e f i n e m e n t f a i l e d , however, when th e c a l -c u l a t i o n d i v e r g e d . O n l y by h o l d i n g f f i x e d c o u l d the c a l c u l a t i o n be c o m p l e t e d . Because o f t h i s , i t i s f e l t c e r t a i n t h a t the d i f f i c u l t y i n the p r o b l e m i s i n s u f f i c i e n t d a t a t o c a l c u l a t e the t h r e e f o r c e con-s t a n t s f , f and f even though t h e number o f o b s e r v e d f r e q u e n c i e s r ' a r a - 81 -T a b l e 2-7. Symmetric modes: symmetry f o r c e c o n s t a n t s , s o l i d f r e q u e n c i e s and p o t e n t i a l e nergy d i s t r i b u t i on F ] j = 7-74 ± 0.07 a J / A 2 F ^ = 0.23 ± 0.02 a J / r a d 2 F^h = 0.10 ± 0.02 a J / r a d 2 H e l d f i x e d : F^ = 1.62 a J / A 2 , F ^ =1.12 a J / r a d 2 , F 2 3 = 0.122 aJ/A rad 'V2 f r e q u e n c y PED obs. c a l . F ^ F^ 2 i 7 ^ / , a s s i g n m e n t 1306 1309.8 0.95 0.01 0.03 0.00 00 s t r . 615 604.0 0.00 0.69 0.42 0.03 OF s t r . 369 373-9 0.04 0.29 0.55 0.17 00F bend 205 203.3 0.01 0.01 0.05 0.85 t o r s i o n 1239 1234.0 0.95 0.01 0.03 0.00 586 579-1 0.00 0.72 0.39 0.03 362 366.5 0.04 0.27 0.57 0.18 186.3 0.01 0.01 0.06 0.83 Average f r e q u e n c y e r r o r : 5.3 cm ' (1.00%) - 82 -T a b l e 2 -8 . F o r c e c o n s t a n t s f rom the i . r . f r e q u e n c i e s o f s o l id 0„F o Cons t a n t symmetry i n te rna I c o n v e n i e n t i F l l f R 7-74 F 2 2 ' F 5 5 f r 1.62 F 3 3 ' F 6 6 f a 1 . 12 f T 0.23 F23' F 5 6 f r a 0. 122 f ax 0.071 F 1 3 f R a 0 F12 f R r 0 - 83 -i s i n e x c e s s . For t h i s t o be s o , the l e a s t s q u a r e s normal e q u a t i o n s must be i l l - c o n d i t i o n e d - i . e . t h e e q u a t i o n s a r e v e r y n e a r l y not i n -dependent so t h a t s o l v i n g them f o r the unknown A $ (see c h a p t e r l ) i s v e r y i n a c c u r a t e . Or i n o t h e r w o r d s , t h e m a t r i x J Z ' A A J Z i s v e r y n e a r l y s i n g u l a r so t h a t e r r o r s r e s u l t i n t a k i n g i t s i n v e r s e . Removing a v a r i a b l e f r o m t h e normal e q u a t i o n by f i x i n g f e l i m i n a t e s the i l l - c o n d i t i o n i n g and t h e c a l c u l a t i o n c o n v e r g e s . The i l l - c o n d i t i o n i n g can be f u r t h e r seen by a g a i n c o n s i d e r -i n g the c a l c u l a t i o n u s i n g t h e a s y m m e t r i c symmetry b l o c k . A l t h o u g h the c a l c u l a t i o n i s c o m p l e t e l y d e t e r m i n e d and c o n v e r g e s t o m e a n i n g f u l f o r c e c o n s t a n t s , a l o o k a t the l e a s t s q u a r e s m a t r i x i n d i c a t e s n e a r s i n g u l a r i t y . T h i s i s done by comparing the d e t e r m i n a n t o f t h i s m a t r i x (23) t o t h e p r o d u c t o f i t s d i a g o n a l e l e m e n t s . A l d o u s and M i l l s have -3 found t h a t i f t h e r a t i o i s i n the o r d e r o f 10 o r l e s s , t h e n s i n g u -l a r i t y problems can o c c u r and c a u t i o n s h o u l d be used i n t h e c a l c u l a -_3 t i o n . In t h i s c a l c u l a t i o n IAI/IIA.. = k x 10 and i s v e r y near the j 11 danger l i m i t . In the s y m m e t r i c c a l c u l a t i o n , because ^2' 3^3 a n { ^ F22 a r e h e l d f i x e d , t h i s p r o b l e m does not o c c u r . However, f u r t h e r r e f i n e m e n t o f the c o m p l e t e m o d i f i e d f o r c e f i e l d l e a d s t o d i v e r g e n c e u n l e s s a f u r t h e r m o d i f i c a t i o n i s made by h o l d i n g f f i x e d . The ' 3 r a answer t o the p r o b l e m p r o b a b l y l i e s i n the o b t a i n i n g o f more d a t a . However, f o r ^2^2 c e n t r ' ^ u 9 a ^ d i s t o r t i o n c o n s t a n t s , C o r i o l i s coup-l i n g c o n s t a n t s and f l u o r i n e i s o t o p i c d a t a a r e not a v a i l a b l e . The f o r c e f i e l d r e f i n e d t o f i t the m a t r i x d a t a h o l d i n g - 84 -f f i x e d i s g i v e n i n t a b l e 2-9 a l o n g w i t h o b s e r v e d and c a l c u l a t e d f r e q u e n c i e s and p o t e n t i a l e nergy d i s t r i b u t i o n . I t i s f e l t t h a t t h i s i s the b e s t f o r c e f i e l d a v a i l a b l e f o r C^F^ a r | d p r o b a b l y t h e b e s t t h a t can be c a l c u l a t e d from a v a i l a b l e d a t a . F o r c e c o n s t a n t s f o r (18 2k) •O^F ' a r e l i s t e d i n t a b l e 2-10 f o r t h e purpose o f c o m p a r i s o n . (c) D i s c u s s i o n : The p o t e n t i a l energy d i s t r i b u t i o n i n t a b l e 2-9 shows t h a t t h e 1257 cm 1 a b s o r p t i o n i s n e a r l y a pure 0-0 s t r e t c h . T h i s l a c k o f m i x i n g i s e x p e c t e d s i n c e t h e f r e q u e n c y o f t h i s mode i s o v e r 600 cm ' l a r g e r than the n e x t h i g h e s t f r e q u e n c y . The c a l -°2 c u l a t e d f o r c e c o n s t a n t f o r O^F^ o f 7-14 aJ/A i s much lower than the s i m i l a r f o r c e c o n s t a n t s f o r 0^  and ^2^ (11.4 and 10.5 a J / A 2 ^ ^ ) . However, i f t h e f r e q u e n c y o f 1257 cm 1 i s c o r r e c t f o r t h i s mode, then t h i s f o r c e c o n s t a n t i s a l s o c o r r e c t . I t does not appear r e a s -o n a b l e t o r a i s e t h i s f o r c e c o n s t a n t by the use o f u n l i k e l y l a r g e i n t e r a c t i o n c o n s t a n t s as Loos e t a l have done. In f a c t , i t appears t h a t f n i _ and f„ a r e not even d e t e r m i n a b l e from a v a i l a b l e d a t a . Ri- Ra I n s t e a d i t i s f e l t t h a t t h i s low f o r c e c o n s t a n t p r o b a b l y r e f l e c t s t h e d i f f e r e n c e i n s e n s i t i v i t y o f t h e 0-0 f o r c e c o n s t a n t and 0-0 bond l e n g t h t o changes i n b o n d i n g i n the 0-0 bond. F i g u r e s 2~3(a) and 2~3(b), i n w h i c h f o r c e c o n s t a n t and bond l e n g t h a r e p l o t t e d a g a i n s t bond o r d e r f o r s e v e r a l 0-0 bonds, i n d i c a t e t h a t t h i s i s t he c a s e . The f o r c e c o n s t a n t c u r v e r i s e s a l m o s t v e r t i c a l l y i n the r e g i o n o f s t r o n g 0-0 bonds. Hence, i n t h i s r e g i o n f o r c e c o n s t a n t s a r e v e r y s e n s i t i v e t o s m a l l changes i n bond o r d e r . The bond l e n g t h - 85 -T a b l e 2-9. Be s t f o r c e f i e l d f o r O^F^ - m a t r i x f r e q u e n c i e s . C a l c u l a t e d and o b s e r v e d f r e q u e n c i e s and PED. f R = 7-14 ± 0.03 a J / A 2 °2 f = 1.70 ± 0.02 aJ/A r f - 1.11 ± 0.02 a J / r a d 2 a f = 0.266 ± 0.010 a J / r a d 2 T f = 0.104 ± 0.007 a J / r a d 2 ax f = 0.122 aJ/A rad ( h e l d f i x e d ) a r f r e q u e n c y PED obs. c a l . fR f r f a f ass i gnment , 6 0 F u 2 2 1257-0 1260.9 0.95 0.02 0.03 0.0 0-0 s t r . 624.2 628.4 0.0 0.65 0.45 0.0 asym. OF s t r . 612.0 608.2 0.0 0.74 0.38 0.03 sym. OF s t r . 461.9 460.1 0.0 0.36 0.56 0.0 asym. OOF bend 368.1 371-7 0.04 0.23 0.62 0.25 sym. OOF bend 205.0 203-9 0.01 0.02 0.06 0.79 t o r s i o n l 6 O l 8 O F 2 1225.5 0.95 0.02 0.03 0.0 614.5 619.8 0.0 0.68 0.42 0.0 596.6 591 -3 0.0 0.74 0.38 0.03 455-7 452.7 0.0 0.34 0.58 0.0 366.1 0.04 0.22 0.64 0.24 202.6 0.01 0.01 0.05 0.81 1193-0 1188.8 0.95 0.02 0.03 0.0 596.6 601.8 0.0 0.69 0.41 0.0 586.6 584.0 0.0 0.77 0.35 0.03 449.1 445.2 0.0 0.32 0.60 0.0 360.5 360.9 0.04 0.21 0.66 0.24 201.3 0.01 0.01 0.05 0.82 - 86 -T a b l e 2 -10 . F o r c e c o n s t a n t s f o r 0_F c o n s t a n t S p r a t l e y 0 8 ) (24) Nob le and P i m e n t e l f R 10.47 10.50 f r 1.43 1.32 f ct 0.94 1.01 f r a 0 .027 f R r 0 .30 f R a 0.045 * U n i t s o f a J / A 2 f o r s t r e t c h e s , 2 a J / r a d f o r bends and o a J / A rad f o r s t r e t c h - b e n d i n t e r a c t i o n s . - 87 -l . O 1.5 2 . 0 O - O Bond Order F i g u r e 2 ~ 3 ( a ) . F o r c e c o n s t a n t - bond o r d e r c o r r e l a t i o n f o r s e v e r a l 0-0 bonds. - 88 -1.50H 1.40H v_0 1 . 3 0 1.20H 1 . 0 1 .5 2.0 O - O B o n d O r d e r F i g u r e 2 ~ 3 ( b ) . Bond l e n g t h - bond o r d e r c o r r e l a t i o n f o r s e v e r a l 0-0 bonds. - 89 -c u r v e , on the o t h e r hand, shows n e a r l y a l i n e a r r e l a t i o n s h i p w i t h bond o r d e r and i s not as s e n s i t i v e t o b o n d i n g as the f o r c e c o n s t a n t i s i n the r e g i o n o f O^F^ 1s 0-0 bond. The bond o r d e r s o f 1.80 and 1.90, e s t i m a t e d from the f o r c e c o n s t a n t and bond l e n g t h c u r v e s r e s -p e c t i v e l y , a r e not r e a l l y so d i f f e r e n t . As w e l l , t h i s l a c k o f l i n e a r dependence o f f o r c e c o n s t a n t on b o n d i n g f u r t h e r r e f l e c t s on t h e d i f f -i c u l t y i n t r a n s f e r r i n g v a l e n c e f o r c e c o n s t a n t s w i t h i n a m o l e c u l a r s e r i e s . The o t h e r i m p o r t a n t p o i n t i s the c l e a r a s s i g n m e n t made by the PED o f t h e 205 cm 1 a b s o r p t i o n t o the t o r s i o n a l mode. The need f o r t he f i n t e r a c t i o n t o g i v e an a c c u r a t e f i t was d e m o n s t r a t e d i n ax 3 the s y m m e t r i c c a l c u l a t i o n s above. Loos e t a l have i g n o r e d t h i s i n -t e r a c t i o n even though i t i s e x p e c t e d t h a t i t s h o u l d be i m p o r t a n t due t o the n e a r n e s s o f the low l y i n g f r e q u e n c i e s and r e s u l t a n t m i x i n g o f the c o o r d i n a t e s . The c o n f u s i o n i n the low f r e q u e n c y modes seen i n the e i g e n v e c t o r s o f Loos e t a l ^ " ^ has been removed by u s i n g t h i s i n t e r a c t i o n and a c l e a r a s s i g n m e n t can be made. The l a r g e amount o f t o r s i o n a l c o o r d i n a t e i n v o l v e d i n t h e 205 cm ' mode a l s o l e n d s c r e d -i b i l i t y t o the c a l c u l a t i o n o f t h e b a r r i e r t o i n t e r n a l r o t a t i o n made by T u r n e r ^ 2 ' ^ u s i n g h i s s o l u t i o n v a l u e o f 195 cm \ H i s b a r r i e r o f 34 k c a l i s about 1.5 time s the b a r r i e r o f 21 k c a l c a l c u l a t e d by (14) P e d e r s e n u s i n g t h e CNDO/2 method. T h i s r a t i o o f 1.5 i s o b s e r v e d f o r o t h e r m o l e c u l e s where b a r r i e r s a r e c a l c u l a t e d u s i n g the CNDO/2 m e t h o d ^ 1 ^ . A l s o , t h e v a l u e o f 0.472 mdyn/A g i v e n by Loos e t a l ^ " ^ - 90 -may p o s s i b l y be l a r g e f o r a t o r s i o n a l c o n s t a n t w h i l e the v a l u e o f 2 0.26 a J / r a d o b t a i n e d i n t h i s c a l c u l a t i o n i s o f t h e same o r d e r as 2 the v a l u e o f 0.25 a J / r a d found f o r the t o r s i o n a l c o n s t a n t i n c i s -HNSO (see c h a p t e r I I I ) where m u l t i p l e b o n d i n g i s a l s o i n v o l v e d . Two problems have been e n c o u n t e r e d i n t h i s c a l c u l a t i o n . That o f i1 I - c o n d i t i o n i n g has been d i s c u s s e d and i t has been i l l u s -t r a t e d how f u r t h e r a p p r o x i m a t i o n s a r e o f t e n needed t o c i r c u m v e n t t h i s p r o b l e m . The o t h e r p r o b l e m i s t h a t o f m u l t i p l e s o l u t i o n s o f l e a s t s q u a r e s c a l c u l a t i o n s based on l i m i t e d d a t a . O f t e n a s e l e c t i o n o f t h e c o r r e c t s o l u t i o n from s e v e r a l p o s s i b i l i t i e s can be made u s i n g o t h e r d a t a such as c e n t r i f u g a l d i s t o r t i o n o r C o r i o l i s c o n s t a n t s . H e r e , however, t h e s e a r e not a v a i l a b l e and the c h o i c e must be made on " c h e m i c a l i n t u i t i o n " . Loos e t a l ^ " ^ f e l t t h a t t h e low 0-0 f o r c e c o n s t a n t was u n r e a s o n a b l e and thus chose a s o l u t i o n w i t h u n u s u a l l y l a r g e i n t e r a c t i o n c o n s t a n t s and c o m p l e t e l y ambiguous p o t e n t i a l e nergy d i s t r i b u t i o n and e i g e n v e c t o r s . By use o f f i g u r e 2-3 i t i s shown h e r e t h a t t h e low 0-0 f o r c e c o n s t a n t i s not n e c e s s a r i l y u n r e a s o n a b l e and i t i s argued t h a t r e a s o n a b l e i n t e r a c t i o n c o n s t a n t s and r e a s o n a b l e , c l e a r a s s i g n m e n t s (PED and e i g e n v e c t o r s ) make the f o r c e f i e l d s e l e c -t i o n found i n t h i s t h e s i s t he c o r r e c t one. - 91 -C. 0 3 F 2 : OZONE FLUORIDE 1. REPORTED PREPARATION Ozone f l u o r i d e ( o r t r i o x y g e n f l u o r i d e ) was f i r s t " i s o l a t e d " and " a n a l y s e d " by Ki rshenbaum and G r o s s e ^ ^ . T h e i r p r e p a r a t i o n i n v o l v e d an e l e c t r i c a l d i s c h a r g e o f oxygen and f l u o r i n e g ases mixed i n a 3:2 r a t i o u s i n g a p y r e x v e s s e l immersed i n a l i q u i d n i t r o g e n b a t h (77°K). They o b s e r v e d t h a t ®-^2 w a s a " b l o o d - r e d , v i s c o u s l i -q u i d " w h i c h s o l i d i f i e d a t 83°K and decomposed a t about 116°K t o g i v e ^2^2 a n C ' ^2" ^ 6 e ^ e m e n t a ' a n a l y s i s made by s t u d y i n g t h e f i n a l decom-p o s i t i o n p r o d u c t s , 0^ and F^, showed t h a t oxygen and f l u o r i n e were p r e s e n t i n the " p u r i f i e d " sample i n a r a t i o o f 3:2 - t h e same r a t i o as the o r i g i n a l gas m i x t u r e . Upon t h i s a n a l y s i s the c l a i m t o 0^2 p r o d u c t i o n was made. However, f o l l o w i n g t h i s i n i t i a l c o n f i d e n t r e -p o r t , a t t e m p t s by o t h e r w o r k e r s t o s t u d y O^F^ v i a v a r i o u s s p e c t r o s -c o p i c t e c h n i q u e s have not r e s u l t e d i n t h e i d e n t i f i c a t i o n o f an O^F,, m o l e c u l a r s p e c i e s . 2. REVIEW OF SPECTRAL EVIDENCE (a) The V i s i b l e Spectrum: The v i s i b l e s p e c t r a o b t a i n e d by K i r s h e n b a u m (25) (26) and S t r e n g and S t r e n g and S t r e n g f o r 02^2' ®k^2 a n ^ ^3^2 a r e shown i n f i g u r e 2-k. I t a p p e a r s t h a t t h e s e s p e c t r a say l i t t l e about 0^F 2. However, i t i s p o s s i b l e t h a t the a b s o r p t i o n o f 425 mu f o r b o t h 0^F 2 and 0^F 2 i s p r o duced by the same s p e c i e s . There would have t o - 92 -F i g u r e 2-h. V i s i b l e a b s o r p t i o n s p e c t r a o f s e v e r a l oxygen f l u o r i d e s ( r e f e r e n c e 26). - 93 -be o n l y h a l f as much o f t h i s a b s o r b e r i n O^F^ as i n O^F^ t o g i v e the 2:1 r a t i o o f e x t i n c t i o n c o e f f i c i e n t s ; I f ' s a m o ' e c u l a r e n t i t y , p r o b a b l y a l o o s e l y bound d i m e r o f " C ^ ' t n e n c o u l d be the a b s o r b -i n g s p e c i e s i n both s p e c t r a . In t h a t c a s e O^F^ w o u ' d have t o be a m i x t u r e o f 1/2(° 2 F2^ + ^2^°kF2^ ' l f t h e a b s o r b e r i s ' ° 2 F ' w e a k l v bound t o some t h i n g e l s e , t h e n FO ^ £ F ' l o o s e l y bound, i s a n o t h e r p o s s i b i l i t y . In e i t h e r c a s e the e x t i n c t i o n c o e f f i c i e n t r a t i o would be c o r r e c t . Thus the v i s i b l e s p e c t r a s u g g e s t t h a t e i t h e r t he Q^2 m o l e c u l e does not e x i s t and t h a t ' s a m ' x t u r e o f two o t h e r com-pounds o r t h a t i f i t does e x i s t , i t might be e x p e c t e d t o be unsymme-(13) t r i e and o f t h e form s u g g e s t e d by S p r a t l e y and P i m e n t e l , FO ^ 2 F * (27) (b) E.P.R. Spectrum: K a s a i and Kirshenbaum have s t u d i e d t h e e l e c t r o n p a r a m a g n e t i c r e s o n a n c e s p e c t r a o f O^F^ and O^F^. They found both s p e c t r a t o be i d e n t i c a l and a t t r i b u t a b l e t o * 0 2 F s i n c e , as expec-t e d , n e i t h e r 0 2 F 2 n ° r ^3^2 ' S P a r a m a 9 n e t ' c - They f o u n d , however, t h a t •O2F i s 0.1 mole p e r c e n t i n the O2F2 sample and 5 mole p e r c e n t i n O^F^. In b o t h c a s e s i t i s assumed t o r e s u l t from d e c o m p o s i t i o n . A l t h o u g h the E.P.R. s p e c t r u m sheds no l i g h t on t h e n a t u r e o r e x i s t e n c e o f O^F^, i t i s i m p o r t a n t t h a t t h e sample p o s s e s s e s a l a r g e amount o f '®2^' (c) Mass S p e c t r o s c o p y : U s i n g c r y o g e n i c mass s p e c t r o m e t r i c t e c h n i q u e s t h a t had been s u c c e s s f u l l y been a p p l i e d t o 0^F2 and '^2^' Malone and (28) McGee a t t e m p t e d t o s t u d y O^F^. However, from t h e i r sample they were not a b l e t o o b t a i n any c u r r e n t s a t t r i b u t a b l e t o p o s i t i v e i o n s o r n e g a t i v e i o n s o f 0 ^ , ^^2' ^2^2' % F > ^ 3 F 3 ° r % F 2 " ^hey ^ i d see 94 OF , 0 F 2 , 0 2 , 0 2 F , O^ and F 2 . A g a i n , t h e m o l e c u l e 0 ^ c o u l d not be seen and a l l t h a t c o u l d be s a i d was t h a t i t does not e x i s t o r e l s e t h a t i t f o l l o w s a d e c o m p o s i t i o n p a t t e r n s u c h as t h e f o l l o w -i n g : 2F0 2-OF - > 2F0-+ 2 F 0 ~ T a s t T * ° 2 F 2 + 2 F 0 2 TTclr- 2 0 2 F 2 + °2 IV y 20F„ + 20, T h i s scheme w o u l d a c c o u n t f o r t h e p r e s e n c e o f t h e o b s e r v e d i o n s and t h e a bsence o f t h e o t h e r s . I t a l s o s u g g e s t s t h a t O^F^ i f i t e x i s t s , i s o f t h e a s y m m e t r i c form. However, th e o b s e r v e d i o n s c o u l d a l s o r e s u l t f r o m a sample w h i c h was not ®^2' 3 m ' x t u r e °^ ^ 2 F 2 a n ^ 0 ^ F 2 where 0 ^ F 2 decomposed t o 'O^F t o g i v e the o b s e r v e d i o n s , (d) N.M.R. Spectrum: The above s t u d i e s have no t been a b l e t o show t h e e x i s t e n c e o f 0^ F2 ^ u t a ' s o have not c o n c l u s i v e l y n e g a t e d i t s e x i s t e n c e . However, th e s e v e r a l n u c l e a r m a g n e t i c r e s o n a n c e s t u d i e s , 17 19 (29) 19 b o t h 0 and F , on Q-^2 ^ a v e been q u i t e c o n c l u s i v e . The F s p e c t r u m c o n s i s t s o f two s e p a r a t e l i n e s t h a t must be a t t r i b u t e d , on the b a s i s o f c h e m i c a l s h i f t , t o two 0 2 ^ 2 t y p e f l u o r i n e s r a t h e r than 0 F 2 t y p e f l u o r i n e s ^ ^ d ) ^ 17Q S p e c t r u m c o n s i s t s o f t h r e e l i n e s -two low f i e l d l i n e s o f e q u a l i n t e n s i t y and a t h i r d a t h i g h e r f i e l d - 95 -o f about 60% o f t h e sum o f t h e o t h e r two i n t e n s i t i e s ^ 2 " ^ . I t i s not p o s s i b l e t o f i n d a s i n g l e O^F^ m o l e c u l a r s t r u c t u r e t o a c c o u n t f o r t h e o b s e r v e d s p e c t r a . I n s t e a d , Solomon e t a l ^ 2 " ^ s u g g e s t t h a t the b e s t e x p l a n a t i o n o f the s p e c t r a comes from the f o l l o w i n g e q u i l -i b r i u m : [ 0 2 F 2 , < V 2 ] 2.OOF • 0 2 F 2 + 0 2 That i s , does not e x i s t as a m o l e c u l a r s p e c i e s but i s a c t u a l l y an e q u i m o l a r m i x t u r e o f ®2^2 anc* 4^F2* ^ e d e c o m p o s i t i o n t o 02^ 2 and O2 i s i r r e v e r s i b l e and r e s u l t s as t h e t e m p e r a t u r e i s i n c r e a s e d . T h i s e q u i l i b r i u m p i c t u r e i s c o m p a t i b l e w i t h the e x t i n c t i o n c o e f f i -c i e n t s o f the v i s i b l e s p e c t r a , t h e p r e s e n c e o f * 0 2 F i n the E.P.R. s p e c t r a and t h e o b s e r v e d i o n s i n t h e mass s p e c t r u m . (e) I n f r a r e d Spectrum: As y e t , because o f t h e d i f f i c u l t i e s i n t e c h -n i q u e , no i n f r a r e d e v i d e n c e has been o b t a i n e d r e g a r d i n g ®^2' ^ow~ e v e r , t h e somewhat s i m i l a r m o l e c u l e s O ^ H ^ 3 ^ and O^(CF^) have been s t u d i e d and found t o c o n s i s t o f s y m m e t r i c c h a i n s o f 0-0 s i n g l e bonds i n a z i g - z a g form. T h e i r 0-0 s t r e t c h i n g f r e q u e n c i e s a r e found between 750 cm ' and 900 cm However, a s i m i l a r s t r u c t u r e f o r 0^F 2 appears t o be i n c o m p a t i b l e w i t h the s p e c t r s c o p i c e v i d e n c e g i v e n above. - 96 -A t t e m p t s t o produce ^ v P a s s ' n 9 ^£ a n < ^ F 2 9 a s m ' x t u r e s t h r o u g h a f l o w d i s c h a r g e and t o o b t a i n i t s i . r . s p e c t r a from the r e -s u l t i n g s o l i d f i l m on a c o l d C s l window a r e d e s c r i b e d below. As w e l l , a s t u d y o f a l l the p r o d u c t s o f such a d i s c h a r g e i s a l s o made. 3- 0 2 / F 2 DISCHARGES (a) E x p e r i m e n t a l : The a p p a r a t u s used i n t h e s e e x p e r i m e n t s c o n s i s t e d o f t h e metal vacuum s y s t e m , c r y o s t a t , s p e c t r o m e t e r and microwave gen-e r a t o r d e s c r i b e d i n c h a p t e r I . The compressed gases used were f l u o r -i n e ( M a t h e s o n ) , oxygen (Matheson, e x t r a d r y grade) and argon (Matheson, p r e p u r i f i e d g r a d e ) . The f l u o r i n e was p a s s e d t h r o u g h a sodium f l u o r i d e t r a p t o remove HF w h i l e the oxygen and argon were used w i t h o u t f u r t h e r p u r i f i c a t i o n . (b) R e s u l t s : As a r e s u l t o f l a c k o f s e l e c t i v i t y i n the p r e p a r a t i v e method ( d i s c h a r g e ) and t h e u n a v o i d a b l e p r e s e n c e o f i m p u r i t i e s i n s u b s t a n t i a l q u a n t i t i e s , t h e s p e c t r a o b t a i n e d were al w a y s v e r y c o m p l i -c a t e d . The r e a s o n f o r t h i s i s t h a t many o f t h e i m p u r i t i e s , b o t h p r e s e n t i n the o r i g i n a l samples and produced i n t h e d i s c h a r g e , a r e much more s t a b l e than t h e o x y g e n - f l u o r i n e compounds so t h a t t h e y tended t o be formed p r e f e r e n t i a l l y and remain a f t e r p r o d u c t i o n i n -s t e a d o f decomposing. S e v e r a l i m p u r i t i e s t h a t were o f t e n p r e s e n t and w h i c h caused c o n s i d e r a b l e t r o u b l e were CO, C 0 2 > F 2 C 0 , FCO, CF^, S i F ^ , 0^, FN0 2 and NF^. A l l but the l a s t t h r e e o f t h e s e appear t o have been p r e s e n t i n t h e o r i g i n a l F„ sample and c o u l d not be removed. - 97 -As w e l l , d i s c h a r g e was found t o i n c r e a s e t he amount o f F^CO and FCO, FNO^ and NF^ were p r o b a b l y formed i n the d i s c h a r g e from N 2 p r e s e n t as an i m p u r i t y w h i l e 0^ was formed i n the d i s c h a r g e from 0^. Numer-ous e x p e r i m e n t s were a t t e m p t e d w i t h and w i t h o u t m a t r i c e s u s i n g v a r i -ous r a t i o s o f 0^ t o F^. The r e s u l t s and d i s c u s s i o n o f t h e m a t r i x e x p e r i m e n t s w i l l be g i v e n f i r s t f o l l o w e d by t h e r e s u l t s o f e x p e r i m e n t s w i t h u n d i l u t e d 0^ and F^. ( i ) M a t r i x E x p e r i m e n t s - F i g u r e s 2-5, 2-6, 2-7 and 2-8 show f o u r t y p i c a l i . r . s p e c t r a o f d i s c h a r g e d 0^, F^ and argon m i x t u r e s condensed on a c o l d C s l window. The r a t i o o f t h e gases i n t h e f i r s t i s 0 2 : F 2 : A r = 4:1:50, i n the second i s 0 2 : F 2 : A r = 1:4:50, i n the t h i r d i s 0 2 : F 2 : A r = 1:2:200 and i n the l a s t i s 0 2 : A r = 1:200. T a b l e 2-11, 2-12 and 2-13 l i s t a l l t h e peaks o b s e r v e d i n t h e s e f o u r e x p e r -i m e n t s . Of t h e s e , t a b l e 2-11 c o n t a i n s t h o s e a b s o r p t i o n s a s s i g n e d t o o x y g e n - f l u o r i d e s , t a b l e 2-12 c o n t a i n s t he a b s o r p t i o n s w h i c h have been a s s i g n e d w i t h v a r y i n g d e grees o f c o n f i d e n c e t o i m p u r i t i e s w h i l e t a b l e 2-3 l i s t s a group o f peaks o f g e n e r a l l y low i n t e n s i t y w h i c h c o u l d not be a s s i g n e d a t a l l . Those a b s o r p t i o n s t h a t a r e o f p a r t i c u l a r i n t e r e s t w i l l be d i s c u s s e d i n d i v i d u a l l y and the b a s i s f o r t h e i r a s s i g n m e n t s out 1i ned. C a r e f u l a n a l y s i s o f t h e 1020-1040 cm ' r e g i o n i s i m p o r t a n t (4) -1 because A r k e l e t a l have shown t h a t *0F a b s o r b s a t 1028 cm i n an argon m a t r i x . I t would be i n t e r e s t i n g t o see i f *0F i s produced by the d i s c h a r g e . As w e l l , i f w e r e t o t a k e the form o f an 'OF F i g u r e 2-5. Spectrum o f condensate o f d i s c h a r g e d F«/0„/Ar = 4/1/50. F i g u r e 2-7. Spectrum o f condensate o f d i s c h a r g e d F„/0 /Ar = 1/2/200. F i g u r e 2-8. Spect rum o f condensate o f d i s c h a r g e d Q^kr = 1/200. - 102 -T a b l e 2-11. I.R. a b s o r p t i o n s a s s i g n e d t o o x y g e n - f l u o r i d e s i n an argon m a t r i x . From 0./F /Ar d i s c h a r g e s . v(cm ) m o l e c u l e a s s i g n m e n t 2940 1725 1591 1520 1490 1260 1028 926 918 822 627 61 1 582 463 372 365 ° 2 F 0F„ OF, ° 4 F 2 ° 2 F ° 2 F 2 OF OF, OF, ° 2 F 2 ° 2 F 2 ° 2 F ° 2 F 2 0F„ ° 2 F ° 2 F 2 2 v ( 0 0 ) v ( 0 F ) , sym + v ( 0 F ) , asym. 2 v ( 0 F ) , asym. v( 0 0 ) v ( 0 0 ) v ( 0 0 ) v ( 0 F ) , sym; 2v(F0F) v ( O F ) , asym. v ( O F ) , asym. v ( O F ) , sym. v ( 0 F ) v ( 0 0 F ) , asym. v ( F 0 F ) v ( 0 0 F ) v(OOF), sym. - 103 -T a b l e 2 - 1 2 . A b s o r p t i o n s a s s i g n e d t o i m p u r i t i e s i n argon m a t r i c e s . From 0^ / F 2 / A r d i s c h a r g e s v(cm ') i m p u r i t y v(cm ^) i m p u r i t y 3 9 1 5 HF 1 2 3 8 F 2 C 0 3 8 0 0 N 1 145 F N 0 2 3 7 1 8 j H 2 0 1114 NF 3 7 0 0 1 0 7 0 N F 2 2 3 3 0 c o 2 1 0 3 9 | 2 2 8 0 FCN 1 0 3 3 J ° 3 2 2 2 0 N 2 0 1 0 2 8 OF, NF 2 8 c ;p S 1 Fjj 2 1 4 0 CO 1023 2 1 0 5 ° 3 1014 2 9 S i F ^ 1 9 4 0 } F 9 C 0 1005 3 0 s i F ^ 1910 > L 9 6 2 F 2 C 0 1871 NO 9 3 0 NF 2 1861 F N 0 2 8 9 7 N F 3 1855 FC0 811 F N 0 2 1851 FN0 7 6 9 F 2 C 0 1790 F N 0 2 7 5 0 FNO 1620 7 4 8 N 0 2 1 6 1 0 I H 2 0 7 3 2 F N 0 2 1590 7 0 0 ° 3 1610 N 0 2 661 c o 2 1 5 4 8 °2 6 2 0 1 3 8 8 ° 3 5 6 8 F N 0 2 1307 F N 0 2 5 0 8 FNO 1272 C F 4 4 9 0 NF3 1 2 6 0 N 2 0 3 8 2 S i F l | - 104 -T a b l e 2-13- Weak, u n a s s i g n e d a b s o r p t i o n s in argon m a t r i c e s . From d i s c h a r g e s , v (cm )^ comment found i n 0 2 F 2 / A r sample b e f o r e d i s c h a r g e 1755 1295 } 798 1896 1258 1209 1205 1195 1181 1170 1140 1097 950 p o s s i b l y 0 £ F : 372 + 582 = 954 860 828 781 656 490 400 p o s s i b l y 0 ^ : 2 x 205 = 410 - 105 -w e a k l y bonded t o a '^2^' , F a * r r : d then t h e OF s t r e t c h a b s o r p t i o n may be i n t h i s r e g i o n near the d i a -t o m i c *0F a b s o r p t i o n . T h i s r e g i o n c o n t a i n s s e v e r a l a b s o r p t i o n s -1039, 1033, 1028 and 1023 cm 1 - shown under h i g h r e s o l u t i o n i n f i g u r e 2-9. E x p e r i m e n t s w i t h o u t F^ produced ozone, whose h i g h r e s -o l u t i o n s p e c t r u m ( f i g u r e 2-10) shows a d o u b l e t a t 1039 cm ' and a b r o a d e r s i n g l e peak a t 1033 cm \ The 1033 cm ' a b s o r p t i o n , w h i c h shows a s l i g h t c o n c e n t r a t i o n dependence, r e s u l t s from some fo r m o f a s s o c i a t i o n o r p o s s i b l y from o c c u p a t i o n o f a d i f f e r e n t m a t r i x s i t e . The d o u b l e t n a t u r e o f t h e 1039 cm ^ a b s o r p t i o n i s c h a r a c t e r i s t i c o f s p l i t t i n g s seen f o r t h e a s y m m e t r i c s t r e t c h e s o f two o t h e r bent t r i -a ss i 1 (32) a t o m i c s , NO^ and SO^, and i g n e d t o r o t a t i o n on t h e b a s i s o f temp-e r a t u r e dependence s t u d i e s The peak a t 1023 cm ' has been a s s i g n e d t o the i m p u r i t y S i F ^ p r e s e n t i n t h e o r i g i n a l f l u o r i n e sample. B a s s l e r , Timms and (33) Margrave , w h i l e a t t e m p t i n g t o s t u d y S i i n an argon m a t r i x , o b s e r v e d a group o f peaks s p r e a d between 990 cm ' and 1040 cm \ The most i n t e n s e o f t h e s e was a t 1023 cm \ The whole group was a s s i g n e d t o S i F ^ but no e x p l a n a t i o n f o r t h e s p l i t t i n g c o u l d be g i v e n . H e r e , however, t h i s s p l i t t i n g has not been o b s e r v e d and the - 106 -O to _Q < 0 . 5 H i/ ( c m - ' ) 1 0 4 0 1030 _ l I r / ( c m _ 1 ) 1Q2Q F^:02: Ar = 2 : i : 2 0 0 O . V O . S H 1 0 5 0 1 0 4 0 1 0 3 0 _l I I 02: Ar = 1 : 2 0 0 F i g u r e 2-9. H i g h r e s o l u t i o n s p e c t r u m o f F 2 / 0 2 / A r d i s c h a r g e . F i g u r e 2-10, High r e s o l u t i o n s p e c t r u m o f d i s c h a r g e showing o f o z one. - 107 -a s s i g n m e n t t o S i h a s been made on t h e b a s i s o f t h e i r i n t e n s e 1023 cm 1 peak, the c o r r e l a t i o n o f t h i s peak w i t h one a t 382 cm 1 w h i c h i s the o t h e r i . r . a c t i v e S i F ^ a b s o r p t i o n and the o b s e r v a t i o n o f weak peaks a t 1014 cm 1 and 1005 cm 1 w h i c h can be a s s i g n e d t o the d i f f e r e n t s i l i c o n i s o t o p e s . S i l i c o n i n n a t u r a l abundance con-28 29 30 s i s t s o f 32% S i , 5% S i and 3% S i . The t h r e e a b s o r p t i o n s show i n t e n s i t y r a t i o s o f peak h e i g h t o f 92:6:4. Thus t h e 1023 cm 1 ab-s o r p t i o n can be a s s i g n e d t o o f S i F ^ . The r e m a i n i n g peak i n t h i s r e g i o n , 1028 cm \ can be a s s i g n -ed t o both «0F and NF^. A f u r t h e r d i f f i c u l t y w i t h NF^ a r i s e s because i t s a b s o r p t i o n o f 897 cm ' i s i n the r e g i o n e x p e c t e d f o r an 0-0 s i n g l e bond s t r e t c h i n g mode such as might o c c u r i n t h e m o l e c u l e F-0-0-0-F. The p o s i t i o n s o f a b s o r p t i o n s o f NF^ as w e l l as NF^ and NF were d e t e r -mined by p a s s i n g a m i x t u r e o f N^, F^ and argon t h r o u g h the d i s c h a r g e . The a s s i g n m e n t s were based upon l i t e r a t u r e v a l u e s : NF^, 1070 cm 1 and 930 cm" 1 ^ ] NF, 1114 cm" 1 ^ 3 5 ^ ; and N F ^ 1028 cm" 1, 897 cm" 1, and 490 cm 1 (36)^  - r n ; s a l l o w e d f o r the a s s i g n m e n t o f t h e s e a b s o r p t i o n s i n ®2^2 e x P e r ' m e n t s ' n w h i c h N^ was p r e s e n t . W h i l e i t was found t h a t the 897 cm 1 a b s o r p t i o n o f NF^ was much s t r o n g e r (by a f a c t o r o f 5) than t h e 1028 cm 1 a b s o r p t i o n , i n f i g u r e 2-7 the 1028 cm 1 peak i s s t r o n g e r . T h e r e f o r e a n o t h e r a b s o r b i n g s p e c i e s i s a c c o u n t i n g f o r a l a r g e p a r t o f t h e i n t e n s i t y and t h i s s p e c i e s i s most l i k e l y «0F. However, i t must be emphasized t h a t no o t h e r a b s o r p t i o n s a r e found between 900 cm 1 and 1050 cm 1 t h a t might be a s s i g n e d t o t h e F0 - 108 -s t r e t c h o f t h e unsymmetric FO'O^F. S e v e r a l o t h e r i m p u r i t i e s w i l l be d i s c u s s e d b r i e f l y . F^CO i s f o und i n the F^ sample i n s m a l l amounts, but i t s c o n c e n t r a t i o n i n c r e a s e s m a r k e d l y when the sample i s d i s c h a r g e d . I t s a b s o r p t i o n s and i n t e n s i t i e s i n a m a t r i x , a l o n g w i t h t h o s e o f FCO, c o r r e s p o n d t o t h o s e g i v e n by M i l l i g a n e t a l . The i n c r e a s e o f F^CO and t h e o c c u r r e n c e o f FCO and CO on d i s c h a r g e i s a t t r i b u t e d t o r e a c t i o n i n the d i s c h a r g e o f F^ and CO^, t h e l a t t e r an i m p u r i t y i n the F^ sample. B e s i d e s the i m p u r i t i e s r e s u l t i n g f r o m a l r e a d y d i s c u s s e d , NO, N 0 2 , FNO and FNO^ were a l s o o b s e r v e d under v a r i o u s c o n d i t i o n s , NO and N 0 2 b e i n g found o n l y i n t r a c e amounts when f l u o r i n e was p r e s -e n t . F N 0 2, however, appears t o show a d i s c r e p a n c y w i t h t h e gas phase ( 3 8 ) work o f Dodd, R o l f e and Woodward who l i s t t h e AjCv^+v^) mode a t 1282 cm 1 as v e r y s t r o n g w h i l e the A ^ ( v^) mode a t 1312 cm 1 as weak. Here o n l y an a b s o r p t i o n a t 1307 cm 1 was o b s e r v e d w h i c h i s t o o h i g h t o be t h e c o m b i n a t i o n and so must be the fundamental s h i f t e d from i t s gas phase f r e q u e n c y . The i n t e n s i t i e s i n r e f e r e n c e 38 must be assumed r e v e r s e d . The r e m a i n i n g peaks show p o s i t i o n s and i n t e n s i t i e s c o n s i s t e n t w i t h t h o s e o f r e f e r e n c e 38 and a r e thus a s s i g n e d on t h i s b a s i s . FNO i s found t o be p r e s e n t under the same c i r c u m s t a n c e s t h a t f a v o u r F N 0 2 > I t , a l o n g w i t h NO and FCO r e s u l t i n the c o n f u s i o n be-tween 1850 cm 1 and 1900 cm \ However, i t a p p e a r s t h a t a l l the a b s o r p t i o n s i n t h i s r e g i o n can be a t t r i b u t e d t o t h e s e t h r e e m o l e c u l e s . Of the oxygen f l u o r i d e s , O^' w n ' c n ' s t n e m°st s t a b l e , i s - 109 -produced i n the l a r g e s t q u a n t i t i e s and i s f a v o u r e d when an e x c e s s o f i s p r e s e n t as can be seen by n o t i n g t h a t the 8 2 2 cm ' peak i s more i n t e n s e i n f i g u r e 2 - 5 than i n f i g u r e 2 - 6 . ®2^2 a n c ' * ^ 2 F w n ' c n a r e not as s t a b l e , a r e not produced i n as l a r g e a q u a n t i t y . Of i n t e r e s t , however, i s t h e change i n r e l a t i v e i n t e n s i t i e s o f ^^2 and -O^F a b s o r p t i o n s i n f i g u r e s 2 - 5 and 2 - 6 . I t i s v e r y e v i d e n t , and e x p e c t e d , t h a t e x c e s s 0 ^ i n c r e a s e s t h e amount o f 'O^F o v e r 0 2 ^ 2 ' U n f o r t u n a t e l y , i n t e n s i t i e s cannot be e a s i l y compared f o r -OF under v a r i o u s c o n d i t i o n s because o f t h e o v e r l a p p i n g a b s o r p t i o n s d i s c u s s e d above. F o l l o w i n g the above o b s e r v a t i o n s on O^F^ and '®2^' ' c might be e x p e c t e d t h a t e x c e s s 0 ^ would a l s o f a v o u r 0 ^ 2 p r o d u c t i o n . I f the a s y m m e t r i c s t r u c t u r e o f O j F ^ ' s c o r r e c t , then t h e i n c r e a s e o b s e r v e d i n ^ 2 ^ s h o u l d r e s u l t i n more 0^F^ w h i l e i f the s y m m e t r i c c h a i n form i s c o r r e c t , then the l a r g e i n c r e a s e i n 0 ^ might be e x p e c -ted t o c o i n c i d e w i t h more ®^2' ^° s u c n ' " c r e a s e s i n i n t e n s i t y t h a t might be a t t r i b u t e d t o 0 ^ 2 ab s°rptions a r e o b s e r v e d i n g o i n g from f i g u r e 2 - 5 t o f i g u r e 2 - 6 . In t h e f i r s t c a s e t h e p r e s e n c e o f o n l y a s m a l l peak a t 1 520 cm ' i n f i g u r e 2 - 6 i n d i c a t e s t h a t o n l y a l i t t l e 0 ^ 2 i s formed and t h e r e a r e no o t h e r i n d i c a t i o n s o f an 0 - 0 s t r e t c h i n t h i s r e g i o n a t t r i b u t a b l e t o the s p e c i e s F 0 - 0 2 F . As p o i n t e d o u t above, no a b s o r p t i o n i n t h e r e g i o n o f 1 000 cm ' e x i s t s t o be a s s i g n e d to the F0 s t r e t c h i n t h i s m o l e c u l e . A t the same time none o f the u n a s s i g n e d weak a b s o r p t i o n s i n t h e 7 0 0 - 9 0 0 cm ' r e g i o n show an - no -i n c r e a s e t h a t might i n d i c a t e the p r e s e n c e o f a s y m m e t r i c F-0-0-0-F w i t h 0-0 s i n g l e bonds. In c o m p a r i s o n w i t h 0 and O^(CF^) two a b s o r p t i o n s might be e x p e c t e d i n the 700 cm ' t o 900 cm 1 r e g i o n f o r F-0-0-0-F. A l t h o u g h a peak a t 828 cm 1 on the s i d e o f t h e OF^ a b s o r p t i o n i n f i g -u r e 2-5 i s i n an a p p r o p r i a t e p o s i t i o n t o be due t o such a m o l e c u l e and weak peaks a t 950 cm ', 860 cm ' and 400 cm 1 a r e p r e s e n t w i t h e x c e s s 0^ i n f i g u r e 2-6, not enough e v i d e n c e i s a v a i l a b l e t o a s s i g n t h e s e weak a b s o r p t i o n s t o s y m m e t r i c O^F^. The u n c e r t a i n t y i n t h e s e p e a k s, r e s u l t i n g from t h e i r low i n t e n s i t y , i s i n c r e a s e d by the f a c t t h a t the one a t 950 cm 1 can be a s s i g n e d t o a c o m b i n a t i o n l e v e l o f •O^F w h i l e the one a t 400 cm 1 can be a s s i g n e d t o an o v e r t o n e o f 02^ 2 as has been done i n the f o l l o w i n g s e c t i o n i n v o l v i n g ^2^2 d i s c h a r g e s w i t h o u t a r g o n . T h e r e f o r e , t h e m a t r i x e x p e r i m e n t s show t h a t even though •O^F, O^ and «0F a r e p r o duced i n r e a s o n a b l e q u a n t i t i e s , no e v i d e n c e p o i n t s t o t h e p r e s e n c e o f ®^2 i s o l a t e d i n s i g n i f i c a n t amounts. ( i i ) ^2^2 o r | l y ~ ^ n e n t n e m a t r i x e x p e r i m e n t s produced no d e f i n i t i v e e v i d e n c e f o r the p r o d u c t i o n o f O^F^ i n O^/F^/Ar d i s c h a r g e s , i t was d e c i d e d t o d u p l i c a t e more c l o s e l y the p r e p a r a t i v e p r o c e d u r e s r e p o r t e d f o r 2^^ 2' ^4^2 a n <^ 3^^ 2" ^° ^° t n ' s ' m i x t u r e s o f u n d i l u t e d 0^ and F^ were p a s s e d t h r o u g h the microwave d i s c h a r g e , f o l l o w e d by c o n d e n s a t i o n on the c o o l e d C s l window and subsequent s p e c t r a t a k i n g . I t was t h ought t h a t the s p e c t r a s h o u l d show t h e m o l e c u l e s i n an - I l l -e n v i r o n m e n t s i m i l a r t o t h a t e x p e r i e n c e d i n t h e i r s o l i d s . F i g u r e 2-11 g i v e s one such s p e c t r u m i n w h i c h e q u a l amounts o f oxygen and f l u o r i n e were d i s c h a r g e d w h i l e t a b l e s 2-14 and 2-15 l i s t t he a b s o r p t i o n s and t h e i r a s s i g n m e n t s . The peaks a s s o c i a t e d w i t h ®2^2 have a l r e a d y been p a r t i a l l y d i s c u s s e d i n s e c t i o n l l - B - 2 . In g e n e r a l , t h e v e r y i n t e n s e a b s o r p t i o n s have been a s s i g n e d t o t h e f u n d a m e n t a l s o f O^, a n <^ ®2^2' t'~ie m e c " u m i n t e n s i t y peaks t o the i m p u r i t i e s F 2 C O , FCO, FNC^ and and the weak peaks t o o v e r t o n e s and c o m b i n a t i o n s o f the oxygen f l u o r i d e s and t r a c e i m p u r i t i e s . In t a b l e 2-14 the o x y g e n - f l u o r i d e a b s o r p t i o n s a r e l i s t e d . The o v e r t o n e s and c o m b i n a t i o n s o f O^F^ have been used i n s e c t i o n l l - B - 2 t o d e t e r m i n e t h e v a l u e o f 1305 cm ^ and 205 cm ^ f o r and v^. The f u n d a m e n t a l s o f ('®2^2 a r S e s s e n t i a 11y t h o s e o f monomer i s o l a t e d i n a m a t r i x w i t h the e x c e p t i o n o f v . The v a l u e o f 1520 cm ' o b s e r v e d r 00 h e r e i s the same as t h a t p r e v i o u s l y a s s i g n e d t o the 0-0 s t r e t c h i n g mode o f 0^2 ' n a n a r 9 o n m a t r i x by A r k e l ^  and i s s h i f t e d about 30 cm ' above t h e 'O^F m o n o m e r f r e q u e n c y . The b o n d i n g between the P a ' r must then be v e r y weak and not i n v o l v e t h e f l u o r i n e end of the m o l e c u l e s i n c e t h e OF s t r e t c h and OOF bend seem u n a f f e c t e d . Because o f t h i s weak b o n d i n g , t h e o t h e r a b s o r p t i o n s a s s o c i a t e d w i t h 0^^2 w o u ' c ' P r ° b a -b l y be a t low energy and not o b s e r v e d i n t h e s e s p e c t r a . As w e l l , c o m b i n a t i o n s o f t h e s e low energy modes w i t h the o b s e r v e d f u n d a m e n t a l s have u n f o r t u n a t e l y not r e s u l t e d i n o b s e r v e d a b s o r p t i o n s . Thus, n o t h i n g more can be s a i d about the 0 ^ 2 v i b r a t i o n s o r about the ^^2 m ° i e c u ' e ' 3000 2500 2000 1500 Z/Ccnrr1) lOOO 500 F i g u r e 2-11. Spectrum o f condensate o f d i s c h a r g e d 0 5 / F ? = 1/1 - 113 -T a b l e 2-14. 0„/F d i s c h a r g e . L i s t o f oxygen f l u o r i d e a b s o r p t i o n s . 0 v(cm ^ ) 4 F2 ass ignment °2 v(cm ') F2 ass ignment v(cm ^ ) 0F2 ass ignment 3010 2 V 1 1905 V1 + V2' V1 + V5 1715 v 3 + v l 2105 V V 2 1760 V v 6 1704 V 2 V 2 1865 V V 3 1665 v l + v 3 1571 2 v 3 1520 v,(00) 1340 v.+lattice 1380 3v 2,v ] +v 2 1160 2V2 1305 v](00) 1270 v 3 + v 2 950 v 2 + v 3 1220 2v2,v2+v5,2\ >5 922 v, (OF) 727 2 V 3 1070 V W V 6 911 2V2 585 v 2 ( 0 F ) 985 V 5 + V 3 815 v 3 ( 0 F ) 370 v 3 ( 0 0 F ) 975 v2 + v3 460 v 2 ( F 0 F ) 727 2 V 3 655 V v 4 620 v 5 ( 0 F ) 611 v 2 ( 0 F ) 568 458 v6(00F) 370 v 3 ( 0 0 F ) 400 2V4 [205] (tors ion) - 114 -T a b l e 2-15- u o ^ F 0 d i s c h a r g e . L i s t o f i m p u r i t i e s . v(cm ) compound 2340 c o 2 2235 N20 2100 °3 1936 F2C0 1905 F 2C0 1809 F N 0 2 1378 °3 1305 FN0 2 1246 F 2C0 1102 °3 963 F 2C0 931 N F 2 890 N F 3 800 F N 0 2 755 F 2C0 702 °3 655 c o 2 540 F N 0 2 - 115 -As has been p o i n t e d o u t i n the d i s c u s s i o n o f 0^2' ®^2 i s e x p e c t e d t o be i n e q u i l i b r i u m w i t h 'C^F i n o r d e r t o p r o v i d e the o b s e r v e d E.P.R. and N.M.R. s p e c t r a . In t h i s work the O^F^ a b s o r p t i o n a t 1520 cm ' i s v e r y i n t e n s e so t h a t i f a few p e r c e n t were p r e s e n t as 'O^F (1490 cm 1 i n an argon matr i x ^ i t woul d l i k e l y be o b s e r v e d . S i n c e n o t h i n g i s seen between 1490 cm 1 and 1500 cm \ "O^F c a n n o t be p r e s e n t i n a p p r e c i a b l e q u a n t i t y . T h i s means e i t h e r t h a t a t 4°K the e q u i l i b r i u m i s s h i f t e d so f a r towards O^F^ t h a t no °®2^ ' s °'3" s e r v e d o r t h a t the E.P.R. r e s u l t s a t 77°K do not come from an e q u i l -i b r i u m but r a t h e r from a s l o w d e c o m p o s i t i o n v i a an 'C^F ' n t e r m e d i a t e . T h i s d e c o m p o s i t i o n t h e n might not o c c u r a t as low a t e m p e r a t u r e as i s used h e r e . For OF^, the f u n d a m e n t a l s and s e v e r a l o v e r t o n e s and com-b i n a t i o n s a r e l i s t e d i n t a b l e 2-14. Of p a r t i c u l a r i n t e r e s t i s the Fermi r e s o n a n c e d i a d r e s u l t i n g f r o m v 3 + v j 3nd v^+Zv^ a t 17'5 cm 1 and 1704 cm However, i t appears t h a t a t 1380 cm 1 a s i m i l a r doub-l e t i s u n r e s o l v e d , p r o b a b l y because o f t h e br o a d n e s s o f t h e peaks i n the s o l i d . As w e l l , a s h o u l d e r a t 1270 cm 1 on the broad peak i n t h e 1300 cm 1 r e g i o n can be a s s i g n e d t o the c o m b i n a t i o n v-^+v2 °^  GF2" The r e m a i n i n g a b s o r p t i o n s can be i d e n t i f i e d w i t h the same i m p u r i t i e s t h a t were o b s e r v e d i n the m a t r i x e x p e r i m e n t s d i s c u s s e d above. These a r e l i s t e d i n t a b l e 2-15- E x p e r i m e n t s u s i n g a t h r e e t o two ^2'^2 r a t ' ° r e s i J l t e d i n an i n c r e a s e d p r o d u c t i o n o f 0^  and a r e l a t i v e d e c r e a s e i n t h e amount of o x y g e n - f l u o r i d e s . The p r o b l e m 116 -r e s u l t i n g from NO^F i m p u r i t y i n the 1300 cm ' r e g i o n has been d i s -c u s s e d i n s e c t i o n l l - B - 2 . The v a l u e o f 1305 cm ' has been a s s i g n e d t o b o t h t h e symm e t r i c NO s t r e t c h o f F N 0 2 > v ^ , and the 0-0 s t r e t c h o f 0 2 ^ 2' a ' s o v l * In t h e d i s c h a r g e o f 0^ and F^ m i x t u r e s a t v a r i o u s r a t i o s , the main p r o d u c t s by f a r have been ^ 2 ^ 2 ' ®k^2' ^2 a n < * ^3* ^° P 6 3 ^ o f near c o m p a r i b l e i n t e n s i t y a r e p r e s e n t t h a t c o u l d be a s s i g n e d t o 0 ^ 2 . In f a c t , a l l the a b s o r p t i o n s , i n c l u d i n g t h e weak o n e s , have been a s s i g n e d t o o t h e r m o l e c u l e s . I t woul d then appear t h a t t h e m a t e r i a l c o l l e c t e d by K i r s h e n b a u n / ' ^ was a c t u a l l y a m i x t u r e o f O^F^ and as s u g g e s t e d above. S i n c e O F 2 , 0^, O2 and F2 have a p p r e c -i a b l e vapour p r e s s u r e s a t 77°K, i t i s not e x p e c t e d t h a t they w o u l d be found by p r e v i o u s w o r k e r s s i n c e t h e i r t e c h n i q u e ^ ^ i n v o l v e d c o n d e n s a t i o n a t t h i s t e m p e r a t u r e . To f u r t h e r see i f ®-^2 m ' 9 n t be p r e s e n t i n s m a l l q u a n t i t i e s and thus o b s c u r e d by t h e o t h e r s t r o n g a b s o r p t i o n s i n f i g u r e 2-11, a s i m i l a r sample was a l l o w e d t o warm t o 77°K by a l l o w i n g the l i q u i d He t o b o i l away and r e p l a c i n g i t i n the r e s e r v o i r w i t h l i q u i d ' ^ . The -k s y s t e m was pumped on u n t i l t he p r e s s u r e f e l l t o about 10 t o r r . By t h i s means 0^, OF2 and o t h e r h i g h vapour p r e s s u r e p r o d u c t s c o u l d be removed l e a v i n g o n l y the h e a v i e r p r o d u c t s 0 ^ 2 , ^2^2 an<^' ' ^  P r e s e r , t » (1) 0^2' T h e r e P ° r t e d m e l t i n g p o i n t s V J / a r e : 0 F 2 > kS.k°K; Q 2 ? 2 ' , 1 9 ° K ; 0 ^ , 82°K; and 0 ^ 2 > 83°K. F i g u r e 2-12 shows the s p e c t r u m o f a sample o f 0 2 : f " 2 = 3:2 d e p o s i t e d a t k°K and warmed t o 77°K. - 118 -I t can be seen t h a t t h e ^2^2 a n d ®k^2 a D S O r P t ' o n s have d e c r e a s e d i n i n t e n s i t y because o f a l o s s o f sample so t h a t the com-b i n a t i o n s and o v e r t o n e s a r e no l o n g e r o b s e r v a b l e . p r o b a b l y a l o n g w i t h 0^ and F^, has a l m o s t c o m p l e t e l y d i s a p p e a r e d . The l e s s v o l a t i l e i m p u r i t i e s , NO^F, CO^ and F^CO, a r e reduced i n i n t e n s i t y but s t i l l p r e s e n t w h i l e 0^ has a l m o s t c o m p l e t e l y d i s a p p e a r e d . Sev-e r a l o t h e r a b s o r p t i o n s , b o t h broad and s h a r p , w h i c h remain even on f u r t h e r warming, a r e a t t r i b u t e d t o r e a c t i o n w i t h the C s l window. A g a i n , no a b s o r p t i o n s remain t h a t might be a s s i g n e d t o °^2' Thus, e x p e r i m e n t s w i t h t h e d i s c h a r g e o f u n d i l u t e d m i x t u r e s o f 0^ and F^ c o n f i r m t h e c o n c l u s i o n o f t h e m a t r i x e x p e r i m e n t s t h a t 0 F 9 i s not produced as a m o l e c u l a r s p e c i e s . - 119 -BIBLIOGRAPHY: CHAPTER I I 1. A.G. S t r e n g ; Chem. Rev., 6j_, 607 (1963) 2. J . J . T u r n e r ; Endeavour, 27 , 42 (1968) 3- J . J . T u r n e r ; Comp. I n o r g . Chem., i n p r e s s 4. A. A r k e l l , R.R. 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P h y s . , 52 , 4A18 (1970) 16. S . J . T u r n e r and R.D. H a r c o u r t ; Chem. Comm., 1967, 4 17- J.W. Nebgen, F . I . M etz, W.B. Rose; J . Am. Chem. S o c , 8 9 , 3118 (1967) - 120 -19- K.R. L o o s , C.T. G o e t s c h e l , V.A. C a m p a n i l e ; Chem. Comm., 1968, 1633 20. D.J. G a r d i n e r , N.J. Lawrence, J . J . T u r n e r ; J . Chem. Soc. ( A ) , 1971, 400 21. J . J . T u r n e r ; p r i v a t e c o m m unication 22. E.B. W i l s o n , J.C. D e c i u s , P.C. C r o s s ; " M o l e c u l a r V i b r a t i o n s " , M c G r a w - H i l l , 1955 23- J . A l d o u s and I.M. M i l l s ; S p e c t r o c h i m . A c t a , _[9.» 15^ 7 (1963) 24. P.N. N o b l e , G.C. P i m e n t e l ; J . Chem. P h y s . , 44, 3641 (1966) 25. A.D. Kirshenbaum, A.G. S t r e n g ; J . Chem. P h y s . , 35., 1440 (1961) 26. A.G. S t r e n g and L.V. S t r e n g ; J . Phys. Chem., 69, 1079 (1965) 27. P.H. K a s a i , A.D. Kirshenbaum; J . Am. Chem. S o c , 87 3069 (1965) 28. I . J . Malone and H.A. McGee, J r . ; J . Phys. Chem., 7J_, 3060 (1967) 29. (a) I . J . Solomon, J.K. Raney, A . J . Kacmarek, R.G. M a g u i r e , G.A. G.A. N o b l e ; J . Am. Chem. S o c , 89, 2015 (1967) (b) J.W. Nebgen, F.I. Me t z , W.B. Rose; J . Am. Chem. S o c , 89, 3118 (1967) (c) N.J.Lawrence, J .S. Ogden, J . J . T u r n e r ; Chem. Comm. 1966, 102 (d) I . J . Solomon, J.N. K e i t h , A . J . Kacmarek, J.K. Raney, J . Am. Chem. S o c , 90, 5408 C1968) 30. P.A. G i g u e r e , K. Herman; Can. J . Chem., 48_, 3473 (1970) 31. R.P. Hi r s c h m a n n , W.B. Fox, L.R. A n d e r s o n ; S p e c t r o c h i m . A c t a , 25A, 811 (1969) 32. M. A l l a v e n a , R. R y s n i k , D. W h i t e , V. C a l d e r , D.E. Mann; J . Chem. Ph y s . , 50, 3399 (1969) - 121 -33- J.M. B a s s l e r , P.L. Timms, J . I . M a r g r a v e ; I n o r g . Chem., S_, 729 (1966) 34. M. Harmony, R.J. Meyers; J . Chem. P h y s . , 37 .636 (1962) 3 5 . D.E. M i l l i g a n and M.E. J a c o x ; J . Chem. P h y s . , 40_, 2461 (1964) 36 . E.L. Pace and L. P i e r c e ; J . Chem. P h y s . , 2 3 , 1248 (1955) 37- D.E. M i l l i g a n , M.E. J a c o x , A.M. B a s s , J . J . Comeford, D.E. Mann; J . Chem. P h y s . , 42 , 3187 (1965) 38 . R.E. Dodd, J.A. R o l f e , L.A. Woodward; T r a n s . Faraday S o c , 52 , 145 (1956) - 122 -CHAPTER I I I Cis-HNSO: MATRIX I.R. STUDIES AND FORCE FIELD A. BACKGROUND 1. PREPARATION The compound c i s - t h i o n y 1 i m i d e , cis-HNSO ( i n g e n e r a l t h r o u g h -o u t t h i s t h e s i s HNSO w i l l o f t e n be used t o mean c i s - H N S O ) , has been p r e p a r e d by two methods. In 19^2 S c h e n k ^ found t h a t m i x i n g s t o i c h i -m e t r i c q u a n t i t i e s o f NH^ and S O C ^ gave HNSO i n q u a n t i t a t i v e y i e l d a c c o r d i n g t o the r e a c t i o n 3NH 3 + S 0 C I 2 •+ HNSO + 2NH i jCl ( 3 " D I t i s g e n e r a l l y found t h a t SO^ i s p r e s e n t as an i m p u r i t y , p r o b a b l y from the r e a c t i o n o f e i t h e r S O C l ^ o r HNSO w i t h w a t e r . Hov/ever, t h e r e i s no e v i d e n c e f o r t h e p r e s e n c e o f NH^, S O C ^ o r HCI i n the f i n a l gas m i x t u r e . The o t h e r method f o r p r e p a r a t i o n o f HNSO has been r e p o r t e d an (3) (2) by Glemser and R i c h e r t . The h y d r o l y s i s o f FSN g i v e s HNSO as an i n t e r m e d i a t e . T h i s has been d e m o n s t r a t e d w i t h mass s p e c t r o s c o p y and was used by K i r c h h o f f as a means o f o b t a i n i n g HNS^O i n h i s microwave s p e c t r o m e t e r c e l l . T h i s method, however, does not a l l o w (2) f o r t h e i s o l a t i o n o f HNSO s i n c e i t i s f u r t h e r h y d r o l y s e d . F o r (2) the f o r m a t i o n o f HNSO from FSN and w a t e r Glemser and R i c h e r t p o s t -u l a t e d a mechanism i n v o l v i n g t he i n t e r m e d i a t e HOSN: - 123 -\ o F N = S H \ N = S N O —> / <v . / H O (3-2) HOSN, however, has not been i d e n t i f i e d , s u g g e s t i n g e i t h e r t h a t t he mechanism i s i n c o r r e c t o r t h a t HOSN i s v e r y u n s t a b l e . 2. INFRARED SPECTRUM (4) In 1958 B e c h e - G o e h r i n g , Schwarz and S p i e s s s t u d i e d t h e i n f r a r e d s p e c t r u m o f the polymer formed from the c o n d e n s a t i o n o f HNSO. T h e i r s p e c t r u m c o n t a i n e d numerous i m p u r i t y a b s o r p t i o n s and due t o a l a c k o f knowledge about t h e f r e e HNSO s p e c t r u m , m i s a s s i g n m e n t s were made. As a r e s u l t l i t t l e c o u l d be s a i d about t h e n a t u r e o f the p o l y -mer e x c e p t t h a t i t s t i l l p o s s e s s e d an i n t e n s e hydrogen s t r e t c h and n o t h i n g was l e a r n e d about the m o l e c u l e HNSO. The gas phase i . r . s p e c t r a o f HNSO and DNSO were o b t a i n e d by R i c h e r t ^ i n I96I. T a b l e 3"1, t a k e n from r e f e r e n c e 5. shows R i c h e r t ' s r e s u l t s and a s s i g n m e n t s . U s i n g t h e s e a s s i g n m e n t s and ap-p r o x i m a t i n g HNSO as SO2 ~ t h a t i s i g n o r i n g t he HN s t r e t c h , t h e HNS bend and the t o r s i o n as w e l l as u s i n g SO^ bond l e n g t h s and a n g l e s -o R i c h e r t c a l c u l a t e d t he f o l l o w i n g f o r c e c o n s t a n t s : f = 8.2 mdynes/A, o f c n = 8.6 mdynes/A and f M C . n = 0.6 mdynes/A. These v a l u e s , s i n c e they - 124 -T a b l e 3~1- \frequencies and a s s i g n m e n t s f o r cis-HNSO and cis-DNSO i n t h e gas phase ( R i c h e r t ^ ) v (cm ) as s i g n m e n t HNSO DNSO V j , HN s t r . 3345 2480 v 2 > OSN asym. s t r . 1261 1257 \>y OSN sym. s t r . 1090 1055 v^, HNS bend 911 757 v 6 , t o r s i o n 759 594 v c , OSN bend 453 410 - 125 -a r e based upon a g r o s s a p p r o x i m a t i o n , s h o u l d not be e x p e c t e d t o be v e r y a c c u r a t e . 3. MICROWAVE SPECTRUM AND STRUCTURE (3) The s t r u c t u r e o f HNSO has been d e t e r m i n e d by K i r c h h o f f From t h e microwave s p e c t r a o f c i s - t h i o n y l i m i d e and i t s i s o t o p i c homologs c o n t a i n i n g d e u t e r i u m , ^ N , '^0 and ^ S ( i n n a t u r a l abund-ance) he was a b l e t o c a l c u l a t e t h e f o l l o w i n g s t r u c t u r a l p a r a m e t e r s : o o o d M u = 1.029 ± 0.01 A, d.. c = 1.512 + 0.005 A, d C A = 1.451 ± 0.005 A, <HNS = 115.8 ± 1°, and <NS0 = 120.4 ± 0.5°. As w e l l , he was a b l e t o show t h a t the m o l e c u l e i s c i s p l a n a r . The s t r u c t u r e o f c i s - t h i o n y -1imide i s g i v e n i n f i g u r e 3~1. K i r c h h o f f a l s o o b t a i n e d the f o l l o w i n g d i p o l e moments from h i s microwave work: u = 0.893 ± 0.003 D, 3 u, = 0.181 ± 0.005 D and u = 0.9H ± 0.003 D. D 4. ULTRAVIOLET SPECTRUM The u l t r a v i o l e t s p e c t r u m o f HNSO i n t h e gas phase has a l s o been o b s e r v e d . A l l e g r e t t i ^ found two a b s o r p t i o n s . The f i r s t was o an i n t e n s e , d i f f u s e band a t 2700 A w h i c h he a s s i g n e d t o a s i n g l e t e x c i t e d s t a t e . The d i f f u s e n e s s , l i k e l y due t o p r e d i s s o c i a t i o n , made tho r o u g h a n a l y s i s i m p o s s i b l e . However, by f o l l o w i n g the v i b r a t i o n a l p r o g r e s s i o n i n t h e OSN b e n d i n g c o o r d i n a t e and e s t i m a t i n g Franck-Condon f a c t o r s , he was a b l e t o show t h a t the e x c i t e d s t a t e had i n c r e a s e d OS and NS bond l e n g t h s c h a r a c t e r i s t i c o f s t a t e s r e s u l t i n g from 7r •*• 7r o r - 126 -F i g u r e 3~ 1 • The s t r u c t u r e o f c i s - t h i o n y 1 i mi de o b t a i n e d by K i r c h h o f f - 127 -n -*• TT t rans i t i o n s . A l 1 e g r e t t i ' s ^ second a b s o r p t i o n was a weak c o n t i n u u m a t o around 3500 A. The co n t i n u u m and the low i n t e n s i t y s u g g e s t e d t h i s t r a n s i t i o n t o be t o a d i s s o c i a t i v e t r i p l e t s t a t e . However, the d i s -s o c i a t i o n o f t h e m o l e c u l e r e s u l t e d i n the c o a t i n g o f t h e m i r r o r s i n the l o n g p a t h l e n g t h c e l l and f u r t h e r s t u d y o f t h i s t r a n s i t i o n was a l s o i m p o s s i b l e . A t t e m p t s t o o b t a i n an u l t r a v i o l e t s p e c t r u m o f HNSO i n a m a t r i x a t k°K met w i t h f a i l u r e as w e l l - the r e s u l t was a c o m p l e t e l y b l a c k e d o ut p h o t o g r a p h i c p l a t e . As w i l l be shown i n c h a p t e r IV, t h i s was p r o b a b l y due t o p h o t o d i s s o c i a t i o n and m o l e c u l a r rearrangement o f HNSO w h i c h r e s u l t e d i n t h e p r e s e n c e o f numerous p h o t o l y s i s p r o d u c t s i n s u f f i c i e n t q u a n t i t i e s i n t h e m a t r i x a t t h e e x p o s u r e t i m e s used t o cause n e a r l y c o m p l e t e a b s o r p t i o n t h r o u g h o u t t h e u l t r a v i o l e t r e g i o n . F i g u r e 3"2 i s t a k e n from r e f e r e n c e (6) and i s a p r o p o s a l f o r t h e o r d e r i n g and t y p e s o f the low l y i n g e l e c t r o n i c s t a t e s o f HNSO. A l t h o u g h i t i s based on a v e r y a p p r o x i m a t e model and the energy s p a c i n g s a r e o f no meaning, the o r d e r i n g o f s t a t e s i s r e a s o n a b l e and can be c o r r e l a t e d w i t h the m o l e c u l e ' s e l e c t r o n i c s p e c t r a as w e l l as the known s t a t e s o f t h e i s o e 1 e c t r o n i c m o l e c u l e SO2. 5. REASONS FOR INTEREST C i s - t h i o n y l i m i d e was o r i g i n a l l y s t u d i e d i n the u l t r a v i o l e t because i t i s s i m i l a r t o S0„ whose e l e c t r o n i c s t a t e s and s p e c t r u m - 129 -have not been f u l l y e x p l a i n e d . I t was hoped t h a t the s p e c t r u m o f HNSO would p r o v i d e some c l u e s f o r a b e t t e r u n d e r s t a n d i n g o f SQ2. However, o f more i n t e r e s t t o the c h e m i s t and the i n f r a r e d s p e c t r o s -c o p i s t a r e t h e NS and SO bonds. W h i l e t h e SO bond i s e x p e c t e d t o be v e r y much l i k e the SO bond i n SO^, the NS bond does not f i n d an easy a n a l o g u e . The NS bonds i n NS, FSN and F^SN as w e l l as o t h e r m o l e c u l e s have been s t u d i e d and t h e i r l e n g t h s and f o r c e c o n s t a n t s c o r r e l a t e d ^ . The v a r y i n g bond s t r e n g t h s r e s u l t i n g from s u l f u r ' s m u l t i p l e v a l e n c y p r o v i d e a v e r y i n t e r e s t i n g s e r i e s . An a c c u r a t e f o r c e f i e l d d e t e r m i n a t i o n f o r HNSO would p r o v i d e more d a t a t h a t might a i d i n t h e u n d e r s t a n d i n g o f t h i s s e r i e s . A l s o , new compounds c o n t a i n i n g NS bonds might be p r e p a r e d by the p h o t o l y s i s o f HNSO i n a m a t r i x . From i . r . s p e c t r o s c o p y t h e f o r c e c o n s t a n t s o f t h e s e c o u l d be found and compared w i t h t he known compounds t o g i v e f u r t h e r i n f o r m a t i o n on the bo n d i n g i n a l l o f them. In a c t u a l f a c t , t he s t u d y o f t h e p h o t o c h e m i s t r y o f HNSO i n a m a t r i x and t he d e t e r m i n a t i o n , v i a i . r . s p e c t r a , o f t h e s t r u c t u r e s o f the p r o d u c t s p r o v e d t o be a v e r y i n t e r e s t i n g r e s e a r c h p r o b l e m . T h i s s t u d y i s p r e s e n t e d i n c h a p t e r IV o f t h i s t h e s i s . - 130 " B. MATRIX I.R. SPECTRA 1. INTRODUCTION B e f o r e a p h o t o l y s i s s t u d y o f HNSO c o u l d be u n d e r t a k e n i n a m a t r i x , i t was f i r s t n e c e s s a r y t o have a d e t a i l e d u n d e r s t a n d i n g o f the i n f r a r e d s p e c t r u m o f HNSO under h i g h r e s o l u t i o n i n the m a t r i x . T h i s was t r u e f o r the v a r i o u s i s o t o p e s t h a t would be r e q u i r e d f o r de-t e r m i n a t i o n o f the s t r u c t u r e o f p h o t o l y s i s p r o d u c t s and f o r the d i f f e r -• en t m a t r i c e s used. I t was a l s o n e c e s s a r y t o have a v a i l a b l e a r e l i a b l e f o r c e f i e l d f o r HNSO t o a l l o w the t r a n s f e r o f f o r c e c o n s t a n t s t o s i m i -l a r m o l e c u l e s formed on p h o t o l y s i s . F o r c e f i e l d s f o r the gas phase s p e c t r a o f HNSO and DNSO (8) have been p u b l i s h e d but t h e s e a r e u n s a t i s f a c t o r y f o r s e v e r a l r e a s o n s . F i r s t l y , t h e m o l e c u l a r p a r a m e t e r s assumed i n t h e s e c a l c u l a t i o n s d i f f e r s i g n i f i c a n t l y from t h o s e d e t e r m i n e d more r e c e n t l y by microv/ave s p e c t r o s -(2) (Q) copy . S e c o n d l y , and more i m p o r t a n t , E y s e l employed a c o m p u t a t i o n -Co,) a l t e c h n i q u e d e v i s e d by Becher and Ma t t e s w h i c h must be r e g a r d e d w i t h s u s p i c i o n . A l t h o u g h a p e r f e c t f r e q u e n c y f i t i s g u a r a n t e e d a t each s t a g e o f t h e c a l c u l a t i o n , t h e prob l e m i s u n d e r d e t e r m i n e d : seven f o r c e c o n s t a n t s a r e c a l c u l a t e d from s i x o b s e r v e d f r e q u e n c i e s (HNSO and DNSO a r e t r e a t e d s e p a r a t e l y ) . Thus the f o r c e f i e l d s r e p o r t e d r e p r e s e n t o n l y one c h o i c e from among the i n f i n i t y o f p o s s i b i l i t i e s g e n e r a t e d by t h e i r method. A d e t a i l e d and i n c i s i v e c r i t i q u e o f t h i s a p p roach has been p u b l i s h e d by A v e r b u k h , Mayants and S h a 1 t u p e r ^ ' ^ . - 131 -In t h i s work an e l e v e n c o n s t a n t f o r c e f i e l d has been a d j u s t e d by a c o n v e n t i o n a l l e a s t s q u a r e s t e c h n i q u e ^ 1 ^ (see c h a p t e r I) t o f i t t w e n t y - n i n e o b s e r v e d f r e q u e n c i e s from HNSO and s i x i s o t o -15 34 p i c a l l y s u b s t i t u t e d m o l e c u l e s c o n t a i n i n g d e u t e r i u m , N and S. 2. EXPERIMENTAL The c r y o s t a t , s p e c t r o p h o t o m e t e r and gas h a n d l i n g equipment used a r e d e s c r i b e d i n c h a p t e r I. Samples were i s o l a t e d i n argon and n i t r o g e n m a t r i c e s (Matheson, p r e p u r i f i e d g r a d e s ) . Mole r a t i o s o f @ m a t r i x gas t o HNSO (M/R) v a r i e d between 50 and 1000. D e p o s i t i o n was c a r r i e d o ut a t r a t e s a v e r a g i n g 2 m i l l i m o l e s t o t a l sample p e r hou r . The HNSO was p r e p a r e d i n the gas phase by the method o f S c h e n k ^ . S i n c e monomeric HNSO p o l y m e r i z e s on c o n d e n s a t i o n , samples were s t o r e d i n t h e gas phase a t room t e m p e r a t u r e . Over a p e r i o d o f weeks a s l i g h t d e c o m p o s i t i o n o f HNSO was i n d i c a t e d by a r e l a t i v e i n -c r e a s e i n SO^, t h e o n l y i n f r a r e d a c t i v e i m p u r i t y p r e s e n t i n m e a s u r a b l e amounts. D e u t e r i u m and ^ N s u b s t i t u t i o n were a c h i e v e d u s i n g ND^ (Merck, Sharp and Domme) and ^NH^ ( i s o m e t C o r p o r a t i o n , 95% p u r i t y ) r e s p e c t i v e l y . 3. RESULTS 34 (a) Sample i s o l a t i o n and S a b s o r p t i o n s : Because HNSO i s p o l y m e r i c as a low t e m p e r a t u r e s o l i d , i t was e s s e n t i a l t o f i n d m a t r i x c o n d i t i o n s w h i c h g u a r a n t e e d i s o l a t i o n o f t h e monomeric s p e c i e s . F o r t u n a t e l y , t he - 132 _ NH s t r e t c h i n g mode o f HNSO pr o v e d t o be an e x c e l l e n t i n d i c a t o r o f monomer i s o l a t i o n . F i g u r e 3~3, (a) and ( b ) , shows a s u r v e y o f HNSO d e p o s i t e d i n argon a t r e l a t i v e l y h i g h d i l u t i o n (M/R = 8 0 0 ) . A l l the a b s o r p t i o n s below 1500 cm 1 can be a s s i g n e d t o e i t h e r HNSO o r the SO2 i m p u r i t y . The two s h a r p , weak a b s o r p t i o n s a t 1233-4 cm 1 and 895-7 cm ' s h i f t e d s l i g h t l y t o low f r e q u e n c y o f the and a b s o r p t i o n s 34 o f HNSO a r e due t o m o l e c u l e s c o n t a i n i n g S i n n a t u r a l abundance. From t h e h i g h r e s o l u t i o n s p e c t r u m the e s t i m a t e d i n t e g r a t e d i n t e n s i t y r a t i o f o r the 1233-4 cm" 1 (HN^SO) peak t o the 1248.7 (HN 3 2SO) peak 34 i s about 1%. The n a t u r a l abundance o f S i s k%. D i f f i c u l t i e s i n c a l c u l a t i n g i n t e n s i t i e s a c c u r a t e l y i s assumed t o a c c o u n t f o r t h e d i s c r e p a n c y . Under h i g h r e s o l u t i o n o f the 900 cm 1 r e g i o n ( f i g u r e 3 - 4 ) , t h e 8 9 5 . 7 cm ' a b s o r p t i o n appears t o g e t h e r w i t h an o v e r l a p p i n g peak a t 8 9 4 . 6 cm The r a t i o o f the combined i n t e n s i t i e s o f t h e s e two peaks t o t h a t o f t h e 9 0 0 . 4 cm ' peak i s found t o be about 12%. To a c c o u n t f o r t h i s l a r g e d i f f e r e n c e from k%, the two peaks a r e -1 34 a s s i g n e d s e p a r a t e l y , t he 8 9 5 . 7 cm t o the S m o l e c u l e and the 8 9 3 . 8 cm ' t o t h e o v e r t o n e o f w h i c h i s o b s e r v e d because o f a s l i g h t Fermi r e s o n a n c e w i t h the = 1 v i b r a t i o n a l l e v e l . T h i s r e s o n a n c e i s f u r t h e r d i s c u s s e d i n the next s e c t i o n . An e s t i m a t e d i n t e n s i t y f o r the s i n g l e 895-7 cm 1 peak was found t o g i v e a r a t i o o f about 6% t o t h e 9 0 0 . 4 cm 1 peak i n t e n s i t y . T h i s i s c o n s i d e r e d 34 r e a s o n a b l e f o r the S m o l e c u l e . F i g u r e 3"3. The i n f r a r e d s pectrum o f cis-HNSO i n argon m a t r i c e s . - 134 -^ (cm-i) 9 0 5 9 0 0 8 9 5 • t • i i i 1 i i — i — i — I — i — i — i c is H N S O F i g u r e 3-4. The h i g h r e s o l u t i o n s p e c t r u m o f o f cis-HNSO showing 34 b o t h t h e S i s o t o p i c s p l i t t i n g and t h e 2 v c o v e r t o n e o t o low f r e q u e n c y . - 135 -The r e g i o n above 3000 cm -1 i s s l i g h t l y more c o m p l i c a t e d t o -1 i n t e r p r e t . F i g u r e 3_3 (a) r e v e a l s a b r o a d , weak a b s o r p t i o n a t 3200 cm , 100 cm 1 below t h e peak a t 3308.5 cm ' w h i c h has been a s s i g n e d t o the HN s t r e t c h . A t lower d i l u t i o n t he i n t e n s i t y o f t h e - f e a t u r e a t 3200 cm 1 i s g r e a t l y enhanced as shown i n f i g u r e 3~3 (c) f o r M/R = 200. The s p e c t r u m shown i n f i g u r e 3-3 (d) r e s u l t e d when t h i s sample was warmed t o about 35°K and r e c o o l e d . The a b s o r p t i o n a t 3200 cm f a v o u r e d a t low d i l u t i o n , has broadened and g a i n e d i n t e n s i t y w h i l e t he f e a t u r e a t 3308.5 cm 1 has d i s a p p e a r e d . T h i s b e h a v i o r i s c h a r a c t e r i s t i c o f a g g r e -g a t i o n i n t h e m a t r i x and s u g g e s t s t h a t t h e 3308.5 cm ' a b s o r p t i o n can be i d e n t i f i e d w i t h t he monomer and t h e 3200 cm ' f e a t u r e w i t h t h e di m e r o r h i g h e r a g g r e g a t e s . I t i s t e m p t i n g t o a s s i g n the low f r e q u e n c y peak t o a d i m e r c o n s i s t i n g o f a hydrogen bonded eight-membered r i n g . N S H O O H S N I t has been p o i n t e d o u t by P i m e n t e l and M c C l e l l a n (12) t h a t hydrogen s t r e t c h i n g modes a r e most s t r o n g l y e f f e c t e d by hydrogen b o n d i n g . - 136 -L a r g e d e c r e a s e s i n s t r e t c h i n g f r e q u e n c i e s and b r o a d e n i n g o f peaks c o u p l e d w i t h d r a m a t i c i n t e n s i t y enhancements a r e o f t e n o b s e r v e d . The 3200 cm ' f e a t u r e shows t h e n e c e s s a r y s h i f t and b r o a d e n i n g f o r hydrogen b o n d i n g . T h e r e f o r e , assuming hydrogen b o n d i n g i s a s s o c i a t e d w i t h HNSO, t h i s i n t e n s i t y enhancement s u g g e s t s t h a t , even though the 3200 cm 1 and 3308.5 cm 1 a b s o r p t i o n s a r e o f near e q u a l i n t e n s i t y a t M/R = 200, t h e a c t u a l c o n c e n t r a t i o n o f d i m e r i s s t i l l q u i t e s m a l l . Thus t h i s peak i s a s e n s i t i v e measure o f i s o l a t i o n . The above c o n c l u s i o n s then a l l o w the a s s i g n m e n t o f o t h e r weaker, but s t i l l b r o a d and c o n c e n t r a t i o n dependent, f e a t u r e s i n t h e M/R = 200 s p e c t r u m t o t h e same d i m e r . These a r e shown as a b r o k e n l i n e i n f i g u r e 3~3 (b) a t 945 cm 852 cm 1 and 478 cm \ On d i m e r -i z a t i o n SO and NS s t r e t c h e s a t 1248.7 cm 1 and 1082.7 cm s i n c e they a r e l e a s t e f f e c t e d by hydrogen bonding, show o n l y s l i g h t b r o a d -e n i n g t o low f r e q u e n c y w h i l e t h e o t h e r a b s o r p t i o n s show l a r g e s h i f t s . The peak a t 945 cm 1 i s t h e HNS bend s h i f t e d up from 900.4 cm ', a t 852 cm 1 i s the t o r s i o n , o r o u t o f p l a n e mode, s h i f t e d f r o m 754.7 cm ' and a t 478 cm 1 i s the NS0 bend s h i f t e d from 447.4 cm These a b s o r p (12) t i o n s show s h i f t s t h a t a r e r e a s o n a b l e f o r each t y p e of mode . They a l s o show the c h a r a c t e r i s t i c b r o a d e n i n g f o r hydrogen bonded d i m e r a b s o r p t i o n s . A s p e c t r u m o b t a i n e d a t M/R = 50 shows t h e s e a b s o r p t i o n s t o be s t i l l more i n t e n s e and a l s o c o n t a i n s numerous o t h e r b r o a d f e a t u r e s t h a t c o u l d l i k e l y be a s s i g n e d t o h i g h e r a g g r e g a t e s o r t o a g g r e g a t i o n - 137 -w i t h S C y The 945 cm" 1, 852 cm" 1 and 478 cm" 1 peaks a t M/R = 50 a r e a l s o shown i n f i g u r e 3_3 (b) as heavy l i n e s . A l t h o u g h t h i s a s p e c t was not f u r t h e r p u r s u e d , t h e a b s o r p t i o n s a s s o c i a t e d w i t h the hydrogen bonded HNSO dimer a r e l i s t e d i n t a b l e 3-2. U s i n g the r e l a t i v e l y l a r g e i n t e n s i t y o f the con c e n -t r a t i o n dependent f e a t u r e a t 3200 cm 1 as a measure o f a g g r e g a t i o n , a d i l u t i o n o f M/R = 400 was found t o p r o v i d e s a t i s f a c t o r y i s o l a t i o n and was used f o r most o f the e x p e r i m e n t s r e p o r t e d h e r e . (b) Fermi Resonance o f and 2v,.: As p o i n t e d o u t above, a weak -1 14 a b s o r p t i o n a t 894.6 cm i n t h e H NS0 s p e c t r u m has been a s s i g n e d t o the o v e r t o n e o f v^, t h e NS0 bend. The peak i s seen o n l y because i t has g a i n e d a s m a l l amount o f i n t e n s i t y from as a r e s u l t o f a Fermi r e s o n a n c e i n t e r a c t i o n . In H^NSO the e f f e c t becomes much l a r g e r and a n e a r e q u a l i n t e n s i t y d o u b l e t r e s u l t s as shown i n f i g u r e 3_5» S i n c e the d o u b l e t components a r e o f near e q u a l i n t e n s i t y , t h e m i x i n g o f t h e = 1 and Vj. = 2 s t a t e s r e s u l t i n g from the i n t e r a c t i o n i s c o m p l e t e and t h e v a l u e o f must be ta k e n as an a v e r a g e o f the 890.6 cm 1 and -1 -1 14 887.7 cm peaks. T h i s i s found t o be 889.2 cm In H NS0, s i n c e t h e r e s o n a n c e i s weak, t h e f r e q u e n c y f o r i s ta k e n as 900.4 cm the f r e q u e n c y o f the s t r o n g a b s o r p t i o n . T a b l e 3_3 shows the d i f f e r e n c e s between and 2v^  f o r the v a r i o u s i s o t o p e s o f HNSO i n argon and n i t r o g e n m a t r i c e s . For the '"'N s u b s t i t u t e d m o l e c u l e i n argon the s e p a r a t i o n i s o n l y 0.4 cm 1 14 and thus a s t r o n g r e s o n a n c e o c c u r s w h i l e f o r the N m o l e c u l e t h e - 138 -T a b l e 3 - 2 . Cis-HNSO dimer a b s o r p t i o n s and a s s i g n m e n t s , v(cm ^) a s s i g n m e n t 3200 HN s t r . 1245 SO s t r . 1080 NS s t r . 945 HNS bend 852 o u t o f p l a n e 478 NSO bend - 139 -Z / C c r r r 1 ) 8 9 4 - 8 9 0 8 8 6 i i i 1 1— F i g u r e - 140 -T a b l e 3_3« A s t u d y o f Fermi r e s o n a n c e i n cis-HNSO. S e p a r a t i o n s o f u n p e r t u r b e d v, and 2vc (cal.) l e v e l s . i s o t o p e and m a t r i x v 2 t(cm ] ) 2v 5(cm~ 1) c a l . v4"2v5 -1 cm HNSO/Ar 900.4 894.8 (obs.893-8) 5.6 HNS0/N 2 923 910 13 H 1 5 N S 0 / A r 889-2* 888.8 (obs.887.7) 0.4 H 1 5NS0/N 2 911 904 7 DNSO/Ar 751.5 800.6 -49.1 "Average o f d o u b l e t . - 141 -d i f f e r e n c e i s 5.6 cm and t h e r e i s o n l y a weak i n t e r a c t i o n . For the d e u t e r a t e d s p e c i e s no resonan c e was o b s e r v e d f o r the l a r g e s e p a r a t i o n s o f and 2 v ^ w h i l e w i t h a n i t r o g e n m a t r i x , s e p a r a t i o n s between and 2 V j . o f 13 cm 1 f o r and 7 cm f o r 1 a l s o r e s u l t e d i n no d e t e c t a b l e r e s o n a n c e . Of i n t e r e s t here i s the c l o s e n e s s o f the o b s e r v e d o v e r t o n e t o two t i m e s the fundamental (v^(v=2) = 893-8 cm 1 and 2v,- = 894.8 cm 1 14 f o r H NSO i n A r ) . T h i s s u g g e s t s t h a t the a n h a r m o n i c i t y i n the mode i s v e r y s m a l l . Fermi r e s o n a n c e , w h i c h r e s u l t s from a breakdown o f t h e harmonic o s c i l l a t o r a p p r o x i m a t i o n , a l s o depends on a n h a r m o n i c i t y P e r t u r b a t i o n t h e o r y shows t h a t t h e s t r e n g t h o f the i n t e r a c t i o n between two z e r o t h o r d e r ( h a r m onic o s c i l l a t o r ) v i b r a t i o n a l s t a t e s depends on the m a t r i x element o f t h e c u b i c term i n the p o t e n t i a l e nergy e x p r e s s i o n i n v o l v i n g both c o o r d i n a t e s d i v i d e d by t h e z e r o t h o r d e r energy s e p a r a t i o n 2 o [ < * 1 ( v 1 = D | K 1 2 2 Q 1 Q 2 | <J)2(v2=2)>]2 AE = (3-3) E°( V l=l) - E°(v 2=2) The n u m e r a t o r , and thus t h e r e s o n a n c e , then depends on the c u b i c f o r c e c o n s t a n t i n normal c o o r d i n a t e s , ^ ] 2 2 ^ ^ ' ' N T N E C A S E ° ^ H ^ N S O an energy s e p a r a t i o n o f o n l y 5-6 cm ' r e s u l t s i n a weak i n t e r a c t i o n . How-e v e r , even f o r H'^NSO, where t h e z e r o t h o r d e r s e p a r a t i o n i s e s t i m a t e d a t 0.4 cm ' and the i n t e n s i t i e s s u g g e s t a c o m p l e t e m i x i n g o f z e r o t h . o r d e r s t a t e s , t he resonance o n l y causes a s p l i t t i n g o f 2.9 cm ' o r a s h i f t from the a v e r a g e , AE, o f 1.5 cm '. By c o m p a r i s o n i n C O ^ where a s t r o n g Fermi resonance i s o b s e r v e d the s e p a r a t i o n o f the d o u b l e t i s - 142 -102.8 cm . Thus i t i s e v i d e n t t h a t the resonance between 2v,_ and o f HNSO i s v e r y weak. T h i s r e q u i r e s t h a t the c u b i c f o r c e c o n s t a n t K j 2 2 °e s m a ' ' _ i.e. the anha rmon i c i t y i s s m a l l . Thus both the f r e q u e n -cy o f the o v e r t o n e and t h e e x t e n t o f the resonance s u g g e s t t h a t v,. has a v e r y low a n h a r m o n i c t y . S i n c e the f o r c e f i e l d i s c a l c u l a t e d i n the a p p r o x i m a t i o n o f z e r o a n h a r m o n i c i t y , t h i s o b s e r v a t i o n w i l l make the f o r c e c o n s t a n t s more m e a n i n g f u l u n l e s s an u n u s u a l l y l a r g e a n h a r -m o n i c i t y i n a n o t h e r mode overwhelms the e f f e c t . (c) M a t r i x S p l i t t i n g : The HN s t r e t c h i n g and the t o r s i o n a l modes o f HNSO i n an a r g o n m a t r i x c o n s i s t e n t l y appear as d o u b l e t s . S i m i l a r l y , the a s y m m e t r i c s t r e t c h o f SO^ i s always a d o u b l e t . These a r e a l l shown under h i g h r e s o l u t i o n i n f i g u r e 3 -6. The s p l i t t i n g s a r e f o r v(HN) about 5-1 cm \ f o r v ( t o r s i o n ) 1.7 cm 1 and f o r o f SO^ 4.1 cm In a l l c a s e s both peaks o f the d o u b l e t a r e r e l a t i v e l y s h a r p , i n t e n s i t i e s do not show a d e f i n i t e c o n c e n t r a t i o n dependence and a b s o r p t i o n s appear as s i n g l e t s i n N^ m a t r i c e s . These s u g g e s t t h a t t h e s p l i t t i n g s a r e not due t o a s s o c i a t i o n . The p o s s i b i l i t y t h a t t h e s e s p l i t t i n g s a r e due t o r o t a t i o n w i t h i n the m a t r i x cannot be r u l e d o u t w i t h o u t c a r e f u l t e m p e r a t u r e s t u d i e s w h i c h were not p o s s i b l e i n t h i s work. However, i t i s g e n e r a l l y f e l t t h a t m o l e c u l e s o f t h e s i z e o f HNSO w i l l not r o t a t e i n a m a t r i x w h i l e the r o t a t i o n a l s p l i t t i n g o f o f SO^, o n l y 0.5 cm 1 i n a k r y p t o n m a t r i x ^ 1 ^ , i s not e x p e c t e d t o be as l a r g e as 4.1 cm In f a c t , the r o t a t i o n i s p r o b a b l y p r e s e n t but u n r e s o l v e d i n the i n d i v i d u a l peaks o f the d o u b l e t . F i g u r e 3~°. v. and o f cis-HNSO and v_ o f S0„ showing m a t r i x I D 5 L s p l i t t i ngs. - 144 -T h e r e f o r e , t h e s e s p l i t t i n g s have been a s c r i b e d t o the o c -cupancy o f d i f f e r e n t s i t e s w i t h i n t he argon l a t t i c e . T h i s t y p e o f s p l i t t i n g i s c h a r a c t e r i s t i c o f argon m a t r i c e s and f a l l s under t h e h e a d i n g o f " m a t r i x s p l i t t i n g s " d i s c u s s e d i n c h a p t e r I . I t s h o u l d be p o i n t e d o u t t h a t t h e o t h e r peaks s h o u l d show an e f f e c t due t o t h i s d i f f e r e n c e i n s i t e s , but t h e s p l i t t i n g s f o r t h e s e modes a r e p r o b a b l y t o o s m a l l t o r e s o l v e and appear as no more than s l i g h t b r o a d e n i n g s o f t h e peak s . (d) M a t r i x S h i f t s : A r and N^: T a b l e 3~4 r e p r e s e n t s t h e o b s e r v e d f r e q u e n c i e s o f HNSO i n argon and n i t r o g e n m a t r i c e s and the s h i f t s from t h e gas phase v a l u e s ^ (A=\> . -v ) . These r e s u l t s a r e 3 r m a t r i x gas c o n s i s t e n t w i t h o t h e r o b s e r v a t i o n s o f m a t r i x e f f e c t s ^ ' : t h e av e r a g e a b s o l u t e s h i f t i s s l i g h t l y l e s s i n argon (13 cm ') than i n n i t r o g e n (16 cm ' ) ; t h e argon f r e q u e n c i e s a r e c o n s i s t e n t l y l o w e r than t h o s e i n the gas phase whereas both p o s i t i v e and n e g a t i v e s h i f t s a r e found i n n i t r o g e n ; and modes i n v o l v i n g hydrogen show p a r t i c u l a r l y l a r g e s h i f t s i n n i t r o g e n . T a b l e 3 - 5 compares t h e argon m a t r i x s h i f t s f o r HNSO and DNSO. Of i n t e r e s t a r e the d e c r e a s e s on d e u t e r a t i o n o f A(A=v. - V ) Ar gas f o r V | , and v^. These modes must p o s s e s s a l a r g e amount o f h y d r o -gen d i s p l a c e m e n t , f o r the d e c r e a s e i n a m p l i t u d e upon s u b s t i t u t i o n o f the l a r g e r mass o f d e u t e r i u m and t h e r e s u l t i n g d e c r e a s e i n i n t e r a c t i o n w i t h the m a t r i x i s r e f l e c t e d as a s m a l l m a t r i x s h i f t f o r DNSO i n t h e s e modes. T h i s i s f u r t h e r s u p p o r t o f t h e a s s i g n m e n t s g i v e n i n t a b l e 3 " 1 . - 145 -T a b l e 3"4 . M a t r i x s h i f t s f o r cis-HNSO i n argon and n i t r o g e n . . (a) gas phase v ( cm )^ A r v ( cm m a t r i x A ( c n T V b > N 2 v ( cm ' ) ma t r i x A ( c m - V b ) V l 3345 3308 .5 -37 3303 -42 V 2 1261 1248.7 -12 1252 - 9 V 3 1090 1082.7 - 7 1094 + 4 v 4 911 900.4 -11 923 + 12 V 5 453 4 4 7 . 4 - 6 455 + 2 v 6 759 7 5 4 . 7 - 4 774 + 15 (a) from r e f e r e n c e 5 (b) A = v ( m a t r i x ) - v ( g a s ) - 146 -T a b l e 3~5. Comparison o f m a t r i x s h i f t s [A = v ( m a t r i x ) - v ( g a s ) j f o r HNSO and DNSO i n a r g o n . A(cm HNSO DNSO v -37 -12 - 7 -11 - 6 - k -27 -12 - 7 - 5 ? 0 - 147 -The r e s u l t s o f p h o t o l y s i s o f HNSO i n s o l i d were g r e a t l y c o n f u s e d by the a p p a r e n t i n t e r a c t i o n o f t h e p h o t o l y s i s p r o d u c t s w i t h the m a t r i x . For t h i s r e a s o n argon was chosen as the most s u i t a b l e m a t r i x m a t e r i a l and t h e m a j o r i t y o f the r e s u l t s t o be d e s c r i b e d were o b t a i n e d i n s o l i d a r g o n . - 148 -C. FORCE FIELD T a b l e 3 _ 6 l i s t s t h e f r e q u e n c i e s measured f o r cis-HNSO and i t s i s o t o p i c homologs i s o l a t e d i n s o l i d a r g o n . Complete s p e c t r a were r e c o r d e d f o r m o l e c u l e s c o n t a i n i n g ^ N and d e u t e r i u m w h i l e f o r 34 32 S o n l y peaks w i t h l a r g e enough s e p a r a t i o n from S peaks and w i t h s u f f i c i e n t i n t e n s i t y t o be seen i n n a t u r a l abundance were ob-s e r v e d . These 29 f r e q u e n c i e s were f i t t e d w i t h a harmonic p o t e n t i a l energy e x p r e s s i o n u s i n g e l e v e n c o n s t a n t s by means o f t h e l e a s t s q u a r e s r e f i n e m e n t program FPERT w r i t t e n by J.H. S c h a c h t s c h n e i d e r ^ ' ^ (3) The s t r u c t u r a l p a r a m e t e r s used were t h o s e d e t e r m i n e d by K i r c h h o f f and g i v e n p r e v i o u s l y . W h i l e a t t e m p t i n g t o c a l c u l a t e t h e m o d i f i e d f o r c e f i e l d f o r t h i s m o l e c u l e , the f o l l o w i n g c r i t e r i a were used: r e a s o n a b l e f o r c e c o n s t a n t s w i t h s m a l l e r r o r s ; good agreement between o b s e r v e d and c a l c u l a t e d d a t a ; a s e n s i b l e v i b r a t i o n a l a s s i g n m e n t r e v e a l e d t h r o u g h the p o t e n t i a l energy d i s t r i b u t u i o n ^ . The f i r s t two c r i t e r i a a r e q u i t e e a s i l y s a t i s f i e d f o r a f o r c e f i e l d where many i n t e r a c t i o n con-s t a n t s a r e s e t equal t o z e r o ; the t h i r d i s o f t e n a s e n s i t i v e i n d i c a -t o r o f the r e l a t i v e s u c c e s s o r f a i l u r e o f a p a r t i c u l a r c a l c u l a t i o n as has been i l l u s t r a t e d i n c h a p t e r II i n the c a l c u l a t i o n s f o r ®2^2' Of c o u r s e , the t h i r d c r i t e r i u m r e q u i r e s t h a t the a s s i g n m e n t be c o r -r e c t l y known p r i o r t o the c a l c u l a t i o n . T h i s was the c a s e f o r HNSO. Once c a l c u l a t i o n s were begun, i t soon became a p p a r e n t t h a t a s i n g l e f o r c e f i e l d w ould not be a b l e t o f i t b o t h the hydrogen - 149 -Table 3-6. Observed frequencies f o r several isotopes of cis-HNSO in argon matrices. v(cm ) ± 0.5 cm HNSO 34 HIT SO DNSO 34 DN SO H 1 5NS0 H 1 5N 3 i*S0 D 1 5NS0 v l 3308.5 2453.1 3301.4 2 4 4 1( b ) V 2 1248.7 1233.4 1244.8 1230.1 1243.3 1228.4 1239.4 V3 1082.7 1048.0 1072.4 1 0 3 0 ( b ) v4 900.4 895-7 751.5 749.6 889-2(a) 750.0 v6 754.7 593.8 750.9 587-6 V5 447.4 400.3 444.4 398.8 (a) Average of Fermi doublet (b) accuracy ± 2 cm ' - 150 -c o n t a i n i n g m o l e c u l e s and t h e i r d e u t e r i u m homologues. The r e s u l t s gave poor f r e q u e n c y f i t s f o r and p e c u l i a r p o t e n t i a l energy d i s t r i -b u t i o n s f o r t h e s t r o n g l y i n t e r a c t i n g modes near 1000 cm ' ( v i z . v ^, and v ^ ) . The problem stems, o f c o u r s e , from the use o f o b s e r v e d r a t h e r t h a n harmonic f r e q u e n c i e s i n the c a l c u l a t i o n s . The e f f e c t s o f a n h a r m o n i c i t y a r e g r e a t e s t i n t h e h i g h a m p l i t u d e hydrogen modes V j and v^. A s s i g n m e n t s i n d i c a t e t h a t V | i n v o l v e s a l m o s t c o m p l e t e l y t h e HN s t r e t c h i n g c o o r d i n a t e w h i l e has a l a r g e c o n t r i b u t i o n from the HNS bend. On d e u t e r a t i o n , t h e s e v i b r a t i o n s sample s i g n i f i c a n t l y d i f f e r e n t p a r t s o f the p o t e n t i a l e nergy s u r f a c e , hence t h e i r f o r c e c o n s t a n t s a r e not i s o t o p i c i n v a r i a n t s . Thus the " e f f e c t i v e " f o r c e c o n s t a n t s f o r t h e s e modes w i l l change i n d e u t e r a t i o n . B e a r i n g t h e s e p o i n t s i n mind we p e r m i t t e d r e f i n e m e n t o f d i f f e r e n t v a l u e s o f the d i a g o n a l f o r c e c o n s t a n t s f . , u , f,,.,,- and f . f o r H- and D - c o n t a i n -3 NH HNS t o r s i o n i n g m o l e c u l e s . G i v e n t h i s f reedom, the p r o b l e m soon c o n v e r g e d . The b e s t s e t o f f o r c e c o n s t a n t s so o b t a i n e d i s g i v e n i n t a b l e 3_7> I t s h o u l d be no t e d t h a t t h e f o r c e c o n s t a n t s q u o t e d i n t a b l e 3_7 a r e not bond l e n g t h w e i g h t e d but a r e i n t h e c o n v e n i e n t u n i t s d i s c u s s e d i n c h a p t e r I : . aJ/A 2(lCT' dynes/cm) f o r s t r e t c h e s , -1 1 0 "3 a J ( l O e r g s ) f o r bends and a J / A ( l O ergs/cm) f o r b e n d - s t r e t c h i n t e r a c t i o n s . The p o t e n t i a l e nergy d i s t r i b u t i o n (hence v i b r a t i o n a l a s s i g n m e n t ) f o r the common i s o t o p e o f HNSO i s g i v e n i n t a b l e 3_8. The c a l c u l a t e d f r e q u e n c i e s a r e l i s t e d w i t h d i f f e r e n c e s from o b s e r v e d f r e q u e n c i e s i n t a b l e 3_9• The a v e r a g e f r e q u e n c y e r r o r u s i n g the - 151 -T a b l e 3-7. F o r c e f i e l d f o r cis-HNSO i n c l u d i n g l e a s t s q u a r e s e r r o r e s t i m a t e s . c o n s t a n t °2 0 aJ/A , aJ/A r a d , a J / r a d 2 e r r o r fHN 6.05 0.01 fDN 6.20 0.01 fNS 6.47 0.06 f S 0 9.01 0. 10 fHNS 0.457 0.009 fDNS 0.469 0.012 fNS0 1.66 0.04 f t o r s 1 on 0.225 0.001 fHNS-S0 -0.14 0.03 fHNS-NS -0.15 0.02 fHNS-NS0 -0.18 0.01 - 152 -T a b l e 3-8. P o t e n t i a l e nergy d i s t r i b u t u i o n and ass i g n m e n t r e s u l t i n g from f o r c e f i e l d i n t a b l e 3-7-v(cm P.E. D. ca 1. fHN fNS f s o fHNS fNS0 f X ass i gnment 3308.8 0.998 0.001 0.0 0.0 0.001 HN s t r . 1250.8 0.0 0.2A0 0.711 0.046 0.004 SO s t r . 1086.3 0.0 0.401 0.262 0.253 0.002 NS s t r . 899-5 0.001 0.320 0.013 0.528 0.116 HNS bend 755.7 1 .000 t o r s i o n 447.4 0.0 0.046 0.019 0.234 0.925 NS0 bend T a b l e 3-9. C a l c u l a t e d f r e q u e n c i e s and t h e i r e r r o r s f o r c i s -HNSO. HNSO 34 HN SO DNSO 34 DN^ SO H15NS0 H 1 5 N 3 l * SO D 1 5 NS0 3308.8 -0.3 3308.8 2452.6 0.5 2452.6 3301.1 0.3 3301. 1 2441.5. -0.5 1250.8 -2. 1 1236.1 -2.7 1246.4 -2.1 1224.6 5-5 1244.8 -1.5 1223.1 5.3 1241.5 -2.1 1086.3 -3.6 1083.7 1049.2 -1 .2 1042.2 1069.0 3-4 1065.6 1028.4 1.6 899-5 0.9 892.9 2.8 754.8 -3-3 747.0 2.6 892.9 -3.7 882.7 749.1 0.9 755-7 -1.0 754.6 591.9 1.9 590.0 751.8 -0.9 750.3 587.0 0.6 447.4 0.0 444.9 400.6 -0.3 398.4 443.9 0.5 440.3 399.1 -0.3 Average f r e q u e n c y e r r o r : 1.8 cm (0.18%) - 154 ~ f o r c e c o n s t a n t s i n t a b l e 3_7 was 1.8 cm The v a l u e s o f f . . . and f . . ) C a r e , as e x p e c t e d , s l i g h t l y DN DNS l a r g e r (by 2%) than t h e i r h y d r o g e n i c c o u n t e r p a r t s : t h e d e u t e r i u m v i b r a t i o n s a r e s a m p l i n g a l o w e r , more s t e e p l y c u r v e d segment o f t h e p o t e n t i a l f u n c t i o n . The t o r s i o n c o n s t a n t , f . , d i d not d i f f e r y t o r s i o n s i g n i f i c a n t l y from HNSO so o n l y one v a l u e was a l l o w e d i n l a t e r r e -f i n e m e n t s . T h i s presumably i n d i c a t e s a low a n h a r m o n i c i t y i n the t o r s i o n a l c o o r d i n a t e . E v e r y o f f - d i a g o n a l f o r c e c o n s t a n t ( e x c e p t t h o s e i n v o l v i n g the HN s t r e t c h i n g c o o r d i n a t e ) was t r i e d i n the c a l -c u l a t i o n a t one time o r a n o t h e r . Only t h o s e t o w h i c h the r e s u l t s were s i g n i f i c a n t l y s e n s i t i v e were r e t a i n e d . - 155 -D. THERMODYNAMIC FUNCTIONS The thermodynamic f u n c t i o n s c a l c u l a t e d f o r cis-HNSO o v e r the t e m p e r a t u r e range 100°K t o 1500°K a r e g i v e n i n t a b l e 3 - 1 0 . These c a l c u l a t i o n s were made u s i n g v i b r a t i o n a l f r e q u e n c i e s t a k e n from t h e argon m a t r i x e x p e r i m e n t s . - 156 -T a b l e 3-10. Thermodynamic f u n c t i o n s f o r HNSO c a l c u l a t e d f rom v i b r a t i o n a l f r e q u e n c i e s , ca1/mole°K. t e m p e r a t u r e S C p - <G-H0> (H-H Q) °K T T 273-15 65.95369 10.57143 57.22361 8.72942 298.10 66.89681 11.01364 57-99400 8.90214 100.00 56.94764 8.08657 48.97709 7.96982 200.00 62.86990 9.30116 54.57762 8.29160 300.00 66.96689 11.04697 58.05060 8.91562 400.00 70.37307 12.65691 60.71599 9.65644 500.00 73.33858 13-90948 62.95019 10.38776 600.00 75-96145 14.84618 64.90432 11.05651 700.00 78.30584 15-55864 66.65427 11.65096 800.00 80.42138 16.11936 68.24502 12.17576 900.00 82.34713 16.57512 69-70647 12.64007 1000.00 84.11371 16.95465 71.06002 13.05310 1100.00 85.74513 17.27597 72.32177 13.42278 1200.00 87.26042 17.55101 73-50422 13.75563 1300.00 88.67484 17.78821 74.61735 14.05693 1400.00 90.00079 17.99393 75.66926 14.33096 1500.00 91.24849 18.17315 76.66666 14.58127 - 157 -BIBLIOGRAPHY: CHAPTER I I I 1. P.W. Schenk; B e r . , 6_5, 94 (1942) 2. 0. Gl e m s e r , H. R i c h e r t ; Z. Anor g . A l l g e m . Chem., 307, 313 ( i 9 6 0 3. W.H. K i r c h h o f f ; J . Am. Chem. S o c , 9J_, 2437 (1969) 4. M. B e c h e - G o e h r i n g , R, Schwarz, W. S p i e s s ; Z. A n o r g . A l l g e m . Chem., 293, 294 (1958) 5. H. R i c h e r t ; Z. A n o r g . A l l g e m . Chem., 309, 171 (1961) 6 . J.M. A l l e g r e t t i ; M a s t e r s T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1971 7. 0. Glemser, A. M l i l l e r , D. B B h l e r , B. K r e b s ; Z. A n o r g . A l l g e m . Chem., 357, 184 (1968) 8. H.H. E y s e l ; J . M o l . S t r u c t u r e , 5., 257 (1970) 9. H.J. Becher and R. M a t t e s ; S p e c t r o c h i m . A c t a , 23A, 2449 (1967) 10. B.S. A v e r b u k h , L.S. Mayants, G.B. S h u l t u p e r ; J . M o l . S p e c t r y . , 30, 310 (1969) 11. J.H. S c h a c h t s c h n e i d e r ; S h e l l Development Company, Tech. Rep. #263 _62 12. G.C. P i m e n t e l , A.L. M c C l e l l a n ; "The Hydrogen Bond", Freeman, I960 13- G. H e r z b e r g ; " I n f r a r e d and Raman S p e c t r a " , D. Van N o s t r a n d , 1945 14. M. A l l a v e n a , R. R u s n i k , D. W h i t e , V. C a l d e r , D.E. Mann; J . Chem. P h y s . , 50, 3399 (1969) 15. Y. M o r i n o , K. K u c h i t s u ; J . Chem. Phys . , 20, 1809 (1952) - 158 -CHAPTER IV THE PHOTOLYSIS OF CIS-HNSO A. INTRODUCTION That the p h o t o l y s i s o f cis-HNSO might be o f i n t e r e s t was d e m o n s t r a t e d e a r l i e r i n t h i s t h e s i s when i t s u l t r a v i o l e t s p e c t r u m was d i s c u s s e d . The p o s s i b i l i t y e x i s t e d t h a t t h e f r e e r a d i c a l NSO would be t h e p r i n c i p a l p h o t o l y s i s p r o d u c t . S i n c e H-atoms a r e known t o t r a v e l e a s i l y t h r o u g h argon m a t r i c e s , t h i s p r e s e n t e d an i d e a l c a s e f o r s t u d y by the m a t r i x i s o l a t i o n t e c h n i q u e . There would be a good chance o f o b t a i n i n g t h e i s o l a t e d NSO r a d i c a l f o r i n f r a r e d o b s e r v a t i o n . In a d d i t i o n , o t h e r i n t e r e s t i n g p h o t o l y s i s p r o d u c t s might be o b s e r v e d : f o r example, trans-HNSO and o t h e r s t r u c t u r a l isomers r e s u l t i n g from m o l e c u l a r r e a r r a n g e m e n t s . A p r e l i m i n a r y e x p e r i m e n t was pe r f o r m e d i n w h i c h cis-HNSO i n argon (M/R=800) was d e p o s i t e d w i t h s i m u l t a n e o u s i r r a d i a t i o n by a hydrogen resonance lamp. The f i r s t s p e c t r u m o f the p r o d u c t s ( f i g u r e 4-1) r e v e a l e d a l m o s t e m b a r r a s s i n g r i c h e s : about twenty a b s o r p t i o n peaks were o b s e r v e d - b e s i d e s t h o s e due t o cis-HNSO and i t s SO2 i m p u r i t y . I t was o b v i o u s t h a t s e v e r a l s p e c i e s were produced by the vacuum u.v. p h o t o l y s i s o f cis-HNSO. D e t a i l e d s t u d y o f the s p e c t r a r e s u l t i n g from p h o t o l y s i s c u l m i n a t e d i n the i d e n t i f i c a t i o n o f s i x new m o l e c u l e s i n c l u d i n g two f r e e r a d i c a l s . T h i s c h a p t e r c o n t a i n s t h e r e s u l t s o f t h i s i n v e s t i g a t i o n . F i g u r e 4-1. Spectrum f o l l o w i n g the vacuum u.v. p h o t o l y s i s o f cis-HNSO i n an argon m a t r i x (M/R = 8 0 0 ) . - 160 -B. IDENTIFICATION OF MOLECULES: GENERAL To i d e n t i f y t he m o l e c u l e s produced i n a p h o t o l y s i s r e q u i r e s t h a t f i r s t t h e a b s o r p t i o n s a s s o c i a t e d w i t h each p r o d u c t be grouped t o g e t h e r . When the a b s o r p t i o n s a r e known f o r each m o l e c u l e , t h e s t r u c t u r e s can be deduced u s i n g i s o t o p i c s u b s t i t u t i o n and c o r r e l a -t i o n s w i t h s p e c t r a o f known m o l e c u l e s . W i t h t h e s e s t r u c t u r e s and o b s e r v e d f r e q u e n c i e s , f o r c e c o n s t a n t s can be c a l c u l a t e d t o d e m o n s t r a t e the c o r r e c t n e s s o f a s s i g n m e n t and t o l e a r n more about t h e m o l e c u l e s p r o d u c e d . A l s o , knowing the p r o d u c t s and n a t u r e o f the r e a c t i o n s , i t may be p o s s i b l e t o say some t h i n g o f the r e a c t i o n mechanisms i n v o l v e d . 1. GROUPING OF ABSORPTIONS The f i r s t p r o b l e m i s t o group the a b s o r p t i o n peaks t h a t b e l o n g t o each o f t h e m o l e c u l e s p r o d u c e d . The main method used i s c o r r e l a t i o n o f i n t e n s i t i e s . I f i n t e n s i t y r a t i o s o f peaks under v a r i o u s c o n d i t i o n s a r e d i f f e r e n t , t h e peaks cannot b e l o n g t o t h e same m o l e c u l e . G e n e r a l l y i f t h e r a t i o s remain the same, the a b s o r p -t i o n s e i t h e r b e l o n g t o t h e same m o l e c u l e o r t o two m o l e c u l e s t h a t a r e produced a t t h e same r a t e under a l l c o n d i t i o n s s t u d i e d . The need, t h e n , i s t o f i n d c o n d i t i o n s such t h a t the r a t i o s o f t h e v a r i -ous p r o d u c t s change. T h i s i s a c c o m p l i s h e d by c h a n g i n g the energy o f p h o t o l y s i s l i g h t , by c h a n g i n g the n a t u r e o f p h o t o l y s i s ( i . e . p h o t o l y s i s a f t e r i s o l a t i o n i n the m a t r i x o r d u r i n g s p r a y on) and by s t u d y i n g the i n t e n s i t i e s a t v a r i o u s p h o t o l y s i s t i m e s . - 161 -In t h i s work, t o o b t a i n d i f f e r e n t p h o t o l y s i s e n e r g i e s t he t h r e e lamps and two f i l t e r s d e s c r i b e d i n c h a p t e r I were us e d . The vacuum u.v. lamp p r o v i d e d v e r y h i g h e n e r g y l i g h t , a l m o s t e x c l u s i v e l y o a t 1216 A. The mercury and xenon lamps, used i n c o n j u n c t i o n w i t h o o f i l t e r s , gave l i g h t o f w a v e l e n g t h s g r e a t e r than 4000 A, 3000 A and o 2000 A w i t h f i l t e r 3~73, f i l t e r 0-52* and no f i l t e r r e s p e c t i v e l y . B e s i d e s i n t e n s i t i e s , t h e p r e s e n c e o f an i s o t o p i c s h i f t i n one a b s o r p t i o n a l o n g w i t h t h e absence o f a s h i f t i n a n o t h e r i s o f t e n s u f f i c i e n t t o show t h a t t he two a b s o r p t i o n s b e l o n g t o d i f f e r e n t mole-c u l e s . The p r e s e n c e o f a s h i f t i n bo t h a b s o r p t i o n s , however, i s not s u f f i c i e n t t o say t h a t they b e l o n g t o the same m o l e c u l e . Because hydrogen i s the o n l y atom t h a t can e a s i l y s e p a r a t e from a m o l e c u l e i n a m a t r i x ( f l u o r i n e w i l l a l s o s e p a r a t e but has no i s o t o p e s f o r s u b s t i t u t i o n ) , h y d r o g e n - d e u t e r i u m s h i f t s a r e t h e most i m p o r t a n t i s o -t o p i c i n d i c a t o r s . T h i s i s f o r t u n a t e because t h e s h i f t s o b s e r v e d f o r t h i s s u b s t i t u t i o n a r e o f t e n v e r y l a r g e . 2. SPECTRA, STRUCTURES, ASSIGNMENTS AND NORMAL COORDINATE ANALYSIS Once the s p e c t r u m o f each new m o l e c u l e i s s e p a r a t e d from the o t h e r s , i t can be used t o guess a m o l e c u l a r s t r u c t u r e . To do t h i s a knowledge o f c h a r a c t e r i s t i c f r e q u e n c i e s from known m o l e c u l e s i s r e q u i r e d . From t h i s i n f o r m a t i o n , s p e c i f i c t y p e s o f bonds and v i b r a t i o n a l modes a b s o r b i n g i n t h e r e g i o n o f the o b s e r v e d peaks can be e s t a b l i s h e d . A f t e r t he p o s s i b l e m o l e c u l e s have been p r e d i c t e d , - 162 -t h i s a l l o w s the e l i m i n a t i o n o f most o f the c h o i c e s , o f t e n l e a v i n g o n l y one p o s s i b i l i t y . A p p e n d i x I l i s t s the a b s o r p t i o n s o f numerous m o l e c u l e s t h a t p r o v i d e u s e f u l c o r r e l a t i o n s w i t h the a b s o r p t i o n s s t u d i e d i n t h i s t h e s i s . To f u r t h e r s u b s t a n t i a t e t h i s c h o i c e , o r t o s e l e c t between s e v e r a l p o s s i b i l i t i e s , i s o t o p i c s u b s t i t u t i o n i s c a r r i e d o u t . The s t u d y o f v i b r a t i o n a l f r e q u e n c y s h i f t s on i s o t o p i c s u b s t i t u t i o n more c l e a r l y d e m o n s t r a t e s the n a t u r e o f t h e v i b r a t i o n a l mode and t h e i n -t e r n a l c o o r d i n a t e i n v o l v e d . To more a c c u r a t e l y use the o b s e r v e d s h i f t s , an a p p r o x i m a t e model f o r the m o l e c u l e i s deduced and a n o r -mal c o o r d i n a t e a n a l y s i s i s c a r r i e d o u t . The c l o s e n e s s o f f i t o f the c a l c u l a t i o n s t o the i s o t o p i c f r e q u e n c i e s a l o n g w i t h i n t u i t i v e l y -r e a s o n a b l e f o r c e c o n s t a n t s i s good e v i d e n c e f o r the c o r r e c t n e s s o f the s t r u c t u r e and o f the a s s i g n m e n t . 3. A REACTION MECHANISM Knowing t h e s t r u c t u r e o f t h e m o l e c u l e s produced and t h e way i n w h i c h t h e y a r e produced ( i . e . p h o t o l y s i s energy and r a t e ) a l l o w s t h e d e d u c t i o n o f a r e a c t i o n mechanism. R e a c t i o n s i n a m a t r i x a r e r e s t r i c t e d because the i s o l a t i o n p r e v e n t s the e n e r g y t r a n s f e r o r r e a c t i o n between m o l e c u l e s t h a t i s o b s e r v e d i n the gas phase. A l s o , e ntrapment o f t h e m o l e c u l e i n t h e m a t r i x r e s t r i c t s d e c o m p o s i t i o n t o the s p e c i f i c t y p e p o i n t e d out i n c h a p t e r I - o n l y when es c a p e from the cage can be a c h i e v e d . The r e s u l t i s t h a t r e a r r a n g e m e n t s a r e - 163 -f a v o u r e d and m a t r i x i s o l a t i o n p r e s e n t s a good means f o r s t u d y i n g t h e s e r e a c t i o n s . I f a r e a s o n a b l e mechanism can be p r e s e n t e d f o r the n e c e s s a r y r e a c t i o n s , t h e c o n f i d e n c e i n the i d e n t i f i c a t i o n o f t h e m o l e c u l e s i s enhanced. - 164 -C. IDENTIFICATION OF MOLECULES: RESULTS When i t was found t h a t some o f the a b s o r p t i o n s i l l u s t r a t e d i n f i g u r e 4-1 became v e r y i n t e n s e a f t e r o n l y a few m i n u t e s p h o t o l y s i s o w i t h l i g h t o f X>2000 A, i t was d e c i d e d t o f o l l o w the i n t e n s i t y o f a l l the a b s o r p t i o n s as a f u n c t i o n o f mercury lamp p h o t o l y s i s t i m e . What was found was t h a t a l l t h e i n t e n s e a b s o r p t i o n s and most o f t h e weak ones f o l l o w e d one o f t h r e e growth c u r v e s . In f i g u r e 4-2 a r e shown the t h r e e growth c u r v e s and i n t a b l e 4-1 a r e l i s t e d the a b s o r p t i o n s t h a t a r e a s s o c i a t e d w i t h each c u r v e . As w e l l , a s e t o f weak a b s o r p -t i o n s seen i n f i g u r e 4-1 and found most i n t e n s e when o n l y l i g h t o f o w a v e l e n g t h g r e a t e r than 3000 A was used a r e shown i n column D o f t a b l e 4-1. These a b s o r p t i o n s were not seen on p h o t o l y s i s w i t h o u t the 0-54 f i l t e r and c o u l d be made t o d i s a p p e a r by removing t h e f i l t e r f r om t h e l i g h t beam. In column E o f t a b l e 4-1 i s a s i n g l e a b s o r p t i o n t h a t was produced o n l y w i t h vacuum u.v. p h o t o l y s i s and t h a t c o u l d a l s o be made t o d i s a p p e a r by a s h o r t e x p o s u r e t o mercury lamp r a d i -a t i o n . These e x p e r i m e n t s w i t h d i f f e r e n t e n e r g i e s and l e n g t h s o f p h o t o l y s i s r e s u l t e d i n the g r o u p i n g s i n t a b l e 4-1. The use o f t h e p r o c e d u r e s o u t l i n e d i n s e c t i o n B above r e s u l t e d i n t h e i d e n t i f i c a t i o n o f the v a r i o u s r e a c t i o n p r o d u c t s . The f o l l o w i n g s e c t i o n s p r o v i d e i n d e t a i l the b a s i s f o r each m o l e c u l a r i d e n t i f i c a t i o n and each v i b r a t i o n -a l a s s i g n m e n t . "1 I 1 I 2 12 T i m e (m in ) F i g u r e 4 - 2 . Growth c u r v e s o f t h r e e d i f f e r e n t groups o f peaks u s i n g Hg lamp p h o t o l y s A - 6 7 3 cm" 1, B = 1597 cm" 1, C = 1523 cm 1 - 166 -T a b l e 4 - 1 . S e t s o f a b s o r p t i o n s produced on t h e p h o t o l y s i s o f cis-HNSO. v(cm ) Curve Curve Curve A B C D 3520 1597 1523 1382 1321 1571 790 986 992 876 881 674 858 651 418 542 374 500 385 306 298 - 167 -1. trans-HNSO (a) S p e c t r a : On p h o t o l y s i s w i t h l i g h t o f w a v e l e n g t h g r e a t e r than o 4000 A, no r e a c t i o n was o b s e r v e d . However, w i t h l i g h t o f w a v e l e n g t h g r e a t e r than 3000 A, s l o w r e a c t i o n was o b s e r v e d , g i v i n g numerous ab-s o r p t i o n s . I f a p e r i o d o f t h i s low e nergy p h o t o l y s i s was f o l l o w e d o by h i g h e r energy p h o t o l y s i s ( o f X g r e a t e r than 2 0 0 0 A ) , most o f t h e new a b s o r p t i o n s grew r a p i d l y . However, f o u r o f the weak a b s o r p t i o n p e a k s, column D i n t a b l e 4-1, d e c r e a s e d i n i n t e n s i t y w i t h t h i s s e c -ondary p h o t o l y s i s . F i g u r e 4-3 (a) shows t h e s e peaks produced by the 14 p h o t o l y s i s o f c i s - H NS0 f o r 4 5 m i n u t e s u s i n g a mercury lamp and f i l -o _ t e r so t h a t X>3000 A as w e l l as t h e i r d i s a p p e a r a n c e on f u r t h e r p h o t o l y -o s i s f o r 5 m i n u t e s u s i n g l i g h t o f X > 2 0 0 0 A. F i g u r e 4-3 (b) shows si-mi-o ° 15 l a r r e s u l t s - 1 hour a t X>3000 A and 3 m i n u t e s a t A > 2 0 0 0 A - f o r N s u b s t i t u t e d cis-HNSO. The use o f ' **N p r o v e d t h a t t h e d o u b l e t a b s o r p --1 -1 14 t i o n s a t 986 cm and 881 cm i n t h e N sample were indeed c a u s e d by o v e r l a p p i n g a b s o r p t i o n s o f two s e p a r a t e m o l e c u l e s . On p h o t o l y s i s w i t h h i g h e nergy l i g h t , one component o f each d o u b l e t d e c r e a s e d i n i n t e n s i t y a l o n g w i t h t h e cis-HNSO a b s o r p t i o n s w h i l e t h e o t h e r compon-ent i n c r e a s e d . T a b l e 4 -2 l i s t s the measured f r e q u e n c i e s o f t h e s e f o u r 14 15 14 v i b r a t i o n s when s t a r t i n g w i t h c i s - H N S 0 , -H NS0 and -D N S 0 . S i n c e t h e r e a r e f o u r a b s o r p t i o n s o b s e r v e d , t h e m o l e c u l e cannot be a t r i a t o m -i c and s i n c e i t shows s h i f t s o f a b s o r p t i o n s on d e u t e r i u m and '"*N sub-s t i t u t i o n , b o t h t h e s e atoms a r e c o n s t i t u e n t s . S i n c e t h e p e a k s , though - 168 -1/ ( c m - 1 ) 14CO 1 3 5 0 1 0 0 0 9 0 0 TOO j .1 ! 1 1 1 . 1 T r r ~i 1 1 r J_... 6 0 0 L -i 1 r If 1 4 N , m / R = 4 0 0 X > 3 0 0 0 A , 4 3 m i n + X> 2 0 0 0 A , 5 min 15 N , m / R = 4 0 0 X > 3 0 0 0 A , 1 hr + X > 2 0 0 0 A , 3 min F i g u r e 4~3. The f o u r o b s e r v e d a b s o r p t i o n s o f trans-HNSO: p r o d u c t i o n o w i t h p h o t o l y s i s u s i n g X>3000 A and d i s a p p e a r a n c e u s i n g o A>2000 A. - 169 " weak, a r e f a i r l y s h a r p , i t i s assumed t h a t i s o l a t i o n was m a i n t a i n e d d u r i n g t h e r e a c t i o n w h i l e the M/R o f kOO was c e r t a i n l y adequate f o r i s o l a t i o n o f the i n i t i a l cis-HNSO m o l e c u l e s . The a b s o r b i n g s p e c i e s must then be a s i m p l e isomer o f cis-HNSO and i t must be assumed t h a t i t s two r e m a i n i n g a b s o r p t i o n s a r e not o b s e r v e d due t o low i n t e n s i t y o r o v e r l a p p i n g w i t h i n t e n s e a b s o r p t i o n s . C o n s i d e r f i r s t t h e 1382 cm ' a b s o r p t i o n . T h i s r e g i o n s ug-g e s t s e i t h e r an S=0 s t r e t c h , an SeN s t r e t c h o r a hydrogen bend. The low ' ^ N s h i f t o f 3 cm ' i s t o o s m a l l f o r an SN s t r e t c h and the low 0 s h i f t o f 2 cm ' shows t h a t i t i s not a hydrogen bend. The peak a t 1382 cm 1 must then be a s s i g n e d t o an S=0 s t r e t c h . Numerous v i b r a t i o n s c o u l d a b s o r b i n t h e r e g i o n o f the n e x t peak, 986 cm The two major p o s s i b i l i t i e s a r e t h e S=N s t r e t c h and the hydrogen bend. The ' "*N s h i f t o f 23 cm ' i s r e a s o n a b l e f o r an S=N s t r e t c h w h i l e t h e D s h i f t o f 13 cm 1 i s c o n s i s t e n t w i t h an S=N s t r e t c h but i s c e r t a i n l y t o o s m a l l f o r a hydrogen b e n d i n g mode. The peak a t 986 cm ' i s thus c o n s i d e r e d t o be an N=S s t r e t c h . S i m i l a r l y , numerous v i b r a t i o n s can o c c u r a t 881 cm ' a l t h o u g h m u l t i p l e - b o n d e d s u l p h u r , oxygen and n i t r o g e n s t r e t c h e s w o u l d p r o b a b l y be a t h i g h e r f r e q u e n c y and s i n g l e bonds o f t h e s e atoms would p r o b a b l y be l o w e r . The p o s s i b i l i t y o f a hydrogen bend i s f o r e m o s t . The ^ N s h i f t o f 13 cm 1 i s s i m i l a r t o t h a t found f o r t h e HNS bend o f cis-HNSO ( l l cm The f a c t t h a t t h i s peak was not o b s e r v e d on d e u t e r a t i o n f u r t h e r s u g g e s t s b o t h a s h i f t t o a n o t h e r r e g i o n where i t c o u l d not - 170 -be seen and a l o w e r i n g o f i n t e n s i t y . These o b s e r v a t i o n s a r e c o n s i s -t e n t w i t h a s s i g n m e n t o f t h e 881 cm ' a b s o r p t i o n t o a hydrogen bend i n w h i c h hydrogen i s a t t a c h e d t o a n i t r o g e n . The r e m a i n i n g peak a t 651 cm ' i s c o n s i s t e n t w i t h a s i n g l e bond s t r e t c h , a bend o r a t o r s i o n . The s m a l l '^N s h i f t o f 1 cm ' s u g g e s t s t h a t i t i s not a b e n d i n g o r s t r e t c h i n g mode i n v o l v i n g n i t r o -gen. S i n c e t h e m o l e c u l e has o n l y f o u r atoms, t h i s e x c l u d e s the m a j o r -i t y o f t h e bends and s t r e t c h e s . The d i s a p p e a r a n c e o f t h e peak on d e u t e r a t i o n i s p r o b a b l y due t o a l a r g e s h i f t t o a d i f f e r e n t r e g i o n . For t h i s r eason the v i b r a t i o n must be a t o r s i o n about a m u l t i p l e bond and i n v o l v i n g l a r g e hydrogen d i s p l a c e m e n t s . W i t h a weak NS s t r e t c h , a s t r o n g SO s t r e t c h , an HNS bend and a t o r s i o n , the m o l e c u l e has t o be HNSO - presumably t h e t r a n s isomer. H \ O The a s s i g n m e n t s a r e i n d i c a t e d i n t a b l e 4-2; t h e HN s t r e t c h and t h e NSO bend a r e not o b s e r v e d . I t i s assumed t h a t a l a r g e m i x i n g w i l l be found w i t h the 986 cm 1 and 881 cm ' a b s o r p t i o n s , thus c o n f u s i n g t h e i r a s s i g n m e n t s . However, from t h e d a t a a v a i l a b l e , the g i v e n a s s i g n m e n t s a r e most p r o b a b l e . - 171 " T a b l e 4 -2 . Observed a b s o r p t i o n f r e q u e n c i e s (cm ) o f trans-HNSO i n an a r g o n m a t r i x . 14 H NSO H 1 5NS0 14 D NSO ass i gnment 1382 986 881 651 1379 963 868 650 1380 951 SO s t r . SN s t r . HNS bend t o r s i o n - 172 -As a f u r t h e r p i e c e o f e v i d e n c e f o r t h i s i d e n t i f i c a t i o n , a co m p a r i s o n o f c i s - t r a n s f r e q u e n c y s h i f t s f o r HNSO and the s t r u c t u r -a l l y s i m i l a r m o l e c u l e HONO i s made i n t a b l e 4 - 3 - The HONO v a l u e s a r e t a k e n from D'Or and T a r t e ^ . S i n c e b o t h m o l e c u l e s a r e p l a n a r and might be e x p e c t e d t o have s i m i l a r bonded and non-bonded i n t e r -a c t i o n s , i t i s b e l i e v e d t h a t t h e y s h o u l d show c i s - t r a n s s h i f t s i n the same d i r e c t i o n a l t h o u g h p r o b a b l y o f d i f f e r e n t m a g n i t u d e s . The s i m i l a r i t i e s i n the s h i f t s shown i n t a b l e 4-3 a r e v e r y e n c o u r a g i n g t o the a s s i g n m e n t s made f o r trans-HNSO. (b) Normal C o o r d i n a t e A n a l y s i s : An a t t e m p t t o f i t a f o r c e f i e l d t o the d a t a i n t a b l e 4 -2 has been made. The s t r u c t u r e used was t h a t o f cis-HNSO t a k i n g t h e d i h e d r a l a n g l e a t 1 8 0 ° . As u s u a l , t he s h o r t a g e o f d a t a - i n t h i s c a s e t he absence o f any NSO bend f r e q u e n c y - r e s t r i c t s t h e q u a l i t y o f the c a l c u l a t i o n s . O nly two d e u t e r i u m modes a r e o b s e r v e d and due t o poor i n t e n s i t y , t h e s e have a l a r g e u n c e r t a i n t y . However, an a p p r o x i m a t e f o r c e f i e l d has been o b t a i n e d w h i c h g i v e s a good f r e q u e n c y f i t and r e a s o n a b l e p o t e n t i a l e nergy d i s t r i b u t i o n s . Because o f t h e absence o f the c o r r e s p o n d i n g f r e q u e n c i e s , t h e HN s t r e t c h and NSO bend f o r c e c o n s t a n t s were h e l d f i x e d t o v a l u e s ob-t a i n e d f o r cis-HNSO. The DNS bend f o r c e c o n s t a n t was c o n s t r a i n e d t o 1.03 t i m e s t h e HNS bend c o n s t a n t t o improve t h e f i t by t a k i n g i n t o a c c o u n t t h e d i f f e r e n c e i n a n h a r m o n i c i t y o f t h i s c o o r d i n a t e f o r t he two i s o t o p e s . As e x p e c t e d , t h e c l o s e n e s s o f th e 986 cm 1 and 881 cm ' a b s o r p t i o n s r e s u l t e d i n a g r e a t d e a l o f m i x i n g so t h a t an HNS bend -- 173 -T a b l e 4-3. Comparison o f c i s - t r a n s f r e q u e n c y s h i f t s f o r HNSO and HONO. s h i f t ( c m ) HNSO HONO* V S 0 -133 -61 V o V S N 97 62 , V o VHNS 19 97 VH0N V 104 93 V X X d a t a from r e f e r e n c e ( 1 ) . - 174 -NS s t r e t c h i n t e r a c t i o n c o n s t a n t was r e q u i r e d . T h i s meant t h a t 5 f o r c e c o n s t a n t s were a d j u s t e d t o f i t 10 f r e q u e n c i e s . T a b l e 4-4 l i s t s t he f o r c e c o n s t a n t s o b t a i n e d and t h e i r l e a s t s q u a r e s e s t i m a t e d e r r o r s . T a b l e 4-5 g i v e s the c a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s between c a l c u l a t e d and o b s e r v e d f r e q u e n c i e s f o r the v a r i o u s i s o t o p e s w h i l e the d i a g o n a l c o n s t a n t p o t e n t i a l e nergy d i s t r i b u t i o n i s g i v e n f o r 14 each v i b r a t i o n o f t r a n s - H NSO i n t a b l e 4 - 6 . (c) P i s c u s s i o n ( i ) The s h i f t i n the SO s t r e t c h i n g f r e q u e n c y from 1248.7 cm 1 t o 1382 cm ' i n g o i n g from cis-HNSO t o trans-HNSO has r e s u l t e d 0 2 0 2 i n a change o f SO f o r c e c o n s t a n t from 9-0 aJ/A t o 11.6 aJ/A . A t the same t i m e the NS s t r e t c h c o n s t a n t has d e c r e a s e d from 6.5 t o 5-3 °2 aJ/A . T h i s s u g g e s t s a change i n t h e b o n d i n g has o c c u r r e d : an i n c r e a s e i n b o n d ing between s u l f u r and oxygen and a d e c r e a s e between s u l f u r and n i t r o g e n . A p o s s i b l e e x p l a n a t i o n i s the f o l l o w i n g . In the c i s - form t h e r e i s a hydrogen bond t y p e i n t e r a c t i o n between h y d r o -gen and oxygen. T h i s w o u l d a c c o u n t f o r the c i s isomer's a p p a r e n t g r e a t e r s t a b i l i t y r e s u l t i n g i n i t s p r e f e r e n t i a l f o r m a t i o n and the absence o f any t r a n s isomer i n the gas phase. T h i s c o u l d a l s o be one r e a s o n f o r the l a r g e r t o r s i o n a l c o n s t a n t f o r the c i s compared t o t h e t r a n s isomer (0 .225 aJ compared t o 0.193 a J ) . T h i s hydrogen b o n d i n g s h i f t s some oxygen e l e c t r o n d e n s i t y away f r o m t h e SO bond, thus weakening the bond and r e l e a s i n g s u l f u r e l e c t r o n s f o r g r e a t e r NS b o n d i n g . In the t r a n s form the oxygen e l e c t r o n s a r e r e l e a s e d - 175 -T a b l e 4-4. F o r c e f i e l d f o r trans-HNSO. a J / c o o r d 2 e r r o r f N 6.05 h e l d f i x e d f N S 5.30 0.04 f S Q 11.60 0.03 f H N S 0.476 0.005 f l l o A 1 .66 h e l d f i x e d NoU f 0.193 0.001 x fHNS-NS °- , 9° °-°° 5 - 176 -T a b l e 4 - 5 - C a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s from o b s e r v e d f r e q u e n c i e s (A) f o r trans-HNSO. 14 H NSO v(cm A H , 5NS0 v(cm A 14 D NSO v(cm ^) A 3 3 0 8 3301 2422 1381 1 1380 -1 1380 0 982 4 9 6 6 - 3 951 0 878 3 870 -2 687 651 0 650 0 484 496 4 9 1 474 Average f r e q u e n c y e r r o r = 1.4 cm - 177 -T a b l e 4-6. P o t e n t i a l e n ergy d i s t r i b u t i o n and a s s i g n m e n t s f o r trans-HNSO. v(cm ') fHN fNS P.E f S 0 . D. fHNS fNS0 f T ass ignment 3308 0.998 0.001 0.0 0.0 0.001 HN s t r . 1381 0.0 0.037 0.951 0.004 0.005 SO s t r . 982 0.0 0 .548 0.005 0.531 0.045 NS s t r . 879 0.001 0.401 0.034 0.460 0.001 HNS bend 651 1 .0 t o r s i on 496 0.001 0.028 0.009 0.020 0.948 NSO bend - 178-i n t o t h e SO bond, s t r e n g t h e n i n g i t . A t t h e same t i m e t h i s r e s u l t s i n a t r a n s f e r o f s u l f u r e l e c t r o n s away from the NS bond, c a u s i n g i t to be weaker. T h i s would a l s o r e f l e c t i n the lower t o r s i o n a l c o n -s t a n t f o r t h e t r a n s form as w e l l as t h e lower NS s t r e t c h i n g c o n s t a n t . (2) F o l l o w i n g t h e f o r m u l a t i o n o f t h i s i n t e r a c t i o n scheme, a paper ap-pea r e d c o n t a i n i n g a s i m i l a r e x p l a n a t i o n t o a c c o u n t f o r the s t r u c t u r a l d i f f e r e n c e s found i n c i s - and trans-HONO. ( i i ) The l a c k o f an NSO b e n d i n g mode may r e s u l t i n some e r r o r i n t h e f o r c e c o n s t a n t s w h i c h would not be r e f l e c t e d i n the l e a s t s q u a r e s e r r o r e s t i m a t e s . As was seen i n cis-HNSO, some i n t e r -a c t i o n does t a k e p l a c e between t h e HNS bend and t h e NSO bend so t h a t t h e i r i n t e r a c t i o n c o n s t a n t was i m p o r t a n t . The o t h e r p r o b l e m i s the as s i g n m e n t o f t h e 986 cm ' and 881 cm ^ a b s o r p t i o n s . The a s s i g n m e n t o f t h e s e two modes i s r e v e r s e d i n t h e P . E . D . o f t h e ^ N m o l e c u l e as 14 compared t o t h e P . E . D . o f the N m o l e c u l e i n t a b l e 4 - 6 . However i n the d e u t e r a t e d m o l e c u l e , where the s e p a r a t i o n o f t h e s e modes i s much l a r g e r and t h u s t h e i r i n t e r a c t i o n i s l e s s , t h e a s s i g n m e n t i n t a b l e 4-2 i s a g a i n f o l l o w e d . T h i s i s then t h e a s s i g n m e n t chosen h e r e f o r trans-HNSO. ( i i i ) A t t e m p t s t o o b s e r v e more peaks f o r the d e u t e r a t e d m o l e c u l e i n t h e r e g i o n s t h a t t h e c a l c u l a t i o n s u g g e s t e d were unsuc-c e s s f u l , p r o b a b l y because o f t h e i r low i n t e n s i t y and the p r e s e n c e o f numerous s t r o n g e r peaks t h a t might o b s c u r e them. ( i v ) Because t h i s m o l e c u l e i s produced w i t h low en e r g y - 179 -l i g h t , i t i s c o n s i s t e n t t o p o s t u l a t e a c i s - t r a n s i s o m e r i s m r a t h e r than a bond c l e a v a g e because t h e c l e a v a g e would l i k e l y r e q u i r e more en e r g y . The d i s a p p e a r a n c e o f t h i s m o l e c u l e w i t h h i g h e r energy pho-t o l y s i s a l s o f o l l o w s t h e d i s a p p e a r a n c e o f cis-HNSO. Both t h e s e f a c t s s u p p o r t t h e trans-HNSO i d e n t i f i c a t i o n . An e q u i l i b r i u m between t h e c i s and t r a n s isomers w o u l d a c c o u n t f o r the l i m i t e d amount o f t h e t r a n s t h a t c o u l d be produced i n t h e s e e x p e r i m e n t s . 2. cis-HOSN (a) S p e c t r a : A second group o f p e a k s , column A i n t a b l e 4-1, were i d e n t i f i e d w i t h the f o l l o w i n g c h a r a c t e r i s t i c s . On p h o t o l y s i s w i t h O low energy l i g h t (X>3000 A) they grew s l o w l y but then s t o p p e d grow-i n g and then d e c r e a s e d s l i g h t l y w i t h t i m e as o t h e r a b s o r p t i o n s grew o s l o w l y . On h i g h e r e n e r g y p h o t o l y s i s (X>2000 A) t h i s group o f peaks grew v e r y r a p i d l y , r e a c h e d a maximum w i t h i n 5 m i n u t e s and then de-c r e a s e d as o t h e r peaks grew (see f i g u r e 4-2). At t h e i r maximum, they r e p r e s e n t e d t h e s t r o n g e s t p r o d u c t peaks i n t h e m a t r i x w i t h i n -t e n s i t i e s comparable t o t h o s e o f cis-HNSO i t s e l f . W i t h t i m e , o t h e r p r o d u c t s showed s t r o n g e r a b s o r p t i o n s than t h i s g r o u p . F i g u r e 4-4 shows a s p e c t r u m t a k e n o f cis-HNSO i n an argon m a t r i x w i t h M/R = 400 f o l l o w i n g one m i n u t e p h o t o l y s i s . T a b l e 4-7 l i s t s t he v a l u e s f o r the ab-14 s o r p t i o n s o f t h i s new s p e c i e s w i t h s t a r t i n g m o l e c u l e s c i s - H NSO, 15 14 -H NSO and -D NSO. S i x a b s o r p t i o n s were o b s e r v e d f o r the new mole-c u l e and the i s o t o p i c s h i f t s show t h a t H and N a r e p r e s e n t i n t h e z/(cm - 1) 1000 200 F i g u r e k-k. Spectrum f o l l o w i n g the 1 min. Hg lamp p h o t o l y s i s o f cis-HNSO i n argon (M/R « 400) - 181 -m o l e c u l e - b o t h p o i n t s s u g g e s t i n g a n o t h e r r e a r r a n g e m e n t o f cis-HNSO. As b e f o r e , each peak can be c o n s i d e r e d s e p a r a t e l y . The a b s o r p t i o n a t 3519-8 cm ' must be e i t h e r an HN o r HO s t r e t c h . HS s t r e t c h e s a r e g e n e r a l l y much lower and i n f a c t even HN s t r e t c h e s a r e seldom t h i s h i g h . On s u b s t i t u t i o n w i t h '^N, the mode shows a l m o s t no s h i f t , thus d e m o n s t r a t i n g t h a t i t i s an HO r a t h e r than a HN s t r e t c h . The a b s o r p t i o n a t 1320.8 cm ' i s most l i k e l y a m u l t i p l y bonded SO, SN o r NO s t r e t c h o r e l s e a hydrogen bend. The d e u t e r -ium s h i f t o f 1.8 cm ' removes t h e p o s s i b i l i t y o f a hydrogen bend and t h e '^N s h i f t o f 26.5 cm ' e l i m i n a t e s an SO s t r e t c h . The pos-s i b i l i t y t h a t i s i s a weak NO s t r e t c h o r a s t r o n g SN s t r e t c h s t i l l r e m a i n s . However, i t i s g e n e r a l l y f ound t h a t NO s t r e t c h e s a r e v e r y i n t e n s e because o f t h e l a r g e c o n t r i b u t i o n made by t h i s bond t o t h e d i p o l e moment. Because S and N have s i m i l a r e l e c t r o n e g a t i v i t i e s , t h e i r bonds a r e l e s s p o l a r and u s u a l l y g i v e l ower i n t e n s i t i e s . T h i s a b s o r p t i o n must be s a i d t o have a low i n t e n s i t y compared w i t h t he 673-9 cm ' peak and i s thus a s s i g n e d t o an SN s t r e t c h . In the mole-c u l e FSN t h e s t r e t c h i n g f r e q u e n c y o f the SN t r i p l e bond i s 1372 cm Thus the p r e s e n t m o l e c u l e i s l i k e l y t o have a s i m i l a r bond r a t h e r than t h e near d o u b l e bond found f o r cis-HNSO w h i c h a b s o r b s a t 1082.7 -1 cm The n e x t peak i s a t 991.8 cm '. I t has a s h i f t o f o n l y 0.7 cm ' on ' "*N s u b s t i t u t i o n and i s not o b s e r v e d on D s u b s t i t u t i o n . - 182 -S i n c e i t i s i n t h e a p p r o p r i a t e r e g i o n , i t i s a s s i g n e d t o an H bend w h i c h does not i n v o l v e a N atom. On d e u t e r a t i o n t h i s peak i s s h i f t e d t o a p o s i t i o n where i t i s not o b s e r v e d . The 673.9 cm ' a b s o r p t i o n i s t h e most i n t e n s e i n the s p e c -trum o f t h i s m o l e c u l e . I t shows l i t t l e ' "*N o r D s h i f t (0.6 cm ' and 2.6 cm ' r e s p e c t i v e l y ) . The mode i s l i k e l y a s i n g l e bond s t r e t c h , a bend o r a t o r s i o n . The s m a l l '"*N and D s h i f t s e l i m i n a t e a l l p o s s i b i l -i t i e s e x c e p t the SO s t r e t c h . Both i n t e n s i t i e s and s h i f t s s u p p o r t t h i s a s s i g n m e n t . As w e l l , i t i s i n the r e g i o n e x p e c t e d f o r an SO s i n g l e bond s t r e t c h . The ne x t medium i n t e n s e peak i s a t 417-5 cm '. I t shows a l a r g e D s h i f t o f 92.3 cm 1 but a s m a l l 1 s h i f t o f 1.0 cm T h i s l a r g e D s h i f t r e q u i r e s a l a r g e hydrogen movement on v i b r a t i o n and f o r the f r e q u e n c y t o be t h i s low, i t can o n l y be a t o r s i o n a l t y p e o f mode. The r e m a i n i n g peak i s v e r y weak and i s not o b s e r v e d i n t h e d e u t e r i u m e x p e r i m e n t s because o f t h e low q u a n t i t i e s o f sample. However, i t s s h i f t on s u b s t i t u t i o n i s from 374 cm 1 t o 368 cm \ Because o f t h e low f r e q u e n c y and the medium '^N s h i f t o f 6 cm ', t h i s peak w i l l be a s s i g n e d t o a b e n d i n g v i b r a t i o n i n v o l v i n g a n i t r o g e n atom. The above d i s c u s s i o n shows t h a t t h e m o l e c u l e p o s s e s s e s an HO bond, an OS s i n g l e bond and an SN t r i p l e bond. The m o l e c u l e i s t h e r e f o r e HOSN. The a s s i g n m e n t s d i s c u s s e d above a r e g i v e n a l o n g w i t h the f r e q u e n c i e s i n t a b l e 4-7. T h i s d a t a a l o n e does not a l l o w f o r t h e c h o i c e o f t h e c i s , t r a n s o r o u t o f p l a n e c o n f i g u r a t i o n , but o t h e r - 183 -T a b l e k-~J. I.R. a b s o r p t i o n s and a s s i g n m e n t s f o r cis-HOSN i n an argon m a t r i x . a s s i gnment HOSN v(cm ') DOSN H 0 S 1 5 N i n t e n s i t y v,(HN) 3519.8 2597.1 3519.3 m. v 2 ( S N ) 1320.8 1319.0 1294.3 w. v 3 ( H 0 S ) 991.8 991.1 w. v 4 ( S 0 ) 673.9 671.3 673.3 v . s . v ^ ( t o r s i o n ) 417.5 325.2 416.5 m. v 5 ( 0 S N ) 374 368 v.w. v . s . = v e r y s t r o n g ; m. = medium; w. =» weak; v.w. = v e r y weak - 184 -c o n s i d e r a t i o n s g i v e n below s u g g e s t t h a t t h e m o l e c u l e i s cis-HOSN. (b) Normal C o o r d i n a t e A n a l y s i s : The s t r u c t u r e o f HOSN was a p p r o x i -o o mated w i t h t h e f o l l o w i n g p a r a m e t e r s : r ( H 0 ) = O.96 A, r ( 0 S ) = 1 . 6 2 A, r(SN) = 1.46 A, < ( H 0 S ) = 1 0 0 ° and < ( 0 S N ) = 1 1 5 ° . F i g u r e 4-5 i s a p l o t o f v i b r a t i o n a l f r e q u e n c y v e r s u s SN bond l e n g t h f o r s e v e r a l o known m o l e c u l e s . The v a l u e f o r HOSN o f 1.46 A i s t a k e n from t h i s o o g r a p h . The i o n HOSO^SO^ has SO s i n g l e bonds o f 1.64 A and 1 .60 A o s u g g e s t i n g an a v e r a g e v a l u e o f 1 . 6 2 A f o r t h e m o l e c u l e HOSN. S e v e r a l o t h e r m o l e c u l e s have OS s i n g l e bonds o f s i m i l a r l e n g t h . The HO bond o l e n g t h i s f a i r l y c o n s t a n t i n a l l m o l e c u l e s a t ne a r 0 . 9 6 A. The OSN a n g l e o f 115° i s ta k e n from t h e FSN a n g l e o f 117° i n FSN and 1 2 2 ° i n F^SN w h i l e the HOS a n g l e o f 1 0 0 ° i s chosen l a r g e l y on c o m p a r i s o n t o the H 0 0 a n g l e o f 1 0 0 ° i n H 2 O 2 . The normal c o o r d i n a t e a n a l y s i s i s u s u a l l y f a i r l y i n s e n s i t i v e t o bond a n g l e s so i n a c c u r a t e a n g l e s p r o b -a b l y do not c r e a t e l a r g e e r r o r s i n t h i s c a l c u l a t i o n . The c h o i c e o f d i h e d r a l a n g l e i s however q u i t e i m p o r t a n t . I f t h e m o l e c u l e i s chosen p l a n a r , t h e n the t o r s i o n a l c o o r d i n a t e i s o f a d i f f e r e n t symmetry than the o t h e r c o o r d i n a t e s and thus w i l l not mix w i t h the OSN bend w h i c h i s o f s i m i l a r e n e r g y . In the n o n - p l a n a r c a s e the m i x i n g o f t h e s e - 185 -1550 - . 1.40 1.4-5 1.50 r ( A ) N - S F i g u r e k~5. C o r r e l a t i o n o f NS bond l e n g t h w i t h NS s t r e t c h i n g f r e q u e n c y . - 186 -i n t e r n a l c o o r d i n a t e s w i l l r e s u l t i n c o m p l i c a t e d normal c o o r d i n a t e s and a more d i f f i c u l t c a l c u l a t i o n . A c c o r d i n g l y , w i t h t h e above s t r u c t u r e a t t e m p t s were made to f i t the o b s e r v e d f r e q u e n c i e s t o c i s , t r a n s and 90° o u t o f p l a n e m o l e c u l e s . In a l l c a s e s the f o u r h i g h energy modes c o u l d be w e l l f i t . However, i n t h e o u t o f p l a n e m o l e c u l e t h e f i t t o the 417-5 cm and 374 cm ' a b s o r p t i o n s had l a r g e e r r o r s w i t h o u t a t o r s i o n - OSN bend i n t e r a c t i o n c o n s t a n t w h i l e w i t h t h i s c o n s t a n t the l e a s t s q u a r e s i t e r a t i o n would not c o n v e r g e . On t h e o t h e r hand, i n bo t h t h e c i s and t r a n s p l a n a r forms c o n v e r g e n c e and good f i t c o u l d be o b t a i n e d . The b e s t s o u r c e o f c o m p a r i s o n between t h e two i s the t o r s i o n a l mode. S i n c e i t i s t h e o n l y out o f p l a n e mode o f the m o l e c u l e , i s o t o p i c s u b s t i t u t i o n r e s u l t s i n as good a c o m p a r i s o n as i t does f o r d i a t o m i c m o l e c u l e s . T a b l e 4-8 g i v e s the o b s e r v e d and b e s t c a l c u l a t e d f r e -q u e n c i e s f o r t h e t o r s i o n a l mode u s i n g c i s and t r a n s forms o f HOSN. Assuming t h a t e r r o r s i n t h e s t r u c t u r e have not r e s u l t e d i n bad G - m a t r i x e l e m e n t s , t h e f i t i s b e t t e r f o r t h e c i s i s o m e r . From ex-p e r i e n c e o b t a i n e d w i t h cis-HNSO, i t a p p ears t h a t t h e t r a n s e r r o r s a r e t o o l a r g e w h i l e the c i s e r r o r s a r e i n a r e a s o n a b l e range t o be a r e s u l t o f d i f f e r e n c e s i n a n h a r m o n i c i t y . For t h i s r e a s o n i t i s s u g g e s t e d t h a t the m o l e c u l e p r oduced on p h o t o l y s i s i s cis-HOSN and t a b l e 4-9 g i v e s the f o r c e c o n s t a n t s and t h e i r l e a s t s q u a r e s e s t i m a t e d e r r o r s f o r t h i s isomer w h i l e t a b l e 4-10 g i v e s the c a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s from o b s e r v e d - 187 " T a b l e 4-8. Comparison o f t h e f i t o f the c i s and t r a n s forms o f HOSN t o the o b s e r v e d t o r s i o n a l f r e q u e n c i e s . -1 cm c i s fx=0.0782 aJ t r a n s f = 0.0854 a J T o b s . 417.5 417-5 HOSN c a l . 419-3 421 .7 A -1.8 -4.2 o b s . 416.5 416.5 H 0 S 1 5 N c a l . 418.9 421.3 A -2.4 -4.8 o b s . 325.2 325.2 DOSN c a l . 319-6 312.1 A 5.6 13.1 - 188 -T a b l e k-S. F o r c e f i e l d f o r cis-HOSN. a J / c o o r d e r r o r fH0 6.91 0.00 fD0 7.10 0.01 f0S 2.97 0.02 f S N 9-90 0.01 fH0S 0.500 0.001 f0SN 1.03 0.01 fH0S-0S 0.259 0.021 f T 0.0782 0.0006 - 189 -T a b l e 4-10. C a l c u l a t e d f r e q u e n c i e s and d i f f e r e n c e s from o b s e r v e d f r e q u e n c i e s (A) f o r cis-HOSN. HOSN H0S , 5 N D0SN v (cm ) A v(cm ^) A v(cm A 3519-6 0.2 3519.5 -0.2 2597.5 0.0 1321.5 -0.7 1291.4 2.9 1321.1 -2.1 991.6 0.2 991.3 -0.2 741.8 673-9 0.0 673.4 -0. 1 671.2 0.1 373.8 0.2 368.2 -0.2 362.8 419-3 -1.8 418.9 -2.4 319.6 5.6 A v e r a g e f r e q u e n c y e r r o r = 1.1 cm (0.21%) - 190 -T a b l e 4-11. P o t e n t i a l e n e r g y d i s t r i b u t i o n and a s s i g n m e n t s f o r cis-HOSN. P.E. D. v(cm ') fH0 f o s fSN fH0S f0SN f r ass i gnment 3519-6 1 .000 0.0 0.0 0.0 0.0 HO s t r . 1321.5 0.0 0.009 0.985 0.007 0.004 SN s t r . 991.6 0.0 0.002 0.005 1 .005 0.005 H0S bend 673.9 0.0 0.991 '0.006 0.034 0.047 OS s t r . 373.8 0.0 0.046 0.005 0.002 0.944 OSN bend 419-3 1 .0 t o r s i o n - 191 ~ f r e q u e n c i e s f o r the v a r i o u s i s o t o p e s . The P.E.D. and r e s u l t i n g a s -14 s i g n m e n t s a r e g i v e n f o r cis-HOS N i n t a b l e 4 - 1 1 . In t h e s e c a l c u l a t i o n s t h e HO and DO f o r c e c o n s t a n t s were f i t t e d s e p a r a t e l y , w h i l e the c o n s t r a i n t t h a t the DOS bend c o n s t a n t was 1.03 t i m e s t h e HOS bend c o n s t a n t was used. Both o f t h e s e were used t o a c c o u n t f o r d i f f e r e n c e s i n a n h a r m o n i c i t y . The l a t t e r c o n -s t r a i n t was used because the DOS b e n d i n g a b s o r p t i o n was not o b s e r v e d and so i n s u f f i c i e n t d a t a was a v a i l a b l e t o c a l c u l a t e a second p a r a -meter. I t was a l s o found t h a t an HOS bend - OS s t r e t c h i n t e r a c t i o n c o n s t a n t was n e c e s s a r y t o o b t a i n a good f i t o f the 991 -8 cm ' and 673-9 cm ' a b s o r p t i o n s . T h e r e f o r e e i g h t c o n s t a n t s were c a l c u l a t e d from s i x t e e n o b s e r v e d f r e q u e n c i e s . (c) Thermodynamic F u n c t i o n s : The a v a i l a b i l i t y o f a c o m p l e t e s e t o f f r e q u e n c i e s a l l o w e d t h e c a l c u l a t i o n o f the thermodynamic f u n c t i o n s S, Cp, -(G-H )/T and (H-H Q)/T. The p r i n c i p l e moments o f i n e r t i a 14 were c a l c u l a t e d f r o m the above s t r u c t u r e a p p r o x i m a t e d f o r cis-HOS N. These moments and t h e thermodynamic f u n c t i o n s from 100°K t o 1500°K a r e g i v e n i n t a b l e 4 - 1 2 . (d) D i s c u s s i o n ( i ) F i r s t a n o t e about t h e m i s s i n g DOS bend a b s o r p t i o n . From t a b l e 4 -10 the c a l c u l a t e d f r e q u e n c y f o r t h i s mode i s 741.8 cm S i n c e a s e a r c h o f t h i s r e g i o n d i d not l e a d t o i t s o b s e r v a t i o n , i t i s assumed t h a t i t i s a c t u a l l y a t near 750 cm ' and t h e r e f o r e o b s c u r e d by the cis-HNSO t o r s i o n a l a b s o r p t i o n . - i 9 2 -T a b l e 4-12. The p r i n c i p l e moments o f i n e r t i a and thermodynamic f u n c t i o n s (cal/mole°K) f o r cis-HOSN. P r i n c i p l e moments: 52.197, 11-945, 6-141 ( u A 2 ) t e m p e r a t u r e S C (G-H Q) ( H ~ H Q ) °K ' T ~~} 273- 15 67.18324 11.89993 57-77571 9.40686 298. 10 68.24130 12.31109 58.60771 9-63293 100. 00 57-22940 8.40560 49-19969 8.02898 200. 00 63.69289 IO.52383 54.95343 8.73877 300. 00 68.31961 12.34123 58.66896 9-64999 400. 00 72.06742 13-71124 61.56415 10.50263 500. 00 75.24078 14.71590 63.99006 11.25008 600. 00 77-99244 15.45539 66.09947 11.89235 700. 00 80.41895 16.01788 67.97512 12.44322 800. 00 82.58804 16.46481 69.66848 12.91895 900. 00 84.54925 16.83402 71.21461 13-33404 1000. 00 86.33954 17-14769 72.63883 13-70012 1 100. 00 87.98690 17-41894 73-96016 14.02615 1200. 00 89.51293 17-65596 75.19337 14.31898 1300. 00 90.93455 17-86433 76-35013 14.58385 1400. 00 92.26531 18.04818 77.43987 14.82487 1500. 00 93-51616 18.21083 78.47030 15.04529 - 193 -( i i ) A c o n s i d e r a t i o n o f the p o s s i b l e n a t u r e o f t h e r e a c -t i o n a l s o l e n d s some s u p p o r t t o the prop o s e d c i s s t r u c t u r e . I t has been d e m o n s t r a t e d above t h a t t h e r e i s l i k e l y an i n t e r a c t i o n between the hydrogen and oxygen o f cis-HNSO. A l s o , i t appears t h a t HOSN i s produced by a s i m p l e hydrogen t r a n s f e r . A l t h o u g h l i t t l e i s known about the e x c i t e d s t a t e o f cis-HNSO t h a t r e s u l t s i n t h e b r e a k i n g o f the HN bond, i t i s p o s s i b l e t h a t because o f the i n t e r a c t i o n a l r e a d y p r e s e n t , t h e bond r u p t u r e l e a d s d i r e c t l y t o the f o r m a t i o n o f the OH bond. Thus the c i s form would be made i n i t i a l l y . Even though the HOSN m o l e c u l e may then have enough energy t o undergo i n t e r n a l r o t a -t i o n , i t a ppears t h a t t he m a t r i x p r e v e n t s t h i s s i n c e o n l y one fo r m o f HOSN has been o b s e r v e d . I t i s f e l t t h a t t h i s one o b s e r v e d f o r m must then be the c i s isomer - a c o n c l u s i o n w h i c h a g r e e s w i t h t he N.C.A. r e s u l t s . ( i i i ) As i s seen i n t a b l e 4-7, a weak a b s o r p t i o n a t 1342 cm ' has been a s s i g n e d t o the o v e r t o n e o f the SO s t r e t c h i n g f u n d a -mental ( 2 V g n = 1 3 4 8 cm ^ ) . F o r t h i s a b s o r p t i o n t o be seen r e q u i r e s t h a t t he o v e r t o n e be i n Fermi r e s o n a n c e w i t h v^, the SN s t r e t c h i n g f u n d a m e n t a l . The s e p a r a t i o n between t h e s e two peaks i s 2 1 cm '. However, t h e o v e r t o n e o v e r l a p s w i t h an SO^ a b s o r p t i o n making i n t e n s i t y c o m p a r i s o n d i f f i c u l t and f u r t h e r m o r e , i t i s not seen f o r e i t h e r 14 DOSN o r HOS N - t h e r e f o r e a t h o r o u g h a n a l y s i s o f t h e re s o n a n c e i s not p o s s i b l e . The resonan c e c r e a t e s a s l i g h t u n c e r t a i n t y i n the f r e q u e n c y o f t h e SN s t r e t c h i n g f undamental o f cis-HOSN w h i c h c o u l d - 194 -a c c o u n t f o r the e r r o r s i n f i t t i n g t h i s a b s o r p t i o n ( t a b l e 4 - 1 0 ) . Even though t h e use o f a somewhat h i g h e r v a l u e might have r e s u l t e d i n a b e t t e r f i t , t h e o b s e r v e d f r e q u e n c y was used i n the NCA because the c o r r e c t i o n c o u l d not be e s t i m a t e d . I t i s l i k e l y t h a t t h e c o r r e c t i o n w o u l d be s m a l l enough t o p r e c l u d e any s i g n i f i c a n t f o r c e c o n s t a n t e r r o r . ( i v ) In t h e p h o t o l y s i s o f i s o c y a n i c a c i d , HNCO, i n a m a t r i x , J a c o x and M i l l i g a n ^ o b s e r v e d the f o r m a t i o n o f HOCN. T h i s r e a c t i o n i s s i m i l a r t o the one o b s e r v e d h e r e - HNSO -»• HOSN - and thus p r o v i d e s an a d d i t i o n a l c o r r e l a t i o n i n s u p p o r t o f the c o n c l u s i o n s r e a c h e d above t h a t t he m o l e c u l e g i v i n g t he a b s o r p t i o n s l i s t e d i n t a b l e 4 -6 i s HOSN. (v) A f i n a l word on t h i s cis-HOSN i d e n t i f i c a t i o n . P r o b a b l y the o n l y o t h e r m o l e c u l e t h a t c o u l d be r e a d i l y formed from cis-HNSO and s t i l l have a peak a t 3520 cm ' i s trans-HNSO. A t t e m p t s t o o b t a i n a r e a s o n a b l e a s s i g n m e n t f o r t h i s m o l e c u l e u s i n g t h e a b s o r p t i o n s i n t a b l e 4 -7 were c o m p l e t e l y u n s u c c e s s f u l . A l t h o u g h an a s s i g n m e n t f o r the s p e c i e s c o n t a i n i n g t h e common i s o t o p e s was p o s s i b l e , t h e i n t e n s -i t i e s were not c o m p a t i b l e w i t h t h i s a s s i g n m e n t and t h e s h i f t s on i s o t o p i c s u b s t i t u t i o n showed i t t o be c o m p l e t e l y f a l s e . S i n c e r e a s -o n a b l e a s s i g n m e n t s f o r trans-HNSO c o u l d be made i n p a r t 1, the ab-s o r p t i o n s d i s c u s s e d i n p a r t 2 must b e l o n g t o cis-HOSN. 3. HSNO - c i s and t r a n s (a) S p e c t r a : R e c h e c k i n g f i g u r e 4 - 1 , i t i s seen t h a t numerous peaks - 195 -s t i l l remain u n e x p l a i n e d , most n o t i c e a b l y t h e i n t e n s e a b s o r p t i o n s near 1600 cm F i g u r e 4-6 shows the sample seen i n f i g u r e 4-4 f o l l o w i n g a f u r t h e r 41 m i n u t e s p h o t o l y s i s w i t h the mercury lamp. The peaks between 1500 cm ^ and 1600 cm ' have g a i n e d c o n s i d e r a b l e i n t e n s i t y w h i l e t h o s e b e l o n g i n g t o cis-HNSO and cis-HOSN have de-c r e a s e d . S e v e r a l low energy a b s o r p t i o n s , marked by B's i n f i g u r e 4-6, have a l s o grown. By more c a r e f u l s t u d y o f t h e s e a b s o r p t i o n s a t i n t e r m e d i a t e p h o t o l y s i s t i m e s and i n p a r t i c u l a r by c o m p a r i n g t h e 1523 cm ' and 1595 cm ' peaks i n f i g u r e s 4-1 and 4-6, i t i s seen t h a t t h e 1523 cm ' and 790 cm ' a b s o r p t i o n s b e l o n g t o a s e p a r a t e s p e c i e s and a r e t h e r e f o r e d i s c u s s e d i n a l a t e r s e c t i o n o f t h i s c h a p t e r . The r e m a i n i n g a b s o r p t i o n s , w h i c h a l l f o l l o w c u r v e B i n f i g u r e 4-2, a r e l i s t e d f o r a l l i s o t o p e s i n t a b l e 4-13. The p r o b l e m o f a t l e a s t two a b s o r p t i o n s n e a r 1600 cm ' must f i r s t be r e s o l v e d , f o r i t w o u l d not be e x p e c t e d t h a t one mol-e c u l e , i s o l a t e d i n a m a t r i x and c o n t a i n i n g o n l y an H, an S, an N and an 0 atom, c o u l d g i v e two a b s o r p t i o n s i n t h i s r e g i o n . Not s u r -p r i s i n g l y , a c o m p a r i s o n o f t h e two s p e c t r a o f p r o d u c t s p r oduced by mercury lamp p h o t o l y s i s a f t e r i s o l a t i o n and by hydrogen reso n a n c e lamp p h o t o l y s i s d u r i n g s p r a y on ( f i g u r e 4-7) shows t h a t 1596 cm ' and 1570 cm ' b e l o n g t o d i f f e r e n t a b s o r b e r s . A change i n t h e i n t e n -s i t y r a t i o by a f a c t o r o f t h r e e o c c u r s . F i g u r e s 4-7 and 4-8, showing t h e s e a b s o r p t i o n s under h i g h r e s o l u t i o n f o r the v a r i o u s i s o t o p e s , d e m o n s t r a t e t h e i r c o m p l e x i t y . These s p e c t r a a l s o show t h a t a l t h o u g h *cis- HNSO t s o 2 F i g u r e 4-6. Spectrum f o l l o w i n g t h e 42 min. Hg lamp p h o t o l y s i s o f cis-HNSO i n argon (M/R = 400). - 197 -T a b l e 4-13- Observed a b s o r p t i o n s and p o s s i b l e a s s i g n m e n t s f o r HSNO. i n t e n s i t y ^ HNSO v(cm ') DNSO H 1 5NS0 poss i b l e a s s ignment v. s. 1596.8* 1595.1* 1569.4* 1595.0 1593.5 1568.0 N=0 s t r . 1591.1 1592.4 1564.2 1587.8 w. 1576.0 1574.1 1549.3 N=0 s t r . s. 1571.0* 1568.8* 1544.4* 725.9 876.2 724.0 874.2 HSN bend m. 876 722.7* 872.8* v.v.w. 858 850 HSN bend? 536.9 535-5 N-S s t r . m. 542 488? 533-0* w. 500 488? 495 t o r s i o n v.v.w. 385 380 ? w. 306 304 304.1 m. 298* 294* 294.9* SNO bend v = v e r y , s = s t r o n g , m = medium, w = weak most i n t e n s e peak o f the m u l t i p l e t - 198 -1/ ( c m - ' ) 1595 1585 1575 1595 1585 ' . i i ! 1 i 1 1 L o.H \ (D U C o v_ O CO JD O 0.5H '1596 _ A 1 5 7 Q = 2.3 1575 I 1565 A 1596 _ A = 6.T 1570 O.l h O . 5 (a) (b) F i g u r e 4-7- Comparison o f 1596 cm ' and 1570 cm ' a b s o r p t i o n i n t e n s i t i e s * (a) Hg lamp p h o t o l y s i s (b) hydrogen r e s o n a n c e lamp p h o t o l y s i s w i t h s p r a y - o n . - 199 -1/ ( c m - i ) 1595 1585 1575 . 1566 1556 1546 F i g u r e 4-8. S p e c t r a o f t h e NO s t r e t c h i n g r e g i o n f o r DSNO and HS NO. - 200 -peak h e i g h t s s u g g e s t s i m i l a r i n t e n s i t i e s , i n t e g r a t e d i n t e n s i t i e s o f the 1597 cm ' m u l t i p l e t a r e always much g r e a t e r than t h o s e o f the 1571 cm ' peak. The r e m a i n i n g a b s o r p t i o n s i n t a b l e 4-13 a r e weak and b r o a d . High r e s o l u t i o n o f some o f t h o s e a b s o r p t i o n s i n e x p e r i m e n t s where enough i n t e n s i t y was o b t a i n e d t o g i v e good s p e c t r a show t h a t t h e y p o s s e s s complex s p l i t t i n g s i m i l a r t o t h a t o f t h e 1597 cm ' peak p r i n c i p a l l y a t r i p l e t s t r u c t u r e and s p l i t t i n g s o f 3 t o 10 cm ' ( f i g u r e 4-9). E x c l u d i n g peaks l a b e l e d v e r y , v e r y weak i n t a b l e 4-13, a l l a b s o r p t i o n s e x c e p t 500 cm ' d e f i n i t e l y show t h i s s i m i l a r -i t y w i t h 1597 cm U n f o r t u n a t e l y low i n t e n s i t y o f the 500 cm ' a b s o r p t i o n made h i g h r e s o l u t i o n s p e c t r a u n o b t a i n a b l e . F u r t h e r , as p o i n t e d o u t above, t h e 1597 cm ' peak i s much more i n t e n s e t h a n the 1571 cm 'peak so t h a t one might e x p e c t t o see a b s o r p t i o n s a s -s o c i a t e d w i t h i t l o n g b e f o r e t h o s e a s s o c i a t e d w i t h 1571 cm F o r t h e s e r e a s o n s , e x c e p t f o r t h e v.v.w. peaks, a l l t he a b s o r p t i o n s i n t a b l e 4-13, i n c l u d i n g 500 cm w i l l be a s s o c i a t e d w i t h the 1597 cm ' a b s o r p t i o n . Now t h a t t h e g r o u p i n g i s e s t a b l i s h e d , i t i s n e c e s s a r y t o make the i d e n t i f i c a t i o n and a s s i g n m e n t s . Both t h e 1597 cm ' and 1571 cm ' a b s o r p t i o n s a r e v e r y i n t e n s e and show s i m i l a r s h i f t s o f about 2 cm ' on d e u t e r a t i o n and 27 cm ' on s u b s t i t u t i o n . The f r e q u e n c i e s , i n t e n s i t i e s and i s o t o p i c s h i f t s a r e a l l c o m p a t i b l e w i t h d o u b l y bonded NO s t r e t c h i n g modes. The n e x t a b s o r p t i o n , a t 7 3 0 J - 201 -v ( c m - 1 ) 722 5 3 8 Deuterium ^ D S N H S N — I — 8 7 8 871 15 N NS 15 N 5 3 4 5 3 0 S N O 3 0 6 2 9 2 F i g u r e 4-9. The h i g h r e s o l u t i o n s p e c t r a o f s e v e r a l trans-HSNO a b s o r p t i o n s showing s p l i t t i n g s . - 202 -876 cm f o r the common i s o t o p e s , shows a l a r g e s h i f t o f 153 cm on d e u t e r a t i o n so i t must be a hydrogen bend. However, s i n c e no o t h e r h i g h f r e q u e n c y a b s o r p t i o n s a r e s e e n , i t i s f e l t t h a t b e s i d e s the NO d o u b l e bond, no o t h e r m u l t i p l e bonds a r e p r e s e n t i n t h i s m o l e c u l e . For t h i s t o be s o , s u l f u r must be d i v a l e n t and t h i s can o n l y happen i f i t i s bonded t o a hydrogen atom. T h e r e f o r e , s i n c e t h e '"*N s h i f t o f 3 cm ' r e q u i r e s t h e i n v o l v e m e n t o f n i t r o g e n i n t h e bend, i t must be o f an HSN a n g l e . An HSN bend and an NO d o u b l e bond s t r e t c h w o u l d r e q u i r e t he m o l e c u l e t o be HSNO: S N / \ H O c i s t r a n s F o l l o w i n g t h e c i s - t r a n s c o r r e l a t i o n s f o r HNSO and HONO i n p a r t 1 above, i t i s not u n l i k e l y t h a t t he 1597 cm ' and a s s o c i a t e d a b s o r p t i o n s b e l o n g w i t h trans-HSNO w h i l e t h e 1571 cm ' a b s o r p t i o n b e l o n g s t o cis-HSNO. However, because the r e m a i n i n g peaks a s s o c i a t e d w i t h 1597 cm ' a r e v e r y c l o s e t o g e t h e r , complex normal c o o r d i n a t e s a r e e x p e c t e d making a s s i g n m e n t s d i f f i c u l t . Even t h e i s o t o p i c s h i f t s a r e o f l i t t l e h e l p . T h e r e f o r e i n t u i t i v e a s s i g n m e n t s were made by t a k i n g t he SNO bend t o be the l o w e s t , 298 cm ^ and the NS s t r e t c h t o be t h e h i g h e s t , 5^2 cm w i t h the t o r s i o n a t 500 cm \ These - 203 ~ a s s i g n m e n t s a r e g i v e n i n t a b l e 't—13- I t was hoped t h a t t h e f o r c e f i e l d c a l c u l a t i o n might r e s o l v e t h e u n c e r t a i n t y . (b) Normal C o o r d i n a t e A n a l y s i s : A l t h o u g h u n c e r t a i n t i e s i n the s p e c -trum o f HSNO e x i s t , a t t e m p t s were made t o f i t the a s s i g n m e n t s s u g g e s t -ed i n t a b l e 4-13- A s t r u c t u r e was a p p r o x i m a t e d w i t h t h e f o l l o w i n g p a r a m e t e r s o b t a i n e d by c o m p a r i s o n w i t h s i m i l a r m o l e c u l e s : r(HS) = 1.33 A, r(NS) = 1.70 A, r(N0) = 1.15 A, ct(HSN) = 95° and ct(SNO) = 115°. The d i f f i c u l t p a r a m e t e r t o e s t i m a t e was r(SN) s i n c e few s i n g l e o o SN bonds e x i s t . These run from 1.65 A t o 1.8 A w h i l e e x t r a p o l a t i o n o o f t h e p l o t i n f i g u r e 4-5 s u g g e s t s 1.65 A. T a k i n g an a v e r a g e , t h e o v a l u e o f 1.70 A was s e l e c t e d . F i t s were a t t e m p t e d f o r o n l y the c i s and t r a n s p l a n a r forms s i n c e the s i m i l a r m o l e c u l e H0N0 i s known t o be p l a n a r . For the t r a n s m o l e c u l e t h e c a l c u l a t i o n c o n v e r g e d w i t h t h e use o f one i n t e r a c t i o n c o n s t a n t , H^^ J^ -SN " ^ n e ^ s t r e t c h c o n s t a n t was h e l d f i x e d s i n c e t h i s v i b r a t i o n was not o b s e r v e d , w h i l e t h e v a l u e f o r t h e DSN bend c o n s t a n t was c o n s t r a i n e d t o 1.03 t i m e s the HSN bend c o n s t a n t t o a c c o u n t f o r a n h a r m o n i c i t y d i f f e r e n c e s . Thus, s i x c o n s t a n t s were used t o f i t 14 o b s e r v e d f r e q u e n c i e s . The f o r c e c o n s t a n t s a r e l i s t e d i n t a b l e 4-14 w h i l e t h e o b s e r v e d f r e q u e n c i e s , c a l c u l a t e d f r e q u e n c i e s , p o t e n t i a l energy d i s t r i b u t i o n and a s s i g n -ments a r e g i v e n i n t a b l e 4-15. Because o f t h e complex n a t u r e o f the low f r e q u e n c y modes, t h e P.E.D. f o r each i s o t o p e i s l i s t e d . I t s h o u l d be no t e d t h a t because o f u n c e r t a i n t y i n a s s i g n -- 204 " T a b l e 4-14. F o r c e f i e l d f o r trans-HSNO. a J / c o o r d e r r o r ^HS 4.0 h e l d f i x e d f C K ) 1.79 0.02 fN0 11.04 0.04 f H S N 0.671 0.004 f S N Q 0.562 0.003 f 0.200 0.001 T fHSN-NS - ° - 2 3 0 ° - 0 0 6 T a b l e 4-15- Observed f r e q u e n c i e s , c a l c u l a t e d and assignment f o r trans-HSNO. f r e q u e n c i e s , p o t e n t i a l energy d i s t r i b u t i o n v (cm • • > P.E.D. obs. ca 1. fHS fSN fN0 fHSN fSN0 f T ass i gnment HSNO 2636.9 1.0 HS s t r . 1596.8 1597.0 0.009 0.983 0.008 0.004 NO s t r . 876.O 877.0 0.075 0.002 0.799 0.021 HSN bend 542.0 543.9 0.707 0.004 0.227 0.230 SN s t r . 500.0 498.6 1.0 t o r s i o n 295.0 295.2 0.256 0.01 I 0.012 0.745 SN0 bend HS15N0 2336.9 1.0 1569.4 1567 .7 0.008 0.984 0.007 0.004 872.8 873.6 0.067 0.002 0.814 0.018 533.0 532.2 0.720 0.004 0.213 0.228 495.0 496.3 1.0 294.9 293-9 0.251 0.010 0.012 0.750 DSNO 1893-8 1.0 1595.1 1596.7 0.009 0.984 0.0 0.004 722.7 721.3 0.288 0.0 0.473 0.086 488.0 487.0 0.492 0.0 0.553 0.166 390.7 1 .0 294.0 294.8 0.256 0.011 0.012 0.744 Average f r e q u e n c y e r r o r = 1.1 cm (0.19%) - 2 0 6 " ment the 4 8 8 cm f r e q u e n c y o f DSNO was not i n i t a l l y e n t e r e d i n the c a l c u l a t i o n . But when a v a l u e o f 4 8 2 cm 1 was c a l c u l a t e d , i t was d e c i d e d t o add t h i s a b s o r p t i o n as i m p o r t a n t a d d i t i o n a l d a t a f o r the d e t e r m i n a t i o n o f complex normal c o o r d i n a t e s . The P.E.D. f o r t h i s peak shows a r e v e r s a l o f a s s i g n m e n t on g o i n g from H t o D w h i c h i l l u s -t r a t e s t h e d i f f i c u l t y i n making a s s i g n m e n t s even w i t h the use o f PED's when a g r e a t d e a l o f m i x i n g o c c u r s . A t t e m p t s a t f i t t i n g a c i s s t r u c t u r e t o t h e same d a t a were u n s u c c e s s f u l even w i t h a d d i t i o n a l i n t e r a c t i o n c o n s t a n t s . I t i s f e l t t h a t t h i s i s because the a p p r o x i m a t e d c i s s t r u c t u r e i s not c o m p a t i b l e w i t h the o b s e r v e d i s o t o p i c s h i f t s . T h i s c o u l d be as a r e s u l t o f p o o r l y chosen p a r a m e t e r s , i n c o r r e c t o r i n s u f f i c i e n t d a t a o r the i n -a c c e p t a b i 1 i t y o f the c i s form. The f a c t , t h a t t h e t r a n s isomer d i d f i t t h e d a t a s u g g e s t s t h e l a s t r e a s o n thus s u p p o r t i n g the trans-HSNO i dent i f i c a t i o n . (c) D i s c u s s i o n ( i ) The i d e n t i f i c a t i o n o f t h e a b s o r p t i o n s i n t a b l e 4-15 w i t h trans-HNSO and t h e a s s i g n m e n t s s u b s t a n t i a t e d by the P.E.D.'s a r e f e l t t o be q u i t e c e r t a i n . The p r o b l e m o f the m u l t i p l i c i t y o f pe a k s , however, has not been e x p l a i n e d . The b e s t e x p l a n a t i o n i s t h a t b o t h c i s - and trans-HSNO a r e produced and t h a t the m u l t i p l e t s t r u c t u r e o f the t r a n s a b s o r p t i o n s i s due t o m a t r i x s p l i t t i n g . I t would not be s u r p r i s i n g t o f i n d t h a t a r e a c t i o n i n v o l v i n g the com-p l e x r e a r r a n g e m e n t t h a t y i e l d s trans-HSNO from cis-HOSN would a l s o - 207 " r e s u l t i n l o c a l d i s r u p t i o n s o f the argon l a t t i c e and thus the c r e a t i o n o f m u l t i p l e t r a p p i n g s i t e s . ( i i ) The e x p l a n a t i o n o f the p r e s e n c e o f b o t h t h e c i s and t r a n s forms as w e l l as t h e i r d i f f e r e n t r a t i o s i n v o l v e s a more d e t a i l e d d i s c u s s i o n o f the r e a c t i o n s i n v o l v e d . T h i s i s found i n s e c t i o n D o f the c h a p t e r . B r i e f l y , however, s i n c e i t appears t h a t both a r e p r o -duced a t t h e same t i m e , i t i s e x p e c t e d t h a t t h e y a r e produced i n the same r e a c t i o n - t h a t i s from an i n t e r m e d i a t e t h a t can go t o e i t h e r c i s - o r trans-HSNO. A l a g i n t h e appearance o f one r e s u l t i n g from i t s p r o d u c t i o n from the o t h e r by i s o m e r i s m would be n e c e s s a r y u n l e s s the i s o m e r i s m was so f a s t t h a t e q u i l i b r i u m was reached i n a t i m e p e r -i o d t o o s h o r t t o be d e t e c t e d i n t h e s e e x p e r i m e n t s . 4. SNO: A RADICAL (a) S p e c t r a : On c o n t i n u i n g p h o t o l y s i s w i t h a mercury lamp t h r o u g h q u a r t z two more peaks were o b s e r v e d t o grow i n i n t e n s i t y a f t e r the HSNO a b s o r p t i o n s had slowed i n t h e i r p r o d u c t i o n . Compare c u r v e s B and C i n f i g u r e k-2. However, t h e g r e a t e s t i n t e n s i t y f o r t h e s e peaks was o b s e r v e d u s i n g vacuum u.v. p h o t o l y s i s w i t h s i m u l t a n e o u s s p r a y on o f sample. The two peaks were i n the same p o s i t i o n s - 1523-0 cm ' and 789.7 cm 1 - when HNSO o r DNSO were p h o t o l y s e d and a t 1^98.1 cm ' and 777.6 cm ' when H^NSO was used. The m o l e c u l e i s most c e r t a i n l y a t r i a t o m i c c o n t a i n i n g no hydrogen. Of the t h r e e p o s s i b l e t r i a t o m i c s , SON i s c o n s i d e r e d - 208 -u n l i k e l y because t h e much more e l e c t r o n e g a t i v e oxygen i s not e x p e c t e d t o be found i n t h e m i d d l e . The o t h e r p o s s i b i l i t i e s a r e NSO and SNO. A l t h o u g h the 1523.0 cm ^ a b s o r p t i o n shows an '^N s h i f t o f 25 cm ' w h i c h i s c o m p a t i b l e w i t h e i t h e r an NS o r NO s t r e t c h , t h e h i g h f r e q u e n -cy w o u l d not be e x p e c t e d f o r t h e NS s t r e t c h o f NSO. The SO s t r e t c h w ould be n e i t h e r as h i g h nor show such a l a r g e '"*N s h i f t . Even though a l a r g e m i x i n g o f t h e s t r e t c h i n g c o o r d i n a t e s might o c c u r , i t i s s t i l l not f e l t p o s s i b l e f o r t h i s r a d i c a l t o a b s o r b a t 1523 cm \ On the o t h e r hand, the s p e c t r a show a ready c o m p a t i b i l i t y w i t h the r a d i c a l SNO. A f r e q u e n c y f o r an NO s t r e t c h o f 1523 cm ' i s v e r y l i k e l y and the '**N s h i f t i s a p p r o p r i a t e . The s t r o n g i n t e n s i t y o b s e r v e d i s c o n s i s t e n t w i t h an NO s t r e t c h w h i l e the low i n t e n s i t y e x p e c t e d f o r the SN s t r e t c h a c c o u n t s f o r i t s not b e i n g s e e n . The f r e q u e n c y o f 789.7 cm ' and the s h i f t o f 12 cm ' a r e r e a s o n a b l e f o r an SNO bend. A l s o , s i n c e t h e r a d i c a l i s l a t e i n b e i n g p r o d u c e d , i t i s l i k e l y t o be formed from HSNO. S i n c e s u l f u r - h y d r o g e n bonds a r e r e l a t i v e l y weak, t h e removal o f a hydrogen t o g i v e SNO would not be u n e x p e c t e d . Both the 1523 cm ' and 789-7 cm ^ a b s o r p t i o n s a r e shown i n f i g u r e 4 - 1 0 . The d o u b l e t c h a r a c t e r o f the 1523 cm ' a b s o r p t i o n i s c h a r a c t e r i s t i c o f the s p l i t t i n g s o f t h e a s y m m e t r i c s t r e t c h i n g mode o f bent t r i a t o m i c s i n argon m a t r i c e s (compare w i t h the ab-s o r p t i o n o f ozone i n f i g u r e 2 - 1 0 ) . The r e m a i n i n g a b s o r p t i o n , - 209 " F i g u r e 4-10. The h i g h r e s o l u t i o n s p e c t r a o f the NO s t r e t c h and SNO bend o f SNO. - 210 -p r o b a b l y the s y m m e t r i c s t r e t c h c o n s i s t i n g l a r g e l y o f NS s t r e t c h i n g c o o r d i n a t e , , i s e x p e c t e d t o be weak and has not been o b s e r v e d . The o b s e r v e d f r e q u e n c i e s and a s s i g n m e n t s f o r SNO a r e g i v e n i n t a b l e 4-16. (b) N.C.A.: Because o f t h e l a c k o f an NS s t r e t c h i n g f r e q u e n c y , i t was not p o s s i b l e t o o b t a i n a f o r c e f i e l d f o r SNO. S i n c e a g r e a t d e a l o f m i x i n g o f i n t e r n a l c o o r d i n a t e s i s e x p e c t e d , not even a p p r o x i m a t e f o r c e c o n s t a n t s based on c h a r a c t e r i s t i c f r e q u e n c i e s w o u l d be meaning-f u l . (c) D i s c u s s i o n ( i ) The removal o f t h e hydrogen from trans-HSNO t o g i v e SNO has r e s u l t e d i n a s h i f t o f t h e NO s t r e t c h i n g f r e q u e n c y from 1597 cm 1 t o 1523 cm '. In a s i m i l a r s y s t e m , g o i n g from trans-HONO t o N 0 2 s h i f t s t h e s t r e t c h from 1696 cm" 1 t o 1618 cm 1 The s i m i l a r -i t y i n s h i f t s u p p o r t s the i d e n t i f i c a t i o n o f SNO. The lower NO f r e -quency can be e x p l a i n e d by the f o l l o w i n g s i m p l e scheme. The removal o f t h e hydrogen atom r e l e a s e s s u l f u r e l e c t r o n d e n s i t y i n t o t he d e l o c a l -i z e d TT o r b i t a l s o f t h e new SNO system. The SN bond thus i n c r e a s e s i n s t r e n g t h . A t the same t i m e , e l e c t r o n s t h a t were i n l o c a l i z e d TT bond-i n g o r b i t a l s i n the d o u b l e NO bond o f trans-HSNO now a l s o become d e l o c a l i z e d . S i n c e o n l y one o f t h e TT o r b i t a l s o c c u p i e d i n SNO i s a bonding o r b i t a l , t he NO bond o r d e r d e c r e a s e s w i t h an accompanying d e c r e a s e i n v i b r a t i o n a l f r e q u e n c y . - 211 " T a b l e 4-16. Observed f r e q u e n c i e s and a s s i g n m e n t s f o r the r a d i c a l SNO. v(cm ') as s i g n m e n t S^NO S 1 5 N 0 NO s t r . 1523.0 1498.1 SN s t r . SNO bend 789.7 777.6 - 212 " 5. THE 1195 CH DOUBLET, NSO o F o l l o w i n g 1216 A p h o t o l y s i s w i t h s i m u l t a n e o u s s p r a y o n , an a b s o r p t i o n was o b s e r v e d a t about 1195 cm T h i s i s the remain-i n g u n d i s c u s s e d peak i n f i g u r e 4-1. T h i s f e a t u r e was broad under low r e s o l u t i o n but e a s i l y r e s o l v e d i n t o a d o u b l e t . F i g u r e 4-11 shows t h i s a b s o r p t i o n f o r the ca s e s i n w h i c h t h e p h o t o l y s e d m a t e r i a l was HNSO, DNSO and H^NSO. The d e u t e r i u m s u b s t i t u t i o n d i d not cause a s h i f t a l t h o u g h the low i n t e n s i t y made a c c u r a t e measurement d i f f i -c u l t . Thus, the m o l e c u l e p r o b a b l y does not c o n t a i n a hydro g e n . T h i s r e g i o n o f the s p e c t r u m s u g g e s t s an SO o r NS bond s t r e t c h . In f a c t , i t i s i n the c o r r e c t p o s i t i o n t o be the d i a t o m i c m o l e c u l e NS, but the '^N s h i f t o f 9-4 cm ' i s too s m a l l . T h i s w o u l d be t r u e f o r any NS s t r e t c h so t h i s a b s o r p t i o n i s p r o b a b l y due t o an SO s t r e t c h i n g mode. The r e m a i n i n g e v i d e n c e f o r t h i s m o l e c u l e i s t h a t i t was o n l y produced w i t h vacuum u.v. p h o t o l y s i s and t h a t f o l l o w i n g i t s p r o -d u c t i o n , s h o r t e x p o s u r e (2 m i n u t e s ) t o mercury lamp r a d i a t i o n caused (3) i t t o d i s a p p e a r . T h i s i s shown i n f i g u r e 4-11.. M i l l i g a n e t a l have shown the same b e h a v i o u r f o r t h e 1240 cm ' a b s o r p t i o n r e s u l t i n g from the vacuum u.v. p h o t o l y s i s o f NO^ and a s s i g n e d i t t o the H0^ i o n . T h e r e f o r e , the p o s s i b i l i t y t h a t t he 1190 cm ' band i s due t o the SNO i o n , w i t h t h i s a b s o r p t i o n a s s i g n e d t o t h e NO s t r e t c h , has been c o n s i d e r e d . However, due t o the l o w ^ N i s o t o p i c s h i f t , t h i s does not seem l i k e l y . As shown p r e v i o u s l y , i n the n e u t r a l SNO - 213 -•u ( cm - 1 ) 1250 1150 1250 1150 1250 1150 f ft . x(<" w 1 5 N Deuter ium 1200 1190 1190 1180 F i g u r e 4-11. The SO s t r e t c h i n g mode o f NSO produced by vacuum u.v. p h o t o l y s i s o f cis-HNSO. (a) shows t h e d i s a p p e a r a n c e o f the a b s o r p t i o n f o l l o w i n g Hg lamp p h o t o l y s i s . - 214 " m o l e c u l e the s h i f t i s 25 cm The o t h e r p o s s i b i l i t y , and the one c o n s i d e r e d most l i k e l y , i s t h a t t h e a b s o r p t i o n i s due t o the SO s t r e t c h o f NSO pr o d u c e d by o p h o t o d i s s o c i a t i o n o f cis-HNSO. P h o t o l y s i s i n the 2000-4000 A r e g i o n then causes t h e NSO t o r e a r r a n g e t o SNO o r decompose t o some o t h e r f r a g m e n t s not se e n . The hydrogen reso n a n c e lamp, w i t h low i n t e n s i t y i n t h i s r e g i o n , does not g i v e the r e a r r a n g e m e n t . The p o s s i b i l i t y t h a t the s p e c i e s i s t h e NSO i o n i s u n l i k e l y because i t s d i s a p p e a r -ance would r e q u i r e t h e appearance o f NSO and new a b s o r p t i o n s . T h i s i s n ot o b s e r v e d . The p o s i t i o n o f the a b s o r p t i o n and the ' "*N s h i f t a r e b o t h c o m p a t i b l e w i t h a s s i g n m e n t t o the NSO r a d i c a l . As i n the c a s e o f HSN0, SNO and H0N0, 0N0, the removal o f t h e hydrogen from HNSO w o u l d tend t o i n c r e a s e t h e bonding between t h e n i t r o g e n and s u l f u r and weaken i t between s u l f u r and oxygen. T h i s would s h i f t t h e SO s t r e t c h i n g v i b r a t i o n t o a lower f r e q u e n c y . The r e s u l t i n g p r o x i m i t y o f t h e NS and SO s t r e t c h i n g f r e q u e n c i e s would i n c r e a s e the m i x i n g o f t h e s e c o o r d i n a t e s and a l l o w t h e SO s t r e t c h t o have a s h i f t o f 9.4 cm ' on '^N s u b s t i t u t i o n . The SO s t r e t c h would have the g r e a t e s t i n t e n s i t y so t h a t the NS s t r e t c h and NSO bend would not be o b s e r v e d . As w e l l , the d o u b l e t s t r u c t u r e i s a s s i g n e d t o m a t r i x s p l i t t i n g s i m i l a r t o t h a t a l w a y s seen f o r t h e a s y m m e t r i c s t r e t c h e s o f bent t r i a t o m i c s i n argon (see f i g u r e 1-3). - 215 " D. REACTIONS 1. PRODUCTS The p h o t o l y s i s o f c i s - t h i o n y l i m i d e has l e d t o the i d e n t -i f i c a t i o n , w i t h v a r y i n g d e grees o f c o n f i d e n c e , o f s i x compounds: trans-HNSO, cis-HOSN, trans-HSNO, cis-HSNO, SNO and NSO. However, o n l y f o u r o f t h e s e a r e o b s e r v e d when p h o t o l y s i s i s c a r r i e d o u t th r o u g h q u a r t z u s i n g a mercury lamp. The o t h e r two r e q u i r e s p e c i a l c o n d i t i o n s : trans-HNSO i s o b s e r v e d o n l y w i t h low energy u l t r a v i o l e t o p h o t o l y s i s (X>3000 A) w h i l e NSO r e q u i r e s vacuum u.v. r a d i a t i o n f o r o p r o d u c t i o n and mini m a l amounts o f l i g h t o f X>2000 A t o keep from b e i n g p h o t o l y s e d i t s e l f . F i g u r e 4-12 i s a p l o t o f t h e a b s o r b a n c e i n t e n s i t i e s o f t h e 447 cm' 1 peak o f cis-HNSO, the 674 cm"' peak o f cis-HOSN, t h e 1597 cm ' peak o f trans-HSNO and t h e 1523 cm ' peak o f SNO as a f u n c t i o n o f p h o t o l y s i s time d u r i n g a s i n g l e e x p e r i m e n t . In t h e c a s e o f the p r o d u c t s the most i n t e n s e a b s o r p t i o n i n each s p e c t r u m was c h o s e n . For ease o f c o m p a r i s o n the i n t e n s i t i e s have been n o r m a l i z e d t o t h e i r own maximum a b s o r p t i o n w i t h i n the e x p e r i m e n t . F i g u r e 4-13 i s a s i m i l a r p l o t o f t h e cis-HOSN and trans-HSNO a b s o r p t i o n s when p h o t o l y s i s was t h r o u g h a C o r n i n g 0~54 f i l t e r w i t h low w a v e l e n g t h c u t - o f f o f o 3000 A. T h i s e f f e c t i v e l y expanded t h e time s c a l e by s l o w i n g t he r e a c t i o n s and thus a l l o w e d a c a r e f u l s t u d y o f the p r o d u c t growth r a t e s i n t h e e a r l y s t a g e s o f p h o t o l y s i s . A l s o , s i n c e cis-HSNO f o l -lowed t h e same c u r v e as trans-HSNO, a s e p a r a t e p l o t has not been - 216 ~ S N O T i m e (min) F i g u r e 4-12. I n t e n s i t y o f a b s o r p t i o n s as a f u n c t i o n of p h o t o l y s i s o t i m e , A>2000 A. - 217 -T i m e ( m i n ) 4-13. I n t e n s i t y o f a b s o r p t i o n s as a f u n c t i o n o f p h o t o l y s i s o t i m e , X>3000 A. - 218 -made f o r i t . S i n c e t he m o l e c u l e s i n v o l v e d i n the r e a c t i o n s a r e i s o l a t e d i n t he m a t r i x , t h e y c a n n o t r e a c t w i t h one a n o t h e r and s i n c e the f i l m -2 -3 i s v e r y t h i n (<10 cm) and the c o n c e n t r a t i o n i s v e r y low (~5xl0 M), the i n t e n s i t y o f t h e l i g h t a b s o r b e d s h o u l d be n e a r l y p r o p o r t i o n a l t o the c o n c e n t r a t i o n o f the. a b s o r b i n g s p e c i e s . T h e r e f o r e , t h e r e a c t i o n s s h o u l d be n e a r l y f i r s t o r d e r i n the r e a c t i n g s p e c i e s , i . e . r a t e a [ r e a c t a n t ] . The f o l l o w i n g a n a l y s i s w i l l be based upon t h i s a s s u m p t i o n . Two f e a t u r e s o f t h e p l o t s i n f i g u r e s 4-12 and 4-13 a r e most i m p o r t a n t : cis-HOSN i s produced v e r y q u i c k l y , r e a c h e s a maximum co n -c e n t r a t i o n and i s then removed by f u r t h e r p h o t o l y s i s and b o t h HSNO and SNO show i n f l e c t i o n p o i n t s i n t h e i r growth c u r v e s . The p r e s e n c e o f i n f l e c t i o n p o i n t s i n c o n c e n t r a t i o n v e r s u s t i m e p l o t s i s an i n d i c a -(4) t i o n o f c o n s e c u t i v e r e a c t i o n s . S i n c e the i n f l e c t i o n p o i n t i n the HSNO c u r v e f a l l s near t h e maximum i n cis-HOSN c o n c e n t r a t i o n , i t must be p r oduced f r o m cis-HOSN and s i n c e t he i n f l e c t i o n p o i n t o f SNO comes l a t e r , i t must be produced from HSNO. The r e a c t i o n s can then be summarized by t h e f o l l o w i n g sequence: cis-HNSO cis-HOSN •> trans-HSNO + SNO r e a c t i o n r e a c t i o n r e a c t i on 2 3 2. REACTION 1 (a) O b s e r v a t i o n s : The f o l l o w i n g have been o b s e r v e d w i t h r e g a r d s - 219 " r e a c t i o n 1: ( i ) The r e a c t i o n i s v e r y f a s t on t h e time s c a l e o f m a t r i x p h o t o l y s i s r e a c t i o n s w h i c h commonly r e q u i r e s e v e r a l h o u r s . ( i i ) O n ly cis-HOSN has been o b s e r v e d i n t h i s r e a c t i o n -i . e . n e i t h e r trans-HOSN nor t h e d i s s o c i a t i o n p r o d u c t NSO a r e formed by the u.v. p h o t o l y s i s o f cis-HNSO. o ( i i i ) The r e a c t i o n i s v e r y q u i c k w i t h l i g h t o f X>2000 A o but c o n s i d e r a b l y s l o w e r when o n l y l i g h t o f X>3000 A i s used . The p h o t o l y s i s t a k e s p l a c e o v e r a f a i r l y l a r g e w a v e l e n g t h r e g i o n , most (5) o f w h i c h i s under 3000 A. I t has a l s o been o b s e r v e d by A l l e g r e t t i o t h a t cis-HNSO has a s t r o n g e l e c t r o n i c a b s o r p t i o n a t 2700 A w h i c h i n v o l v e s e x c i t a t i o n o f e l e c t r o n s o c c u p y i n g o r b i t a l s c e n t e r e d i n the NSO p a r t o f t h e m o l e c u l e . ( i v ) W h i l e cis-HNSO i s e a s i l y s y n t h e s i z e d a t room tempera-t u r e u s i n g NH^ and S O C ^ , c i s - HOSN has not been produced and i s o l a t e d . As p o i n t e d o u t i n c h a p t e r I I I , Glemser and R i c h e r t ^ s t u d i e d the room t e m p e r a t u r e h y d r o l y s i s o f FSN. A l t h o u g h t he p r o d u c t was e n t i r e l y c i s -HNSO, the y p r o p o s e d the e x i s t e n c e o f HOSN as a r e a c t i o n i n t e r m e d i a t e . H 20 + FSN [HF + HOSN] -*• cis-HNSO Thus, i f t h e i r mechanism i s c o r r e c t , HOSN i s u n s t a b l e w i t h r e s p e c t t o cis-HNSO a t room t e m p e r a t u r e w i t h o n l y a s m a l l a c t i v a t i o n e n e r g y . A t 4°K i n a m a t r i x , however, cis-HOSN i s s t a b l e . o (b) D i s c u s s i o n : From o b s e r v a t i o n ( i i i ) i t i s c e r t a i n t h a t the 2700 A a b s o r p t i o n o f cis-HNSO l e a d s t o t h e f o r m a t i o n o f cis-HOSN. S i n c e no - 220 -trans-HOSN o r NSO i s p r o d u c e d , i t i s c e r t a i n t h a t the pathway i s not v i a a d i s s o c i a t i o n o f the hydrogen f o l l o w e d by a r e c o m b i n a t i o n a t a new s i t e , but r a t h e r by a c o n c e r t e d t r a n s f e r o f the hydrogen from the n i t r o g e n t o t h e oxygen. T h i s s i m p l e pathway would be f a v o u r e d by the i n t e r a c t i o n a l r e a d y p r e s e n t i n cis-HNSO, and p o s s i -b l y enhanced i n the e x c i t e d s t a t e , between the H and the 0 as d i s -c u s s e d e a r l i e r i n t h i s c h a p t e r and would a l s o h e l p a c c o u n t f o r the speed o f t h e r e a c t i o n . S i n c e from o b s e r v a t i o n ( i v ) i t i s thought t h a t a t room t e m p e r a t u r e cis-HNSO i s more s t a b l e than cis-HOSN, i t i s c e r t a i n t h a t a t k°K t h i s r e v e r s e rearrangement i s p r e v e n t e d by i n s u f f i c -i e n t t h e r m a l energy t o overcome the a c t i v a t i o n b a r r i e r . However, f i g u r e k-1k shows a p l o t o f the l o g o f t h e i n t e n s i t y o f a cis-HNSO a b s o r p t i o n v e r s u s t i m e . The f a c t t h a t t h i s p l o t i s not l i n e a r as would be e x p e c t e d f o r a f i r s t o r d e r r e a c t i o n , s u g g e s t s t h a t a r e -v e r s e p h o t o l y t i c r e a c t i o n y i e l d i n g cis-HNSO must be p r e s e n t a l o n g the r e a c t i o n scheme p r e s e n t e d i n p a r t 1. R e a c t i o n 1 s h o u l d then i n c l u d e the r e v e r s e r e a c t i o n p o s s i b l y i n v o l v i n g t h e r e v e r s e h y d r o -gen m i g r a t i o n as w e l l as a more complex rearrangeme n t i n v o l v i n g i n i t i a l l y t he b r e a k i n g o f the OS bond as d i s c u s s e d i n the n e x t s e c t i on. - 221 -, 1 1 1 10 2 0 3 0 4 0 T i m e ( m i n ) F i g u r e 4-14. L o g a r i t h m i c p l o t o f the d i s a p p e a r a n c e o f cis-HNSO o on p h o t o l y s i s , X>2000 A. - 222 -3. REACTION 2 (a) O b s e r v a t i o n s : The f o l l o w i n g o b s e r v a t i o n s r e l a t i n g t o t h e second r e a c t i o n i n t h e sequence have been r e c o r d e d . ( i ) The p h o t o l y s i s o f cis-HOSN y i e l d s HSNO. ( i i ) W i t h i n the l i m i t s o f the measurements, i t appears t h a t b o t h t h e t r a n s and c i s isomers o f HSNO a r e produced a t t h e same time ( i . e . a t a c o n s t a n t r a t i o ) but a t d i f f e r e n t r a t e s on mercury lamp p h o t o l y s i s . ( i i i ) The re a r r a n g e m e n t i s o b v i o u s l y complex: two bonds a r e b r o k e n and two new ones a r e for m e d . ( i v ) The i . r . a b s o r p t i o n s o f trans-HSNO show complex m a t r i x s p l i t t i n g s , p resumably f r o m occupancy o f d i f f e r e n t s i t e s i n the m a t r i x . (v) No OSN r e s u l t i n g from the mercury lamp p h o t o l y s i s o f cis-HOSN has been o b s e r v e d n o r have the d i a t o m i c f r a g m e n t s HO and SN been o b s e r v e d i n any e x p e r i m e n t s . ( v i ) The f o r c e c o n s t a n t s o f cis-HOSN c a l c u l a t e d i n s e c t i o n C o f t h i s c h a p t e r i n d i c a t e an OS s i n g l e bond. W i t h a p r o b a b l e bond e n e r g y o f 60-70 k c a l / m o l e , t h i s i s t h e weakest bond i n the m o l e c u l e . o ( v i i ) The use o f l i g h t o f X>3000 A f o r p h o t o l y s i s r e s u l t s i n a s l o w e r r e a c t i o n . However, i t appears t h a t r e a c t i o n 1 i s sl o w e d o more than r e a c t i o n 2 s i n c e i n the two e x p e r i m e n t s u s i n g X>3000 A and o X>2000 A t h e r a t i o o f i n i t i a l a b s o r p t i o n i n t e n s i t i e s f o r cis-HNSO i s near 1 w h i l e t he r a t i o o f maximum i n t e n s i t i e s a t t a i n e d by the cis-HOSN a b s o r p t i o n i s about 0.15. - 223 -( v i i i ) The use o f vacuum u.v. p h o t o l y s i s w i t h s i m u l t a n e -ous s p r a y - o n i n c r e a s e s the r a t i o o f cis-HSNO isomer t o trans-HSNO isomer. ( i x ) A t t e m p t s t o c a r r y o u t t h e p h o t o l y s i s o f cis-HNSO i n a n i t r o g e n m a t r i x f a i l e d . A l t h o u g h r e a c t i o n 1 pr o c e e d e d w i t h o u t c o m p l i c a t i o n , t h e f u r t h e r p h o t o l y s i s r e s u l t e d i n the c o m p l e t e d i s -a p p e a r a n c e o f a l l i . r . a b s o r p t i o n s - t h o s e o f cis-HNSO and t h o s e o f cis-HOSN - w i t h o u t t he appe a r a n c e o f any new a b s o r p t i o n s . A t t h e same ti m e the a b s o r p t i o n s o f SO^ i m p u r i t y showed b r o a d e n i n g and a sh a r p d e c r e a s e i n i n t e n s i t y . (b) P i s c u s s i o n : From o b s e r v a t i o n ( v i i ) i t appears t h a t an e l e c t r o n i c t r a n s i t i o n o f cis-HOSN c e n t e r e d i n t h e w a v e l e n g t h r e g i o n j u s t below o 3000 A r e s u l t s i n i t s p h o t o l y s i s t o g i v e c i s - and trans-HSNO. A l t h o u g h the r e a c t i o n i s o b v i o u s l y complex, o b s e r v a t i o n ( i i i ) s u g g e s t i n g s e v e r a l s t e p s , o b s e r v a t i o n s (v) and ( v i ) show t h a t the i n i t i a l s t e p i s p r o b a b l y t h e r u p t u r e o f t h e SO bond r a t h e r than t h e HO bond. I t i s f e l t t h a t i n t he m a t r i x cage t h e two f r a g m e n t s , u n a b l e t o s e p a r a t e ( a f a c t a t t e s t e d t o by t h e absence o f OH o r NS i . r . a b s o r p t i o n s ) , w o u l d r e -combine t o g i v e b o t h c i s - and trans-HSNO and p o s s i b l y cis-HOSN and cis-HNSO as w e l l . S i n c e c i s - and trans-HSNO would be pr o d u c e d s i m u l -t a n e o u s l y , t h e r e q u i r e m e n t o f o b s e r v a t i o n ( i i ) would be met. u/°~S^u [HO + SN] • HSNO, HOSN, HNSO - 22k -The i n c r e a s e i n c i s t o t r a n s r a t i o w i t h vacuum u.v. p h o t o -l y s i s w i t h s i m u l t a n e o u s s p r a y - o n , o b s e r v a t i o n ( v i i i ) , w o u l d be due e i t h e r t o t h e g r e a t e r l i g h t e n ergy o r t o the p h o t o l y s i s , as a r e s u l t o f t h i s t e c h n i q u e , o f more l o o s e l y t r a p p e d m o l e c u l e s i n t h e not y e t c o m p l e t e l y c o o l e d s u r f a c e l a y e r . E i t h e r r e a s o n c o u l d f e a s i b l y f a v o u r one i s o m e r , but e v i d e n c e i s i n c o n c l u s i v e . The d i s a p p e a r a n c e o f the sample i n t h e m a t r i x i s d i f f i -c u l t t o e x p l a i n . The p o s s i b i l i t y o f r e a c t i o n w i t h i s not l i k e l y b ecause o f i t s h i g h bond s t r e n g t h . T h e r e f o r e , i t i s s u g g e s t e d h e r e t h a t what o c c u r s i s a u n i q u e energy t r a n s f e r , p r o b a b l y from an e x c i t e d f r agment such as SN", t o t h e N^ m o l e c u l e s w h i c h r e s u l t s i n e l e c t r o n i c -a l l y e x c i t e d m a t r i x m o l e c u l e s . These would then decay t o v i b r a t i o n -a l l y e x c i t e d m a t r i x m o l e c u l e s i n t h e i r e l e c t r o n i c ground s t a t e s . T h i s JL. e f f i c i e n t d e a c t i v a t i o n o f SN ( o r o t h e r fragment) would p r e v e n t t h e f u r t h e r bond b r e a k i n g r e q u i r e d f o r HSNO f o r m a t i o n and a c c o u n t f o r i t s not b e i n g o b s e r v e d . The fr a g m e n t s would s i m p l y recombine t o HOSN. T h i s u n i q u e energy t r a n s f e r would a l s o r e s u l t i n v i b r a t i o n a 1 l y e x c i t e d m a t r i x m o l e c u l e s and thus warming o f t h e m a t r i x w h i c h would l e a d t o d i f f u s i o n o f the t r a p p e d m o l e c u l e s w i t h the d i s a p p e a r a n c e o f t h e i r i . r . a b s o r p t i o n s . In the argon m a t r i x a c o n s i d e r a b l e amount o f the p h o t o l -y s i s e nergy goes i n t o l a t t i c e modes when e x c i t e d m o l e c u l e s a r e d e a c t i -v a t e d t h r o u g h c o l l i s i o n s w i t h the m a t r i x . However, t h i s p r o c e s s must be s l o w e r than t h a t d e s c r i b e d f o r N^ s i n c e i t does not d e a c t i v a t e SN" (or o t h e r fragment) b e f o r e t h e r e a c t i o n can pr o c e e d t o HSNO. Because - 225 -the d e a c t i v a t i o n i s s l o w e r , the heat i s c o n d u c t e d away b e f o r e l o c a l warming o f the m a t r i x can r e s u l t i n a l o s s o f r i g i d i t y . T h e r e f o r e , the sample does not d i s a p p e a r i n an argon m a t r i x . 4. REACTION 3 The t h i r d r e a c t i o n o f the sequence i s HSNO «SN0 + H The HS bond i s p r o b a b l y o f t h e o r d e r o f 80 k c a l / m o l e and so weak enough t o be bro k e n w i t h r a d i a t i o n from a mercury lamp and s t i l l l e a v e t he hydrogen atom w i t h s u f f i c i e n t k i n e t i c e nergy t o b r e a k from t h e cage. T h i s d i f f u s i o n t y p e r e a c t i o n i s o f t e n found i n ma-t r i x p h o t o l y s i s and i s u s u a l l y s l o w , a c c o u n t i n g f o r SNO's s l o w p r o d u c t i o n . SNO's g r e a t e r p r o d u c t i o n on vacuum u.v. p h o t o l y s i s w i t h s p r a y - o n c o u l d be a t t r i b u t e d t o h i g h e r energy and/or l o o s e r c a g e s , b o t h i n c r e a s i n g hydrogen's chances o f d i f f u s i n g away. Sim-o i l a r l y SNO's v e r y s l o w p r o d u c t i o n w i t h l i g h t o f A>3000 A ( i . e . <95 k c a l / m o l e ) w o u l d be due t o e i t h e r a d e c r e a s e i n a b s o r b e d l i g h t o r t o a d e c r e a s e i n the number o f H atoms h a v i n g s u f f i c i e n t e n ergy t o e s c a p e t h e cage. In f i g u r e 4-12 i t i s seen t h a t t he i n f l e c t i o n i n t h e p r o d u c t i o n o f SNO comes b e f o r e t h e maximum i n HSNO i s r e a c h e d . To a c c o u n t f o r t h i s i t i s n e c e s s a r y t h a t SNO be removed by f u r t h e r r e a c t i o n . I t appears l i k e l y t h a t some H atoms, produced i n r e a c t i o n - 2 2 6 " 3 , w h i l e d i f f u s i n g t h r o u g h the m a t r i x a r e e n c o u n t e r i n g NSO r a d i c a l s from p r e v i o u s d i s s o c i a t i o n s . These combine t o g i v e HSNO, thus i n e f f e c t s l o w i n g SNO's p r o d u c t i o n more as i t s c o n c e n t r a t i o n i n c r e a s e s w h i l e a t the same time s l o w i n g HSNO's d i s a p p e a r a n c e . T h i s p u t s SNO's i n f l e c t i o n p o i n t e a r l y and HSNO's maximum l a t e . , 5 . HNSO: CIS-TRANS ISOMERISM The f o r m a t i o n o f trans-HNSO i s o n l y o b s e r v e d w i t h p h o t o l -o y s i s u s i n g l i g h t o f 3 0 0 0 t o 4000 A. The amount produced always r e -mains v e r y s m a l l compared t o cis-HNSO s u g g e s t i n g t h a t the e q u i l i b r i u m i n the r e a c t i o n hv cis-HNSO •« ' trans-HNSO l i e s f a r t o t h e l e f t . I t i s not known i f the i s o m e r i s m i s c a u s e d o by the h i g h w a v e l e n g t h t a i l o f the 2 7 0 0 A a b s o r p t i o n o f cis-HNSO o r (5) by the weak c o n t i n u u m o b s e r v e d by A l l e g r e t t i a t 3 5 0 0 A. However, s i n c e no NSO i s o b s e r v e d , t h e r e a c t i o n p r o b a b l y does not i n v o l v e t h e b r e a k i n g o f the HN bond, but r a t h e r an i n t e r n a l r o t a t i o n about the NS bond, p r o b a b l y i n the e x c i t e d s t a t e . 6 . NSO: PRODUCTION AND PHOTOLYSIS I t has been s u g g e s t e d t h a t NSO i s formed on vacuum u.v. p h o t o l y s i s o f cis-HNSO. T h i s would r e q u i r e b r e a k i n g t h e HN bond and g i v i n g the H atom enough energy t o escape the cage - c e r t a i n l y o p o s s i b l e w i t h 1 2 1 6 A r a d i a t i o n . The l o o s e t r a p p i n g i n the s u r f a c e - 227 " l a y e r , t h e l a y e r i n w h i c h most o f the p h o t o l y s i s o c c u r s i n t h i s t e c h n i q u e , w o u l d a l s o a i d i n the hydrogen e s c a p e and thus f a v o u r NSO p r o d u c t i o n . However, t h e r e a c t i o n would s t i l l be s l o w and t h i s w o u l d a c c o u n t f o r i t s i n a b i l i t y t o compete w i t h t he f a s t e r r e a c t i o n t h a t g i v e s cis-HOSN. Subsequent p h o t o l y s i s w i t h l o w e r o energy r a d i a t i o n , X>2000 A, r e s u l t s i n t h e d i s a p p e a r a n c e o f NSO and i t i s s u g g e s t e d , on l i t t l e e v i d e n c e , t h a t SNO i s p r o d u c e d . The r e a c t i o n can be w r i t t e n as f o l l o w s : • u i . c n A = 1216A . . . . A>2000A cis-HNSO »• NSO »- SNO The r e a c t i o n would f u r t h e r a c c o u n t f o r the s m a l l amount o f NSO ob-s e r v e d even w i t h hydrogen r e s o n a n c e lamp p h o t o l y s i s . No NSO i s o b s e r v e d w i t h o n l y mercury lamp p h o t o l y s i s . 7- CONCLUSIONS A l t h o u g h i d e n t i f i c a t i o n o f the v a r i o u s m o l e c u l e s was made w i t h o u t any c o n s i d e r a t i o n o f the r e a c t i o n s i n v o l v e d , t he k i n e t i c i n f o r m a t i o n and t h e proposed mechanisms seem i n p e r f e c t a c c o r d w i t h t h i s i d e n t i f i c a t i o n . T h i s p r o v i d e s , t h e n , an a f f i r m a t i o n o f the c o n c l u s i o n s reached on p u r e l y s p e c t r o s c o p i c g r o u n d s . - 228 -BIBLIOGRAPHY: CHAPTER IV 1. L. D'Or, P. T a r t e ; B u l l . Soc. Roy. S c i . L i e g e , 8, 478 (1951) 2. A.P. Cox, A.H. B r i t t a i n , D.J. F i n i g a n ; T r a n s Faraday S o c , 67(8) , 2179 (1971) 3. D.E. M i l l i g a n , M.E. J a c o x ; J . Chem. P h y s . , 1952 (1969) 4. W.J. Moore; " P h y s i c a l C h e m i s t r y " , P r e n t i c e - H a l l , 1962, page 226 5. J.M. A l l e g r e t t i ; M a s t e r ' s T h e s i s , U.B.C., 1971 6. 0. Glemser, H. R i c h e r t ; Z. A n o r g . A l l g e m . Chem., 307, 313 (1961) 7. M.E. J a c o x , D.E. M i l l i g a n ; J . Chem. P h y s . , 40, 2457 (1964) - 229 -APPENDIX I T a b l e o f " C h a r a c t e r i s t i c F r e q u e n c i e s " used i n t h i s t h e s i s v i b r a t iona1 mode m o l e c u l e v(cm ') NS 'SO "NO "HO F ^ N FSN NS cisHNSO S 0 2 cisHNSO c i 2 s o cisHONO transHONO N0 2 HNO FNO HOCN cisHONO transHONO H 20 1515 1372 1158 1090 1362 1151 1261 1229 1640 855 1700 793 1618 1318 1570 1844 3572 3425 3590 3756 3657 v i b r a t iona1 mode molecu 1e v(cm ') HS v HBend Bend "HN H 2S cisHONO transHONO H20 H2°2 H 2 S 2 H 2S cisHNSO NH 3 HNCO cisHNSO S02 cisHONO transHONO N0 2 cisHNSO NH 3 HNCO 2627 2615 1370 1267 1595 1402 1260 897 1183 911 1628 932 777 453 518 525 598 750 3345 3335 3432 

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