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Quantum yields of decomposition in the photolytic oxidation of methyl mercaptan, dimethyl sulphide and… Sheraton, Donald Frederick 1979

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QUANTUM YIELDS OF DECOMPOSITION IN THE PHOTOLYTIC OXIDATION OF METHYL MERCAPTAN, DIMETHYL SULPHIDE AND DIMETHYL DISULPHIDE by DONALD F R E D E R I C K SHERATON B . A . S c . , T h e 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 , 1369 9 1 A T H E S I S SUBMITTED IN P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PH I LOSOPHY in THE FACULTY OF GRADUATE S T U D I E S . DEPARTMENT OF CHEMICAL E N G I N E E R I N G V/e a c c e p t t h i s ' t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA J u n e 1 9 7 9 ( e ) D o n a l d F r e d e r i c k S h e r a t o n , 1979 In p resen t ing 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 l m e n t o f the requirements f o r an advanced degree at The U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t 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 for , re fe rence and s tudy . I f u r t h e r agree tha t permiss ion f o r ex tens i ve copying o f 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 o f my department o r h i s r e p r e s e n t a t i v e . I t i s understood tha t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed w i thou t my w r i t t e n pe rm i s s i on . Donald F. Sheraton Department o f Chemical Eng ineer ing The U n i v e r s i t y o f B r i t i s h Columbia Vancouver, Canada Date: ^ U y f / f ? f A B S T R A C T The K r a f t pu lp ing process produces vas t q u a n t i t i e s of su l ph i de vapours which are r e l ea sed to atmosphere. The major components are methyl mercaptan, hydrogen s u l p h i d e , d imethyl su l ph ide and dimethyl d i s u l p h i d e . The f a t e o f these compounds i n the atmosphere and the k i n e t i c s o f t h e i r degradat ion processes i n the atmosphere are use fu l i n the model ing o f the environment o f areas proximate to K r a f t pulp m i l l s . The i n f o rma t i on may a l s o be use fu l i n deve lop ing p o l l u t i o n abatement p rocesses . The p h o t o l y t i c o x i d a t i o n o f methyl mercaptan, d imethyl su l ph ide and dimethyl d i s u l p h i d e was s tud i ed i n a batch p h o t o l y s i s appara tus . Shor t wavelength u l t r a - v i o l e t l i g h t was prov ided by a deuter ium d i s cha rge lamp and monitored by a monochromator equipped w i th an extended response photo-m u l t i p l i e r tube. Su lph ide concen t ra t i ons were determined on a gas chromato-graph equipped w i t h a f lame photmetr i c d e t e c t o r hav ing 365 nm su lphur response. The r a t e o f r e a c t i o n o f methyl mercaptan was found to be a l i n e a r f u n c t i o n o f the photon abso rp t i on r a t e and e x h i b i t e d a quantum y i e l d o f decompos i t ion of 13 .9 . The methyl mercaptan pho to -ox i da t i on r a t e was found to be una f fec ted by i n c reased oxygen c on c en t r a t i o n , decreased atmospher ic pressure o r the presence o f excess su lphur d i o x i d e . The quantum y i e l d o f dimethyl su l ph i de decompos i t ion was found to be dependent upon atmospher ic p r e s su re . A pressure o f one atmosphere gave a quantum y i e l d o f 4 and the y i e l d i nc reased to 8 a t one-quar te r atmosphere. i i The quantum y i e l d o f d imethyl d i su lph ide .was found to be 1.9 at atmospher ic pressure at a concen t r a t i on o f 7.04 x 10~ 5 M. The apparatus was a l s o operated i n a c o n f i g u r a t i o n which a l lowed the d e t e c t i o n o f l i g h t emi t ted a t 90° to the path o f i l l u m i n a t i o n . A slow deve lop ing emiss ion was found f o r d imethyl s u l p h i d e , hydrogen su l ph i de and •sulphur d i o x i d e . Only s l i g h t emiss ion was found f o r methyl mercaptan and d imethyl d i s u l p h i d e . The emiss ion from dimethyl su lph ide was found to be l i n e a r i l y dependent upon the n i t r ogen pressure o f a dry n i t r ogen atmosphere. The emiss ion i s a t t r i b u t e d to aeroso l f o rmat ion and i s due to the l i g h t s c a t t e r e d from p a r t i c l e s i n the r e a c t i o n m a t r i x . i i i T A B L E OF C O N T E N T S Page. ABSTRACT i i LIST OF TABLES i x LIST OF FIGURES -• x ACKNOWLEDGMENTS x i i i Chapter 1 INTRODUCTION 1 1.1 General 1 1.2 The Pr imary Processes 9 1.3 The Hot Rad i ca l s Produced and The i r Reac t i ons . . . . . . . H< 1.4 React ions o f the Hot Hydrogen Atom I 3 1.5 React ions o f the Hot Methyl Rad ica l I 4 1.6 React ions o f the Methyl Th i y l Rad i ca l 17 1.7 Gas Phase Pho to -ox ida t i ons 2 0 1.8 Pho to -ox i da t i on Reac t ion Sequence. . . 2 2 2 EQUIPMENT 2 3 2.1 General System De s c r i p t i o n 2 3 2.2 Da i l y Procedure f o r React ion A n a l y s i s 2^ 07 2.3 Chemical Sources 2.4 The Reac t ion C e l l s . . . . 2 9 i v Chapter Page. 2.5 The Vacuum System . 3 2 2.6 The Deuterium Lamp 32 2.7 The C o l l i m a t i o n System 33 2.8 The React ion Ce l l Support System 33 2.9 The Emiss ion Con f i gu r a t i o n 36 2.10 The Monochromator 36 2.11 The P h o t o m u l t i p i i e r System . 38, 2.12 Ac t inometry 40 2.13 The Make-up o f Potassium F e r r i o x a l a t e C r y s t a l s . . . . . 40 2.14 P repa ra t i on o f the Fe C a l i b r a t i o n Graph . 41 2.15 Deuterium L i g h t I n t e n s i t y C a l i b r a t i o n 43 2.16 The G rav ime t r i c I n t e g r a t i o n Method 46 2.17 Gas Chromatography 47 2.18 Chromatograph C a l i b r a t i o n Procedure 51 3 EXPERIMENTAL RESULTS AND DISCUSSION OF PHOTO-OXIDATION OF SULPHIDES • 5 6 3.1 P r e l im i n a r y Experiments • u 3.1.1 The E f f e c t o f Us ing Room A i r . 58 3.1.2 The E f f e c t o f Wet A i r 59 3.1.3 The E f f e c t o f Pure Oxygen. . 59 3.2 Resu l t s I nvo l v i ng Quantum Y i e l d s o f Removal of Su lph ides • . • 6 0 3.2.1 The Quantum Y i e l d o f CH3SH Removal 60 3.2.1.1 The I n i t i a t i o n React ions . . . . . 63 3 .2 .1 .2 React ions i n v o l v i n g H Atoms. . . . 5 5 v Chapter Page 3 .2 .1 .3 React ions i n v o l v i n g the Methyl T h i y l Rad ica l 68 3 .2 .1 .4 React ions i n v o l v i n g the Methoxy and Methyl Peroxy R a d i c a l s . . . . 72 3 .2 .1 .5 React ions i n v o l v i n g the Hydrogen Peroxy Rad ica l 73 3 .2 .1 .6 React ions i n v o l v i n g Methyl Rad i ca l s 73 3 .2 .1 .7 React ions i n v o l v i n g Atomic Oxygen Rad i ca l s 76 3 .2 .1 .8 React ions i n v o l v i n g Su lphur Monoxide Rad i ca l s 77 3 .2 .1 .9 React ions i n v o l v i n g Su lphydry l Rad i ca l s 78 3.2.1.10 React ions E l i m i n a t i n g Elemental Su lphur 79 3.2.2 The Chain Mechanism 79 3.2.3 The Quantum Y i e l d o f CH3SH Ox ida t i on as as Funct ion of Atmospher ic Pressure 82 3.2.4 The Quantum Y i e l d of Dimethyl Su lph ide Decomposit ion . . . . . 82 3.2.5 The Quantum Y i e l d o f Dimethyl Di s u l ph i de Decomposit ion 84 3.3 Other Exper imenta l S tud ies 87 3.3.1 . The E f f e c t o f Added Su lphur D iox ide . . . . . 87 3.3.2 A Su lphur Balance f o r Methyl Mercaptan Ox i da t i on 9 0 3.3.3 The Quantum Y i e l d o f Product Formation f o r Su lphur D iox ide and Dimethyl Di su l ph i de 9 3 3.3.4 The Depos i t on the i n s i d e C e l l Wal l 9 4 4 LIGHT EMISSION FROM SULPHUR-CONTAINING GAS MIXTURES 1 0 1 4.1 Observa t ion and Time Dependence 101 v i Chapter Page 4.2 P o s s i b l e Mechanisms to Descr ibe the Delay of Emiss ion 106 4.2.1 F lourescence 106 4 .2 .2 Delayed F luorescence 106 4 .2 .3 Chemi luminescence 107 4.2 .4 Presence o f Quenching Impur i ty 108 4 .2 .5 Photochemical Aeroso l Formation 113 4.3 Concen t ra t i on Dependence o f Emiss ion 117 4.4 P ressure Dependence of Emiss ion 117 4.5 The Emiss ion as an Aeroso l S c a t t e r i n g E f f e c t 120 4.5.1 Prev ious Work 120 4 .5 .2 D i s cuss i on o f Resu l t s as a P a r t i c l e E f f e c t 122 4 .5 .3 S t a b i l i t y o f the Aeroso l 125 4 .5 .4 Concen t ra t i on Dependence o f the Aeroso l . . 128 4 .5 .5 P ressure Dependence o f the Emiss ion . . . . 128 4.6 The Number o f P a r t i c l e s Formed. . 129 4.6.1 Attempted Op t i c a l V e r f i c i a t i o n o f P a r t i c l e S i z e and Number. 131 5 CONCLUSIONS I 3 2 BIBLIOGRAPHY 1 3 4 APPENDICES A CH3SH React ion Data I 3 9 B C H 3 S S C H 3 Reac t ion Data 144 C C H 3 S C H 3 Reac t ion Data 146 D Su lphur Balance Data 147 v i i Appendix Page E Concent ra t i on Dependence o f Emiss ion from Dimethyl Su lph ide A e r o s o l . . . . . . . . . 149 F Dependence o f I n t e n s i t y of Emiss ion from Dimethyl Su lph ide Aeroso l upon Atmospher ic P ressure o f A i r 150 G Dependence o f I n t e n s i t y of Emiss ion from M 2S Aeroso l upon Atmospher ic P ressure o f Dry N i t rogen 153 H Es t ima t i on o f Rate Constant f o r React ions (3-7) and (3-15) . . . . . . . . 155 v i i i L I S T OF T A B L E S Table Page 1 Bond -D i s so c i a t i on Energ ies o f I n t e r e s t 8 2 Energy Excess f o r P a r t i c u l a r Bond D i s rup t i on s 9 3 The Energy D i s t r i b u t i o n o f the Fragments o f Methyl Mercaptan Pho t o l y s i s 12 4 Pho t o l y s i s Products from Long Term Dimethyl Su lph ide Pho t o l y s i s 21 5 Quantum Y i e l d s i n CH 3SH P h o t o l y s i s •.• ' . . . ^2 6 React ions Invo lved i n the Pho to l y t i c . -Ox i da t i on o f Methyl Mercaptan .64 7 . The Chain Mechanism ..80 8 The E f f e c t o f Atmospher ic P ressure on the Quantum Y i e l d of CH3-SH Decomposit ion 82 9 The quantum Y i e l d o f Dimethyl Su lph ide Decomposit ion v . s . Atmospher ic P ressure . . , 10 The Quantum Y i e l d o f Dimethyl D i su l ph i de Decomposit ion . 11 The E f f e c t o f Added Su lphur D iox ide 12 The Abso rp t i on C o e f f i c i e n t f o r CH 3SH, S 0 2 , CH 3SCH 3 and C H 3 S S C H 3 : . ' 13 A Sulphur Ba lance , Based on 25 Minutes CH3SH O x i d a t i o n , per ml React ion Volume . 14 The Quantum Y i e l d s o f Product Format ion. . i x L I S T OF F I G U R E S F igure Page 1 The abso rp t i on spectrum o f methyl mercaptan 2 2 The abso rp t i on spectrum o f dimethyl d i su l ph ide 3 3 The abso rp t i on spectrum o f d imethyl s u l ph i de 4 4 The abso rp t i on spectrum o f su lphur d i o x i d e 5 5 Mod i f i ed J ab l on sk i diagram f o r photon abso rp t i on and subsequent r e l a x a t i o n 6 6 The apparatus as used f o r r e a c t i o n 24 7 The r e a c t i o n c e l l s . . . . . . . . . . . . . . . . . 20 8 Transmiss ion spectrum o f s u p r a s i l windows . . . . ".' . . . . . . . 30 31 9 The vacuum man i f o l d and emiss ion c e l l 10 Emiss ion spectrum o f deuter ium l i g h t supp ly measured on EMI 9558 QBM operated a t 800 V • • • • 34 11 The emiss ion c o n f i g u r a t i o n 37 12 Spec t r a l response o f EMI 9558 QBM 39 +2 13 Absorbance o f Fe - 1, 10-phenanthro l ine complex 42 14 The emiss ion c e l l and ac t inomet ry c e l l s . . 4 4 15 Transmiss ion curve o f 1.5 cm K 2 Fe ( C 2 O 1 J 3 .006 M ac t i n ome t r i c s o l u t i o n and o f the b o r o s i l i c a t e g l a s s f i l t e r 1.08 mm. . 45 x F igure Page 16 The gas chromatograph and f lame photometr ic d e t e c t o r -48 17 Carbopak BHT-100 9 f t . column r e t e n t i o n data 49 18 Chromatograph s t anda rd i z i n g b o t t l e s and Hami l ton sy r i nges 52 19 Typ i ca l d a i l y c a l i b r a t i o n curve f o r CH3SH . 54 20 S 0 2 c a l i b r a t i o n curve . 55 21 . The abso rp t i on of po lychromat i c u-v l i g h t by methyl mercaptan. 57 22 Mo lecu l a r r e a c t i o n r a t e o f CH3SH v . s . photon abso rp t i on r a t e . 61 23 The quantum y i e l d o f CH 3SCH 3 decompos i t ion v . s . atmospher ic pressure . . . . 83 24 The quantum y i e l d o f d imethyl d i s u l p h i d e decompos i t ion v . s . c oncen t r a t i on o f - s u l ph i d e ,. . . . 86 25 React ion r a t e CH 3SH decompos i t ion v . s . l i g h t absorbance w i t h added S 0 2 . . . • . . . . . . . . . 88 26 Quantum y i e l d CH3SH decompos i t ion v . s . % t o t a l l i g h t absorbed by S 0 2 . . . 89 27 Photomicrograph o f c e l l depos i t 97 28 Photomicrograph of c e l l depos i t '.. . . 98 29a Pho t o l y s i s c e l l depos i t xlOO 20 kv 99 29b Pho t o l y s i s c e l l depos i t x400 20 kv 99 29c P h o t o l y s i s c e l l depos i t xlOOO 10 kv. . 99 29d Su lphur x- ray emiss ion sources superimposed over the c e l l depos i t a t xlOOO 20 kv 99 xi F igu re Page 30 X- ray emiss ion spectrum o f c e l l wa l l depos i t on . end window o f " ze ro " c e l l . 31 Emiss ion i n t e n s i t y o f s u l phu r - c on t a i n i ng compounds under po lychromat i c i l l u m i n a t i o n v . s . wavelength 102 32 The time dependence o f CH 3SCH 3 emiss ion 104 33a The t ime dependence o f S 0 2 emiss ion a t ,240 nm 105 33b The t ime dependence o f S 0 2 emiss ion a t 320 nm . . 105 34 Emiss ion behav iour du r i ng i n t e r r u p t e d i l l u m i n a t i o n o f CH 3 SCH 3 109 35 Emiss ion behav iour dur ing i n t e r r u p t e d i l l u m i n a t i o n o f so2 no 36 Emiss ion behaviour dur ing i n t e r r up t ed i l l u m i n a t i o n o f S 0 2 . H I 37 The CH 3 SCH 3 emiss ion a t ' 370 nm w i th b o r o s i l i c a t e g l a s s f i l t e r 114 38 Emiss ion of CH 3SCH 3 i n a i r v . s . volume CH 3SCH 3 added to emiss ion c e l l . . .' 39 Emiss ion from CH 3SCH 3 a t 270 nm i n a i r v . s . atmospher ic pressure H ° 40 Emiss ion from CH 3SCH 3 i n dry n i t r ogen v . s . atmospher ic p ressure H " 41 R e l a t i v e importance o f abso rp t i on and s c a t t e r i n g to e x t i n c t i o n c o e f f i c i e n t f o r carbon p a r t i c l e s 124 42 E x t i n c t i o n curve f o r the theory o f Mie f o r p a r t i c l e s of r e f r a c t i v e index m = 1.5 124 43 Behaviour o f the 370 nm emiss ion dur ing i n t e r r u p t e d sho r t wavelength i l l u m i n a t i o n o f S0 2 127 x i i A C K N 0 W L E D G fl E N T S I would l i k e to thank Dr. F.E. Murray f o r the oppo r tun i t y to c a r r y out t h i s research and f o r h i s cont inued support throughout the p r o j e c t . I would l i k e a l s o to thank Dr. D.G.L. James f o r h i s h e l p f u l d i s c u s s i on s w i th respec t to the mechanism o f r e a c t i o n . The a s s i s t an ce of the chemical eng ineer ing workshop has been a prime f a c t o r i n the complet ion of t h i s work. I would l i k e to thank Mr. John Baranowski f o r h i s he l p f u l sugges t i ons , Mr. Paddy J a r v i s f o r h i s machining e xpe r t i s e and Mr. I rw in Szabo f o r r e b u i l d i n g the e l e c t r o n i c s whenever i t stopped work ing . I w ish a l s o to thank Sha r i H a l l e r f o r t r a n s l a t i n g a sequence o f handwr i t ten h i e r og l y ph i c s i n t o a readable t h e s i s . x i i i 1. Chapter 1 I N T R O D U C T I O N 1.1 General The K r a f t pu lp i ng process produces vas t amounts o f su lph ide vapours which are emit ted to the atmosphere. These vapours c o n s i s t most ly o f hydrogen su lph ide ( H 2 S ) , methyl mercaptan (CH 3 SH), d imethyl su l ph i de (CH 3SCH 3) and dimethyl d i s u l p h i d e (CH 3 SSCH 3 ) . The gases have odour th resho lds of 5, 2, 1, and 16 ppb r e s p e c t i v e l y [ 4 2 ] . The f a t e o f these compounds i n the atmosphere and knowledge o f t h e i r breakdown by atmospher ic processes would be usefu l i n mode l l i ng the environment o f areas proximate to K r a f t m i l l s . Such i n f o rma t i on may a l so be, use fu l i n deve lop ing p o l l u t i o n abatement measures. The major mode o f r e m o v a l o f su lph ides from the atmosphere appears to be o x i d a t i o n l i k e l y f o l l owed by washout through p r e c i p i t a t i o n . The ra t e o f thermal o x i d a t i o n at atmospher ic temperatures i s r a t h e r low, however, the gases are capable o f absorb ing u l t r a - v i o l e t l i g h t which leads to the o x i d a t i o n o f the su lphur content to su lphur d i o x i d e ( S 0 2 ) . Murray and Rayner [32] determined tha t reduced su lph ides i n an a i r atmosphere would o x i d i z e under the i n f l u en ce o f u l t r a - v i o l e t l i g h t . Shor t o wavelength u l t r a - v i o l e t (2537 A) was found to be supe r i o r to longer wave-o l eng th (3600 A) and the o rder o f r e a c t i v i t i e s was found to be CH3SH > ( C H 3 ) 2 S 2 »• ( C H 3 ) 2 S . The o x i d a t i o n o f ( C H 3 ) 2 S was found to be very s low. 1400 2180 2040 1920 1800 N . 1440 Wavelength Figure 2. The absorption spectrum of dimethyl disulphide. 510h 480}-F igure 3. The abso rp t i on spectrum o f dimethyl s u l p h i d e . •s This work desc r i bes the p h o t o l y t i c o x i d a t i o n o f the su lph ides from K r a f t pulp m i l l sources and measures the r a t e o f d isappearance o f the com-pounds. The quantum y i e l d (<}>) of removal i s measured i n terms o f the number o f molecu les removed per photon absorbed. The gases s t ud i ed were methyl mercaptan, d imethyl su l ph i de and •dimethyl d i s u l p h i d e . These molecu les are capable o f absorb ing u l t r a - v i o l e t r a d i a t i o n o f the wavelengths shown i n the abso rp t i on spec t ra (F igures 1, 2, 3) (This work) The abso rp t i on o f a quantum o f energy r e s u l t s i n the e l e c t r o n i c e x c i t a t i o n of the absorb ing mo lecu le . Th is energy may be d i s t r i b u t e d about the molecu le and i f s u f f i c i e n t , cause any one o f a number of processes to take p l a c e . The normal photochemical processes may be i l l u s t r a t e d by a mod i f i ed J ab l on sk i diagram (F i gu re 5 ) . — i c 5 0 = s i n g l e t ground s t a t e 51 = s i n g l e t f i r s t e x c i t e d man i f o l d T i = t r i p l e t f i r s t e x c i t e d man i f o l d T 2 = second e x c i t e d t r i p ! e t man i f o l d F igure 5. Mod i f i ed J ab l on sk i diagram f o r photon abso rp t i on and subsequent r e l a x a t i o n . 7, The s i n g l e t s t a t e i s one i n which a l l mo lecu la r e l e c t r o n s are pa i r ed w i th oppos i t e sp ins such tha t the m u l t i p l i c i t y o f the s t a t e [(2s + 1) where s i s the net s p i n ] i s one. The t r i p l e t s t a t e r e s u l t s from e x c i t a t i o n to the e l e c t r o n i c s t a t e where not a l l e l e c t r on s are sp i n p a i r e d , r e s u l t i n g i n a net s p i n o f one and a m u l t i p l i c i t y o f t h r ee . The abso rp t i on o f a photon w i l l g ene r a l l y r a i s e the molecu le to the f i r s t e x c i t e d s i n g l e t man i fo ld due to sp i n c on se r va t i o n . I f t h i s s t a t e i s r e p u l s i v e , the molecu le may d i s s o c i a t e e i t h e r r a p i d l y o r s l ow l y depending upon the degree o f r e p u l s i o n . React ion of the mo lecu la r fragments produced w i l l g ene r a l l y r e s u l t and cha in propagat ing s teps may be i nvo l ved due to r e a c t i v e secondary f ragments. Should the e x c i t e d s i n g l e t prove s t a b l e , o the r pathways e x i s t f o r the removal o f energy. The f i r s t o f these may be r e a c t i o n d i r e c t l y from the e x c i t e d mo lecu la r s i n g l e t s t a t e w i th molecu les i n the atmosphere. Such r e a c t i o n may o r may not i n vo l v e cha in propagat ing steps which would r e s u l t i n a quantum y i e l d g r ea t e r than one. Another pathway i n vo l ve s the r a d i a t i o n l e s s r e l a x a t i o n to another e x c i t e d e l e c t r o n i c c o n f i g u r a t i o n . The e x c i t e d s i n g l e t may i n t e r n a l l y conver t to an upper v i b r a t i o n a l l y e x c i t e d l e v e l o f the ground s t a t e s i n g l e t . Th is r e s u l t s i n a mo lecu la r heat ing a c t i o n i n which the molecu le l o se s energy by c o l l i s i o n a l t r a n s f e r to atmospher ic mo lecu les . Such a process i s l e s s l i k e l y to produce chemical r e a c t i o n . The f i r s t e x c i t e d s i n g l e t may a l so undergo i n t e r - s y s t em c r o s s i n g and pass i n t o the f i r s t e x c i t e d t r i p l e t man i f o l d . Mo lecu l a r c o l l i s i o n w i l l remove the v i b r a t i o n a l e x c i t a t i o n and the t r i p l e t may remain i n the t r i p l e t e x c i t e d s t a t e f o r a r e l a t i v e l y long pe r i od s i n ce r e tu rn to the s i n g l e t ground 8. s t a t e i s s p i n - f o r b i d den . The t r i p l e t may r ea c t w i t h atmospher ic molecu les o r p i c k up s u f f i c i e n t k i n e t i c energy through c o l l i s i o n to r e tu rn to the e x c i t e d s i n g l e t s t a t e . The ex c i t ed t r i p l e t may r e t u rn to the ground s t a t e s i n g l e t by em i t t i n g phosphorescent r a d i a t i o n c h a r a c t e r i s t i c o f the energy d i f f e r e n c e between the t r i p l e t and va r i ous v i b r a t i o n a l l e v e l s o f the ground s t a t e s i n g l e t . S i m i l a r l y the e x c i t e d f i r s t s i n g l e t may r e t u rn to the ground s t a t e by em i t t i ng a photon of f l u o r e s c en ce . These t r a n s i t i o n s i n v o l v i n g r a d i a t i o n do not r e s u l t i n chemical r e a c t i o n and g ive a quantum y i e l d o f r e a c t i o n of z e r o . The i n c i d en t energy i n t h i s study was prov ided by a deuter ium d i s charge lamp f i t t e d w i t h a S u p r a s i l , leached-sodium s i l i c a window. The o emiss ion spectrum extended to 1700 A. The wavelength o f most i n tense absorpt o f o r methyl mercaptan was near 2350 A. Thus, the average energy i npu t , f r om E = h v , i s 121.6 k c a l / e i n s t e i n o f photons absorbed. The bond energ ies o f the var ious spec ies i nvo l ved are l i s t e d i n Tab le 1. Tab le 1 Bond D i s s o c i a t i o n s o f I n t e r e s t D(S-H) = 88.8 kcal/mol [ 2 , 6, 18] D(C-S) = 75.2 [5] D(S-S) = 67 [48] The energy absorbed exceeds the i n d i v i d u a l bond energ ies o f the molecu les under s tudy . There i s , t h e r e f o r e , a h igh p r o b a b i l i t y t ha t the absorb ing molecule w i l l d i s s o c i a t e due to the energy i n excess o f the bond energy. The spec ies formed w i l l c a r r y o f f t h i s excess energy i n the form o f e l e c t r o n i c e x c i t a t i o n as we l l as v i b r a t i o n a l and r o t a t i o n a l e x c i t a t i o n d i s t r i b u t e d between the f ragments . The excess energy f o r the f o l l o w i n g o d i s s o c i a t i o n s assuming abso rp t i on o f r a d i a t i o n o f average wave lenth 2350 A i s shown i n Tab le 2. Tab le 2 Energy Excess f o r P a r t i c u l a r Bond D i s rup t i on s E'h - D ( C H 3 S -H) = 32.8 kca l/mol E h v - D (CHa-SH) = 46.4 kcal/mol E h v " D ( C H 3 S ~ S C H 3 ) 54.6 kca l/mol Each o f the fragments may c a r r y o f f e l e c t r o n i c a l l y e x c i t e d o r hot energy and as such may r e a d i l y undergo r ea c t i on s t ha t the rma l i zed spec ies would no t . They may e x h i b i t unusua l l y low apparent energ ies o f a c t i v a t i o n i n t h e i r r e a c t i o n w i t h environmental molecu les [ 8 , 11 , 12 , 13 , 16 , 17 , 18 , 19 , 21 , 22 , 23 , 25 ] , Dzant iev and Sh ishkov c l a im [23] t ha t the r ea c t i on s entered i n t o by such hot atoms o r r a d i c a l s i s determined l a r g e l y by the s t e r i c f a c t o r . The hot r a d i c a l s formed en te r i n t o r e a c t i o n w i t h atmospher ic molecu les and amongst themse lves . These r ea c t i on s may propagate a cha in sequence thereby m u l t i p l y i n g the e f f e c t of i n i t i a t i o n . The r e a c t i o n o f the s u l phu r - c on t a i n i n g r a d i c a l group w i t h oxygen i s amongst the cha in sequence. 1.2 The Pr imary Processes The abso rp t i on of a quantum o f l i g h t predominant ly r e s u l t s i n the d i s s o c i a t i o n o f the absorb ing mo lecu l e . The modes o f decompos i t ion o f the methyl o rgan i c su l ph ides have been found to be the f o l l o w i n g . 10. CH3SH + hv - CH 3S + H - CH 3 + SH [1-7 ,10 ,11 ,14-19 ,21 ,26-28] CH 3SCH 3 + hv ^ CH 3S + CH 3 [5 ,12] CH 3SSCH 3 •+ hv * 2 CH 3S [ 2 , 5 , 8 , 9 , 2 0 ] D i s s o c i a t i o n of the bonds produces r a d i c a l s which r e t a i n some o f the excess e l e c t r o n i c energy. There are f ou r i n d i v i d u a l spec ies produced: 1. The methyl t h i y l r a d i c a l (CH 3S) 2. The hydrogen atom (H) 3. The methyl r a d i c a l (CH 3) 4. The mercaptan r a d i c a l (SH) The d i s s o c i a t i o n products share the excess energy i n d i c a t e d i n Table 2. The pr imary processes above are a l so accompanied by e i t h e r cha in r e a c t i on s o r other pr imary processes which produce a y e l l o w , o i l y depos i t which adheres to the r e a c t i o n c e l l w a l l s and entrance window [1 , 12 ,16 ,37 ,41 , 4 2 ] . Th is depos i t has been found to c on t a i n su lphu r and i s pos tu l a t ed to be a m ix tu re o f th io formaldehyde and elemental su lphur [ 1 6 ] . The decomposi t ion o f the methyl mercaptan molecu le occurs a t both the C-S bond and at the S-H bond. C a l l e a r and Dickson [5] have found the o r a t i o o f S-H to C-S s c i s s i o n a t 1950 A f l a s h p h o t o l y s i s to be 1.7 to 1. Th is i s not what one would expect s i n c e the C-S bond i s 13.6 kcal/mol lower i n energy than the S-H bond. Th is suggests t ha t the e l e c t r o n i c a l l y e x c i t e d (1 .1) (1 .2) (1 .3) (1.4) 11. * methyl mercaptan molecu le (CH 3SH ) f i n d s a s t a t e where the S-H p o t e n t i a l energy i s r e p u l s i v e . The molecu le i s q u i c k l y ab l e to ad ju s t by d i s s o c i a t i o n o f the very low mass H atom. The C-S s c i s s i o n w i l l be produced when the system i s s lower to move to the S-H d i s s o c i a t i v e s t a t e thereby more equa l l y appor-t i o n i n g the energy excess over a l l mo lecu la r bonds before d i s s o c i a t i o n takes p l a c e . The C-S s c i s s i o n has been found to i n c rease a t h i ghe r i n c i d e n t energ ies ( lower wave lengths) . At a l l wavelengths i n the p h o t o l y s i s o f pure CH 3SH, the sum o f quantum y i e l d s o f p roduc t i on o f H 2 and CH 4 i s u n i t y [10 , 15 , 16 ] . The quantum y i e l d o f d isappearance o f CH3SH approaches two. The main products i n the s t e ady - s t a t e p h o t o l y s i s o f pure CH3SH have been found to be O-k, H 2 and CH 3SSCH 3 [ 1 , 3 , 4 , 6 , 7 , 1 0 , 1 1 , 1 5 , 1 6 ] . Dimethyl d i s u l p h i d e p h o t o l y s i s y i e l d s CH 3SH a l though much recombinat ion takes p lace [ 8 , 9 ] , Dimethyl su l ph i de has been found to produce CH 3SH and d i s u l p h i d e [ 1 2 ] . I t i s apparent t ha t subsequent r ea c t i on s take p lace due to the mo lecu la r fragments produced. 1.3 The Hot Rad i ca l s Produced and The i r React ions The mo lecu la r fragments produced by p h o t o l y s i s a re h i g h l y ene rge t i c and i n i t i a t e secondary r ea c t i on s which c on t r i b u t e to the cha in nature of the r e a c t i o n sequence. The energy a v a i l a b l e to the hot H atom has been i n v e s t i g a t e d by Sturm and White [ 26 , 27 , 28 ] . The p h o t o l y s i s o f CH 3SH was c a r r i e d out i n the presence o f deuter ium (D 2 ) to i n v e s t i g a t e the produc t ion o f HD through deuter ium atom a b s t r a c t i o n by hot H [ 2 6 ] . The H2/HD r a t i o , found by mass spec t roscopy , i s a f u n c t i o n o f the H atom energy. The H 2/HD r a t i o i s compared to the known H 2/HD r a t i o s 12. produced from the pho t o l y s i s of HBr i n D 2 a t va r i ous i n c i d en t wave lengths . Comparison o f the two r a t i o s y i e l d s the energy o f the H atom d i s s o c i a t e d from o the photo lysed CH 3SH mo lecu le . The H atom energy was found to peak a t 2138 A and to decrease both a t l onge r and s ho r t e r wave lengths . The energ ies o f the CH 3SH fragments found are shown i n Tab le 3 [ 2 6 ] , Tab le 3 The Energy D i s t r i b u t i o n o f the Fragments o f CH3SH Pho t o l y s i s X Emax E 0 E m a x " E o 2537 1.05 + .1 eV 24.21 kcal/mol .89 eV 20.5 kcal/mol .16 eV 3.69 kcal/mol 2288 1.57 + .1 36.2 1.23 28.4 .34 7.84 2138 1 .94 + .1 44.7 1.40 32.3 .54 12.45 1849 2.83 + .1 65.3 1.13 26.1 1.70 39.2 X = wavelength i n c i d e n t E = ( l i g h t energy)-(bond energy) E 0 = H atom energy E m -E 0 = CH 3S energy The hot H atom appears to have a maximum energy a t an i n c i d e n t o wavelength of about 2138 A wherea f te r the C-S s c i s s i o n appears to i n c r ease i n p r o b a b i l i t y . The energ ies i n both fragments a re s u f f i c i e n t to produce f u r t h e r r e a c t i o n s . The hot H may r ea c t w i t h CH3SH to a b s t r a c t the su l phyd ry l H atom. Th is process appears, temperature independent, thus having no apparent Ar rhen ius 13. a c t i v a t i o n energy [ 1 0 ] . Converse ly , H atom a b s t r a c t i o n from CH3SCH3 by hot CH3S r a d i c a l s was found to have an a c t i v a t i o n energy o f 5.4 kcal/mol [ 1 2 ] . The a c t i v a t i o n energy f o r H atom a b s t r a c t i o n from CH 3SSCH 3 by hot CH 3S r a d i c a l s was found to be 1.5 kcal/mol [ 8 ] , The a c t i v a t i o n energy f o r H atom a b s t r a c t i o n from CH3SCH3 by hot CH 3 r a d i c a l s was found to be 2.3 kca l /mol [ 1 2 ] . 1.4 React ions o f the Hot Hydrogen Atom The hot H atom can possess up to 32 kca l /mo l o f d i s s o c i a t i o n excess o energy a t 2138 A. The major r e a c t i o n o f the hot H atom i n the presence o f CH 3SH i s the a b s t r a c t i o n o f the su l phyd ry l hydrogen atom to form H 2 and the methyl t h i y l r a d i c a l [ 3 , 6 , 1 0 , 1 1 , 1 5 , 1 7 , 1 8 ] . H + CH3SH - H 2 + CH 3S (1.5) The hot H does not a t t a ck the methyl hydrogen atoms. Inaba and Darwent, i n o the pho t o l y s i s o f pure CH 3SD at 2537 A found on ly D 2 and CH3D as products [ 3 ] , Th is suggests a r e a c t i o n sequence as shown below. CH 3SD + hv - CH3S + D D + CH 3SD - CH 3S + D 2 and CH 3SD + hv - CH 3 + SD CH 3 + CH 3SD - CH3D + CH 3S No H 2 and no HD were found as p roduc t s . The r e a c t i o n o f the H atom terminates the r eac t i ons o f tha t r a d i c a l . The CH 3S r a d i c a l formed w i l l propagate f u r t h e r 14. cha in r eac t i ons from the o r i g i n a l absorbed quantum. The o r i g i n a l hot H may become quenched and undergo r ea c t i on s o f a thermal na tu re . The order o f quenching e f f i c i e n c y f o r va r i ous gases has been found to be: He > C0 2 > N 2 > C 2 H 6 > C 2 D 6 [21] Argon does not a f f e c t the quantum y i e l d o f H 2 o r CH 4 and thus i s not a quencher f o r hot H atoms. In the presence of an app rec i ab l e quan t i t y o f oxygen the hydrogen atom w i l l o x i d i z e to form the hydrogen peroxy r a d i c a l H + 0 2 - H00 (1.6) A v a i l a b l e r a t e data w i l l be d i s cussed l a t e r i n the mechanism s e c t i o n , however, the o x i d a t i o n r e a c t i o n appears to proceed at a r a t e somewhere between 1/3 and three times the r a t e o f hydrogen a b s t r a c t i o n from CH 3SH. The hydrogen peroxy r a d i c a l i s capable o f c on t i nu i ng the cha in r e a c t i o n by a b s t r a c t i n g the su lphydry l hydrogen atom from CH3SH to form hydrogen perox ide . H00 + CH3SH + HOOH + CH 3S (1.7) The cha in i s f u r t h e r cont inued by r e a c t i o n s i n v o l v i n g the methyl t h i y l r a d i c a l . 1.5 React ions of the Hot Methyl Rad i ca l Hot methyl r a d i c a l s have been found to ab s t r a c t methyl hydrogen atoms from CH 3SCH 3 w i t h an apparent a c t i v a t i o n energy of 2.3 kcal/mol [ 1 2 ] . 15. CH 3 + CH3SCH3 - ChU + CH 2SCH 3 (1 .8) They a l s o undoubtedly a b s t r a c t su lphydry l hydrogen from CH 3SH. CH 3 + CH3SH --CH* + CH 3S (1.9) The r a t e constant f o r r e a c t i o n (1 .9) has been found to be 1.8 x }0h M"1 s - 1 [ 5 4 ] . Th is r a t e i s s lower than o the r r e a c t i o n s which may occur to a methyl r a d i c a l i n an oxygen-conta in ing atmosphere. A more complete d i s c u s s i o n of ra tes o f competing r ea c t i on s w i l l be found i n Chapter 3. In the presence o f an app re c i ab l e concen t r a t i on o f oxygen, the major r e a c t i o n o f a methyl group i s to o x i d i z e to the methyl peroxy r a d i c a l [ 6 1 ] . CH 3 + 0 2 + M - CH3OO + M k = 3.1 x 10 8 M" 1 s - 1 (1.10) Adachi and James [61] developed a computer s imu l a t i o n o f a methyl r a d i c a l i n an oxygen-conta in ing atmosphere. The mechanism o f mutual i n t e r a c t i o n o f the methyl peroxy r a d i c a l r e s u l t e d i n the f o l l o w i n g p roduc ts : 2 CH3OO - 2 CH3O + 0 2 - C H 3 O H + HCHO + 0 2 CH3OOCH3 + 0 2 k = 3.5 x 10 8 \A~1s'\ (1 .11) 16. The most notab le product o f t h i s i n t e r a c t i o n i s the p roduc t i on o f the methoxy r a d i c a l CH 3 0. The methoxy r a d i c a l i s a r e a c t i v e o x i d i z i n g spec ies which i s capable o f r e a c t i n g w i t h i t s e l f or w i th reduced s p e c i e s . In an oxygen-conta in ing atmosphere, the major product o f CH 30 r ea c t i on s w i t h 0 2 i s the fo rmat ion o f the hydrogen peroxy r a d i c a l . CH 30 + 0 2 - HCHO + H00 k = 4 x 1 0 5 M~1 s " 1 (1 .12) The hydrogen peroxy r a d i c a l may r e a c t w i th reduced spec ies o r may mutua l l y i n t e r a c t . 2 H00 - HOOH + 0 2 k = 2 x 10 9 M~1 s " 1 [61] (1.13) The Adachi-James program was employed to es t imate the concen t ra t i ons o f CH 3 00, CH 30 and H00 i n r e a c t i v e atmospheres con ta i n i ng va ry i ng amounts o f oxygen. A h igh 0 2 c oncen t r a t i on was chosen as 3.23 x 1 0 " 2 M (78% by v o l . ) . The low 0 2 c oncen t r a t i on was chosen as 1 x 10~ 3 M . (2.44% by v o l . ) . A t the h igh 0 2 c oncen t r a t i on 99.97% o f the a v a i l a b l e CH 3 r a d i c a l s form CH 300 w i t h i n 50 ys a f t e r the photo f l a s h . The remain ing 0.03% form CH 30 r a d i c a l s . Dur ing the high concen t r a t i on s imu l a t i o n the H00 concen t r a t i on e ven t ua l l y reaches 12% of the o r i g i n a l CH 300 c on c en t r a t i o n . At low concen t ra t i ons of 0 2 96.9% of the a v a i l a b l e CH 3 r a d i c a l s o x i d i z e to CH 3 00. Only 3.1%.appear as C H 3 O r a d i c a l s . The u l t ima t e concen t r a t i on o f H00 r a d i c a l s reached on ly 3% of the CH 300 c on c en t r a t i o n . 17. Thus f o r f r e e CH 3 r a d i c a l s i n an oxygen con ta i n i ng atmosphere, the predominant r e a c t i o n i s the fo rmat ion o f methyl peroxy r a d i c a l s . These o x i d i z i n g spec ies w i l l f u r t h e r r eac t w i th reduced spec ies i n the r e a c t i o n m a t r i x . 1.6 React ions o f the Methyl Th i y l Rad ica l o The methyl t h i y l group may possess between 3.69 kcal/mol (2537'A) o and 39.2 kcal/mol (1849 A) excess energy a f t e r bond s c i s s i o n . In an oxygen-con t a i n i ng atmosphere the methyl t h i y l r a d i c a l r a p i d l y reac t s w i th the oxygen. F l a sh pho t o l y s i s s tud i e s by C a l l ear and Dickson [5] showed tha t 100 t o r r 0 2 o suppressed the 2185 A abso rp t i on band a t t r i b u t e d to the CH 3S r a d i c a l . The o 2000 A f l a s h p e r s i s t e d 20 us to h a l f i n t e n s i t y and the f i r s t t r a n s i e n t spec t r a were recorded at 5 us de l ay . The e l i m i n a t i o n o f the CH 3S abso rp t i on spectrum i n d i c a t e s very r ap i d r e a c t i o n w i th 0 2 . Su lphur d i o x i d e (S0 2 ) i s not the i n i t i a l product o f the su lphur o x i d a t i o n [ 35 ,36 ,38 ,40 ) . McGarvey and McGrath photo lysed hydrogen su l ph i de i n the presence o f a 3:1 r a t i o o f 0 2 :H 2 S and observed the very r ap i d appearance o f SO abso rp t i on bands. The SO bands were s l ow l y rep laced by S 0 2 abso rp t i on bands. The appearance o f the SO bands co i n c i ded w i th a broad band abso rp t i on o o continuum extending from 2000 A to 2500 A. The band appeared 50 us a f t e r f l a s h i n i t i a t i o n and had d isappeared by 1 ms. A f t e r 1 ms the SO bands were s t i l l p resent a l though weakened and the S0 2 bands were s t a r t i n g to become apparent . A f l a s h pho t o l y s i s o f pure S 0 2 revea led a group o f bands from o o 1780 A to 1840 A. The group a l s o appeared i n 0 2 / H 2 S f l a s h e s . The nature of the S 0 2 abso rp t i on spectrum suggested the appearance o f an i somer i c form 18. of S 0 2 [ 3 5 ] . The i somer i c form was suggested s i n c e an e l e c t r o n i c a l l y e x c i t e d form would be expected to have a l i f e t i m e under 1 0 " 8 s and a v i b r a t i o n a l l y e x c i t e d form would be expected to dea c t i v a t e by c o l l i s i o n f a s t e r than was i n d i c a t e d by the observed bands. The isomer probably forms from SO and rearranges to S 0 2 . No r r i sh and Ze lenberg [40] found the e a r l y fo rmat ion o f S 2 0 2 ( the s t a b l e form o f SO below 300°C)to precede the fo rmat ion of S 0 2 i n the f l a s h o x i d a t i o n of H 2 S. Thus the o x i d a t i o n sequence seems to f o l l o w a pa t t e rn such as CH 3S + 0 2 - CH 30 + SO A H f = -25 .3 kcal/mol (1.14) CH 3S + 0 - CH 3 + SO AH f = -53.6 kcal/mol (1.15) Th is i n i t i a l r ap i d o x i d a t i o n . w i l l be f o l l owed by the s lower o x i d a t i o n : SO + 0 2 - S 0 2 + 0 (1.16) SO + 0 - S0 2 (1.17) Methyl t h i y l r a d i c a l s are a l so ab l e to undergo o ther r e a c t i o n s . The main f a t e o f CH 3S r a d i c a l s produced i n non -ox i da t i ve atmospheres i s combinat ion to form dimethyl d i s u l p h i d e [ 5 , 8 , 9 ] 2 CH 3S - C H 3 S S C H 3 (1 .18) D i su l ph i de molecules i n pho t o l y s i s can d i r e c t l y expel e lemental su lphur [5] 19. CH 3SSCH 3 + hv -> S 2 + 2 CH 3 (1.19) The CH 3S r a d i c a l i s s u f f i c i e n t l y r e a c t i v e to a b s t r a c t the methyl hydrogen atom o f CH 3SSCH 3 to form CH3SH dur ing d i s u l p h i d e photo lyses [ 8 ] . CH 3S + CH 3SSCH 3 -»• CH 3SH + CH 2SSCH 3 (1.20) The add i t i o n o f n i t r i c ox ide (MO) i n gas phase photo lyses scavenges the CH 3S r a d i c a l to produce methyl t h i o n i t r i t e (CH 3SN0) [ 8 ] . The a d d i t i o n o f NO to pure d i s u l ph i de pho t o l y s i s r e s u l t e d in a CH3SN0 produc t ion r a t e twenty t imes t ha t o f CH3SH [ 8 ] . Th is i n d i c a t e s the hydrogen a b s t r a c t i o n r a t e to be much l e s s favoured than i s recomb ina t i on . The d i s u l p h i d e fo rmat ion i s a main cha in t e rm ina to r and d i s u l p h i d e i s present as a r e a c t i o n product even a t oxygen pressures of 150 t o r r . The methyl hydrogen a b s t r a c t i o n does not take p lace in l i q u i d photo lyses p o s s i b l y due to r a p i d c o l l i s i o n a l c o o l i n g o f the CH3S [ 9 ] . The pho to l y s i s o f l i q u i d mixtures o f d i e t h y l d i s u l p h i d e and d imethyl d i s u l p h i d e gave a mixed methy l -e thy l d i s u l p h i d e c ross -p roduc t [ 9 ] . The r a t e o f fo rmat ion o f the c ro s s -p roduc t i n d i c a t ed a p roduc t i on quantum y i e l d o f 330 [ 9 ] . Th is i n d i c a t e s an a t tack by the methyl o r e thy l t h i y l r a d i c a l upon the S-S bond w i th an average cha in l eng th of 165. In the case of CH 3S a t t a ck upon pure CH 3 SSCH 3 , the exchange i s not d e t e c t ab l e . The methyl t h i y l r a d i c a l t r a p , NO, has been found to suppress the recombinat ion o f CH 3S to d i s u l p h i d e [ 7 ] . N i t r i c ox ide a l s o stops the CH 3SH fo rmat ion i n d i s u l ph i d e pho t o l y s i s by t r app ing the CH 3S as CH 3SN0. 20. Pho t o l y s i s o f CH3SH i n the presence o f NO produces very long cha in l eng ths probably i n v o l v i n g r ea c t i on s o f H and NO i n the cha in propagat ion [ 1 0 ] . No dark r e a c t i o n was found between CH 3SH and NO. The p h o t o l y t i c quantum y i e l d o f H 2 f o rmat ion was decreased at NO pressures above 20 t o r r i n d i c a t i n g p a r t i c i p a t i o n o f hot H i n r e a c t i on s o ther than those forming H 2 . The H 2 y i e l d was una f fec ted a t pressures below 20 t o r r . The r a t e o f appearance of CH3SN0 (8.02 x 1 0 1 7 mo lecu les/min) a t the absorbed energy (9:45 x 1 0 1 5 phot/min) i n d i c a t e s a quantum y i e l d o f 84.9 a t NO pressures o f 20 t o r r . Th i s i s a l ong cha in l e n g t h . Increased concen t ra t i ons o f NO up to 125 t o r r caused a r e a c t i o n sequence which cont inued f o r 35 minutes a f t e r t e rm ina t i on o f r a d i a t i o n . Th is conf i rms a long cha in l eng th and CH 3SN0 p roduc t i on r a te s i n d i c a t e a quantum y i e l d o f 339 [ 1 0 ] . The hot H i s i n vo l ved i n the cha in l eng th and S tee r and Kn ight suggest p a r t i c i p a t i o n o f a HN0 cha in such as the f o l l o w i n g : H + NO -> HN0 (1.21) HN0 + CH3SH + CH3SN0 + H 2 . (1.22) S t ee r and Kn ight were unable to demonstrate a maximum i n CH3SN0 p roduc t i on r a t e w i th added NO. The r a t e i s not due to NO abso rp t i on s i n c e i t i s l a r g e l y o t r anspa ren t a t wavelengths g r ea t e r than 1900 A [ 49 ] . 1 .7 Gas Phase Photoox ida t ions Murray and Rayner [32] determined tha t pho to -ox i da t i on of su l ph ides took p lace under u l t r a - v i o l e t l i g h t . Su lphur d i o x i d e was a major p roduc t . 21. Shor t wavelength (2537 A) u l t r a - v i o l e t was s upe r i o r to longer wavelength o (3600 A) and the o rder o f r e a c t i v i t i e s , uncor rec ted f o r a b so r p t i o n , was found to be CH3SH > CH 3SSCH 3 » CH 3 SCH 3 . R.W. Murray and S . L . J . I nda l l [33] found d i a l k y l d i s u l p h i d e s to o x i d i z e i n 0 2 s a tu ra ted s o l u t i o n under the i n f l u en ce of methylene b lue s e n s i t i z e r . Graham and S i e [ 34 ] , however, found C H 3 S H to undergo very slow pho toox ida t i on to produce S0 2 w i th a quantum y i e l d about 3 to 6 x 1 0 - 5 . Th is i s i n c o n f l i c t w i t h o ther groups not ing the r ap i d appearance o f SO and S0 2 s pec t r a upon f l a s h pho t o l y s i s i n a i r [ 5 ,32 ,35 ,37 ,38 ,40 ] and w i t h those groups not ing r ap i d appearance o f S 0 2 as product . Ben t l e y , Douglass and Lacadie. [37] photo lysed CH 3 SCH 3 f o r s i x hours o under high i n t e n s i t y mercury a rc (2537 A) i n the presence o f oxygen. Many r e a c t i o n products were found con t a i n i ng both methyl group photoproducts and c on t a i n i ng the methyl t h i y l group. Tab le 4 Pho t o l y s i s Products from Long Term CH 3SCH 3 P ho t o l y s i s 1. d imethyl su lphox ide CH 3S0CH 3 2. d imethyl sulphone CH 3 S0 2 CH 3 3. methane su lphon i c a c i d CH 3 S0 3 H 4. d imethyl d i s u l p h i d e CH 3SSCH 3 5. methane methaneth io l su lphonate CH 3 S0 2 SCH 3 6. su lphur d i o x i d e S 0 2 7. su lphur t r i o x i d e S0 3 8. methanol CH30H 9. formaldehyde HCHO 10. fo rmic a c i d HC0 2H 11. methyl formate HC0 2 CH 3 22. An aeroso l product was no t i ced s h o r t l y a f t e r the s t a r t o f the r e a c t i o n . Th is was f e l t to i n vo l ve the water content of the a i r ( .43 mg H20/£) and the condens ib le photoproducts [ 3 7 ] . 1.8 Photo Ox i da t i on React ion Sequence In view of the p r e v i ou s l y mentioned r e a c t i o n s , the sequence o f r e a c t i o n s of methyl mercaptan upon photo o x i d a t i o n i s probably the f o l l o w i n g . CH3SH + hv - CH 3S + H 1--1 - CH 3 + SH 1 -2 H + 0 2 - HOO 1 -6 CH 3S + 0 2 ^ CH 30 + SO 1 -14 CH 3S + 0 - CH 3 + SO 1 -15 CH 3 + 0 2 + M CH 300 + M 1 -10 CH 300 + C H 3SH - CH300H + CH 3S 1 -23 CH 30.+ CH3SH - CH30H + CH 3S 1 -24 CH 30 + 0 2 - HCHO + HOO 1 -12 HOO + CH3SH - HOOH + CH 3S 1 -7 SO + 0 2 - S 0 2 + 0 1 -16 SO + 0 - S 0 2 1 -17 CH 3S + CH 3S - C H 3 S S C H 3 1 -18 CH 3S + CH 30 - C H 3 S O C H 3 1 -25 CH 3S + C H 3 O O - CH 3 S O O C H 3 1 -26 A more d e t a i l e d c on s i d e r a t i o n of the r e a c t i o n mechanism i s to be found i n the r e s u l t s and d i s c u s s i o n . 23. Chapter 2 E Q U I P M E N T 2.1 General System D e s c r i p t i o n The r ea c t i on s were performed i n a d ry -n i t r ogen- swep t , p a r a l l e l -ended, g rease - f r ee t ubu l a r r e a c t o r . The system was designed to t r ansm i t l i g h t to 180.nm. I l l u m i n a t i o n was prov ided by a medium pressure deuter ium d i s -charge lamp c o l l ima t ed by two quar t z l e n s e s . The po lychromat i c i l l u m i n a t i o n passed through a t e f l o n - s e a l e d 10 cm pyrex r e a c t i o n vesse l f i t t e d w i t h s u p r a s i l windows. T ransmi t ted l i g h t was ana lysed by a J a r r e l l - A s h 0.25 meter Eber t -type monochromator. The 0.25 nm bandwidth e x i t beam was measured by an EMI 9558 QBM pho t omu l t i p ! i e r tube and recorded on a cha r t r e c o r de r . The r e a c t o r support system cou ld be manipu lated to i n s e r t va r i ous r e a c t o r c e l l s w i thout a l t e r i n g the o p t i c a l a l ignment of the system. The monochromator and p h o t o m u l t i p l i e r assembly cou ld a l s o be brought pe rpend i cu l a r to the o p t i c a l path f o r use as an emiss ion d e t e c t i o n system. A photograph o f the apparatus i n r e a c t i o n c o n f i g u r a t i o n i s shown i n F igure 6. Gas concen t ra t i ons were monitored by a gas chromatograph equipped w i th a f lame photometr ic d e t e c t o r . The chromatograph was c a l i b r a t e d d a i l y . 25. 2.2 Da i l y Procedure f o r React ion Ana l y s i s The d a i l y process was begun by measuring the f l ow r a t e to the gas chromatograph of he l ium c a r r i e r gas , and a i r , oxygen and hydrogen i f l ow to the f lame photometr ic d e t e c t o r . Flow ra tes were checked us ing a soap-bubble gas f l ow meter and when c o r r e c t l y ad jus ted to 20, 20, 20 and 250 ml/min respec-t i v e l y , the pho to-de tec to r f lame was i g n i t e d . The pho to -de tec to r was a l l owed to warm up f o r a t l e a s t one hour. The deuter ium lamp was i g n i t e d and a l lowed a t l e a s t 30 minutes to reach thermal e q u i l i b r i u m before the f i r s t spec t ra were recorded . The r e a c t i o n c e l l s were swept w i t h b o t t l e d compressed a i r passed through a g lass tube f i l l e d w i th D r i e r i t e d r y i ng compound. Be fo re en t e r i ng the c e l l , the.gas was f i l t e r e d through a Whatman gama 12 grade 10, 1.0 micron p a r t i c l e f i l t e r which permi t ted passage o f on ly .0001% of 0.6u p a r t i c l e s . Th is prevented d ry i ng compound and o the r f o r e i g n mat te r from en t e r i ng the r e a c t i o n c e l l s . The o p t i c a l pathway was swept w i t h dry n i t r ogen at a f low r a t e o f 1.0 cub i c f o o t per hour (CFH) f o r a minimum of 12 hours before the s t a r t o f a r e a c t i o n sequence and t h i s f low was con t i nuous l y main-t a i ned dur ing the s e r i e s o f runs . The sample c e l l s , f i l l e d w i t h a i r , were p laced i n the o p t i c a l path and exposed to po lychromat i c r a d i a t i o n . A t r an sm i s s i on spectrum from 150 nm to 500 nm was recorded by the monochromator coupled to a cha r t reco rder i n o rde r to measure the amount o f l i g h t en t e r i ng the r e a c t i o n v e s s e l . The area under the i n t en s i t y -wave l eng th curve was r e l a t e d to the c a l i b r a t e d area measured w i t h the same c l e a r c e l l dur ing the a c t i n ome t r i c s t ud i e s i n o rder to determine the photometr i c energy i npu t . Input energy curves were run f o r each c e l l each day and a cont inuous p r o f i l e was mainta ined on the t r an sm i s s i on o f a l l c e l l s . 2 6 . The c e l l s were f i l l e d from Matheson compressed gas c y l i n d e r s us ing Hami l ton te f l on-ended " G a s - t i t e " s y r i n g e s . L i q u i d samples o f d imethyl su l ph i de and d imethyl d i s u l p h i d e were mainta ined i n g l a s s b o t t l e s and the r e a c t i o n c e l l s were f i l l e d w i th l i q u i d us ing Hami l ton m i c r o - l i t r e l i q u i d s y r i n g e s . The f i l l e d r e a c t i o n c e l l s were a l lowed to s i t f o r one -ha l f hour to e q u i l i b r a t e . The r e a c t i o n c e l l s were sampled by i n j e c t i n g 0.25 ml a i r and f l u s h i n g the s y r i nge numerous t imes be fore removing a 0.25 ml gas sample and ana l y s i ng on the gas chromatograph. A 0.25 ml sample was used f o r many runs however h ighe r concen t ra t i on runs r equ i r ed the use o f 0.1 ml sample volumes i n order to s tay i n the reg ion o f maximum s e n s i t i v i t y o f the gas chromatograph c a l i b r a -t i o n cu rve . The c a l i b r a t i o n o f the gas chromatograph was c a r r i e d out s imu l taneous l y w i t h the f i l l i n g and ana l y s i ng of the r e a c t i o n gas. Th is c a l i b r a t i o n was performed each day i n o rde r to more a c cu r a t e l y measure the s e n s i t i v i t y to CH 3SH. C a l i b r a t i o n c on s i s t ed o f measuring four concen t ra t i ons o f each su l ph i de i n f ou r known samp le -bo t t l e volumes. The average o f th ree reproduceab le i n j e c t i o n peaks was taken as the best va lue f o r each c on cen t r a t i o n . The c a l i b r a t e d r e a c t i o n c e l l s were p laced i n the o p t i c a l path between the t e l e s c op i ng ends o f the r e a c t o r support system. The dark s l i d e was removed and the c e l l was exposed to po lychromat i c r a d i a t i o n f o r a per iod of one -ha l f to one hour depending on the gas concen t ra t i ons and the degree o f absorbance. Immediately a f t e r i n i t i a t i o n o f the photo r e a c t i o n , a second t r a n s -m i s s i on curve was run on the same s u l p h i d e - f i l l e d c e l l c o i n c i d i n g w i t h the t r ansm i s s i on curve o f the a i r - f i l l e d c e l l . The area between these two curves i s the measure o f the amount o f l i g h t absorbed by the s u l phu r - c on t a i n i ng gas. 27. The spectrum requ i red about f i v e minutes to sweep from 150 nm to 500 nm. The monochromator was then ad jus ted to f o l l o w the 290 nm absorbance peak of S 0 2 and a cont inuous measurement was recorded a t 290 nm to i n d i c a t e the fo rmat ion o f S 0 2 and CH 3 SSCH 3 . A t the end of the r e a c t i o n r un , the c e l l s were a l lowed to e q u i l i b r a t e f o r one -ha l f hour and-then ana lyzed on the gas chromatograph. A l l runs were ana lyzed f o r CH 3 SH, CH 3 SCH 3 , S 0 2 , and H 2S at 65°C and the column was then r a i s e d i n temperature to 100°C to ana lyse the CH 3SSCH 3 and the po l y su l ph i des trapped on the column. At the conc l u s i on o f a n a l y s i s , the c e l l s were f l u shed w i t h d r y , f i l t e r e d , b o t t l e d a i r and the r e a c t o r support was c l o sed by corks to ma in ta in the dry n i t r ogen f l u s h over n i g h t . 2.3 Chemical Sources The su l phu r - c on t a i n i ng gases CH 3SH, S0 2 and H 2S were supp l i ed i n p r e s su r i z ed l e c t u r e b o t t l e s by the Matheson Company o f Canada. The b o t t l e s were f i t t e d w i th s t a i n l e s s s t e e l va lves connected to lengths o f rubber t u b i n g . The rubber tub ing l ed to a f l a s k o f water which a l lowed a i r from the tube to be d i s p l a c ed by bubb l ing through the wa te r . Volumes of gas were removed by p i e r c i n g the rubber tube and wi thdrawing the -appropr iate amount i n a Hami l ton G a s - t i t e s y r i n g e . The l i q u i d s CH 3SCH 3 and CH 3SSCH 3 were supp l i e d by the Eastman Kodak Company from l o t s 711-1 and 702-1 r e s p e c t i v e l y . The CH 3SCH 3 was t r a n s f e r r e d to a pyrex bu lb f i t t e d w i t h a t e f l o n stopcock and a sampl ing septum. The CH 3SSCH 3 was s to red in a dark screw-cap b o t t l e . A l l m a t e r i a l s were ana lyzed f o r s u l phu r - c on t a i n i n g contaminants and were found to be g r ea t e r than 99% pure by gas chromatographic a n a l y s i s and were used w i thou t f u r t h e r p u r i f i c a t i o n . Figure 7. The react ion c e l l s . 29. 2.4 The React ion C e l l s The r e a c t i o n c e l l s ( F igu re 7) were f a b r i c a t e d from pyrex tub ing 25.4 mm O J . and were 10.0 cm i n o p t i c a l path l e n g t h . The average volume was 40.05 m l . Each c e l l was sea led by two t e f l o n and g l a ss stopcocks blown i n t o the body of the c e l l . One stopcock was c l o sed by a t e f l o n - f a c e d s i l i c o n e rubber i n j e c t i o n septum l oca ted by a brass f i t t i n g sea led w i t h epoxy cement to the tube o f the stopcock and he ld i n p lace by a cap screw. The o ther stopcock was f i t t e d w i th a QVF vacuum b a l l f i t t i n g e i t h e r blown i n p lace or a t tached us ing epoxy cement. Th is f i t t i n g f a c i l i t a t e d f l u s h i n g the c e l l s w i t h dry a i r and a l lowed the evauca t ion o f the c e l l s on the vacuum system f o r those runs a t reduced p ressu re . The c e l l s cou ld be sampled through the i n j e c t i o n septum at any time dur ing a r un . Each end o f the c e l l was sea led by a 1.5 mm t h i c k o p t i c a l window made o f the 1eached-sodium s i l i c a , S u p r a s i l . Th i s ma te r i a l w i l l t r ansm i t u l t r a - v i o l e t l i g h t o f s ho r t e r wavelengths than w i l l pure quar tz (F igu re 8). The ends of the pyrex c e l l were ground and the i n s i d e per imeter o f each window d i s c was ground to prov ide a roughened s e a l i n g s u r f a c e . The windows were then sea led to the annealed c e l l body by A r a l d i t e 20 AC-0V epoxy r e s i n . Th is r e s i n was chosen because o f i t s extremely low c o e f f i c i e n t o f shr inkage which permits the connect ing o f r i g i d ma t e r i a l s such as g l a s s . A f t e r an i n i t i a l pe r iod o f c o n d i t i o n , the c e l l s mainta ined concen-t r a t i o n s o f CH 3SH, C H 3 S C H 3 and CH 3SSCH 3 l onger than one hour w i thou t de t e c t ab l e l o s s . Two o f the c e l l s could ma in ta in a pressure l e v e l o f one-quar ter atmosphere f o r one-ha l f hour w i thou t de t e c t ab l e change {k i n ' H g ) . 30. 100p 150 200 250 . 300 W a v e l e n g t h ?L n m F igure 8. T ransmiss ion spectrum o f s u p r a s i l windows (1 mm and 10 mm t h i c k n e s s ) . F igure 9. The vacuum man i f o l d and emiss ion c e l l . 32. 2.5 The Vacuum System The r e a c t i o n c e l l s were f l u shed and f i l l e d w i th b o t t l e d , compressed, med ica l -purpose a i r us ing a g l a s s vacuum man i f o l d system (F i gu re 9 ) . Vacuum was c reated by a Welch duo-seal vacuum pump which was i s o l a t e d from the system by a co ld f i n g e r operated at -20°C. The g r e a s e - f r e e , mercury- f ree system was c l o sed by t e f l o n stopcocks and was j o i n ed to the c e l l s by QVF b a l l j o i n t s . The b a l l j o i n t s were covered by .001 inch t h i c k t e f l o n f i l m s t r e t ched to cover the b a l l . Vacuum l e v e l s were measured on a C.P.W. Hydropoise bourdon tube vacuum gauge readab le to 1/4 inch mercury. The vacuum cou ld be mainta ined f o r one -ha l f hour w i thou t l o s s . 2.6 The Deuterium Lamp Po lychromat i c u l t r a - v i o l e t l i g h t was produced by a medium-pressure d e u t e r i u n b i l l e d e l e c t r i c d i s cha rge lamp ra ted a t a nominal 30 o r 60 wa t t s . The lamp was prov ided w i th a s u p r a s i l window and was powered by a J a r r e l l -Ash power supp ly . The emiss ion spectrum measured through a new c e l l by an EMI 9558 QBM pho tomu l t i p l ye r tube on a 1/4 meter Ebert monochromator i s shown , in F i gu re 10. The e f f i c i e n c y o f l i g h t p roduc t ion was determined by p l a c i ng an ammeter in l i n e w i th the lamp supply and a vo l tmete r across the two lamp l e a d s . The lamp was found to draw 29.7 wat ts on high power s e t t i n g . Assuming an average absorbed wavelength o f 235 nm, the e f f i c i e n c y o f photon p roduc t i on from e l e c t r i c a l energy can be c a l c u l a t e d . The f requency o f 235 nm r a d i a t i o n i s 1.276 x 1 0 1 5 s e c - 1 . Thus the energy per photon (E = hv) i s 8.464 x 1 0 ~ 1 9 Jou l e s /pho ton . For one hour a t 29.7 wa t t s , the re are (29 .7 ) (60) (60) (1 ) = 33. 1.069 x 10 5 watt seconds/hour. S ince one Jou l e i s one wat t second, a 100% e f f i c i e n t l i g h t would produce: 1.069 x 1 0 5 wat t seconds 1 photon  hour ' 8.4638 x 1 0 " 1 9 watt seconds = 1.263 x 1 0 2 3 photons per hour From a c t i n ome t r i c s t ud i e s 2.2154 x 1 0 1 8 photons o f wavelength sho r t e r than 300 nm are produced. Thus the deuter ium lamp produces u l t r a - v i o l e t l i g h t of wavelength sho r t e r than 300 nm w i th an e f f i c i e n c y o f 1.7537 x I O " 5 . 2.7 The C o l l i m a t i o n System L i g h t emi t ted from the deuter ium lamp passes through a quar tz lens s i t u a t e d i n the e x i t tube o f the lamp hous ing . A f u r t h e r quar t z l ens of 100 mm foca l l ength i s p laced 10 cm down the entrance tube o f the r ea c t o r support to c o l l i m a t e the d i ve rgen t beam a t 2.5 cm d iameter . The l i g h t passes by a 2.5 cm aper tu re 5 cm be fo re the entrance window and then passes i n t o the r e a c t o r eel 1. 2.8 The Reac t ion C e l l Support System The r e a c t i o n c e l l i s supported i n t e f l o n end caps by two t e l e s c op i ng tubes which ma in ta in o p t i c a l a l ignment o f the sou r ce , r e a c t o r and de te c t o r systems. The atmosphere of the support system i s swept by dry n i t r ogen gas i n order to sweep the o p t i c a l path f r e e o f oxygen. The removal o f 0 2 i s necessary to prevent the fo rmat ion of ozone i n the entrance and e x i t areas Wavelength r\ nm Emiss ion spectrum o f deuter ium l i g h t supp ly measured on EMI95580BM pho t omu l t i p l y e r a t -800 V. 35. o f the support mechanism. The abso rp t i on of very sho r t wavelength u l t r a -v i o l e t l i g h t by 0 2 promotes the fo rmat ion o f ozone as shown below: Q 2 + hv -»• 2 0 0 + 0 2 -*• 0 3 The ozone thus formed absorbs u l t r a - v i o l e t l i g h t o f l onger wave lengths . These are the r ea c t i on s r e spons i b l e f o r the fo rmat ion o f the ozone l a y e r which s h i e l d s the ear th from s o l a r u l t r a - v i o l e t l i g h t . The abso rp t i on by ozone o f u l t r a - v i o l e t l i g h t a t l onger wavelengths breaks up the ozone molecu le to mo lecu la r oxygen and the c y c l e begins anew. 0 3 + hv -> 0 2 + 0 The presence of 0 2 i n the o p t i c a l path would a l l ow t h i s sequence to take p lace and would produce a v a r i a b l e absorbance w i t h i n the o p t i c a l t r a i n . Th is v a r i a b l e absorbance would be d i f f i c u l t to separate from r ea c t i on s w i t h i n the r e a c t o r c e l l and would l ead to v a r i a t i o n s i n the i n c i d e n t l i g h t i n t e n s i t y o r to the i n t e n s i t y detec ted i n the photomul t ip ! ie r-monochromator system. The s i t u a t i o n was avoided by d r y -n i t r ogen purg ing the r e a c t o r tube suppor t segments, the monochromator and the pho t omu l t i p ! i e r tube housing w i th an i n i t i a l over n i gh t f low r a t e o f 2.5 CFH and a s t e ady - s t a t e f l ow o f 1 CFH f o r long per iods o f t ime . The l i g h t sou r ce , c e l l , monochromator and pho t omu l t i p ! i e r system are he ld i n a l ignment by the t e l e s c op i n g system supported on an a c c u r a t e l y a l i g n ed t r a c k ( F i gu re 6 ) . The end p i s t ons move back and f o r t h to accommodate 36. c e l l s o f va ry i ng path l eng th from 1 cm to 25 cm. The c e l l d iameter and r a d i a t i o n path d iameter can be v a r i e d up to 7.6 cm by changing the end caps and the c o l ima t i n g l e n s . The r e a c t i o n c e l l area i s enc losed on f i v e s ides by a l i g h t - t i g h t b l a ck metal box and can be b lacked out complete ly by enc l o s i ng the s i x t h s ide w i t h a c u r t a i n . 2.9 The Emiss ion Con f i g u r a t i o n The monochromator and p h o t o m u l t i p i i e r may be removed from the a l ignment rack to p rov ide an emiss ion observ ing c o n f i g u r a t i o n . In t h i s con-f i g u r a t i o n , the monochromator was p laced pe rpend i cu l a r to the r e a c t i o n l i g h t a x i s i n o rder to measure the v i s i b l e r a d i a t i o n emi t ted by the gases under study (F igu re 11) . The monochromator was mod i f i ed by removing the 150 micron (y) s l i t arrangement and s u b s t i t u t i n g a 2 mm width entrance and e x i t s l i t . The entrance of the monochromator was prov ided w i th a 10 inch l o n g , 1^ inch d iameter t ubu l a r entrance mask. The monochromator-photomult ip l i e r combina-t i o n was mounted pe rpend i cu l a r to the l i g h t a x i s on a smal l s t a nd . The monochromator and p h o t o m u l t i p ! i e r system was enc losed i n two l a y e r s o f b l a c k -out c l o t h which j o i n ed the c e l l shroud i n order to reduce extraneous s i g n a l s . The monochromator motor d r i v e con t ro l was operated by an ex te rna l sw i tch arrangement when i n the emiss ion c o n f i g u r a t i o n . 2.10 The Monochromator The l i g h t e x i t i n g the r e a c t o r c e l l was c h r o m a t i c a l l y ana lyzed by a J a r r e l l - A s h one-quar te r meter f o ca l l eng th Ebert monochromator. The monochromator was f i t t e d w i th two d i f f r a c t i o n g ra t i ngs which cou ld be s e l e c t ed Figure 11. The emission conf igurat ion. 38. to cover the range 150 nm to 500 nm or 150 nm to 1000 nm. The low b l aze g r a t i n g was o p t i c a l l y coated to maximize t r ansm i s s i on a t 300 nm. The d i f f r a c -t i o n g r a t i ng s were s c r i b ed w i t h 50,000 l i n e s per inch (2360 G/rnm) and 30,000 LPI (1180 G/mm). The g r a t i n g d i s pe r s i on s of 1.65 nm/mm and 3.3 nm/mm prov ided a band-pass of 0.25 nm and 0.50 nm r e s p e c t i v e l y f o r the 150 micron s l i t w i d t h s . Dur ing emiss ion runs , the s l i t s were opened to 2 mm to prov ide a s t ronge r p h o t o m u l t i p l i e r s i g n a l . Th i s s l i t w idth a l lowed a band-pass o f 3.3 nm 0 and 6.6 nm f o r the low and h i gh -b l a ze g r a t i ng s r e s p e c t i v e l y . The monochromator wavelength d r i v e was c a l i b r a t e d w i t h the 435.8 nm b lue and 546.0 nm green Hg emiss ion l i n e s of a f l u o r e s c e n t tube. The wavelength d r i v e was operated by a rubber d r i v e b e l t from a synchronous motor f i t t e d w i t h pu l l e y s which co -o rd ina ted the d r i v e r a t e w i t h t ha t o f a Sargent cha r t r e co rde r . The spectrum cou ld be taken at any po in t i n the r e a c t i o n o r s p e c i f i c wavelengths cou ld be f o l l owed i n time throughout the r e a c t i o n . 2.11 The P h o t o m u l t i p l i e r Tube P h o t o e l e c t r i c l i g h t measurement was prov ided by an EMI 9558 QBM p h o t o m u l t i p l i e r tube . Th is tube has a t r i - a l k a l i CsNa 2KSb photocathode and 11 stages o f a m p l i f i c a t i o n . The entrance window i s s u p r a s i l and the tube combinat ion has S 20 Q extended u l t r a - v i o l e t response. The tube manufacturers c l a im a spec t r a l s e n s i t i v i t y shown in F igure 12. The tube was operated a t -800 V cathode p o t e n t i a l and a J a r r e !1 -Ash Model 385 power supply and ammeter were used w i t h a Sargent cha r t r eco rde r to record l i g h t t r a n s m i s s i o n s . During emiss ion runs , the p h o t o m u l t i p l i e r tube housing was mod i f i ed to operate the housing at cathode p o t e n t i a l i n o rde r to reduce the no i se l e v e l . The housing was i n tu rn housed i n a p o l y v i n y l c h l o r i d e enc losure and i s o l a t e d from the 28 | -W a v e l e n g t h A n m F igu re 12. Spe c t r a l response of E M I 9 5 5 8 Q B M pho tomu l t i p l y e r ( E M I ) . 40. monochromator by i n s u l a t i n g pads and ny lon screws. 1 The p h o t o e l e c t r i c l i g h t measuring system was c a l i b r a t e d by use o f a potass ium f e r r i o x a l a t e chemical ac t inometer system. 2.12 Act inometry The p h o t o e l e c t r i c l i g h t measuring system was c a l i b r a t e d d i r e c t l y by use o f the potass ium f e r r i o x a l a t e l i q u i d chemical ac t inometer developed by Hatchard and Parker [ 5 0 ] . Th is method makes use o f the s u l p h u r i c a c i d c a t a l y z ed r educ t i on of Fe to Fe by u l t r a - v i o l e t l i g h t . The Fe i s reduced +2 and the oxa l a t e o x i d i z e d . The r e s u l t i n g Fe i s de tec ted by the 1, 10-phenanthro l i ne complex which forms a red dye t ha t i s ana lyzed us ing a doub le-beam spectrophotometer a t 510 nm. L i g h t abso rp t i on by the s o l u t i o n i s very good a t wavelengths s ho r t e r than 480 nm. The quantum y i e l d i s q u i t e c o n s i s t e n t over the wavelength range o f i n t e r e s t and the s e n s i t i v i t y i s un i fo rm over l a r g e ranges o f l i g h t i n t e n s i t y and r eac t an t c on c en t r a t i o n . The s o l u t i o n s , when s to red i n the dark , are s t a b l e over a per iod o f a few weeks. 2:13 The Make-up o f Potass ium F e r r i o x a l a t e C r y s t a l s The c r y s t a l s of potassium f e r r i o x a l a t e were prepared by mix ing three volumes o f 1.5 M A.R. potassium oxa l a t e w i t h one volume 1.5 M A.R. f e r r i c c h l o r i d e wh i l e s t i r r i n g . The b r i l l i a n t green potass ium f e r r i o x a l a t e c r y s t a l s p r e c i p i t a t e d r a p i d l y and were separated by f i l t r a t i o n . The c r y s t a l s were r e c r y s t a l i z e d three t imes from warm wate r , f i l t e r e d and d r i e d i n a stream o f warm a i r . The c r y s t a l s were s to red i n g l a s s i n the dark. The .006 M a c t i n o -me t r i c s o l u t i o n was prepared under red photographic s a f e - l i g h t as f o l l o w s : 41 1. d i s s o l v e 2.947 g K 3 F e ( C 2 0 4 ) 3 • 3H 20 c r y s t a l s i n 800 ml d i s t i l l e d water 2. add 100 ml 1.0N U2S0h 3. d i l u t e to 1 % and mix we l l M-. store i n the dark ) +2 2 .14 P repa ra t i on o f the Fe C a l i b r a t i o n Graph +2 The c a l i b r a t i o n o f the Fe content as a f un c t i o n o f the 510 nm absorbance of the 1 - 10 , phenanthro l ine complex was c a r r i e d out us ing d i l u t e s o l u t i o n s o f Fe S 0 4 i n h^SOi*. The f o l l o w i n g s o l u t i o n s were prepared: 1. 0.4 x 10~ 6 M/ml FeS0 4 i n 0.1N H 2S0 4 2. 0.1% 1,10-phenanthroline monohydrate i n water 3. Buffer Solution 600 ml IN Sodium Acetate 360 ml 1 N H 2S0 4 d i l u t e d to 1 I The c a l i b r a t i o n l i q u i d s were prepared i n 50 ml vo l ume t r i c f l a s k s as f o l l ows 1. place 1, 2, 3, t , 5 * 10 ml of l i q u i d (1) i n f l a s k 2. add 25 ml - volume (1) of 0.1N H 2S0 4 to make a c i d i t y equivalent to 25 ml 0.1N H2SCH 3. Add 5 ml 1,10-phenanthroline s o l u t i o n 4. Add 12.5 ml buf f e r s o l u t i o n 5. d i l u t e to 50 ml with water and l e t stand one-half hour. The o p t i c a l dens i t y o f the orange .co loured s o l u t i o n was determined a t the +2 510 nm p la teau of the Fe phenanthro l ine absorb ing complex. The spec t r a were determined on a Unicam SP800B , double-beam spectrophotometer i n both 1 42. F igure 13. Absorbance o f Fe - 1, 10-phenanthro l ine complex at 510 nm. 4 3 . and 4 cm matched c e l l s . The c a l i b r a t i o n graph i s shown i n F igu re 1 3 , and the e x t i n c t i o n c o e f f i c i e n t was found to be 1.15 x 101* J l / M cm f o r 4 cm c e l l s and to be 1.175 x IO1* £/M cm f o r 1 cm c e l l s . 2 . 15 Deuterium L i g h t I n t e n s i t y C a l i b r a t i o n The i n t e n s i t y o f the deuter ium lamp was measured us ing a c e l l o f 1 .5 cm path l eng th f i l l e d w i th .005 M K 3 Fe (C 2 0 4 ) 3 . The ac t inomet ry c e l l ( F i gu re 14) was f i t t e d w i t h s u p r a s i l ends and an 8 .45 cm pyrex s k i r t which kept the p h o t o e l e c t r i c l i g h t measuring dev ices i n p o s i t i o n s s i m i l a r to those i n a r e a c t i o n run . A dup l i c a t e 1.5 cm path l eng th c e l l was used uni11uminated as a zero dev i c e . As can be seen from F igu re 1 5 , the 1.5 cm .006 M K 3 F e ( C 2 0 i f ) 3 c e l l absorbed 98% o f the l i g h t up to 400 nm. A b o r o s i l i c a t e g l a s s f i l t e r was used to e l im i n a t e wavelengths s ho r t e r than 300 nm (F igu re 1 5 ) . In t h i s manner the photon f l u x sho r t e r than 300 nm can be found from the d i f f e r e n c e between f i l t e r e d and u n f i l t e r e d ac t inometry r uns . The a c t i n ome t r i c c e l l s and s o l u t i o n s were p laced i n the dark room and handled under red photograph ic sa fe l i g h t . S i x ml .006 M K 3 F e ( C 2 0 4 ) 3 act inometer s o l u t i o n were p i p e t t ed i n t o both the measuring c e l l and the zero c e l l . The zero c e l l was handled i n an i d e n t i c a l manner to the measurement c e l l except f o r exposure to the u l t r a - v i o l e t l i g h t beam. Both c e l l s were p laced i n a l i g h t - p r o o f bag and t r anspo r t ed to the r e a c t o r i n the l a b o r a t o r y . The r eac to r was enc losed i n a l i g h t - p r o o f bag f i t t e d w i th e l a s t i c arm ho les through which the c e l l s cou ld be unwrapped and p laced i n t o p o s i t i o n f o r l i g h t measurement. Once i n p o s i t i o n i n the r e a c t o r , the measurement c e l l was exposed to the f u l l po lychromat i c i n t e n s i t y f o r 15 minutes by removal F igure 14. The emiss ion c e l l and ac t inometry c e l l s . 46. o f the dark s l i d e . The measurement and zero c e l l s were then wrapped i n the l i g h t - p r o o f bag and removed to the dark room. The c e l l s were emptied and r i n s ed i n t o 25 ml vo l ume t r i c f l a s k s . Three ml of b u f f e r s o l u t i o n were added as were 2 ml o f 0.1% 1,10-phenanthro l ine s o l u t i o n . The c e l l s were made up to 25 ml and l e t stand f o r one -ha l f hour i n the dark . The absorbance at 510 nm was then measured on the unicam SP800B double beam spectrophotometer w i th e i t h e r 1 cm or 4 cm c e l l s . The i n t e n s i t y o f the b o r o s i l i c a t e f i l t e r e d runs was sub t r a c t ed from the n o n - f i l t e r e d runs to g i ve the photon f l u x f o r wavelengths s ho r t e r than 300.nm. 2. 16 The G rav ime t r i c I n t eg r a t i o n Method Assessment o f the absorbed l i g h t i n t e n s i t y was done by g r a v i m e t r i c i n t e g r a t i o n o f the pho tomu l t i p l y e r i n t e n s i t y v . s . wavelength cha r t r e c o r d i n g s . Continuous mon i to r i ng o f the photon f l u x through an a i r - f i l l e d r e a c t i o n c e l l a l l owed measurement o f the d a i l y l i g h t i nput and made c o r r e c t i o n s f o r c l oud i ng o f the o p t i c a l window and f o r exhaus t ion of the deuter ium lamp. The i n t en s i t y -wave l eng th curve f o r the m e r c a p t a n - f i l l e d c e l l was superimposed on t ha t f o r the a i r - f i l l e d c e l l . That graph was then xeroxed tw i c e . The sheets were co r r e c t ed f o r paper we ight v a r i a t i o n . The analogous areas under the i npu t and output curves were cut ou t , weighed, c o r r e c t ed f o r a m p l i f i c a t i o n and the d i f f e r en c e s i n t e r p r e t e d as percentage of i n c i d e n t l i g h t absorbed by the gas . The a i r - f i l l e d c e l l read ing was used as a measure o f i n c i d e n t energy r e l a t i v e to t ha t dur ing the pe r i od o f lamp a c t i n o m e t r i c c a l i b r a t i o n . Long and sho r t wavelength c u t - o f f po i n t s were se t a t 300 nm and 150 nm. The long wavelength l i m i t was s e t by the c u t - o f f f requency o f 47 . the b o r o s i l i c a t e g l a s s f i l t e r . No r e a c t i o n was noted f o r runs us ing the b o r o s i l i c a t e f i l t e r . The sho r t wavelength l i m i t was se t to exceed the t r a n s -m i s s i on c h a r a c t e r i s t i c s o f the quar t z l e n s . 2.17 Gas Chromatography The a n a l y s i s o f su lphur con ta i n i ng gases was performed on a Va r i an model 1400 temperature-programmed gas chromatograph. De tec t i on o f the su lphur gases was accompl ished by a Meloy Labo ra to r i e s model FPD100AT f lame photometr ic de te c t o r operated by a T racor 12001 power supply and e l e c t r ome te r . The de t e c t o r and e l ec t romete r were mounted ex te rna l to the chromatograph. The f lame photometr ic de tec to r i s s e n s i t i v e to the l i g h t emi t ted from su l phu r - c on t a i n i ng compounds burned i n a reduc ing f l ame. The de te c t o r was mod i f i ed by p r ov i d i ng a p a r a b o l i c , f r o n t su r f a ce .mir ror oppos i t e the photo m u l t i p l i e r tube window and 394 nm i n t e r f e r e n c e f i l t e r . Th is had the e f f e c t of i n c r e a s i n g s e n s i t i v i t y . The 6 cm f o ca l l ength f r o n t su r f a ce m i r r o r was p laced so t h a t the f lame would be a t i t s f o ca l p o i n t . The m i r r o r was separated from the burn ing chamber by a pyrex window which passed the l i g h t to the phototube. The e n t i r e de tec to r was surrounded by f i b e r g l a s s wool and asbestos packing mate r i a l to t he rma l l y i n s u l a t e the b l o c k . The de te c t o r was mounted on the s i de of the gas chromatograph. Chromatograph column e f f l u e n t was t r a n s f e r r e d from the column to the de te c t o r by a t e f l o n column f i l l e d w i t h T r i t o n X-405 adsorbed on chromosorb W. The t r a n s f e r l i n e was e l e c t r i c a l l y heated and i n s u l a t e d to p rov ide a minimum impedance to passage of e f f l u e n t gases . Th is l i n e was mainta ined a t 80°C. The i n j e c t i o n b lock o f the chromatograph was f i t t e d w i th a t e f l o n i n j e c t o r l i n e r to min imize the s t a i n l e s s - s t e e l - c a t a l y z e d decompos i t ion o f CH 3SH. F i gu re 16. The gas chromatograph and f lame photometr i c d e t e c t o r . 50. The chromatograph columns were f a b r i c a t e d o f 1/8" O.D. heavy-wal l t e f l o n tub ing to min imize wa l l r e a c t i v i t y and permeation o f the w a l l . T e f l o n columns were found to o f f e r performance equal to g l a s s , to be e a s i e r to f i l l and were s i g n i f i c a n t l y more du rab l e . The columns were a t tached to the chromato-graph by t e f l o n swagelock f e r r u l e s and s t a i n l e s s s t e e l swagelock caps . The tubes were prevented from c o l l a p s i n g by the i n s e r t i o n o f a 1" l eng th o f 16-guage s t a i n l e s s t ub ing i n s i d e the column where the swagelock f e r r u l e compressed i t . Th i s procedure was fo l lowed a t each column j o i n t from the i n j e c t i o n b lock to the t r a n s f e r l i n e and i n t o the d e t e c t o r . Numerous columns were used dur ing the work. These i n c l uded : s i l i c o n e gum rubber SE-30 10% T r i C r e s y l Phosphate 20% T r i t o n X-405 20, 30, 40% A c i d Washed D e a c t i g e l 40/60 mesh Carbopak BHT-100 • The most use fu l column was found to be Carbopak BHT-100 i n 9 f e e t o f t e f l o n tube. Th is p rov ided e x c e l l e n t s epa ra t i on o f H 2 S , CH 3SH, CH3SCH3 and S 0 2 . The C H 3 S S C H 3 was r e t a i n ed on the column a t 65°C f o r an extended t ime , so temperature programming was employed. The Carbopak i s a hydrogen-reduced, a c t i v a t ed - ca rbon porous ma te r i a l w i t h no l i q u i d phase to desorb . The column can be run e a s i l y to 100°C and i s l i m i t e d ma in ly by the nature o f the column w a l l m a t e r i a l . Temperature programming was employed to remove the d i s u l p h i d e s a t the end o f each day ' s r uns . The v a r i a t i o n o f r e t e n t i o n t ime w i t h f l ow ra t e and temperature i s shown i n F igu re 17. The c ond i t i o n s s e t t l e d upon, f o r ope r a t i on were: 51 . column temperature 65°C prog, to 100°C @ 20°C/mln He 20 ml/min 20 A i r 20 250 Transfer l i n e 80°C de t e c t o r 140°C i n j e c t o r 70°C 2.18 Chromatograph C a l i b r a t i o n Procedure The chromatograph was c a l i b r a t e d d a i l y s i n ce l a r ge d a i l y v a r i a t i o n s were no t i ced a t e s s e n t i a l l y i d e n t i c a l c o n d i t i o n s . The f l ow ra tes o f He c a r r i e r gas, a i r , 0 2 , and H 2 were ad jus ted us ing bubble tube f low meters a t an oven temperature of 65°C w i t h the de te c to r f lame u n i g n i t e d . The i n j e c t i o n septum was a Hami l ton 75804 t e f l o n - f a c e d s i l i c o n e rubber septum. The t e f l o n face min imized septum b leed and septum con tamina t i on . G lass sample b o t t l e s were f a b r i c a t e d which were c l o sed by a t e f l o n - f a c e d septum he ld i n p lace by mod i f i ed tube f i t t i n g s sea led to the g lass b o t t l e s w i th epoxy cement ( F i gu re 16 ) . Hami l ton t e f l o n - t i p p e d g a s - t i g h t sy r i nges w i th Cheny adapters were used to prov ide a sample volume o f e i t h e r 0.1 ml o r 0.25 m l . The sample s i z e was chosen a p p r o p r i a t e l y f o r the su lphu r gas concen t r a t i on which was to be examined i n the r e a c t i o n v e s s e l . Gas concen t ra t i ons i n the fou r sample b o t t l e s were ad jus ted to span the range under c o n s i d e r a t i o n . • Samples were i n j e c t e d every f i v e minutes i n order to maximize r e p r o d u c e a b i l i t y f o r g iven c on cen t r a t i o n s . A minimum o f th ree rep.roduceable . 5 2 F igure 18. Chromatograph s t anda rd i z i ng b o t t l e s and Hamilton s y r i n g e s . 53. po i n t s were taken to ob ta i n one c a l i b r a t i o n p o i n t . A t y p i c a l d a i l y c a l i b r a -t i o n i s shown f o r CH 3SH i n F igure 19 and i n F i gu re 20 f o r S 0 2 . The i n t e n s i t y of response f o r S 0 2 was much g rea te r than tha t f o r CH 3SH. The S 0 2 c a l i b r a -t i o n i s a s t r a i g h t l i n e . The CH3SH c a l i b r a t i o n i s not a s t r a i g h t l i n e and as can be seen from F igure 19 the response tends to l e v e l o f f a t h igher l e v e l s o f CH 3SH. The p l a teau can l ead to i nac cu ra te ana lyses i f one shou ld c a r r y out the e n t i r e r e a c t i o n i n the p l a teau r e g i o n . For t h i s reason the sample volumes of the s y r i nge were ad jus ted to keep the a n a l y s i s o f va ry i ng c e l l concen t ra t i ons i n reg ions of adequate response s e n s i t i v i t y . F igure 19. Typ i ca l d a i l y c a l i b r a t i o n curve f o r CH3SH (0.1 ml.sample) Jan 11, 1977; Carbopak BHT 100. He = 20 m l /m in . ; 0 2 = 20 m l /m in . ; A i r = 20 m l /m i n . ; H 2 = 250 m l /m in . ; T = 65°C. F igure 20. SO* c a l i b r a t i o n Dec. 18/76, Carbopak BHT-100. He = 20 m l /m in . ; 0 2 = 20 m l /m in . ; A i r = 20 m l /m in . ; H 2 = 250 m l /m in . ; T = 65° C. 56. Chapter 3 E X P E R I M E N T A L R E S U L T S A N D D I S C U S S I O N O F P H O T O -O X I D A T I O N O F S U L P H I D E S 3.1 P r e l i m i n a r y Experiments The pho to -ox i da t i on exper iments were c a r r i e d out i n 40 ml pyrex r e a c t i o n vesse l s equipped w i t h Sup ras i l entrance and e x i t windows. The r e a c t i o n c e l l was f l u shed w i t h . d r y , b o t t l e d , compressed a i r which was passed o through d r i e r i t e , a bed of mo lecu la r s i e ve 5 A , and a Whatman gas f i l t e r to remove water , o i l vapours and p a r t i c u l a t e ma t t e r , r e s p e c t i v e l y . A t r an sm i s s i on spectrum o f the a i r - f i l l e d c e l l was run be fo re the su lph ide a d d i t i o n i n order to prov ide a measurement o f i n c i d e n t l i g h t i n t e n s i t y and to p rov ide a bas i s f o r the measurement o f the amount of l i g h t absorbed by the added su lphur gas. A second t r an sm i s s i on spectrum was run upon commencement o f the photo-r e a c t i o n i n o rde r to measure the absorbed photon r a t e . The absorp-t i o n was found to be a f u n c t i o n o f mercaptan c oncen t r a t i on i n the r e a c t i o n atmosphere. The percentage l i g h t (A < 300 nm) abso rp t i on of the a i r -mercaptan mix ture i s shown i n F i gu re 21 as a f u n c t i o n of the weight o f CH3SH added to a 40 ml r e a c t i o n c e l l . The 58. absorbance o f 10 cm o f a i r was not n o t i c e ab l y d i f f e r e n t from t ha t of pure N2. Th i s i s due to the f a c t tha t the qua r t z lens o f the c o l l i m a t i o n system d id not pass s i g n i f i c a n t i n t e n s i t y a t wavelengths sho r t e r than 185 nm. The amount o f l i g h t t ha t one would expect a i r to absorb may be c a l c u l a t e d from the abso rp t i on c o e f f i c i e n t o f 0 2 . A t 190 nm the l og o f the abso rp t i on c o e f f i c i e n t o f 0 2 i s -2 a t m - 1 c m - 1 [ 5 9 ] . Thus one would expect 0 2 to absorb 4.5% of the i n c i d e n t energy a t 190 nm. As one approaches the i n c i d e n t energy maximum at 220 nm, the l og of the abso rp t i on c o e f f i c i e n t o f 0 2 drops to -4 and the adsorbed i n t e n s i t y drops to 0.046% f o r a 0.2 atm pressure of 0 2 f o r a 10 cm path l e ng t h . The concen t r a t i on of mercaptan i n the c e l l s was measured by gas chromatography and the chromatograph was c a l i b r a t e d d a i l y f o r CH 3SH and S 0 2 . Dur ing an exper iment , the c e l l was exposed to i r r a d i a t i o n f o r a 30 minute p e r i o d . Immediately a f t e r the s t a r t o f a r un , as soon as the second abso rp t i on curve was completed, the monochromator was se t to con t i nuous l y mon i tor the t r ansm i s s i on at 290 nm. Th is frequency was l a r g e l y f r e e from abso rp t i on by mercaptan and showed a l i n e a r decrease i n t r ansm i s s i on w i t h t ime dur ing the r e a c t i o n . The decrease was due to the p roduc t i on o f C H 3 S S C H 3 and S 0 2 which absorb at the 290 nm wave length. 3.1.1 The E f f e c t o f Us ing Room A i r E a r l y exper iments were performed us ing a i r taken from the l a bo r a t o r y atmosphere. The ra tes o f r e a c t i o n measured from exper iments performed i n t h i s way proved to be h i g h l y s c a t t e r e d . Traces o f vapours from l a b o r a t o r i e s were r e spons i b l e f o r i n t e r f e r i n g w i th the photochemical r e a c t i o n . The l a c k o f 59. r e p r o d u c e a b i l i t y was reduced by us ing d r i e d , f i l t e r e d , b o t t l e d a i r to f l u s h the r e a c t i o n c e l l s and to prov ide the r e a c t i n g atmosphere. 3 .1.2 The E f f e c t o f Wet A i r Undr ied atmospher ic a i r was used f o r a number o f i n i t i a l r uns . These exper iments proved to be h i g h l y v a r i a n t and gave a low r a t e o f reac t i on . . . The high v a r i a t i o n and l a ck o f data regard ing H 20 content prevent meaningful c o r r e l a t i o n o f the r e a c t i o n r a t e s w i th water con ten t . I t i s apparent from the ob se r va t i o n s , however, tha t water vapour i n h i b i t s the mercaptan o x i d a t i o n r e a c t i o n . 3.1.3 The E f f e c t o f Pure Oxygen A s e r i e s o f r e a c t i on s were c a r r i e d out us ing an atmosphere c on t a i n i ng 100% oxygen i n s t ead of a i r . The s e r i e s was intended to revea l the r o l e p layed by 0 2 abso rp t i on as a p h o t o - i n i t i a t o r of. the r e a c t i o n sequence. The f i v e -f o l d i n c rease i n 0 2 c oncen t r a t i on would r e v e a l , through an i n c rease i n r e a c t i o n r a t e , the importance o f oxygen as a r a t e c o n t r o l l i n g parameter. The quantum y i e l d i n a i r f o r tha t sequence of exper iments was 11.8 ± 4 . 7 . The quantum y i e l d of experiments performed a t i d e n t i c a l CH3SH concen t ra t i ons i n dry 0 2 was 8.5 ± 2 . 1 . These two y i e l d s are not s i g n i f i c a n t l y d i f f e r e n t . The l a ck o f s i g n i f i c a n t r a te i n c rease demonstrates t ha t l i g h t abso rp t i on by 0 2 i s not the major i n i t i a t i n g pho to-p rocess . Hence, one may conc lude tha t an o zono l y s i s r e a c t i o n w i t h CH3SH i s not a major r a t e c o n t r i b u t i n g r e a c t i o n . Th is r e s u l t suggests t ha t those r e a c t i o n s which i n vo l v e mo lecu l a r oxygen as a r e a c t i o n pa r tne r are a l r eady ope ra t i ng a t a maximum r a t e i n the 60. atmospher ic concen t ra t i on of 0 2 (8.17 x 1 0 " 3 M ) . Thus there i s no b e n e f i t to be gained by ope ra t i ng i n pure 0 2 . 3.2 Resu l t s I n vo l v i ng Quantum Y i e l d s o f Removal of Su lph ides The major purpose o f t h i s work was to examine the photo r e a c t i o n s of odorous su lph ides and to determine the quantum y i e l d o f removal o f the su lph ides CH 3SH, CH 3SCH 3 and CH 3 SSCH 3 . The quantum y i e l d i s de f i ned as the number of molecules o f r eac tan t removed per photon absorbed by the gas m i x t u r e . , _ no. o f molecu les decomposed ^ no. o f photons absorbed 3.2.1 The Quantum Y i e l d of CH3SH Removal The mo lecu la r r a t e of CH3SH removal i s a l i n e a r f u n c t i o n o f the r a t e of photon abso rp t i on ( F i gu re 22) . Th is l i n e a r i t y would be expected o f a r e a c t i o n which i s induced by mercaptan photon a b s o r p t i o n . The l i n e bes t f i t t i n g these po i n t s y i e l d s a s lope o f 13.9 which i n d i c a t e s an average quantum y i e l d o f 13.9 molecu les of mercaptan removed per photon absorbed. The average s tandard d e v i a t i o n o f the quantum y i e l d s i s 4.03 (29%)'. The s lope o f 13.9 represents the data we l l w i t h i n one s tandard d e v i a t i o n . The po i n t 0, 0 has been i nc luded s i n c e the r e a c t i o n i s i n i t i a t e d by abso rp t i on o f energy by the su l ph ide mo lecu le . At C> 0 there i s no a b s o r p t i o n , hence no r e a c t i o n . The s lope o f the l i n e i s l i n e a r a t very low concen t ra t i ons s i n c e the main cha in -p ropagat ing spec ies are i n vo l v ed more w i t h oxygen - and hence are i n t e r a c t i n g w i t h a r eac tan t a t a constant concen t r a t i on - than w i t h su lphu r con ta i n i ng spe c i e s . Thus the cha in e f f e c t w i l l be ope ra t i ng a t normal r a t e F igu re 22. Mo lecu la r r e a c t i o n r a t e of CH3SH v s . photon abso rp t i on r a t e . 62. even a t low su l ph i de c on c en t r a t i o n . Th is po in t w i l l be f u r t h e r covered i n the cha in mechanism d i s c u s s i o n . The r e a c t i o n r a t e can be desc r i bed as a l i n e a r f u n c t i o n o f the range of CH3SH concen t ra t i ons s t ud i ed (2.67 x IO " 6 g/ml to 13.37 x I O - 6 g/ml o r 5.56 x I O " 5 M to 2.78 x IO"1* M). R_ S H = 13.9 l a - 1.44 x 1 0 1 7 mo lecu l es /h r ^ SH = m o ^ e c u ! a r r a t e o f CH3SH decompos i t ion l a = absorbed photon i n t e n s i t y $ s s = quantum y i e l d o f C H ^ S S C H . ^ appearance The major s u l p h u r - c o n t a i n i n g products were su lphur d i o x i d e , d imethyl d i s u l p h i d e and an o i l y y e l l ow l i q u i d which was depos i ted p r i m a r i l y about the entrance area o f the i n s i d e o f the r e a c t o r c e l l . The pho to -exc i t ed mercaptan molecu le forms a methyl t h i y l r a d i c a l which subsequent ly o x i d i z e s o r which may combine w i th another methyl t h i y l to form dimethyl d i s u l p h i d e . The quantum y i e l d o f decompos i t ion o f CH3SH was found to be as shown i n Tab le 5. $ q n = quantum y i e l d o f S 0 9 a p p e a r a n c e . Tab le 5 Quantum Y i e l d s i n C H - S H P h o t o l y s i s [CH SH] x.10 M I e i n s . i n 1 0 a - T — — xlO 1 s - S H a N s o 2 S S 5.56 9.29 8.28 2.22 10 — -8.35 9.31 12.19 2.03 4 - -11.1 20.7 12.73 4.01 11 - -11.1 14.6 12.61 4.53 28 - -11.1 18.6 15.13 4.43 <9 2.35 5.09 16.7 19.3 9.79 5.18 10 - -27.8 40.17 12.91 2.07 13 1.58 4,14 Average 11.97 4 .16 85 63. A quantum y i e l d i n excess of 1 must i nvo l ve a cha in r e a c t i o n mechanism to cont inue the r e a c t i o n beyond the i n i t i a l p h o t o - e x c i t a t i o n . Low pressure photo lyses o f CH3SH i n the absence o f 0 2 i n d i c a t e d a quantum y i e l d of 1.7 when ex t r apo l a t ed to zero pressure ( 1 , 18 ) . When oxygen i s p re sen t , i t appears to be i nvo l ved i n the cha in propagat ing sequence. The r ea c t i on s i n Table 6 are proposed to e x p l a i n the r e a c t i o n o f CH 3SH and the appearance of observed photoproducts . The proposed r a t e s . o f r e a c t i o n are based on a r e a c t i o n t ak i ng p lace i n a i r c on t a i n i ng 20% 0 2 (8.17 x 1 0 " 3 M). The sample concen t ra t i on i s chosen based on 150 u& o f methyl mercaptan i n a 40 ml r e a c t i o n c e l l , which i s equ i va l en t to 1.53 x 10 - 1* M. React ions i n v o l v i n g atomic oxygen have been c a l c u l a t e d assuming tha t the atomic oxygen concen t r a t i on i s I 0 ~ 1 3 t h e concen t r a t i on o f mo lecu la r oxygen. 3.2.1.1 The I n i t i a t i o n React ions I t i s proposed t ha t the i n i t i a l r e a c t i o n i nvo l ve s p h o t o l y t i c s c i s s i o n o f methyl mercaptan ( 3 T 1 , 3-2) i n t o a methyl t h i y l r a d i c a l and hot hydrogen atom, o r i n t o a methyl r a d i c a l and a mercaptan r a d i c a l . These r e a c t i o n s have been we l l documented i n the l i t e r a t u r e ( 1 , 2 , 3 , 4 , 5 , 6 , 7 , 1 0 , 1 1 , 1 4 , 1 5 , 1 6 , 17 ,18 ,19 ,21 ,26 ,27 ,28 ) . React ion 3-1 has been found to predominate a t the wavelengths o f t h i s i n v e s t i g a t i o n and g rea te r than 90% of the i n i t i a t i o n r eac t i ons may be expected to occur i n t h i s manner. React ion 3-2 does o c cu r , e s p e c i a l l y a t s h o r t e r absorbed wave lengths. The photo-products o f these i n i t i a t i n g r eac t i ons prov ide the spec ies to form a r e a c t i o n cha in which i s r e spons i b l e f o r f u r t h e r CH3SH decompos i t i ons . 64. Table 6 Reactions Involved in the Photolytic Oxidation of Methyl Mercaptan IHITIATION 1. IH3SH + hv ->• CH3S + H z. 0 H 3 S H + hv ->• CH, + SH &Hfj9B kcal/mol. Rate Constant >.9 Relative Rate of Reaction j . 4. b. b. RtMlTIUNS INVOLVING H ATOMS H + C H 3 S H - H 2 + C H 3S H + U2 + M + H00 + M H + 0 + H H - H O + M H + C H 3 •* C H * -18.5 -47. -102.1 -104.7 1 -1 - t 2.71 x' 10 M s 1.99 x 1010 7.24 x 10' H R= 4.1 xlo'[H] s 1 R = 6.65 x IO6 [H] s-1 R = low due to low [0] • [H] product . P. = low due to low [H] • [CH3Jp-oduct REACTIONS INVOLVING THE CH3S RADICAL 7. CH3S + U2 -» C H 3 O + SO a. CH3S + 0 -<• CH3 + SO 9. CH3S + CH3S + M •* CH3SSCH3 + M 10. CH3S + CH3O - CH3SOCH, 11. CH3S + C H 3 O O - CH3SOOCH, -25.3 -53.6 -47.6 8.39 X 10 M*s" 1.3 x 10 Ms 2.5 x 1010 .' M-1 6.86 [CH3S] s"1 1. x 10"9 [CHjS] s 1 2.5 x IO10 [CH3S]2 S-1 - low - low REACTIONS INVOLVING THE CH30 AND CH3OO  RAUICALS 12. CH3O + 02 •+ HCHO + HOO 13. C H 3 O + IH3SH - CH3OH + CH3S 14. CH3OU + CH3SH - CHsOOH + CHjS -26.2 -18.1 4.5 x 105 M-1 s-1 R =3.26 x 10 [CHjO] S"1 R = lower than 12 since [CH3SH] < [02] REACTIONS INVOLVING HOO RADICALS 15. HOO + CH3SH - HOOH + CH3S 1 6_ HOU + S02 -<• SO3 + HO 3.36 19. s .1-1 1.15 X 10 M 3 5.4 x lo't-fs" 1 R = 17.6 [HOO] s R = lower than 15 since [S02] < [CH3SH] REACTIONS INVOLVING CH3 RADICALS 17. CH3 + 02 + H - CH300 + H 18. CH3 + 0 - HCHO + H 19. C H 3 + CH3SH - CH* + CH3S -70. -19.2 1 x 10' H-1 s-1 6 x 10" H-1 s-1 1.8 x 10" M-1 s-1 R = 8.17 x 106 [CH3] s-1 R = 4.9 x 10 [CH,] s-1 R = 2.75 [CH3] s-1 REACTIONS INVOLVING ATOMIC 0 RADICALS 20. 0 + C H 3 S H * CH3S + OH HI. O + U + M+ O 2+M 22. 0 + 02 + M •* Oj + M -16.6 -119.1 -24.9 2 x 10' to 9 x IO 1 0 I M-1 s-3.8 x 108M s 1.96 x 10" M"2 s-1 R = 3.06 x 10s [0] to 1.37 x 10' [0] s-1 R = low due to low [0]2 R = 6.54 x 10* [0] s-1 REACTIONS INVOLVING SO RADICALS 23. SO + 02 •» S02 + 0 24. SO + 0 -f S02 -13.03 -59.72 1.5 x 10" H-1 s-1 no recommendation R = 1.22 x 102 [SO] s" REACTIONS INVOLVING SH RADICALS 25. SH + 02 - SO + OH 26. SH + 0 -i- SO + H -25.5 -40.5 < 6 x 10' : M"1 s 1 9.6 x IO1" M-1 s-1 R = 4.9 x 10s [SH] R = 7.8 X 10' [SH]. OTHER REACTIONS 27. CHjSSCHj + hv ->- 2CH3 + S2 28. OH + C H 3 S H -<- H20 + CH,S 29. 2 HOO -* HOOH + 0, 10 .1.1 1.0 X 10 M s 2.0 x I O ' I M S " Basis: [M] = 4.09 x IO"2 M [CH3SH] = 150 pl/cell = 1.53 x 10"* M [02] = .2 Atm = 8.17 x 10"' M [0] = 1 x IO"" [02] 65 . 3 .2 .1 .2 React ions I nvo l v i ng H Atoms The hydrogen atom generated i n 3-1 i s a very r e a c t i v e s p e c i e s . The atom w i l l c on ta i n a g rea t deal o f k i n e t i c energy f o r the f i r s t few c o l l i s i o n s f o l l ow i n g l y s i s . The atom may r eac t w i t h CH 3SH, 0 2 , 0 or CH3 i n the r e a c t i o n atmosphere. The a b s t r a c t i o n of the su lphyd ry l hydrogen atom from methyl mercaptan (3-3) has been desc r i bed i n the l i t e r a t u r e ( 3 , 6 , 1 0 , 1 1 , 15 ,17 ,18 ) . H + CH3SH -»- H 2 + CH 3S (3-3) AH f = -18 .5 kcal/mol S tee r and Knight [10] found the a b s t r a c t i o n r a t e to be independent of tem-pe ra tu re . They photo lysed CH3SH i n the presence o f e thy lene [ 1 0 ] . The hydrogen atom was found to add to e thy lene as we l l as t o . en te r i n t o ( 3 - 3 ) . The r a t i o of the metathes is to H + C 2 h\ -> C 2 H 5 k = 1.17 x 10 8 M- 1 s - 1 t h e add i t i on ,was found to be 2.32 ± . 11 . Th is r a t i o was found to be indepen-dent o f e thy lene pressure up to 200 t o r r . P r a t t and Veltman (62) determined the ra te constant f o r the r e a c t i o n o f hydrogen atoms w i th e thy l ene . At 295°K 8 the ra te constant was determined to be 1.17 x 10 M _ 1 s . Thus the r a t e constant f o r (3-3) w i l l be . k 3 = 2.32 (1.17 x 10 8 ) = 2.71 x 10 8 M" 1 s " 1 \ This would imply a r a t e o f r e a c t i o n o f - i R3 = 2.71 x 10 8 (1.53 x 10"" M) [H] = 4.14 x 10" [H] s The hydrogen atom i s more l i k e l y to r ea c t w i t h oxygen molecu les i n the atmosphere because o f the h igh 0 2 c on c en t r a t i o n . H + 0 2 + M - HOO + M k = 1.99 x 1 0 1 0 .2 s - l (3-4) Hampson and Garv in [52] suggest a b imo l e cu l a r r a t e constant o f k = 6.42 x 10 9 M~2 s _ 1 measured i n argon gas. They suggest t ha t a i r ( 0 2 + N 2) i s 3.1 t imes as e f f i c i e n t a medium f o r forming the HOO r a d i c a l . Thus a r e a c t i o n r a t e constant o f k = 1.99 x 1 0 1 0 I2 M~2 s _ 1 i s suggested f o r a i r . Now t h i s r a t e of r e a c t i o n i s governed by the concen t ra t i ons o f the r e a c t i n g spec ies and a l s o of a i r . Ri. = k 4 [H] [ 0 2 ] [M] We do not know the hydrogen atom concen t r a t i on so i t w i l l be necessary to compare ra tes by f a c t o r i n g out the hydrogen acorn c on c en t r a t i o n . Thus fl .99 x 1 0 1 0 1 M 2s 8.179 x TO" 3 M"1 f4.09 x 1 0 " 2 Ml = 6.65 x 10 6 [H] — s 67. where k 4 = 1.99 x 1 0 1 0 M - 2 s " 1 [ 0 2 ] = .2 atm @ 25°C = 8.179 x 1 0 " 3 M [M] = 1 atm @ 25°C = 4.09 x 1 0 " 2 M Th is r a t e i s 2.64 times the r a t e f o r (3-3) which i s a minimum s i n ce the r a t e o f r e a c t i o n (3-3) was e s t a b l i s h e d as an upper l i m i t . The presence o f a CH 3 group on the mercaptan would l i k e l y decrease the r a t e of (3-3) s u b s t a n t i a l l y . The r e a c t i o n o f a hydrogen atom w i t h atomic oxygen (3-5) i s very exothermic (AH f = -102.1 k c a l /mo l ) . The a v a i l a b l e data on t h i s atomic r e a c t i o n i s based on temperatures i n the range 1000 3000 ° K [ 5 2 ] . H + 0 + M - 0 H + M (3-5) A H f = -102.1 kca l /mol k ~ 7.24 x 10 9 M" 2 s - M n Ar Th i s r e a c t i o n i s not a major s i nk f o r hydrogen atoms due to the low concen-t r a t i o n o f oxygen atoms which are i n the atmosphere. The r a t e o f t h i s r e a c t i o n may be est imated assuming an atomic oxygen concen t r a t i on 1 0 - 5 t ha t o f mo lecu la r 0 2 . R = k 5 [H] [0] [M] f7.24 x 10 9 M 2s f8.17 x TO" 8 Ml 4.09 x l O " 2 Ml [H] 2.4 x 10 1 [H] Th is r a t e i s i n s i g n i f i c a n t r e l a t i v e to o the r H atom r e a c t i o n r a t e s . 6 8 . The r e a c t i o n o f atomic hydrogen w i th the methyl r a d i c a l (3-6) i s a l s o very exothermic . H +• CH 3 + CJ-U (3 -A H f = -104.7 kcal/mol There i s no r e a c t i o n ra te data a v a i l a b l e f o r t h i s r e a c t i o n . The r a t e , however l a r ge the r e a c t i o n r a t e cons tan t , w i l l depend upon the concen t r a t i on product o f two very l ow-concen t ra t i on r a d i c a l s . Th is i s a f a c t o r which removes r e a c t i o n (3-6) as a major s i n k f o r H atoms. The major s i nk f o r hydrogen atoms i s most l i k e l y r e a c t i o n ( 3 - 4 ) . Th is r e a c t i o n generates the hydrogen peroxy r a d i c a l which i s a very r e a c t i v e s p e c i e s . The HOO r a d i c a l w i l l r eac t w i th reduced spec ies i n the r e a c t i o n gas m i x t u r e . 3 .2 .1 .3 React ions I nvo l v i ng the Methyl T h i y l Rad ica l The methyl t h i y l r a d i c a l i s the spec ies most c l o s e l y i nvo l ved i n the o x i d a t i o n sequence o f su lphur to S 0 2 . The o x i d a t i o n r e a c t i o n appears to occur i n two s t e p s . The f i r s t i s the fo rmat ion o f SO a f t e r which the SO i s more s l ow ly o x i d i z e d to S 0 2 [ 15 , 16 ] . C a l l ear and D i ck inson [5] showed t ha t the presence o f 10 t o r r 0 2 suppressed the 215.8 nm abso rp t i on band of the CH 3S r a d i c a l 5 micro-seconds a f t e r f l a s h i n g the CH 3 SH. They d i d not i n v e s t i -gate the S 0 2 bands,however t h i s d i d i n d i c a t e a r a p i d r a t e o f r e a c t i o n o f the CH 3S r a d i c a l w i th 0 2 mo lecu l e s . A two-step sequence f o r the o x i d a t i o n o f H 2S by f l a s h pho t o l y s i s has been suggested [ 35 , 36 , 38 , 40 ] . McGarvey and McGrath [35] observed the o x i d a t i o n o f H 2S under f l a s h p h o t o l y t i c c o n d i t i o n s . The 69. f l a s h was found to r a p i d l y produce SO abso rp t i on bands which were c h a r a c t e r i z e d by a broad-band abso rp t i on spectrum extend ing from 200 nm to 250 nm. A Lyman d i s charge was used as the source of background continuum f o r the abso rp t i on spec t roscopy . A f t e r one m i l l i s e c o n d , the broad bands o f SO were s t i l l p resent and S0 2 abso rp t i on bands were beg inn ing to appear. The 1ong-1ived nature o f the SO abso rp t i on bands suggests a slow t r a n s i t i o n from the SO to the S 0 2 . No r r i sh and Ze lenberg [40] found H 2S combustion to form S 2 0 2 which was the s t a b l e form o f SO at room temperature. The S 2 0 2 l a t e r formed S 0 2 . The sequent i a l o x i d a t i o n o f the s u l phu r - c on t a i n i ng spec ies CH 3S and HS i s t he r e f o r e pos tu l a t ed f o r t h i s p h o t o l y t i c o x i d a t i o n . Due to the h igh concen t r a t i on o f 0 2 , the ma j o r i t y o f the o x i d a t i o n r e a c t i o n i s accompl ished by r e a c t i o n ( 3 - 7 ) . CH 3S + 0 2 ->- CH 30 + SO AH f = -25.3 kca l /mol The o x i d a t i o n r a t e constant f o r r e a c t i o n (3-7) may be es t imated by com-par ing the o x i d a t i o n r a t e to the r a t e o f recombinat ion of CH 3 S. By e s t ima t i ng the r a d i c a l concen t ra t i on from the known r a t e o f CH 3SSCH 3 f o rma t i on , and from the product balance (73% d i s u l p h i d e ) the r a t e constant f o r CH 3S o x i d a t i o n may be eva lua ted r e l a t i v e to the recombinat ion ra te cons tan t . A d e t a i l e d c a l c u l a -t i o n may be found i n Appendix H. k 7 = 8.39 x 1 0 2 M s - 1 R 7 = (8.39 x 10 2 ) (8.17 x l O " 3 M) [CH 3 S] = 6.86 [CH 3 S] (3-7) 70. A secondary mechanism f o r su lphur o x i d a t i o n i s t ha t due to atomic oxygen ( 3 - 8 ) . , CH 3S + 0 - CH 3 + SO (3-8) AH^ = -53.6 kcal/mol k 8 = 1 .34 x 10 6 NT.1 s " 1 There i s no d i r e c t measurement f o r t h i s r e a c t i o n r a t e cons tant but the analogy may be made to the o x i d a t i o n o f HS: HS + 0 - H + SO k =' 9.63 x 1 0 1 0 M"1 s " 1 [52] The ra te o f the methyl su l ph i de o x i d a t i o n may be s lower by a r a t i o s i m i l a r to the speed r a t i o o f the mo lecu la r oxygen o x i d a t i o n o f CH3S to t ha t o f HS. The r a t i o i s 8.4 x 10 2 M s " 1 ( t h i s work) to 6 x 1 0 7 M s " 1 [ 5 2 ] . Th is would suggest a k 8 va lue o f 1.34 x 10 6 from which f o r [0] = 1 0 " f 3 [ 0 2 ] 8 - 4 . x ]°* f 9 . 6 x I O 1 0 6 x 1 0 7 R 8 = 1.0 X . 1 0 9 [ C H 3 S ] s"1 The methyl t h i y l r a d i c a l may escape o x i d a t i o n t empo ra r i l y by com-b i n i n g w i t h another CH 3S to form CH 3 SSCH 3 . CH 3S + CH 3S + M - C H 3 S S C H 3 + M (3-9) k 9 = 2.5 x. 1 0 1 0 M^s- 1 ' Dimethyl d i s u l p h i d e i s found as the major product and t h i s r e a c t i o n must have a very high ra te cons tant c ons i de r i ng the low concen t r a t i on o f the 71. C H 3 S r a d i c a l . A r a t e constant f o r su lphur atom recombinat ion has been suggested by Hampson and Garv in [52] S + S + M-*-S 2 + M we assume k = 2.5 x 1 0 1 0 M s - 1 k Z 4.09 x 1 0 1 0 M" 1 s - 1 i n 1 atm. [M] [52] Th is would appear to suggest a r a t e based on [ C H 3 S ] which would be qu i t e s m a l l . The ac tua l r a t e must be severa l t i m e s t h a t o f the o x i d a t i o n r e a c t i o n s i n c e a su lphur mass balance i n d i c a t e d tha t CH3SSCH.3 accounted f o r 73% of the reac ted CH3SH su lphur atoms whereas 16.8% of the reac ted su lphur atoms appeared as S0 2 (Table 11 ) . The C H 3 S r a d i c a l can r eac t w i t h e i t h e r the methoxy or the methyl peroxy r a d i c a l to form CH 3S0CH 3 and CH 3S00CH 3 (3 -10 , 3-11) . CH 3S + C H 3 0 - C H 3 S O C H 3 CH 3S + CH 300 - CH 3S00CH 3 The ra te o f fo rmat ion of these compounds w i l l undboutedly be low s i n ce i t w i l l be p ropo r t i ona l to the product o f two low r e a c t i v e r a d i c a l concen t ra -t i o n s . Chromatographic a n a l y s i s f a i l e d to show the presence o f e i t h e r o f these compounds. (3-10) (3-11) 72. 3 .2 .1 .4 React ions I nvo l v i ng the Methoxy and Methyl Peroxy Rad i ca l s The methoxy r a d i c a l i s formed i n the CH 3S o x i d a t i o n (3-7) and by decay o f the CH 300 r a d i c a l . The major source i s ( 3 - 7 ) . The CH 30 may r ea c t w i t h e i t h e r 0 2 o r CH3SH - the molecu les o f g r ea t e s t c oncen t r a t i on (3-12, 3-13) . CH 30 + 0 2 - HCHO + HOO (3-12) k i 2 = 4.0 x 10 5 M" 1 s - 1 [61] CH 30 + CH 3SH + CH30H + CH 3S (3-13) AH f = -18.1 kcal/rnol The r a t e constant o f k J 2 4.0 x 10 5 ; M - 1 s - 1 was s e l e c t ed by Adachi and James [61] f o r r e a c t i o n (3-12) a t an oxygen pressure o f one atmosphere. A t an oxygen concen t r a t i on i n a i r o f 8.17 x 1 0 - 3 M, the r a t e of r e a c t i o n (3-12) may be expected to be 3.26 x 1 0 3 [CH 3 0] s " 1 . There i s no data upon which to base a r e a c t i o n r a t e es t imate f o r ( 3 - 13 ) . The r e a c t i o n r a t e i s l i k e l y lower than (3-12) because the concen t ra -t i o n o f CH3SH i s lower than t ha t o f 0 2 . The methyl peroxy r a d i c a l i s formed from the o x i d a t i o n of methyl r a d i c a l s generated by r ea c t i on s ( 3 - 2 ) , (3-8) and (3 -27 ) . Th i s CH 300 r a d i c a l may r ea c t w i th reduced spec ies i n the gaseous environment and i s expected to r eac t w i th CH 3SH as i n (3 -14 ) . CH 300 + CH 3SH - CH 300H + CH 3S (3-14) 73. -The p roduc t ion o f the CH 3S r a d i c a l a l l ows cha in c on t i nua t i o n by way of r e a c t i o n ( 3 - 7 ) . 3 .2 .1 .5 React ions I nvo l v i ng the Hydrogen Peroxy Rad ica l •' The hydrogen peroxy r a d i c a l i s generated by the r e a c t i o n o f mo lecu la r oxygen w i t h the methoxy r a d i c a l ( 3 -12 ) . The HOO r a d i c a l may be expected to r ea c t w i th reduced spec ies - i n p a r t i c u l a r CH3SH - and a l s o w i t h S 0 2 . HOO + CH 3SH - HOOH + CH 3S (3-15) AH.p = -3 .35 kcal/mol k 1 5 = u s x 10 5 M-1 s 1 HOO + S 0 2 - S0 3 + HO (3-16) AH f - -19 kcal/mol k 1 6 = 5.4 x l O 5 M" 1 s - 1 [52] There i s no measure o f the r a t e o f r e a c t i o n (3-15) i n the l i t e r a t u r e . The r a t e constant may be es t imated by c a l c u l a t i n g a ; s teady-s ta te [HOO] as i n Appendix H. The S0 2 o x i d a t i o n by HOO (3-16) has been repor ted [52] to proceed w i th a r a t e constant o f k J 6 = 5.4 x 1 0 5 M " 1 s - 1 . I t i s reasonab le to expect tha t r e a c t i o n (3-15) w i l l proceed w i th a r a t e constant i n excess o f tha t f o r ( 3 - 16 ) . The o v e r a l l r a t e o f r e a c t i o n (3-15) i s expected to be g r ea t e s t due to the h igher c oncen t r a t i on o f CH3SH than o f S 0 2 . 3 .2 .1 .6 React ions I nvo l v i ng Methyl Rad i ca l s Methyl r a d i c a l s are generated i n the i n i t i a l p h o t o l y s i s r e a c t i o n (3-2) and dur ing the o x i d a t i o n o f the CH 3S r a d i c a l . ( 3 - 7 ) . An a d d i t i o n a l 74. minor source of CH3 r a d i c a l s i s from the e l i m i n a t i o n o f e lemental su lphur from dimethyl d i s u l p h i d e (3 -27 ) . The methyl r a d i c a l i s an ext remely r e a c t i v e spec i es and w i l l r eac t r a p i d l y w i t h the oxygen and su l ph ide spec ies i n the r e a c t i o n m a t r i x . Adachi and James [61] have i n v e s t i g a t e d the r ea c t i on s o f methyl r a d i c a l s i n an oxygen-conta in ing atmosphere. The major r e a c t i o n o f the CH 3 r a d i c a l i n an oxygen-con ta in ing atmosphere i s to produce the methyl peroxy r a d i c a l ( 3 -17 ) . CH 3 + 0 2 + M - CH 3 0 2 + M (3-17) k 1 7 = 1 x 10 9 M-1 s " 1 The r a t e constant. k 1 7 i s suggested by Baulch et al. [52] whereas Adachi and James [61] used the va lue k i 7 = 3.1 x 10 8 NT 1 s _ 1 e s t a b l i s h e d by Basco (1972). The cho i ce o f a lower k17 va lue p laced more severe r e s t r i c t i o n s on t h e i r c a l c u l a t i o n o f the f r a c t i o n o f CH 3 r a d i c a l s to form CH 300 r a d i c a l s and they chose the lower r a t e constant f o r t ha t reason . Extending the Basco es t imate to atmospher ic 0 2 concen t ra t i ons suggests the r a t e o f methyl r a d i c a l o x i d a -t i o n to be R 1 7 = 8.17 x 10 6 [CH 3 ] s _ 1 . The methyl peroxy r a d i c a l can mutua l l y i n t e r a c t w i th i t s e l f forming the methoxy r a d i c a l and o ther products 2CH 3 00 - 2CH 30 + 0 2 - CH 30H + HCHO + 0 2 - CH 300CH 3 + 0 2 k = 3.5 x 10 8 M" 1 s " 1 [61] Adachi and James developed a computer s i m u l a t i o n o f the methyl r a d i c a l o x i d a -t i o n and concluded t h a t , i n a n i t rogen-oxygen m i x t u r e , the CH 300 r a d i c a l i s 7 5 . the predominant spec ies [ 6 1 ] . At a h igh 0 2 c oncen t r a t i on (79% v o l ; 3 .23 x 1 0 - 2 M), 99.97% of a v a i l a b l e CH 3 r a d i c a l s were converted to CH 3 00 r a d i c a l s w i t h i n the f i r s t 50 ys a f t e r f l a s h fo rmat ion o f the C H 3 . The HOO concen t ra -t i o n reached 12% o f the i n i t i a l c oncen t r a t i on o f CH 3 00 a t 1900 ys a f t e r the f l a s h . When the oxygen concen t r a t i on was lowered to 2.4% y (1 x 1 0 " 3 M ) , 96.9% o f the a v a i l a b l e C H 3 r a d i c a l s formed CH 3 00 and on ly 3.1% formed C H 3 0 . The HOO concen t ra t i on was maximum at 3.1%, 4400 ys a f t e r i n i t i a t i o n . I t i s apparent tha t the g r ea t e s t p o r t i o n o f methyl groups which o x i d i z e w i l l form the methyl peroxy r a d i c a l . A smal l p o r t i o n o f the methoxy groups w i l l be formed from mutual i n t e r a c t i o n o f the CH 3 00 groups. The methyl r a d i c a l may a l so r eac t w i t h atomic oxygen as i n ( 3 - 1 8 ) . C H 3 + 0 - HCHO + H (3 k 1 8 = 6 x 1 0 1 0 M - 1 s " 1 [ 5 2 ] A H f = - 70 kcal/mol Th is r e a c t i o n i s qu i t e r ap i d but w i l l p lay a smal l pa r t i n the o x i d a t i o n o f the methyl r a d i c a l due to the Tow concen t r a t i on product o f two r e a c t i v e r a d i c a l s ( [ C H 3 ] and [ 0 ] ) . Assuming an atomic oxygen concen t r a t i on 1 0 - t 3 t ha t o f mo lecu la r oxygen, the r a t e o f o x i d a t i o n may be expected to be R = 4 . 9 x 1 0 " 5 [ C H 3 ] s - 1 . An a l t e r n a t i v e to o x i d a t i o n o f the methyl r a d i c a l i s r e a c t i o n w i t h mercaptan to form methane ( 3 -19 ) CH 3 + CH 3 SH - C H 4 + CH 3 S (3 k 1 9 - 1.8 x 101* M- 1 s _ 1 [ 5 4 ] A H , = - 1 9 . 2 kcal/mol 76. Th i s r e a c t i o n ra te constant i s much lower than those o f the competing r ea c t i on s and thus i s l i k e l y to c on t r i b u t e on ly s l i g h t l y to the o v e r a l l r a t e o f removal o f the methyl r a d i c a l . Assuming an i n i t i a l c oncen t r a t i on o f CH 3SH o f 1.53 x l O - " M. The r e l a t i v e r e a c t i o n r a t e o f (3-19) would be R = 2.75 [ C H 3 ] . Th i s r e l a t i v e ra te i s low enough to be d i s r ega rded . 3 .2 .1 .7 React ions I n vo l v i ng Atomic Oxygen Rad i ca l s The atomic oxygen r a d i c a l i s generated dur ing the o x i d a t i o n o f the SO r a d i c a l ( 3 -23 ) . Th is h i gh l y r e a c t i v e spec ies may reac t w i t h CH 3SH, 0 2 or 0 i t s e l f . The r e a c t i o n of CH3SH and 0 w i l l most l i k e l y o x i d i z e the t h i y l hydrogen atom as i n ( 3 -20 ) . 0 + CH3SH CH 3S + OH (3-20) A H f = - 1 6 . 6 kcal/mol k 2 0 = 2 x 1 0 7 to 9 x 1 0 1 0 M - 1 s _ 1 [52] The r e a c t i o n r a t e constant f o r t h i s r e a c t i o n i s est imated from data f o r the o x i d a t i o n o f HS (k = 9 x 1 0 1 0 M- 1 s " 1 ) and f o r the o x i d a t i o n of H 2S . (k = 2.03 x 10 7 M _ 1 s _ 1 ) . The data f o r HS may represent the CH3SH case more a c c u r a t e l y s i n ce the su lphur group i s the l a r g e s t atom o f the group and the H atom w i l l r ep resent a s i m i l a r s t e r i c f a c t o r f o r both CH 3SH and SH. Assuming a CH3SH concen t r a t i on o f 1.53 x lO - 1* M, r e a c t i o n r a te s w i l l range from 3.06 x TO 3 [0] s - 1 to 1.37 x 10 7 [0] s - 1 . Atomic oxygen may a l so combine to re- fo rm mo lecu la r oxygen as i n ( 3 -21 ) . 77. 0 + 0 + M + 0 2 + M (3-21) k 2 1 = 3.8 x 10 8 M~2 s - 1 A H f = -119.1 kca l/mol Th i s r e a c t i o n w i l l have a r e l a t i v e r a t e of 1.5 x 10 7 [ 0 ] 2 s " 1 when i n an a i r t h e rma l i z i n g medium. The expected concen t r a t i on o f 0 spec ies i s su f -f i c i e n t l y low tha t the square reduces the expected r a t e o f r e a c t i o n (3-21) below the range o f c o n s i d e r a t i o n . Atomic and mo lecu la r oxygen may r eac t to form ozone as i n (3 -22) . 0 + 0 2 + M + 0 3 + M (3-22) k 2 2 = 1.96 x 10 8 M- 2 s - 1 A H f = -24.9 kcal/mol At an oxygen concen t r a t i on of 8.17 x I O - 3 M (room a i r a t 25°C), assuming 0 2 and N 2 are e qua l l y good t h i r d bod i e s , the expected r e a c t i o n r a t e would be R = 6.54 x IO 4 [0] s " 1 . The p r ed i c t e d ra tes o f r e a c t i o n f o r r ea c t i on s (3 -20 ) , (3-21) and (3-22) suggest t ha t the r ea c t i on s w i t h CH 3SH and w i t h 0 2 may be equa l l y important as pathways f o r atomic oxygen r e a c t i o n . 3 .2 .1 .8 React ions I nvo l v i ng Sulphur Monoxide Rad i ca l s The r a t e o f o x i d a t i o n o f SO r a d i c a l s has been suggested as be ing s lower than the r e a c t i o n forming SO. The r a d i c a l may be o x i d i z e d by e i t h e r mo lecu la r o r atomic oxygen as in r ea c t i on s (3-23) and ( 3 - 24 ) . 78. SO + 0 2 - S 0 2 + 0 (3-23) k 2 3 = 1 . 5 x 1 0 " M"1 s " 1 A H f = ~13 kcal/mol SO + 0 - S 0 2 (3-24) A H f = -59.7 kcal/mol The mo lecu la r r e a c t i o n (3-23) w i l l be the predominant r e a c t i o n i n an a i r environment due to the g rea te r 0 2 c o n c en t r a t i o n . At p r e v a i l i n g 0 2 concen t ra -t i o n s a r e a c t i o n r a t e o f R = 1.22 x 10 2 [SO] s _ 1 may be expec ted . 3 .2 .1 .9 React ions I nvo l v i ng Su lphydry l Rad i ca l s The su l phyd ry l r a d i c a l may r ea c t by o x i d i z i n g w i t h e i t h e r mo lecu la r o r atomic oxygen; (3-25) o r ( 3 -26 ) . SH + 0 2 - SO + OH (3-25) k 2 5 < 6 x 10 7 M" 1 s " 1 [52] A H f = -25.5 kca l/mol SH + 0 - SO + H (3-26) k 2 6 = 9.6 x 1 0 1 0 M- 1 s - 1 AH f = -40 .5 kca l/mol The mo lecu la r o x i d a t i o n w i l l proceed at a r a t e R = 4.9 x 1 0 5 [SH] s~ f o r normal a i r concen t ra t i ons o f oxygen. The atomic o x i d a t i o n (3-26) may be expected to proceed at a r a t e o f R = 7.8 x 10 5 [SH] s - 1 i n a i r . The mo lecu la r o x i d a t i o n i s the most s i g n i f i c a n t mechanism f o r removal o f the SH r a d i c a l . 79. 3 .2 .1 .10 React ions E l i m i n a t i n g Elemental Su lphur Pho t o l y s i s o f CH 3SSCH 3 has been suggested to d i r e c t l y expel e lemental su lphur (3-27) [ 5 ] . C H 3 S S C H 3 + hv + 2CH 3 + S 2 (3-27) Data upon the quantum y i e l d o f t h i s r e a c t i o n i s l a c k i n g . The r e a c t i o n may be i nvo l ved i n the p roduc t ion o f the y e l l o w i s h , o i l depos i t found on the i n s i d e of the c e l l w a l l s . The depos i t has a l s o been no t i c ed dur ing r ea c t i on s which do not i n vo l v e CH 3SSCH 3 so t ha t o the r r ea c t i on s e x p e l l i n g S 2 must a l s o be c o n t r i b u t i n g . There i s not s u f f i c i e n t ev idence from t h i s work to f u r t h e r specu la te on the nature o f these r e a c t i o n s . 3.2.2 The Chain Mechanism The s lope of the mo lecu la r r e a c t i o n r a t e versus absorbed photon r a t e ( F i gu re 22) i n d i c a t e s a quantum y i e l d of 13.9 molecu les decomposed per photon absorbed. For the quantum y i e l d to exceed one, a cha in mechanism must be i n ope ra t i on i n o rde r to propagate a f r e e - r a d i c a l cha in of spec ies which w i l l r e a c t w i th o the r CH3SH molecu les i n the sur round ing atmosphere. Tab le 7 l i s t s the major r e a c t i on s which are i nvo l ved i n the cha in propagat ing mechanism. The r e a c t i o n i s i n i t i a t e d by photon abso rp t i on and the subsequent l y s i s o f the CH3SH molecu le i n t o H, CH 3 S, CH 3 and SH r a d i c a l s . These f o u r spec ies are a l l very r e a c t i v e and are capable o f r e a c t i n g w i th spec ies i n the r e a c t i o n atmosphere i n such a manner as to i n c rease the number o f cha in c a r r y i n g s p e c i e s . Each o f the r ea c t i on s i n c l uded i n the l i s t of cha in propagators i s one i n which the r e a c t i n g r a d i c a l produces another r a d i c a l 80. Jable 7 The Chain Mechanism INITIATION REACTIONS CH3SH + hv - CH 3S + H (3-1) CH 3SH + hv - CH 3 + SH (3-2) CHAIN PROPAGATING REACTIONS CH 3S + 0 2 C H 3 O + SO (3-7) CH 3S + 0 - CH 3 + SO (3-8) H + 0 2 + M - HOO + M (3-4) H + CH3SH - H 2 + CH 3S (3-3) CH 3 + 0 2 + M - CH3OO + M (3-17) HOO + CH3SH - HOOH + CH 3S (3-15) SO + 0 2 - S 0 2 + 0 ( 3 - 2 3 ) C H 3 O O + CH3SH - C H 3 O O H + CH 3S - (3-14) C H 3 O + CH3SH - C H 3 O H + CH 3S (3-13) CH3O + 0 2 - HCHO + HOO (3-12) SH + 0 2 - SO + OH (3-25) (3-28) (3-29) OH + CH 3SH H 20 + CH 3S TERMINATING REACTIONS CH 3S + CH 3S + M - C H 3 S S C H 3 + M (3-9) CH3S + C H 3 O - C H 3 S O C H 3 (3-10) CH 3S + C H 3 O O - C H 3 S O O C H 3 (3-11) 2H00 HOOH + 0 2 (3-29) Y 81. which i s capable o f r e a c t i n g i n a manner which w i l l u l t i m a t e l y r e a c t w i t h another CH3SH mo lecu le . The spec ies produced by the cha in propagators are CH 3 S, C H 3 , CH 3 0, C H 3 O O , and HOO. Perhaps the most important r ea c t i on s i n cha in propagat ion are (3-4) and ( 3 - 7 ) . The hydrogen atom r e a c t i o n w i t h mo lecu l a r oxygen preserves the . r e a c t i v e r a d i c a l as HOO. The HOO i s ab le to r e a c t w i t h CH3SH to form HOOH (3-15) and a CH 3S r a d i c a l which w i l l o x i d i z e and f u r t h e r supp ly cha in c a r r y i n g r a d i c a l s . The methyl t h i y l o x i d a t i o n (3-7) i s a r e a c t i o n which produces two r e a c t i v e r a d i c a l s as products (CH 30 and SO). The o x i d a t i o n of SO (3-23) produces an oxygen atom which cont inues the chain,. The CH 30 r a d i c a l r eac t s w i t h 0 2 to form a HOO r a d i c a l ( 3 - 12 ) . The 0 atom w i l l r eac t w i th CH 3SH (3-20) to cont inue the cha in o r w i l l r e a c t w i th O2 to form 0 3 which i t s e l f i s l i k e l y to r eac t w i th CH 3SH. The HOO r a d i c a l w i l l r eac t wi th.CH 3 SH (3-15) to remove a f u r t h e r CH3SH and to r e l e a se the CH 3S r a d i c a l as a cha in propagator . The removal of the subsequent CH3SH molecules c reates r e a c t i v e products which themselves cont inue the r e a c t i o n . At the concen t ra t i ons s t u d i e d , the cha in l ength has proven to be 13.9 r ea c t i on s o f CH 3SH. The cha in r e a c t i o n i s te rminated by the quenching o f r e a c t i v e spec ies p r i m a r i l y by recombinat ion w i th o ther a c t i v e spec ies ( 3 -9 , 3-10, 3-11) . The recombinat ion o f two CH 3S r a d i c a l s ( 3 - 9 ) , i s r e spons i b l e f o r the fo rmat ion of CH 3SSCH 3 - a major r e a c t i o n p roduc t . C H 3 S O C H 3 i s formed from the combinat ion o f CH 30 and CH 3S as i n ( 3 -10 ) . C H 3 s o o c H 3 i s formed from recombinat ion by CH 3S and CH 300 r a d i c a l s ( 3 -11 ) . These r eac t i ons account f o r the fo rmat ion of compounds i d e n t i f i e d i n the pho t o l y s i s of CH3SH and CH 3 SCH 3 . Recombinations o f t h i s s o r t a re r e sponsb i l e f o r t e rm ina t i ng two cha in sequences and do not produce r a d i c a l s which cont inue the c h a i n . 82. 3 .2 .3 The Quantum Y i e l d o f CH3SH Ox i da t i on as a Funct ion of Atmospher ic P ressure Tab le 8 The E f f e c t of Atmospher ic Pressure on the Quantum Y i e l d o f CH3SH Decomposit ion Concen t ra t i on o f CH3SH and Pressure Average Quantum Y i e l d • a % Number of T r i a l s 2. 55 x IO- 4 M/£ 1 atm 12.9 2.07 16 13 2. 55 x 10-" M/£ \ atm 6.4 4.0 62 17 2. 55 x 10 - 4 M/£ k atm 10.9 4.3 39 5 The quantum y i e l d s of CH3SH removal a t 1 atmosphere and at % atmosphere are not s i g n i f i c a n t l y d i f f e r e n t . The y i e l d a t \ i s not s i g n i f i -c an t l y d i f f e r e n t from tha t a t \ atmosphere. The y i e l d at \ atmosphere i s on ly s l i g h t l y s i g n f i c a n t l y d i f f e r e n t from tha t a t 1 atmosphere. Thus i t does not seem reasonab le to conclude tha t the CH3SH o x i d a t i o n r e a c t i o n i s a f f e c t e d by atmospher ic pressure as long as there i s a l a r ge excess o f oxygen. 3.2.4 The Quantum Y i e l d o f Dimethyl Su lph ide Decomposit ion The quantum y i e l d o f d imethyl su l ph ide o x i d a t i o n was i n v e s t i g a t e d a t both atmospher ic pressure and at \ atmosphere. The quantum y i e l d of decomposi t ion was found to i n c rease s i g n i f i c a n t l y w i th dec reas ing p ressure (F igu re 23 ) . 14 .25 .50 A i r p r e s s u r e ( a tm) .75 1.0 F igure 23. The quantum y i e l d o f CH 3SCH 3 decomposit ion vs . atmospheric pressure o f a i 84. Tab le 9 The Quantum Y e i l d o f Dimethyl Su lph ide Decomposit ion v . s . Atmospher ic P ressure CH 3 SCH 3 Pressure Atm Absorbed Photons R x Rate a n .71x10-^-1 .71x10-^1 1 \, .04 (1 .934 x 10' 8) .04 (1.615 x 10° ) 74.2 x 6 " 6 g/hr 64.25 x 1 0 - 6 g/hr 4.07 8.02 1 .6 2.9 10 6 The low r a t e o f r e a c t i o n o f d imethyl su l ph ide i s due to the f a c t t ha t the compound absorbs on ly very sho r t wavelength u l t r a - v i o l e t r a d i a t i o n (F igu re 3 ) . Most mercury d i s charge lamps prov ide on ly low l e v e l s o f i l l u m i n a -t i o n i n t h i s r e g i o n . The deuter ium d i scharge prov ides extended shor t wave-leng th em i s s i on , however, \ y£ (£) of CH 3SCH 3 i n a 10 cm, 40 ml c e l l , absorbed on ly 4% of the i n c i d e n t energy below 300 nm. 3.2.5 The Quantum Y i e l d of Dimethyl D i su l ph i de Decomposit ion • Tab le 10 The Quantum Y i e l d o f Dimethyl D i su l ph i de Decomposit ion D i su l ph i de Per Ce l l F r a c t i o na l Absorbance Reac t i on Rate Quantum Y i e l d No. T r i a l s 0 7.05 x 10" 5 M 28.4% 93.6 x 1 0 - 6 g/hr 1 .96 40 .94 14.10 x 10^ M 42.8% 90.5 x 1 0 - 6 g/hr 1.27 7 .825 85. The quantum y i e l d of d imethyl d i s u l p h i d e decompos i t ion i s not s i g n i f i c a n t l y a f f e c t e d by a change i n reac tan t concen t ra t i on ( F i gu re 24) . The average quantum y i e l d o f decomposi t ion i s 1.67. The low quantum y i e l d suggests the presence of few success fu l cha in c a r r i e r s to cont inue the r e a c t i o n s i n i t i a t e d by the photochemical sequence. The low y i e l d a l s o suggests tha t CH 3 0 and HOO r a d i c a l s , when produced by CH 3S o x i d a t i o n , do not s u c c e s s f u l l y a t t a ck the CH3SSCH3 molecu le i n a manner which would decompose the mo lecu l e . The i n i t i a l photochemical a c t i v a t i o n forms two methyl t h i y l r a d i c a l s from the d i s u l p h i d e [ 5 , 8, 9, 2 0 ] . The low ra t e o f decompos i t ion i n d i c a t e s t ha t the main f a t e o f the CH 3S r a d i c a l s i s to recombine to reform d i s u l p h i d e . There was no evidence o f CH3SH fo rmat ion dur ing d i s u l p h i d e p h o t o l y s i s and S0 2 was the on ly de te c t ab l e p roduc t . The cha in sequence i s very sho r t however there i s the p o s s i b i l i t y t ha t atomic oxygen formed from CH 3S o x i d a t i o n c on t r i bu t e s to the cha in i n the f o l l o w i n g manner: CH3SSCH3 + hv -> 2 C H 3 S CH 3S + 0 2 + CH3O + SO SO + 0 2 S 0 2 + 0 0 + CH3SSCH3 -> CH 3S + CH 3 + SO The hydrogen peroxy r a d i c a l may a l s o p a r t i c i p a t e ; however, the i n t e r a c t i o n between HOO and CH 3SSCH 3 i s not e a s i l y p r e d i c t a b l e . CH 3S + 0 2 -> CH3O + SO CH3O + 0 2 + HCHO + HOO HOO + CH3SSCH3 products CO > o CD i- 2 co I O CO co I o e c CO 3 o [CH^5SCHgJ x 106 l/cell .5 2.81 5.62 ' 8.43 11.24 14.05 x 1 0 5 M F igure 24. The quantum y i e l d of CH 3SSCH 3 decomposit ion v s . concen t ra t i on o f s u l p h i d e . 87. 3.3 Other Exper imental S tud ies 3.3.1 The E f f e c t of Added Su lphur D iox ide Su lphur d i o x i d e i s a major r e a c t i o n product o f the CH3SH o x i d a -t i o n and thus must be cons idered as a p o s s i b l e quencher o r promoter o f the o x i d a t i o n r e a c t i o n . Su lphur d i o x i d e has a s i g n i f i c a n t e x t i n c t i o n c o e f f i c i e n t i n the wavelengths o f i n t e r e s t f o r CH3SH o x i d a t i o n . I t might t he r e f o r e absorb l i g h t to form a pho to -exc i t ed spec ies which cou ld t r a n s f e r energy to o the r r e a c t i n g spec ies . The s e r i e s o f runs was done w i t h 50 y£ CH3SH us ing 50 y£ and 100 y£ addends of S 0 2 to the r e a c t i o n c e l l . Tab le 11 The e f f e c t o f Added Su lphur D iox ide CH3SH S 0 2 SH Rate % Absorbed L i gh t 50 yJl 0 y£ , 53 .05 x 1 0 - 6 g/hr 6.13% 8 .24 50 y£ 50 y£ 57 .2 x 1 0 - 6 g/hr 15.05% 3 .61 50 y£ 100 y£ 53 .5 x 1 0 - 6 g/hr 32.3% 1 .57 F igure 25 shows the v a r i a t i o n o f CH3SH o x i d a t i o n r a t e w i th added S 0 2 . There i s no s i g n i f i c a n t e f f e c t on the mercaptan o x i d a t i o n r a t e due to S 0 2 a d d i t i o n f o r low t o t a l amounts of l i g h t absorbed by the r e a c t i n g gas m i x t u r e . Th is i n d i c a t e s t ha t there i s no energy t r a n s f e r from the photo-e x c i t e d S 0 2 spec ies to the r e a c t i n g mercaptan mo lecu les . The S 0 2 does absorb a s i g n i f i c a n t amount o f u l t r a - v i o l e t l i g h t which would o therw ise not be absorbed by the CH 3 SH-a i r m i x t u r e . Due to the i nc reased abso rp t i on the e f f e c t i v e quantum y i e l d of CH3SH decompos i t ion becomes reduced. F igure 26 70 to SI \ 5 0 40 (0 > o e <3> 30 cr 20 r co 03 X o 10 e s o S H so S H 50 S O „ so S H 100 S O 1 , , 1 L _ .1 .2 .3 Fraction of light /\<300nm absorbed in total F igure 25. Reac t ion r a t e o f CH3SH v s . f r a c t i o n o f l i g h t absorbance w i th added S 0 2 . 90. i n d i c a t e s t ha t the quantum y i e l d i s i n v e r s e l y p ropo r t i ona l to the amount o f l i g h t absorbed by the S 0 2 . Thus the major e f f e c t o f the presence of S0 2 i n the r e a c t i o n atmosphere i s to absorb l i g h t which would otherwise be a v a i l a b l e to i n i t i a t e CH 3SH r e a c t i o n . 3 .3.2 A Su lphur Balance f o r Methyl Mercaptan Ox i da t i on The CH3SH o x i d a t i o n experiments were monitored both o p t i c a l l y and ch romatograph i ca l l y to determine the p roduc t i on of r e a c t i o n products con-t a i n i n g su l phu r . The S 0 2 p roduc t ion was most e f f e c t i v e l y moni tored by gas chromatography. The o p t i c a l absorbance a t 290 nm was moni tored dur ing the r e a c t i o n to f o l l o w the combined p roduc t ion o f CH 3SSCH 3 and S 0 2 . The r e a c t i o n showed a l i n e a r p roduc t ion r a t e o f spec ies absorb ing at 290 nm. The abso rp t i on c o e f f i c i e n t s f o r CH 3 SH, S0 2 and CH 3SSCH 3 were determined by measuring known q u a n t i t i e s of known gases i n the c e l l . The abso rp t i on c o e f f i c i e n t s at 290 nm are shown i n Tab le 12. The t o t a l absorbance was cons idered to be the sum of t ha t due to S 0 2 , CH3SH and C H 3 S S C H 3 . l og -1- = - (10 cm) J- 0 (3.-249 x 1 0 3 ) [ S 0 2 ] + (18.304)[CH 3 SH] + (1.390 x 10 3 ) [CH 3 SSCH 3 ] The concen t ra t i ons o f CH3SH and S 0 2 were known ch romatograph i ca l l y and t ha t o f C H 3 S S C H 3 was found by d i f f e r e n c e from the t o t a l absorbance a t 290 nm. Table 12 The Abso rp t i on C o e f f i c i e n t s f o r CH 3SH, S 0 2 , CH 3SCH 3 and CH 3SSCH 3 Th i s .Work Ca l v e r t & P i t t s [59] Dev i a t i on CH3SH 225 nm CH3SH 290 nm S 0 2 290 nm CH 3SCH 3 215 nm CH3SSCH-3 250 nm CH 3SSCH 3 290 nm 147.1 207.9 340 456 131 M cm 2.29 x 10 3 18.3 3.24 x 10 3 5.31 x 10 3 7.12 x 10 3 1.39 x 1 0 3 cc g cm 165 228.6 454 300 59 M cm 2.57 x 10 3 3.57 x 10 3 7.09 x 10 3 4.68 x 10 3 9.22 x 10 3 cc g cm +12.4% +9.95% +33.5% -34% -55% 92. Tab le 13 A Su lphur Ba lance Based on 25 Minutes CH3SH Ox i da t i on Per ml React ion Volume S Atoms Los t as CH3SH 100 y£ Runs 250 y£ Runs 2.712 x 1 0 1 6 A t ° m S ml 4.8449 x 1 0 1 6 A - ^ p -ml S Atoms Found as S 0 2 .458 x 1 0 1 6 .5688 x 1 0 1 6 % of S l o s t 16.8% 11 .7% S Atoms Found as CH 3SSCH 3 1.981 x 1 0 1 6 A t o n ? s ml 2.973 x 1 01 6 A t o f ml % of S l o s t 73.04% 60.8% TOTAL % FOUND 89.95% 73.1% Experiments conducted a t 100 y£ per r e a c t i o n c e l l were ab le to account f o r 89.9% o f the su lphur r e a c t ed . Experiments conducted a t 250 y£/cel l were ab le to account f o r 73.1% of the su lphur atoms decomposed as CH 3SH. A s i g n i f i c a n t amount o f su lphur a l so appeared as a pa le y e l l ow depos i t on the i n s i d e o f the r e a c t i o n c e l l . The heav i e s t depos i t occur red on the entrance window. The depos i t was not l a r ge enough to ana lyze chem i ca l l y but was examined under the o p t i c a l microscope and under the scanning e l e c t r o n mic roscope . X-ray emiss ion spec t ra from the depos i t under e l e c t r o n bombard-ment conf i rmed the presence o f su lphur i n the d epo s i t . The depos i t was produced dur ing both p h o t o l y s i s and l i g h t s c a t t e r i n g s tud ies o f CH 3SH, CH 3 SCH 3 , CH 3SSCH 3 and S 0 2 . The depos i t was not i n c luded i n the su lphur ba l ance . 93 . 3.3.3 The Quantum Y i e l d of Product Formation f o r Su lphur D iox ide and  Dimethyl D i su l ph ide The major products o f the pho to -ox i da t i on o f methyl mercaptan are su lphu r d i o x i d e and d imethyl d i s u l p h i d e . For the i n i t i a l stages o f the r e a c t i o n , the product fo rmat ion may be desc r i bed in the form o f a quantum y i e l d of appearance based on the amount of l i g h t absorbed by the r e a c t i n g compound, CH 3SH. The r e s u l t i n g quantum y i e l d s o f product fo rmat ion are shown i n Tab le 14. Tab le 14 The Quantum Y i e l d s o f Product Format ion CH3SH Level 100 uJo/cel l 250 y£/cell cf> S 0 2 Formation 2.355 1 .585 cj) CH 3SSCH 3 Formation 5.096 4 .144 The quantum y i e l d of appearance o f su lphur atoms shou ld equal the y i e l d o f d i sappearance . S ince d imethyl d i s u l p h i d e conta ins two su lphur atoms, then the atomic quantum y i e l d ba lance shou ld appear as: . .^ SH = *S02 + 2 < j ) CH 3 SSCH 3 • decornp. For the 100 y£ runs us ing the average quantum y i e l d of decompos i t ion o f 13 .9: 13.9 ~ 2.3 + 2(5.1) = 12.5 94. Th is agrees w i t h i n 10% and suggests t ha t some l i g h t produces products o the r than S0 2 and C H 3 S S C H 3 . The su l phu r - c on t a i n i ng c e l l depos i t may account 1 f o r the imbalance. 3.3.4 The Depos i t on the Ins ide Ce l l Wall P ho t o l y s i s o f the s u l phu r - c on t a i n i ng compounds i s accompanied by the appearance o f a y e l l ow depos i t on the i n s i d e o f the pho t o l y s i s c e l l . The depos i t i s most h e a v i l y concent ra ted on the entrance window o f the c e l l . The depos i t has the appearance o f d r op l e t s o f an o i l y l i q u i d of y e l l o w i s h c o l o u r . The y e l l ow l i q u i d i s not s o l u b l e i n H 2 0 , C C U , CKC1 3 , CH30H or acetone [58] but i s repor ted to be s o l u b l e i n carbon d i s u l p h i d e [ 4 1 ] . Chromatographic a n a l y s i s was not p o s s i b l e due to the d i f f i c u l t y o f c o l l e c t i n g the sample and due to the l a ck o f known s t anda rds . The depos i t was found to g i ve o f f a background emiss ion dur ing emiss ion runs which r equ i r ed occas i ona l c l ean i ng of the c e l l . Ce l l c l ean i ng was accompl ished by baking the c e l l ove rn igh t a t 500 °C i n a i r . A s i m i l a r depos i t has been repor ted by o ther i n v e s t i g a t o r s o f su lphur compound p h o t o l y s i s and emiss ion e f f e c t s [ 1 , 5 , 1 2 , 1 6 , 4 1 , 4 2 , 4 8 ] . Kamra and White [16] found the depos i t to d i sappear by heat ing an o x y g e n - f i l l e d c e l l to an unstated tempera-tu re u n t i l the depos i t was gone. Mass s pe c t r a l a n a l y s i s of the gases revea led S 0 2 . The i n v e s t i g a t o r s suspected e lemental su lphur and th io formaldehyde condensing on the s i de w a l l s . Rao and Knight [12] found mass s pe c t r a l a n a l y s i s of the depos i t to suggest a mo lecu la r weight about 258 and tha t the compound conta ined C H 2 S and CH 3S groups. L u r i a et al. [58] observed the appearance o f a c l e a r o i l which turned brown w i th t ime. Th is depos i t appeared on the i n s i d e c e l l wa l l 95. of the r e a c t i o n v e s s e l . L u r i a was pho to l y s i ng a mix ture o f SO2 and a l l e n e . An aeroso l was found to form which was s i m i l a r to the aeroso l He i ck l en found upon pho t o l y s i s of S0 2 - a c e t y l e n e mix tures [ 5 8 ] . An elemental a n a l y s i s was attempted but was not s u c c e s s f u l . The aeroso l was found to grow i n p a r t i c l e s i z e throughout the run but d i d not grow i n p a r t i c l e number. The aeroso l was f e l t to depos i t on the s i des o f the r e a c t i o n v e s s e l . The d epo s i t , i n my exper iments , was r e spons i b l e f o r a general decrease i n sho r t wavelength t r an sm i s s i o n o f the r e a c t i o n v e s s e l . The t r ansm i s s i on decrease was d i r e c t l y r e l a t e d to the amount o f s u l phu r - c on t a i n i ng gas which had been decomposed i n the c e l l . Photographs o f the depos i t w i t h an o p t i c a l microscope revea l a s e r i e s o f l a r g e r d rop l e t s surrounded by much sma l l e r d r op l e t s (F igures 27, 28 ) . The l a r g e r d rop l e t s may have been formed from the condensat ion o f sma l l e r d r op l e t s s i n c e there i s a zone o f c l e a r i n g around each l a r g e r d r o p l e t . Scanning e l e c t r o n microscope photographs revea l a more f l a t depos i t which has decreased i n d iameter and moved to the s i de ( F i gu re 29 ) . A v i s i b l e per imeter g ives ev idence o f the o r i g i n a l shape and l o c a t i o n o f the d r o p l e t ( F i gu re 29c ) . The "change" o f shape i s a r e s u l t o f evapora t i on dur ing the high-vacuum carbon evapora t ion c y c l e o f scanning e l e c t r o n microscope sample p repa ra t i on a t which t ime the sample was r o t a t ed a t 1 0 " 5 mm pressure to ensure a un i form carbon coa t i ng which prov ided e l e c t r i c a l c o n d u c t i v i t y . The evapora-t i o n o f depos i t r evea l s t ha t seme of the depor.it i s v o l a t i l e and some o f the depos i t i s much l e s s v o l a t i l e . The l e s s v o l a t i l e p o r t i o n o f the depos i t was found to b l i s t e r and evaporate under 20 KeV e l e c t r o n bombardment ( F i gu re 29d) . The e l e c t r o n beam can be used to s t imu l a t e x- ray emiss ion c h a r a c t e r i s t i c o f atomic spec ies and i s ab le to de tec t sodium atoms and those of h igher atomic 96. we igh t . An emiss ion spectrum was run on the c e l l window and on the window p lus depos i t ( F igu re 30) . The upper curve r evea l s the peak f o r s i l i c o n found i n the g lass window. No sodium i s seen i n the g l a ss due to the sodium removal stages i n p repar ing s u p r a s i l s y n t h e t i c s i l i c a . The lower curve shows the c h a r a c t e r i s t i c su lphur peak a t 2.31 KeV as we l l as a s i l i c o n peak which r e s u l t s from the under l y ing window. Photographs o f the sample and o f the po in t s o f x - ray emiss ion c h a r a c t e r i s t i c i n energy f o r su lphur are superimposed i n F igure 29d. The depos i t i s l i k e l y an o rgan i c po l y su l ph i de depos i ted from the mo lecu l a r vapour s t a t e . Subsequent r e pho t o l y s i s o f the depos i t on the su r face l i k e l y r e s u l t s i n long cha in f o rma t i on . 97 Figure 27. Photomicrograph of c e l l deposit. 98 mjr w^ F igure 28. Photomicrograph of c e l l d epo s i t . > t ) > ) j ) .*. • I i ) • ) J \ » > > ) 7 « 1 } > 1 »• > Figure 29a. Photolysis ce l l deposit x 100 • 10 KV. Figure 29c. Photolysis ce l l deposit x 1000 • 10 KV. • * - • -• T. .* • -•; . • * /.:v<' - *.- -Figure 29b. Photolysis ce l l deposit x 400 • 20 KV. Figure 29d. Sulphur x-ray emission sources superimposed over the ce l l deposit x 1000 • 20 KV. I X *.'"• •" „"s" ' . .• •.• o eV Si S KeV 2.31 KeV suprasil disc disc -{-deposit v u K e V —i O O X-ray energy level F igure 30. X-ray emiss ion spectrum o f c e l l wa l l depos i t on end window o f " ze ro " c e l l . 101. Chapter 4 L I G H T E M I S S I O N FROM SULPHUR-CO N T A I N I N G A T M 0 S P.H E R E S 4.1 Observat ion and Time Dependence The r e a c t i o n apparatus was mod i f i ed from the form o f a t r ansm i s s i on spectrophotometer i n t o a c o n f i g u r a t i o n which would a l l ow p h o t o - e l e c t r i c obse rva t i on at 90° to the i n c i d e n t l i g h t path (F igu re 11 ) . Th i s c o n f i g u r a t i o n was chosen i n an attempt to de tec t l i g h t emiss ion from the su l phu r - c on t a i n i ng gases as they underwent the pho to -ox i da t i on r e a c t i o n . The arrangement was f u l l y enc losed by a dark shroud and l i g h t r e f l e c t i o n from the s i de o f the containment vesse l was e l im i na t ed by masking the entrance window so t ha t the vesse l s ides were not i l l u m i n a t e d . The gases CH 3SH, CH 3 SCH 3 , CH 3 SSCH 3 , H2S and S 0 2 were i l l u m i n a t e d f o r f i v e minutes i n the po lychromat i c l i g h t beam and the spectrum of l i g h t emiss ion was recorded w i th a 3.2 nm bandpass. S i g n i f i c a n t l e v e l s o f l i g h t emiss ion were recorded f o r H 2 S, S0 2 and CH 3SCH 3 ( F i gu re 31 ) . The non-symmetr ical su lph ides CH3SH and CH 3SSCH 3 d i d not emit s i g n i f i c a n t l e v e l s o f l i g h t (F igu re 31) . The spectrum of emiss ion detec ted from the symmetr ica l su lph ides was s i m i l a r to the t r ansm i s s i on spectrum i n tha t the minimum at 280 nm i n the S 0 2 emiss ion corresponded to the SO2 absorp-t i o n peak a t 280 nm. The emiss ion spec t ra beg in a t f requenc ies where the abso rp t i on c o e f f i c i e n t f o r tha t p a r t i c u l a r gas i s de c r ea s i ng . 150 160 180 200 220 240 260 280 300 240 350 400 420 W a v e l e n g t h X n m F igure 31 . Emiss ion i n t e n s i t y o f s u l phu r - c on t a i n i ng compounds under po lychromat ic i l l u m i n a t i o n v s . wavelencit'h. sso. 500 o ro 103. Dur ing the course o f o ther exper iments the emiss ion spec t ra were recorded at va ry ing times a f t e r beg inn ing i l l u m i n a t i o n o f the gas m i x t u r e . The i n t e n s i t y o f the emi t ted l i g h t was found to vary depending on how long the gas mix ture had been r e c e i v i n g i l l u m i n a t i o n . In o rder to examine t h i s apparent t ime-dependent behav iour , a s e r i e s of exper iments was performed a t . f i x e d wave lengths . The i n t e n s i t y of emiss ion from a CH 3 SCH 3 -A i r m ix ture was f o l l owed from the t ime of i l l u m i n a t i o n us ing the 270 nm band. The t ime-dependent nature o f the detec ted s i gna l i s shown i n F igure 32. The emiss ion s l ow l y grew i n i n t e n s i t y . A f t e r a pe r i od o f s i x minutes the emiss ion reached a maximum va lue and began a s e r i e s o f o s c i l l a t i o n s as the emi t ted i n t e n s i t y s l ow ly decreased. The same procedure was employed to examine the t ime-dependent behaviour of S 0 2 . The wavelengths o f obse rva t i on were chosen on e i t h e r s i de o f the 280 nm abso rp t i on peak o f S0 2 so t ha t a s t rong s i gna l cou ld be reco rded . The r e s u l t s are shown i n F i gu re 33a f o r the s h o r t e r wavelength 240 nm s i g na l and i n F igure 33b f o r the 320 nm s i g n a l . The i n i t i a l l e v e l o f emiss ion develops as r a p i d l y as can be measured by the reco rd ing equipment. Th is i s a f l u o r e s c en t emiss ion from the e x c i t e d S0 2 mo lecu l e . The i n i t i a l l y low l e v e l i nc reases u n t i l a p l a teau i s reached a f t e r f i v e or s i x minutes of i l l u m i n a -t i o n . Observat ion of the emiss ion a t 320 nm revea l s somewhat d i f f e r e n t behav iour . The i n i t i a l f l u o r e s c e n t emiss ion i s much s t r onge r a t 320 nm. The subsequent r i s e i n emiss ion i n t e n s i t y appears to exper ience a de lay when monitored a t the l onger wave length . The de lay has exponent ia l growth and suggests an i n i t i a t i n g e f f e c t may be t a k i ng p lace and t h i s i n i t i a t i o n may be c ha r a c t e r i z e d by a wavelength dependence. The u l t ima t e l e v e l o f emiss ion i s e s t a b l i s h e d seven minutes a f t e r the s t a r t o f i l l u m i n a t i o n . 104. 105. Figure 33b. The time dependence of S0 2 emission at 320 nm. 106. 4.2 P o s s i b l e Mechanisms to Descr ibe the Delay o f Emiss ion 4.2.1 F luorescence The obse rva t i on of a s low-deve lop ing component o f emiss ion r equ i r ed tha t the mechanism r e spons i b l e f o r the emiss ion be de f i n ed . Mechanisms which cou ld have been i nvo l ved i n c l ude f l uo re s cence and de layed f l u o r e s c en c e , chemi luminescence, impu r i t y e f f e c t s such as a r e a c t i n g quenching agent and phys i ca l l i g h t s c a t t e r i n g by p o s s i b l e aeroso l f o rma t i on . A f l u o r e s c e n t e f f e c t was not observed i n the case o f d imethy l s u l p h i d e . The emiss ion d i d not d i s p l a y an i n s t a n t l e v e l o f emiss ion and began the slow growth from a zero l e v e l o f l i g h t emiss ion ( F i gu re 32) . F luorescence was noted f o r S 0 2 a t both 240 nm and 320 nm (F igu re 33 ) . The f l u o r e s c e n t component i s much more s i g -n i f i c a n t a t 320 nm ( F i gu re 33b) . The f l u o r e s c e n t component i s a very smal l p o r t i o n o f the t o t a l emiss ion even f o r S 0 2 a t 320 nm. A f l u o r e s c e n t emiss ion occurs from the s i n g l e t pho to -exc i t ed s t a t e and consequent ly i s f u l l y developed by the time the cha r t r eco rde r records the i n i t i a l emiss ion l e v e l . Thus a f l u o r e s c e n t e f f e c t would not de s c r i be the s low-deve lop ing component o f the em i s s i on . • . 4 .2 .2 Delayed F luorescence The phenomenon o f de layed f l uo rescence i nvo l ve s a slow deve lop ing component o f f l uo rescence which develops a f t e r the i n i t i a l e s tab l i shment of f l u o r e s c en t em i s s i on . The slow component i s due to thermal a c t i v a t i o n of the t r i p l e t pool to the f i r s t e x i c t e d s i n g l e t s t a t e from which f l uo re s cence o c cu r s . The E-type delayed f l uo rescence has been desc r i bed by Parker [46] to occur as f o l l o w s . 107. A + hv + A1 Q + A" + A + Q A' -> A + hv A' -y A 3 A 3 + A • + hv A 3 + M A' + M a c t i v a t i o n quenching f l uo rescence i n t e r - s y s t em- c r o s s i n g phosphorescence energy abso rp t i on A ground s t a t e molecu le A' s i n g l e t s t a t e molecu le A 3 t r i p l e t s t a t e molecu le M atmospher ic t h i r d body molecu le A de layed f l u o r e s c en t e f f e c t would be expected to reach maximum i n t e n s i t y s h o r t l y a f t e r the t r i p l e t pool would reach i t s maximum popu l a t i o n . Th i s would be l i k e l y to occur very r a p i d l y and a s i x minute t ime to maximum would be u n l i k e l y . 4 .2 .3 Chemil uminescence The p o s s i b i l i t y t ha t a chemi luminescent e f f e c t might be ope ra t i ng was i n v e s t i g a t e d . The o x i d a t i o n o f the su lphur atom might have been r e spons i b l e f o r the s low-deve lop ing emiss ion component. Th is was t e s t ed by observ ing the emiss ion curves when the exper iment was performed in one atmosphere o f dry N 2 i n s t ead o f i n a i r . The emiss ion i n a n i t r ogen atmosphere was i d e n t i c a l to tha t from an a i r - c o n t a i n i n g system. Thus the su lphur o x i d a -t i o n r e a c t i o n i s not l i k e l y to be r e spons i b l e f o r the s low-deve lop ing em i s s i on . One f u r t h e r reason to r e j e c t a chemi luminescent exp l ana t i on i s a f f o rded by 108. the C H 3 S H o x i d a t i o n r e a c t i o n . The p h o t o l y t i c o x i d a t i o n o f CH 3SH e x h i b i t s on ly a very low l e v e l o f l i g h t em i s s i on . Th is r e a c t i o n i s a l s o the one i n which the fo rmat ion o f S 0 2 from CH 3S i s the most r a p i d . I f the emiss ion came from the su lphur o x i d a t i o n r e a c t i o n one would e x p e c t . t h i s r e a c t i o n to e x h i b i t the g r ea t e s t l e v e l o f l i g h t em i s s i on . Thus one must conclude t h a t the r ea c t i on s o f o x i d a t i o n o f CH 3S to SO or o f SO to S 0 2 are not r e spons i b l e f o r the s low-deve lop ing em i s s i on . 4 .2 .4 Presence o f Quenching Impur i ty A long de lay i n the es tab l i shment o f emiss ion cou ld be caused by the presence o f a quenching agent i n the o r i g i n a l gas m i x t u r e . I f t h i s quenching agent was to be s l ow l y removed, a f l u o r e s c e n t emiss ion would appear to be s l ow ly growing. As the quenching agent was removed the emiss ion would approach a p la teau l e v e l which' cou ld be ma in ta i ned . .The quenching agent cou ld be removed by r e a c t i o n w i th the a c t i v a t e d su l ph i de or might be deac t i va t ed due to pho t o l y s i s of the quencher i t s e l f by d i r e c t abso rp t i on of u l t r a - v i o l e t l i g h t . Th is p o s s i b i l i t y was examined by i n t e r r u p t i n g the l i g h t beam f o r va r i ous lengths of t ime and examining the l e v e l o f 'emission as the i l l u m i n a -t i o n was resumed. I f there was a quenching agent p resen t , and i f i t was consumed by r e a c t i o n o r p h o t o l y s i s , the emiss ion should resume at the same l e v e l as when the beam was i n t e r r u p t e d . I f the quenching agent was regenerated i n the dark, the emiss ion should resume at a very low l e v e l a f t e r a s u f f i c i e n t l y long dark p e r i o d . The r e s u l t s o f t h i s examinat ion are shown i n F igures 34, 35 and 36. The r e s u l t s are q u i t e d i f f e r e n t f o r CH 3SCH 3 and S 0 2 . The d imethyl su l ph ide emiss ion tends to resume at l e v e l s which are very s i m i l a r to those 109. Time (min.) F igure 34. Emiss ion behav iour dur ing i n t e r r u p t e d i l l u m i n a t i o n of CH 3 SCH 3 . no. F igure 35. Emiss ion behaviour dur ing i n t e r r u p t e d i l l u m i n a t i o n of S 0 2 . F igure 36. Emiss ion behaviour dur ing i n t e r r u p t e d i l l u m i n a t i o n o f S 0 2 . 112. when i l l u m i n a t i o n was suspended. F igures 34c and 34d demonstrate the resump-t i o n o f emiss ion a t l e v e l s which are below those e s t a b l i s h e d when the l i g h t was f i r s t shut o f f . Thus a four -minute dark pe r i od appears to be a s i g n i f i c a n t event to whatever mechanism i s o c cu r r i n g i n t h i s de lay o f em i s s i on . A sho r t e r pe r i od of i l l u m i n a t i o n and dark r e s u l t s i n a pa t t e rn which f o l l ows an i n t e r r u p t e d , smooth cu rve . F igures 34a and 34b show some per iods of anomalous emiss ion weakening dur ing i l l u m i n a t i o n . The major t rend i s toward emiss ion which resumes at the prev ious i n t e n s i t y l e v e l f o r per iods o f darkness l e s s than four minutes . For l onger per iods o f darkness (such as f ou r minutes) the emiss ion resumes at a l e v e l s i g n i f i c a n t l y below tha t o f the f i r s t photo-pe r i o d . The growth o f emiss ion a l so shows a second i nduc t i on per iod a f t e r the fou r minute dark p e r i o d . Th is suggests t ha t i f a quenching agent was p resent , t ha t a p o r t i o n o f i t re-appears a f t e r a f ou r minute p e r i o d . One would expect tha t i f a quenching agent was being photo lysed by u l t r a - v i o l e t l i g h t or i f i t was r e a c t i n g w i th CH 3 SCH 3 , the agent would be s t r o n g l y a l t e r e d and i t s reappearance a f t e r f ou r minutes would be u n l i k e l y . The behav iour of the S0 2 system i s most d i f f e r e n t from tha t of • the CH 3 SCH 3 . The S 0 2 emiss ion resumes a t s i g n i f i c a n t l y h igher l e v e l s o f emiss ion than at the end of the prev ious pho tope f i od . F igure 35 i n d i c a t e s t ha t even f o r a 30 second pho toper i od , the emiss ion resumes at a l e v e l which appears to be unchanged by the dark p e r i o d . For sho r t photoper iods , the dark does not appear to i n t e r r u p t the growth curve o f the emiss ion once a s u f f i c i e n t amount of l i g h t has been absorbed. The i n i t i a l pe r i od of l i g h t abso rp t i on r equ i r ed to promote una l t e red r a t e o f growth appears to be about one minute. Thus the process appears to be i n i t i a t e d by one minute i l l u m i n a -t i o n and i s ab l e to cont inue throughout a sho r t dark p e r i o d . I f t h i s was a 113. quenching agent r e a c t i n g , one would expect the r e a c t i o n not to cont inue dur ing a dark p e r i o d . Photo-produced r a d i c a l s should r ea c t s u f f i c i e n t l y r a p i d l y t ha t the dark r e a c t i o n should cont inue on ly a sho r t t ime i n t o the dark p e r i o d . Thus one would not expect the l a rge i n c rease i n emiss ion found a f t e r a long dark p e r i o d . 4 .2 .5 Photochemical Aeroso l Formation The remain ing p o s s i b i l i t y t ha t the emiss ion might be due to phys i ca l s c a t t e r i n g of the l i g h t by an aeroso l suspens ion was i n v e s t i g a t e d . In o rder to separate the phys i ca l s c a t t e r i n g e f f e c t from an emiss ion r e s u l t i n g from abso rp t i on of l i g h t , one must be ab le to e l im i n a t e absorbab le wavelengths from the i l l u m i n a t i o n envelope of wave lengths . I f an emiss ion p e r s i s t s a t a wavelength which i s i l l u m i n a t i n g the gas mix ture but which i s too long to be absorbed by the gas, then the cause i s some phys i ca l s c a t t e r i n g o f the l i g h t beam. I t i s necessary , o f cou rse , to i l l u m i n a t e the mix ture w i t h po lychromat i c l i g h t f o r an i n i t i a l pe r i od i n order to b u i l d up the emiss i ve e f f e c t . A b o r o s i l i c a t e g lass f i l t e r was used to cut o f f a l l wavelengths sho r t enough to be absorbed by the s u l p h i d e . The emiss ion spectrum was f o l l owed a t 370 nm. Th is wavelength i s e f f i c i e n t l y passed by the b o r o s i l i c a t e f i l t e r w i t h on ly s l i g h t l o s s due to r e f l e c t i o n . A 10% l o s s may be expected. F igure 37 demon-s t r a t e s the e f f e c t o f removing absorbab le wavelengths from the l i g h t path wh i l e a n a l y s i s was mainta ined a t 370 nm. The emiss ion was a l l owed to develop normal ly us ing po lychromat i c i l l u m i n a t i o n . A f t e r a pe r i od when the emiss ion was we l l formed, the b o r o s i l i c a t e f i l t e r was i n s e r t e d i n t o the l i g h t pa th . An immediate decrease i n emiss ion i n t e n s i t y i s caused by r e f l e c t i o n l o sses o f the b o r o s i l i c a t e f i l t e r i n the i l l u m i n a t i n g beam. The l e v e l o f emiss ion 114. 2.7 r 5h •> 1 1 > 1— 1 1 -1 1 1 1 I ' •' • f J * 5 6 V 8 9 10 I t 12 13 . 14 I S 16 17 ' 1( Time (min.) F igure 37. The CH 3SCH 3 emiss ion at 370 nm w i t h b o r o s i l i c a t e g l a s s f i l t e r , 115. mainta ins i t s e l f f o r 30 seconds and begins to decrease s l ow l y f o r th ree minutes . Th i s i n d i c a t e s t ha t the re i s some photo-generated spec ies i n the r e a c t i o n m ix tu re tha t i s capable o f s c a t t e r i n g l i g h t o f many wave lengths . Removal o f the f i l t e r a t the n ine minute po in t i nc reases the l i g h t emiss ion by r ega i n i n g what was l o s t to r e f l e c t i o n . Fu r the r i l l u m i n a t i o n i nc reases the emiss i ve e f f e c t a t a r a t e s i m i l a r to t ha t observed be fore f i l t r a t i o n . Th is experiment e s t a b l i s h e s tha t the emiss ion observed i s caused by a phys i ca l s c a t t e r i n g o f the l i g h t by p a r t i c l e s which are produced under sho r t wavelength u l t r a - v i o l e t r a d i a t i o n . The p a r t i c l e s are very l i k e l y an a e r o s o l . The emiss ion must be due to a s c a t t e r i n g s i n ce the emiss ion i s mainta ined even when a l l wavelengths which can be absorbed by CH 3 SCH 3 are removed from the i l l u m i n a t i o n beam. Thus the emiss ion i s not r e - r a d i a t i o n o f absorbed energy s i n c e energy cannot be absorbed by CH 3SCH 3 a t wavelengths l onger than 320 nm (F igure 3 ) . Shor t wavelength u l t r a - v i o l e t i l l u m i n a t i o n i s r equ i r ed f o r the fo rmat ion o f the aeroso l s i n c e the emiss ion does not form a t a l l du r i ng exposure to b o r o s i l i c a t e f i l t e r e d l i g h t . The emiss ion a l s o drops from i t s prev ious l e v e l o f development when the f i l t e r i s i n s e r t e d i n t o the l i g h t path . Th is i n d i c a t e s t ha t the aeroso l i s not very s t a b l e s i n c e i t decays s i g n i f i c a n t l y once the generat ing energy i s removed. The aeroso l i s then regenerated by admi t t i ng the sho r t wavelength l i g h t . The aeroso l p ro-duc t i on mechanism seems the most success fu l i n e xp l a i n i n g the emiss ion e f f e c t . The r e s u l t s w i l l be d i s cussed i n terms of an aeroso l mechanism i n a l a t e r s e c t i o n . 117. 4.3 Concen t ra t i on Dependence o f Emiss ion The emiss ion was examined to observe a concen t r a t i on dependence upon the amount of CH 3SCH 3 added. The u l t ima t e i n t e n s i t y o f emiss ion a t 270 nm was observed and recorded as a f u n c t i o n o f the volume of l i q u i d CH 3SCH 3 added to the emiss ion c e l l ( F i gu re 38) . The exper iment , when performed on d i f f e r e n t days under apparen t l y i d e n t i c a l c o n d i t i o n s , y i e l d s r a t he r d i f f e r e n t r e s u l t s . The behav iour of emiss ion f o r volumes o f CH 3SCH 3 under 1 y£ i s q u i t e l i n e a r . At these l e v e l s , the emiss ion i s most d e f i n t e l y a f u n c t i o n o f c on c en t r a t i o n . For su l ph ide add i t i on s g rea te r than 1 y£ the emiss ion reaches a maximum and does not appear to i n c rease above a c e r t a i n l e v e l . 4.4 Pressure Dependence of Emiss ion The emiss ion was a l s o examined to determine any dependence upon the atmospher ic pressure o f molecu les i n the em i t t i n g m i x t u r e . The u l t ima t e emiss ion i n t e n s i t y was measured f o r a g iven concen t r a t i on of su l ph ide i n the emiss ion c e l l . The c e l l was evacuated to 3/4, 1/2 and 1/4 atmosphere wh i l e ma in ta i n i ng the same p a r t i a l pressure of s u l p h i d e . The r e s u l t s are shown i n F igure 39. Each i n d i v i d u a l c oncen t r a t i on l e v e l was measured on a d i f f e r e n t day and the deuter ium lamp used f o r t h i s se t o f t r i a l s was approaching the end o f i t s usefu l l i f e . For t h i s reason,each i n d i v i d u a l day can be r e l a t e d but the r e s u l t s from d i f f e r e n t days cannot be r e l a t e d s i n ce the t o t a l l i g h t emi t ted from the deuter ium lamp was r a p i d l y dec reas i ng . The emiss ion i s shown to be a s t rong f u n c t i o n of atmospher ic p r e s su re . The p o s s i b i l i t y o f an oxygen dependence i n t h i s se t o f exper iments was examined by conduct ing the whole se t w i t h a new deuter ium lamp us ing dry n i t r ogen gas as the r e a c t i o n \ 118. .25 .50 .7 5 1J> Air pressure (atm.) F igure 39. Emiss ion from CH 3SCH 3 i n a i r v s . a i r p r e s su r e . —•• 9 P M ! Output current x 10 amps 120. atmosphere ( F i gu re 40 ) . The l e v e l o f emiss ion was g ene r a l l y much g r ea t e r w i th the new deuter ium lamp. The emiss ion revea led a s i m i l a r p ressure depen-dence to the a i r exper iments . Th is a l l ows one to r u l e out an oxygen concen-t r a t i o n e f f e c t as the cause o f the pressure dependence of the em i s s i on . In terms of aeroso l f o rma t i on , the aeroso l appears to be pressure dependent w i th respec t to the u l t ima te•1eve l o f s c a t t e r ed l i g h t . 4 .5 The Emiss ion as an Aeroso l S c a t t e r i n g E f f e c t 4.5.1 Prev ious Work A s low-deve lop ing emiss ion has been observed p r e v i o u s l y by La l o and Vermeil [42] i n s t ud i e s o f S 0 2 f l u o r e s c en ce . The emiss ion was found to be g rea te r f o r shor t -wave length i l l u m i n a t i o n than f o r long wave lengths . The emiss ion was, a t t ha t t ime , a t t r i b u t e d to the emiss ion o f the OH r a d i c a l which was formed from the d i l u t i n g H 2 gas and a pos tu l a t ed a i r l eak i n to the s t a t i c system. The emiss ion was avoided by us ing a f l ow ing gas system. Bent ley and Douglass [37] repor ted an observab le aeroso l to be formed dur ing C H 3 S C H 3 p ho t o l y s i s s t ud i e s us ing a h igh power xenon l i g h t source . The system conta ined measurable amounts of water vapour s i n c e the work was done us ing humid a i r . The high i n t e n s i t y work of Bent ley and Douglass was c a r r i e d to a high degree o f complet ion and the product gases conta ined many su lphox ides and sulphones which may have played a pa r t i n aeroso l f o rma t i on . L u r i a et al. [58] observed the fo rmat ion o f an aeroso l when S 0 2 and a l l e n e were i r r a d i a t e d w i t h wavelengths g rea te r than 300 nm. A s i m i l a r e f f e c t was no t i ced by the same authors upon i r r a d i a t i o n o f a S0 2 - a c e t y l e ne m i x t u r e . No aeroso l fo rmat ion was mentioned when S0 2 was photo lysed w i thou t added 121. hydrocarbon. The pho t o l y s i s of a SO2-C2H2 m ix tu re was found to produce a s o l i d aeroso l which was analysed to have the compos i t ion o f a C 3 I - U S 2 O 3 t r ime r [ 58 ] . L u r i a et al. were unsuccess fu l i n t h e i r attempts to i s o l a t e and ana lyze the aeroso l o i l i n the S0 2 - C 3 hV p h o t o l y s i s . A p a r t i a l mo lecu la r a n a l y s i s i n d i c a t ed a ca rbon- to - su lphur r a t i o o f 4 .85 . The number o f p a r t i c l e s was measured us ing two count ing dev i c e s . P a r t i c l e s l a r g e r than 100 nm were counted i n a thermal d i f f u s i o n chamber. P a r t i c l e s l a r g e r than 25 nm were measured i n an "Environment One Condensat ion Nuc l e i Counte r . " The p roduc t ion of p a r t i c l e s was found to commence a f t e r a sho r t i nduc t i on t ime (45 sec . ) and the number of p a r t i c l e s was found to reach a maximum which would subsequent ly decrease s l o w l y . P a r t i c l e p roduc t i on was found to be e s s e n t i a l l y complete w i t h i n 10 minutes., The s i z e of the p a r t i c l e s was found to inc rease w i th t ime. The number o f p a r t i c l e s g r ea t e r than 2.5 nm was found to r a p i d l y approach the number o f p a r t i c l e s o f s i z e g r ea t e r than 100 nm. Two reasons were suggested to e x p l a i n the maximum i n the number of p a r t i c l e s . The f i r s t was tha t p a r t i c l e p roduc t ion stopped a f t e r a pe r i od o f p h o t o l y s i s . The second was t ha t the p a r t i c l e p roduc t i on r a t e was o f f s e t by a p a r t i c l e removal p rocess . The sequence o f events appears to be photochemical p roduc t ion o f a S O 2 - C 3 H 4 polymer which even tua l l y nuc leates to form p a r t i c l e s . The p a r t i c l e s condense and reach a maximum i n number a f t e r which they grow i n s i z e by accumulat ing f u r t h e r photoproduced polymer. The p a r t i c l e count was checked by f i l t e r i n g the aeroso l on a f i l t e r and examining the f i l t e r under a scanning e l e c t r on microscope. The p a r t i c l e s produced were s u f f i c i e n t l y l a r ge and were s t a b l e enough to w i ths tand the evapora t i ve sample p repa ra t i on s teps w i thout evaporat ing themselves. The f i l t e r count method was found to c o r r e l a t e we l l w i th the p a r t i c l e count ing dev i c e s . 122. 4 .5 .2 D i s cus s i on o f Resu l t s as a P a r t i c l e E f f e c t The emiss ion o f l i g h t from the H 2 S , SO 2 and CH 3SCH 3 systems can bes t be desc r ibed i n terms o f l i g h t s c a t t e r i n g from a s l ow l y growing aeroso l which i s formed by photochemical r e a c t i o n . The aeroso l appears to be the r e s u l t o f condensat ion o f a supe r - sa tu ra ted s o l u t i o n o f o i l molecu les which are produced pho tochemica l l y . The d r op l e t s form and subsequent ly i n c rease i n s i z e by agg lomerat ing molecu les from the photochemical r e a c t i o n atmosphere. Cont inued i r r a d i a t i o n r e s u l t s i n the cont inued growth o f the a e r o s o l . The growth of aeroso l p a r t i c l e s i z e r e s u l t s i n a l i g h t s c a t t e r i n g e f f e c t which i s c h a r a c t e r i s t i c o f p a r t i c l e s i n va ry ing s c a t t e r i n g reg imes. The p a r t i c l e s i z e o f an aeroso l i s o f t e n c h a r a c t e r i z e d by the s i z e o f the p a r t i c l e r e l a t i v e to the wavelength of l i g h t used to observe the p a r t i c l e . For a g iven s i z e , s ho r t e r wavelengths o f l i g h t are s c a t t e r ed more than long wave lengths. The d imens ion!ess o p t i c a l p a r t i c l e s i z e parameter x i s used to de s c r i b e the d iameter-wavelength r e l a t i o n s h i p : dp = p a r t i c l e d iameter X = observ ing wavelength For very smal l p a r t i c l e s where x < . 3 , s c a t t e r i n g f o l l ows the Ray le igh model i n which l i g h t i s s c a t t e r ed symmet r i c a l l y both forward and back. As the dimen-s i o n ! ess p a r t i c l e d iameter i nc reases beyond x = . 3 , the s c a t t e r i n g f o l l ows the Mie t heo ry . Mie theory holds f o r p a r t i c l e s o f d iameter between x va lues o f .3 and 3. As the d iameter i n c r e a s e s , the s c a t t e r ed l i g h t develops a foreward d i r e c t e d symmetry which has a maximum w i t h i n 45° o f the i l l u m i n a t i n g beam. 123. The e x t i n c t i o n c o e f f i c i e n t desc r i bed by Mie i s composed of two f a c t o r s : abso rp t i on and s c a t t e r i n g . For p a r t i c l e s o f ca rbon , the abso rp t i on and s c a t t e r i n g e f f e c t s have been separated [ 6 0 ] . F igure 41 shows the par t p layed by s c a t t e r i n g i n the f l i e - theo ry e x t i n c t i o n o f t r an sm i t t ed l i g h t by carbon p a r t i c l e s [ 6 0 ] . The s c a t t e r i n g o f l i g h t becomes a s i g n i f i c a n t f a c t o r as the d imens ion less d iameter approaches 0 .6 . As the p a r t i c l e grows the s c a t t e r i n g inc reases r a p i d l y u n t i l the p a r t i c l e approaches x = 1.6. Beyond a p a r t i c l e diameter, o f 1.6 the s c a t t e r i n g becomes much l e s s dependent upon p a r t i c l e d iameter and approaches a p la teau l e v e l . The sum o f abso rp t i on and s c a t t e r i n g has been c a l c u l a t e d f o r o rgan i c l i q u i d s of r e f r a c t i v e index m = 1.5 [60] (F igure 42 ) . The t o t a l o f s c a t t e r i n g and abso rp t i on reaches a maximum at x = 4 and subsequent ly decreases i n an o s c i l l a t o r y f a sh i on to approach the va lue two at l a r g e p a r t i c l e d iameters . The e x t i n c t i o n c o e f f i c i e n t i s de f i ned by the Bouguer law which i s a m o d i f i c a t i o n o f Bee r ' s law. I -naK£ j- = e 1 0 n = number o f p a r t i c l e s per un i t volume a = mean p ro j e c t ed p a r t i c l e area K = e x t i n c t i o n c o e f f i c i e n t I = path l ength Th is l i m i t a t i o n on the va lue of the e x t i n c t i o n c o e f f i c i e n t r e s u l t s i n a l i m i t on the i n t e n s i t y o f l i g h t s c a t t e r i n g such tha t a p a r t i c l e may cont inue to grow i n s i z e but the l i g h t s c a t t e r ed from i t w i l l no longer be i n c r e a s i n g i n i n t e n s i t y . Such behav iour i s l i k e l y r e spons i b l e f o r the p la teau e f f e c t 124. P a r t i c l e s i z e X F igure 42. E x t i n c t i o n curve f o r the theory of Mie f o r p a r t i c l e s of r e f r a c t i v e index m = 1.5. • 125. ev i den t i n F igure 32. When observed at 270 nm, the s c a t t e r ed l i g h t grows i n i n t e n s i t y qu i t e l i n e a r l y f o r f i v e minutes before the emiss ion reaches a p l a t eau . At t h i s po i n t the d imens ion less p a r t i c l e d iameter has l i k e l y reached a va lue c l o se to 5. Th is would correspond to an ac tua l p a r t i c l e d iameter of 429 nm. F igure 33 revea l s another f ea tu r e c h a r a c t e r i s t i c o f p a r t i c l e growth. The S0 2 emiss ion was f o l l owed at 240 nm and a t 320 nm under o therw ise s i m i l a r c o n d i t i o n s . At the l onger wave length, there i s a s i g n i f i c a n t l y l onger nu c l e a t i o n per iod before a l i n e a r emiss ion growth i s observed F igure 3 3 . b ) . Th is per iod i s the t ime taken to nuc lea te the p a r t i c l e and to ach ieve a d imens ion less d iameter where x ~ .60. As may be seen from F igure 41 the s c a t t e r i n g may be cons idered to begin about x ~ .60. The l onge r nu c l e a t i o n pe r i od i s r equ i r ed due to the l onger wavelength o f obse rva t i on which r equ i r e s a l a r g e r p a r t i c l e d iameter before app re c i ab l e s c a t t e r i n g takes p l a c e . 4 .5 .3 S t a b i l i t y of the Aeroso l The s t a b i l i t y o f the aeroso l formed appears to vary w i t h the parent compound. F igures 34, 35 and 36 i n d i c a t e the behaviour of the CH 3SCH 3 and S 0 2 aeroso l systems under d i s con t inuous r a d i a t i o n . The CH 3SCH 3 system i s seen to resume emiss ion at a lower l e v e l a f t e r a dark pe r i od of f ou r minutes (F igu re 34) . Th is behav iour was i n v e s t i g a t e d by observ ing the s c a t t e r e d l i g h t i n t e n s i t y as the b o r o s i l i c a t e f i l t e r i s i n s e r t e d i n to the o p t i c a l path (F igure 37 ) . The l o s s o f wavelengths below 320 nm e l im i na t e s energy absorp-t i o n by the s u l p h i d e . The genera t ing mechanism i s stopped and the s t a b i l i t y o f the aeroso l may be i n v e s t i g a t e d by observ ing the s c a t t e r i n g a t 370 nm. A f t e r i n s e r t i o n o f .the f i l t e r a t the s i x minute mark, t he . em i s s i on i s seen to decrease a f t e r a 30 second pe r i od o f s t a b i l i t y . The decrease i s a 126. s i g n i f i c a n t l ower ing o f i n t e n s i t y . Th is gradual decrease i s l i k e l y the r e s u l t o f the agg lomerat ion o f aeroso l p a r t i c l e s i n t o a sma l l e r number of l a r ge p a r t i c l e s . The s i z e i n c rease of the p a r t i c l e s does not r e s u l t i n the i n c r ea se o f emiss ion which one might expect because the p a r t i c l e s are a l ready near the s i z e l i m i t (x ~ 2) where the s c a t t e r ed i n t e n s i t y i s more a f u n c t i o n of number than s i z e . As a r e s u l t o f the agg lomera t ion , the emiss ion i s reduced. The decrease i n emiss ion s h o r t l y a f t e r sho r t wavelength e l i m i n a t i o n suggests tha t the C H 3 S C H 3 aeroso l does not a r i s e from a h i g h l y supe r - sa tu ra t ed gas m i x t u r e . The aeroso l generated from S 0 2 appears to be a more s t a b l e phenomenon. F igure 43 i s the r e s u l t o f examining the S0 2 aeroso l under cond i t i on s s i m i l a r to the above. As the ene rg i z i ng i l l u m i n a t i o n i s removed at 3 3/4 minutes , the emiss ion drops due to r e f l e c t i o n from the f i l t e r s l i d e . The emiss ion cont inues to grow f o r one minute a f t e r the ene r g i z i n g r a d i a t i o n i s removed. The r a t e o f decay o f the emiss ion i s much s lower than tha t shown by CH 3 SCH 3 . The cont inued growth shown i n F igure 43 conf i rms the behav iour noted i n F igures 35 and 36. The emiss ion resumed at s i g n i f i c a n t l y h igher l e v e l s f o r two and three minute dark p e r i o d s . Th is behaviour r equ i r e s tha t the p a r t i c l e s cont inue to grow i n s i z e even a f t e r the a c t i v a t i n g energy i s f i l t e r e d ou t . Th is a l so r equ i r e s a growth r a t e g rea te r than the agg lomerat ion e f f e c t which i s r e spons i b l e f o r the decay of the s c a t t e r ed i l l u m i n a t i o n . Such cont inued growth must be the r e s u l t o f a supe r - sa tu ra ted reac t i on -gas s o l u t i o n which cont inues to condense upon the aeroso l and inc rease i t s s i z e f o r a pe r i od of t ime a f t e r the sho r t wavelength l i g h t i s s topped. The aeroso l appears to be-' more s t a b l e w i t h respec t to agg lomerat ion than is t ha t from the CH 3SCH 3 r e a c t i o n . 127. 128. 4 .5 .4 Concen t ra t i on Dependence o f the Aeroso l The dependence of the emiss ion i n t e n s i t y upon the added volume of CH3SCH3 suggests tha t the number of p a r t i c l e s generated in the nu c l e a t i o n stage depends upon the concen t r a t i on of C H 3 S C H 3 i n i t i a l l y present ( F i gu re 38 ) . At l e v e l s of CH 3SCH 3 a d d i t i o n g rea te r than 1 y£ per 53.91 ml c e l l the dependence drops o f f . Th is p la teau suggests t ha t f o r h igher concen t ra t i ons the number o f p a r t i c l e s formed reaches a maximum and i s not i nc reased beyond tha t number. For l a r g e l e v e l s o f CH 3SCH 3 a d d i t i o n , the p a r t i c l e s i z e may i n c r ease to much l a r g e r d iameters ; however t h i s does not i n c r ease the l e v e l o f s c a t t e r ed l i g h t as the d imens ion less d iameter exceeds x ~ 2. Low l e v e l s o f CH 3SCH 3 added never reach the emiss ion l e v e l s u l t i m a t e l y a t t a i n e d by g rea te r addend amounts. Th is e f f e c t i s not va r i ed by t ime and i s thus independent o f the u l t ima t e s i z e o f the aeroso l p a r t i c l e which must be assumed to be con t i nuous l y growing. The low l e v e l s of CH 3SCH 3 a d d i t i o n must be produc ing a lower number o f p a r t i c l e s which grow by the condensat ion p rocess . Each p a r t i c l e behaves as o u t l i n e d p r e v i ou s l y and the emiss ion grows u n t i l x ~ 2. at which t ime the emiss ion reaches i t s u l t ima t e i n t e n s i t y . The number o f p a r t i c l e s formed i s thus a f un c t i o n o f the s t a r t i n g concen t r a t i on o f C H 3 S C H 3 i n the r e a c t i o n gas m a t r i x . 4 . 5 .5 Pressure Dependence o f the Emiss ion The u l t ima t e l e v e l o f emiss ion f o r any one f i x e d concen t r a t i on o f C H 3 S C H 3 was found a l so to be a f u n c t i o n of atmospher ic p r e s su re . The dependence d id not d i f f e r between M2 and a i r ( F igu res 39, 4 0 ) . The e f f e c t of the s i z e o f the p a r t i c l e s i s removed from c on s i d e r a t i o n by examining f o r the u l t ima t e l e v e l o f emiss ion which occurs a t an average p a r t i c l e s i z e 129. where x ~ 2. Thus the number o f p a r t i c l e s appears to be a f u n c t i o n o f atmospher ic p res su re . The number formed must be a f u n c t i o n of a t h i r d body nu c l e a t i on process i n which an 0 2 or N 2 molecu le can serve as a t h i r d body to s t a b i l i z e fo rmat ion of the aeroso l p a r t i c l e . The g rea te r c o f l i s i o n f requency due to h igher p r e s su re s , nuc leates a g rea te r number of aeroso l p a r t i c l e s which grow to form an inc reased u l t ima t e emiss ion i n t e n s i t y . 4.6 The Number of P a r t i c l e s Formed The number o f p a r t i c l e s formed by the nuc l ea t i on o f the su l ph ide i s dependent upon both atmospher ic p ressure and the amount o f su l ph ide i n i t i a l l y p resen t . The dependence upon su l ph i de concen t r a t i on i s r e l a t e d to the number o f pho to -ac t i va t ed su lph ide molecules which are a v a i l a b l e w i t h i n a c e r t a i n c r i t i c a l volume to aggomerate and form an aeroso l p a r t i c l e . There i s a l s o a c r i t i c a l l e v e l o f su lph ide concen t r a t i on above which l a r g e r numbers o f p a r t i c l e s are not formed. Th is suggests t ha t when s u f f i c i e n t q u a n t i t i e s o f a c t i v a t e d su l ph ide are a v a i l a b l e , t h i s quan t i t y i s no longer the c o n t r o l l i n g f a c t o r as to the number o f p a r t i c l e s - formed. At lower su l ph i de c on cen t r a t i on s , the concen t r a t i on o f pho to -a c t i va t ed spec ies i s r e spons i b l e f o r de termin ing the number of p a r t i c l e s to nuc lea te a t a constant atmospher ic p res su re . The atmospher ic pressure exer ts i t s e f f e c t by means o f t h i r d body c o l l i s i o n frequency which de f ines a volume w i t h i n which a p a r t i c l e i s l i k e l y to form. A t h ighe r p res su res , t h i s volume decreases i n s i z e and r e s u l t s i n a l a r g e r number o f p a r t i c l e s to be formed from a g iven volume o f r e a c t i o n . Th is volume may be cons idered as a nu c l e a t i on volume and i s r e l a t e d to the mean f r e e path o f the N 2 -CH 3 SCH 3 m i x tu re . At lower pressures the mean f r e e path i s l a r g e r and w i t h i n a g iven volume, fewer p a r t i c l e s nu c l e a t e . Th i s may 130. a l s o be cons idered as the v o l u m e o f r e a c t i o n gas which i s swept by N2 molecu les to form one aeroso l p a r t i c l e . For concen t ra t i ons o f CH 3SCH 3 lower than 1 u£ per 53.9 ml both dependencies can be r e l a t e d i n a manner which i n vo l ve s p r o p o r t i o n a l i t y to both su lph ide concen t r a t i on and to atmospher ic p r e s su re . With respec t to su l ph i de concen t r a t i on f o r the r e s u l t s of F igure 38. I = (Vol ) 1 - 8 x 10~~? A s msnr u& msm I = s ca t t e r ed i n t e n s i t y s A = Amps With respec t to atmospher ic pressure from F igure 40 f o r a 1 u£ addend. I = 3.38 x 10 - 9 s Atm P., = atmospher ic pressure of N 2 N2 Combining both p r o p o r t i o n a l i t i e s 1.8 x TO" 9 A 3.38 x 1 0 - 9 A Atm Now the number of p a r t i c l e s i s p r opo r t i ona l to the s c a t t e r ed i n t e n s i t y when x>2, t h e r e f o r e : V 1.8 x 1 0 "9 ^- [MSM] 3.38 x 1 0 - 9 A 1 Atm 131. 4.6.1 Attempted Op t i c a l V e r i f i c a t i o n of P a r t i c l e S i z e and Number An attempt to measure the number o f p a r t i c l e s was made. Th is i nvo i ved genera t i on of the aeroso l and con f i rma t i on by emiss ion i n t e n s i t y growth. At va ry i ng times i n the r e a c t i o n the c e l l was removed and p laced on the vacuum man i f o l d . A Nucleopore f i l t e r was p laced on the o u t l e t o f the emiss ion c e l l and numerous c e l l volumes o f dry M 2 were swept through the f i l t e r . The f i l t e r pores were 0.1 y i n d iameter . Samples were taken from newly generated ae roso l s at 0, 2, 5 and 10 minutes i n t e r v a l s . The f i l t e r s were examined under a scanning e l e c t r o n microscope i n a manner s i m i l a r to L u r i a et al. Very few p a r t i c l e s were found on any f i l t e r . The reason f o r the lack of c on f i rma t i on of p a r t i c l e p roduc t ion by the r e a c t i o n l i e s i n the sample p repa ra t i on stages f o r the e l e c t r o n microscopy. In o rder to a t t r a c t the e l e c t r o n beam to the mylar f i l t e r t a r g e t , the f i l t e r su r f a ce and adherent p a r t i c l e s must be covered by a conduct ive f i l m of g o l d . Th i s f i l m i s evaporated onto the sample under high vacuum. The aeroso l i s not l i k e l y s t a b l e to such low pressures and most probably evaporated a t t h i s t ime. As a r e s u l t on ly a few p a r t i c l e s were found on each f i l t e r and these cou ld not be cons idered to be r ep r e s en t a t i v e o f the a e r o s o l . 132. Chapter 5 C O N C L U S I O N S A. 1. CH3SH o x i d a t i o n i s i n i t i a t e d through photon abso rp t i on by CH 3SH. 2. The quantum y i e l d o f CH3SH decomposi t ion i s 13 . 9 . 3. The quantum y i e l d o f CH3SH i s not a f f e c t ed by atmospher ic p res su re . 4. , A i r c on ta i n i ng water vapour r e t a rds the r e a c t i o n . 5. Oxygen concen t r a t i on g rea te r than tha t o f a i r does not i nc rease the quantum y i e l d . 6. Added S0 2 does not i n c rease the quantum y i e l d o f CH3SH decom-p o s i t i o n and i s r e spons i b l e f o r a decrease i n e f f e c t i v e o v e r a l l quantum y i e l d . B_. 1. The quantum y i e l d of CH 3SCH 3 decomposi t ion i s 4 ± 1.6 a t atmospher ic p res su re . 2. The quantum y i e l d o f CH 3SCH 3 decompos i t ion i n c reases to 8 ± 2.9 a t one-quar te r atmosphere of a i r . 133. C. The quantum y i e l d o f CH 3SSCH 3 decompos i t ion i s 1.96 ± .94 a t con-c en t r a t i o n s of 7.0 x 1 0 " 5 M. D. 1. An aeroso l has been found to be formed from u l t r a - v i o l e t i l l u m i n a t i o n o f H 2 S , S 0 2 and CH 3 SCH 3 . 2. The i n t e n s i t y o f l i g h t s c a t t e r ed from the aeroso l i s dependent upon the atmospher ic p ressure o f t h i r d body molecu les i n the environment. 3. The s c a t t e r ed i n t e n s i t y i s c oncen t r a t i on dependent up to a l i m i t o f 5j-§| 1 o f CH 3SCH 3 (2.58 x 1 0 - 4 M). E. The r e a c t i o n scheme would be a s u i t a b l e sequence f o r computer mode l ing . 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H e i c k l e n , K i n e t i c s o f P a r t i c l e Growth-V: P a r t i c l e Formation i n the Pho t o l y s i s o f S 0 2 - A l l e n e M i x t u r e s , J . Aeroso l S c i . , 5, 435 (1975). [59] C a l v e r t , J . G . aid J .M . P i t t s , Photochemis t ry , John Wi ley & Sons I n c . , New York (1966). [60] F r i e d l a n d e r , S .K . , Smoke, Dust and Haze, Fundamentals o f Aeroso l Behav iour , John Wi ley and Sons, New York, London, Sydney, Toronto , p. 130. [61] Adach i , H. and D.E.L. James, K i n e t i c Spec t ro s cop i c S tud ies of A l k y l , A l k y l pe r oxy and ace ty l r a d i c a l s , Ph.D. The s i s , Department o f Chemis t ry , The U n i v e r s i t y o f B r i t i s h Columbia. [62] Pratt G.and I.Veltman,Kinetics of Reaction of Hydrogen Atcms with Ethylene. J.Chem. soc. Far.I,72,1733(1976) APPENDIX A CH3SH React ion Data [SH] /Ce l l Rx Rate L i g h t Photon F lux % Abs. Date-Ce l1 x 1 0 - 6 I x 1 0 " 5 g h r - 1 • # Photons h r - 1 % x I O - 6 g h r - 1 on Dec. 10 1974 50 57.6 1 1 .317 x 1 01 8 4.94 -11 50 46.4 1 1.317 .13.2 -13 50 40.1 1 1 .317 -16 50 37 1 1 .317 - -19 50 52 1 1 .317 3.5 -March 10 1975 50 88.8 1 1 .317 - -11 50 56.7 1 1 .317 2.9 -17 50 45.4 1 1.317 4.6 -20 50 ' 53.9 1 1 .317 - . -24 50 52.6 1 1 .317 7.6 - -AVG. 53.05 8.24 J u l y 16 1973 75 100.2 1 1.317 - -17 75 80.4 1 1 .317 - -17 75 67.5 1 1 .317 - -18 75 92 1 1.317 - -AVG. 85.02 Ca l c . 6.13 12.19 Oct . 4 1974 100 Wet 22.6 1 1 .317 - - 2.48 7 100 102.8 1 1 .317 - - 11 .29 8 100 83.9 1 1 .317 - - 9.21 8 100 97.1 1 1 .317 - - 10.66 9 100 101 .6 1 1.317 - - 11 .15 9 100 105 1 1 .317 - - 11 .5 10 100 105 1 1.317 - - 11.5 10 100 115.4 1 1 .317 - - 12.6 10 100 123.5 1 1 .317 - - 13.56 17 100 220 1 .317 - - • 24.16 18 100 No 0 2 41 1 1 .317 - - 4.5 Nov. 14 1974 100 97 1 1.317 15.8 • - 10.65 20 100 117 1 1 .317 15.3 12.85 Date--Ce l l [SH]/Cel1 x 1 0 - 6 % Rx Rate L i g h t Photon F lux % Abs. x l O " 6 g h r - 1 # x 1 0 1 8 phot, h r - 1 % No v. 27 1 9 7 4 1 0 0 Pure 0 2 4 8 . 5 1 1 . 3 1 7 -2 8 1 0 0 Pure 0 2 7 9 . 5 1 1 . 3 1 7 9 . 6 Dec. 2 1 0 0 Pure 0 2 1 0 3 1 1 . 3 1 7 1 7 . 2 3 1 0 0 Pure 0 2 79 1 ; 1 . 3 1 7 6 . 2 5 Sept . 20 1 9 7 6 V 1 0 0 184 2 l a t e 1 . 7 3 9 -2 0 0 1 0 0 121 2 L 1 . 7 3 9 -21 v. 1 0 0 ' 231 2 L 1 . 7 3 9 -27 V 1 0 0 7 8 . 5 2 L 1 . 7 3 9 -27 0 1 0 0 1 1 5 . 4 2 L 1 . 7 3 9 -29 V 1 0 0 1 2 2 . 3 2 L 1 . 7 3 9 -29 0 1 0 0 9 6 . 1 2 L . 1 . 7 3 9 -Oct. 4 1 9 7 6 V 1 0 0 8 5 . 9 2 L 1 . 7 3 9 11 . 1 6 4 0 1 0 0 2 0 2 2 L 1 . 7 3 9 6 . 2 1 6 V 1 0 0 224 2 L 1 . 7 3 9 6 . 4 6 19 V 1 0 0 9 2 . 5 2 L 1 . 7 3 9 7 . 3 19 0 1 0 0 8 9 . 7 2 L 1 . 7 3 9 8 . 4 2 20 V 1 0 0 1 3 8 2 L 1 . 7 3 9 -2 0 0 1 0 0 1 5 3 . 9 2 L 1 . 7 3 9 9 . 7 Nov. 2 1 9 7 6 V 1 0 0 7 6 2 L 1 . 7 3 9 6 .1 2 0 1 0 0 1 0 9 2 L 1 . 7 3 9 7 . 9 2 V 1 0 0 1 5 2 2 L 1 . 7 3 9 5.1 2 0 1 0 0 1 8 2 2 L 1 . 7 3 9 3 . 7 3 V 1 0 0 2 0 5 2 L 1 . 7 3 9 7 . 8 3 0 1 0 0 1 6 6 2 L 1 . 7 3 9 6 . 7 4 V 1 0 0 2 5 2 2 L 1 . 7 3 9 11 . 8 4 0 1 0 0 7 6 . 9 2 L 1 . 7 3 9 7 . 7 8 V 1 0 0 1 6 8 2 1 1 . 7 3 9 7 . 9 8 0 1 0 0 1 8 6 2 L 1 . 7 3 9 -8 N 1 0 0 1 1 2 2 L 1 . 7 3 9 7 . 3 9 V 1 0 0 1 6 5 2 L 1 .739 1 "so2 l O " 6 g hr" [ S H J / C e l l Rx Rate L i g h t Photon F lux % Abs. R S 0 2 <J>CU U d L c — L , c 1 1 x 1 0 - 6 I x 1 0 - 5 g h r - 1 # x 1 0 1 8 phot, h r - 1 % x 1 0 - 6 g h r - 1 on Nov. 9 1976 0 100 237 2L 1.739 1 0 . 5 _ 19 .7 9 N 100 224 2L- 1.739 3.7 - 18 .63 Dec. 8 1976 V 100 158 .7 3 2.2154 - 4 9 . 6 1 2 . 8 8 0 100 359 3 2.2154 - " 4 9 . 7 17.01 * 8 N 100 179 .3 3 2.2154 - 58 .4 10 . 9 18 V 100 198 . 3 3 1.9147 - 41 .7 2 0 . 5 18 0 100 298 . 2 3 2 .1125 • - 41 .7 19 . 6 18 N 100 240 . 5 3 2 .095 • - 45 . 46 1 4 . 2 19 V 100 198 • 3 2 .1968 - 4 5 . 5 11 .5 19 N 100 166 . 5 3 2 .2154 - 48 11 . 16 19 0 100 230 . 8 3 2 .2154 - 45 .7 11 .16 Avg 12 . 72 J u l y 4 1973 150 50.1 1 .317 12.71 _ : 3 . 75 5 150 118 1 1.317 Avg. - : 8 . 8 9 150 . 300 1 1 .317 Ca l c . - 22 .4 10 150 167 1 1 .317 - - 1 2 . 5 12 150 170 1 1 .317 - - 12 .7 13 150 121 1 - 1.317 - - 9 .05 15 150 8 7 . 4 1 1.317 - - : 6 .5 16 150 9 2 . 5 ' 1 1.317 . - - : 6 .9 17 150 104 1 1.317 - - 7 .79 18 150 9 7 . 9 1 1.317 - - 7 .34 Avg 9 .79 Dec. 21 1976 V 250 4 8 7 . 7 3 2 .2129 8 .75 66 .12 1 5 . 4 22 N 250 432 3 2.2154 19 . 19 62 .04 1 2 . 7 22 0 250 424 3 2.2154 20 . 8 60.1 11 . 54 22 V 250 288 3 2.2154 20 .07 61 .9 10 . 94 Jan. 11 V 250 280 . 2 3 1.9879 16 .24 57 .8 14 . 76 11 0 250 368 3 2.0854 16 .57 64.1 1 3 . 3 5 11 N 250 304 3 2.0196 16 .3 56 .0 11 . 59 Date -Ce l l 11 1977 V 250 11 0 250 12 V 250 12 N 250 12 0 250 21 1976 0 250 21 N 250 [SH] /Ce l l x l O " 6 I Rx Rate 9 x 1 0 -6 g h r - 1 L i gh t # Photon F lux x 1 0 1 8 phot, h r - 1 % Abs, % " S 0 2 10- e g hr-Jan Dec. 297 240 314 304 328 464 488 3 3 3 3 3 3 3 1.8824 1 .979 1.9153 2.1075 2.2154 2.20 16.25 14.42 16.61 16.18 18.46 15.84 51.6 50 55.8 54 50.1 68 66 Avg. 12.91 Feb. 23 23 23 25 25 25 26 Ju l y 11 11 12 12 13 13 14 14 1977 0 V N V N N 0 1977 Z V V Z Z V V Z 250 250 250 250 250 250 250 250 250 250 250 250 250 250 250 h Atm. ^ Atm. Atm. ^ Atm. ^ Atm. ^ Atm. ^ Atm. ^ Atm. a- Atm. ^ Atm. ^ Atm. \ Atm. 116. 119 168 82. I l l 112 152. 169 202 184 180 194 438 408 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 1.741 1 .420 1.42 1.42 1.412 1.530 2.197 2,208 2.059 2.1533 2,02 2.01 1.91 1.934 18.5 14.1 15.1 16.8 15.4 15.4 15.2 50.1 40.3 45.4 47.1 49 43.3 33 34 Avg. 6.40 CONTINUED Date -Ce l l [SHJ/Ce l l x 1 0 - 6 I Rx Rate x IO - 6 g h r - 1 L i q h t ' • # Photon F lux x 1 0 1 8 phot. h r - 1 % Abs. % R S 0 2 x 1 0 - 6 g h r - 1 *SH Feb. 28 1977 N 28 0 Mar. 1 N 1 0 3 0 3 N 250 h Atm. 250 h Atm. 250 h Atm.' 250 k Atm. 250 h Atm. 250 h Atm. 254 308 144 168 240 3 3 3 3 3 3 1.433 1.570 1.545 1.723 1.559 13.7 17.4 19.1 16.7 -17.4 8.5 16.23 14.14 6.12 : 7.32 11.09 Avg. 10.98 Jan. 11 1975 11 1975 12 1975 13 1975 13 1975 50 SH-50 S0 2 50 SH 50 S0 2 50 SH-50 S0 2 50 SH-100 S0 2 50 SH-100 S0 2 57.6 50.6 63.4 55.6 51.4 1 1.317 1.317 •1.317 1.317 1.317 14.6 14.6 15.5 32.3 32.3 Avg Avg : 1 . 3.61 1.57 144. APPENDIX B C H 3 S S C H 3 REACTION DATA [ S S ] / C e l l x 1 0 - 6 I Rate SS Photon F lux % Abs. .*ss Date X 1 0 - 6 g h r - 1 x 1 0 1 8 Phot, h r - 1 . . % . . Apr. 3 1975 .25 l i q u i d 55.9 1.317 13.6 1.46 .25 36.5 1.317 13.6 .77 June 20 1975 .25 72.4 .9104 30.2 1.38 * .25 65.8 .9104 30.2 1.18 24 1975 .25 36.2 .9104 30.5 .49 .25 82.2 .9104 30.5 1.55 25 .25 69.1 .9104 30.9 1.23 .25 58.15 .9104 30.9 .98^ 27 1975 .25 82.3 .9104 28.45 1 .66 .25 74 .9104 28.45 1 .46 Sept . 17 1975 .25 119 .9104 30.49 2.39 .25 82.3 .9104 30.49 1.55 18 1975 .25 92.17 .9104 30.5 1.78 .25 69.13 .9104 30.5 1.25 Oct. 2 1975 .25 125 . .9104 27.6 2.80 .25 68 . 9104 27.6 1.35 7 1975 .25 59.2 .9104 29.0 1.07 .25 102 .9104 30.9 1.98 .25- • 70.7 .9104 30.9 1.27 8 1975 .25 128 .9104 27.8 2.85 9 1975 .25 49.3 .9104 20.46 1.18 .25 77.3 .9104 20.46 2.14 15 1975 .25 118 .9104 27.4 2.64 .25 74.1 .9104 27.4 1.52 16 1975 .25 148 .9104 32.9 2.84 .25 106 .9104 32.9 1.95 Oct. 20 1975 .25 88.8 .9104 27.3 1.90 ,25 69.13 .9104 27.3 1.39 21 1975 .25 158 ..9104 28.45 3.53 .25 92 .9104 28.45 1.91 22 1975 .25 88.6 .9104 25.2 2.06 .25 60.9 .9104 25.2 ' 1.28 23 1975 .25 82.3 .9104 25.5 1.86 .25 / 65.4 .9104 25.5 1.39 25 1975 .25 190.9 .9104 28.4 4.35 .25 119.2 .9104 28.4 2.58 28 1975 .25 223.8 .9104 28.4 5.15 .25 156.3 .9104 28.4 3.49 29 1975 .25 131.6 .9104 28.45 2.88 .25 97.1 .9104 28.45 2.03 May 13 1975 .5 37.8 .9104 47 .34 CONTINUED 145. Date [ S S ] / C e l l x l O " 6 I Rate SS x 1 0 - 6 g h r - 1 Photon F lux x 1 0 1 8 phot, h r - 1 % Abs. r s s June 3 1975 .5 164 .9104 44.3 . 2.36 .5 128 .9104 44.3 1.79 4 1975 .5 52.6 .9104 44.6 .59 .5 35.5 .9104 44.6 .33 5 1975 .5- 111.9 .9104 37.5 1 .81 .5 103.7 .9104 37.5 1.65 leak t e s t s .25 14.8 x 10 - 6 g over 4 hours APPENDIX C C H 3 S C H 3 REACTION DATA Date [MSM]/Cel l x IO " 5 I C e l l " 1 R -s x 1 0 - 6 g h r - 1 Photon F lux x 1 0 1 8 phot, h r - 1 % Abs. % Rso x 10 - 6 g h r - 1 J u l y 20 1977 N .5 — 1 atm. 64.04 2.170 4 - 3.54 20 V .5 1 atm. 49.6 1.938 4 - 3.44 21 N .5 1 atm. 116 2.189 4 30 3.35 21 Z .5 1 atm. 96 2.029 4 35 4.94 21 V .5 1 atm. 103 1.844 4 36 5.75 22 V .5 1 atm. 119 1.82 4 • 25.8 7.05 22 z .5 1 atm. 86 1.954 4 25 4.74 29 N .5 1 atm. 60 2.1 4 - 3.96 29 V .5 1 atm. 20 1.55 4 - 1.78 29 Z .5 1 atm. 28 1.75 4 - 2.22 -• Avg . 4.07 24 V .5 k atm. 78.5 1.5703 ' 4 24.7 10.4 24 Z .5 k atm. 76 1.7015 4 25 . 8.36 25 V .5 k atm. 66 1.7621 4 31 4.97 Z .5 k atm. 48 1.7510 4 30 4.43 26 V .5 k atm. 61 1.4499 4 25.8 8.06 z .5 k atm. 56 1.5119 4 23 IT.9 Avg . 8.02 APPENDIX D SULPHUR BALANCE DATA Date -Ce l l [SH] S t a r t x IO " 6 g m l " 1 [SH] End x I O - 6 g m l " 1 [ S 0 2 ] End x IO " 5 g m l - 1 I/Io 290 nm [SS] End x I O - 7 g m l " 1 % S a t End Found Dec. 8 1976 V 5.12 3.2 .599 .962 10.66 8 0 5.6 3.2 .620 .948 15.9 8 N _ - .729 - -18 V 5.6 3.2 .504 .956 n .78 18 0 6.6 2.88 .520 .940 18.08 18 N 5.92 2.92 .567 .967 9.12 19 V 5.52 3.12 .55 .926 22.69 19 0 5.2 3.12 .60 .934 19.88 89.9 19 N 5.76 2.88 .570 .944 16.63 21 N 13.8 7.7 .824 .925 22.33 21 V 13.8 7.9 .799 .918 24.82 21 0 14 8.2 .848 .916 25.32 22 N 15.6 10.2 .775 .925 22.27 22 V 14.8 10.1 .749 .920 24.17 22 0 14.4 9.1 .749 .944 16.13 Jan. 11 1977 0 14.4 9.4 .799 .898 31.62 11 V 14.4 9.8 .699 .918 24.96 11 N 13.8 10.0 .699 .939 17.89 11 N 11.8 8.8 .625 .928 2! .77 11 0 _ - - .920 -11 V 11.8 8.2 .62 .922 23.81 12 N 14 10.2 .674 .925 22.78 12 V 14 10.2 .675 .924 22.91 12 0 12.5 8.4 .625 .919 24.85 73.1 13 N 20.8 18.5 1.074 .908 27.46 13 V 20.7 - - - -13 0 21 18 .998 .902 29.65 CONTINUED \ Date -Ce l l [SH] S t a r t x 1 0 " 6 g m l - 1 [SH] End • x l O " 6 g m l " 1 [ S 0 2 ] End x 1 0 - 6 g m l - 1 I / I 0 290 nm a t End [SS] End x 10 - 7 g m l - 1 % S Found Feb. 1 1977 V 25.4 15 2.19 .59 159.5 2 V 23.2 15 3.1 .622 140.9 2 0 22.6 15 3.3 .553 177.2 3 V 23.4 15.2 3.0 .645 129.9 3 N 23.6 14.8 3.4 .576 164.2 5 N 25.4 17 2.8 .60 152.8 95.2 149. APPENDIX E Concen t ra t i on Dependence o f Emiss ion From Dimethyl Su lph ide Aeroso l [MSM]/Cell x 1 0 _ e I per c e l l Time to Max. Emiss ion I n t e n s i t y of Max. Emiss ion 4 12 min . 2.64 x 10 - 9 A 2 12 2.59 1 11 2.49 1/2 10 1.59 1/4 10 .94 1/8 17 835 1 5 1.39 x l O " 9 A 1/2 4 .945 1/4 14.2 .97 1/8 21 67 1 1 1.58 x 1 0 - 9 A 2 2.27 4 . 2.52 . 150. APPENDIX F DEPENDENCE OF INTENSITY OF EMISSION FROM DIMETHYL SULPHIDE AEROSOL UPON ATMOSPHERIC PRESSURE OF AIR [MSM]/Cell x TO - 6 £/Cell Atmospher ic I n t e n s i t y o f Max. Pressure Emiss ion 4 1 atm. .067 x 10" 8 A 4 1 atm. .072 4 1 atm. .052 4 1 atm. .067 4 • 1 atm. .065 . avg. .646 x l O " 9 A 4 1/2 atm. .32 x l O "9 A 4 1/2 atm. .32 avg. .32 x 1 0 - 9 A 4 1/4 atm. .18 x 1 0 "9 A 4 1/4 atm. .16 avg. J 7 x 10 - 9 A 2 1 atm. .75 x 1 0 -9 A 2 1 atm. .72 avg. .735 x l O " 9 A 2 1/2 atm. .37 x 10 -9 A 2 1/2 atm. .32 2 ? 1 / 2 atm. .36 avg. .35 x 10~ 9 A 2 1/4 atm. .18 x l O "9 A 2 1/4 atm. .2 2 1/4 atm. .23 avg. .203 x l O " 9 A CONTINUED 1 5 1 . [MSM]/Cel l Atmospher ic I n t e n s i t y of Max. x IO " 6 £/Cell Pressure Emiss ion ! 1 atm. 1 . 6 5 x 1 0 - 9 A 1 1 atm. 1 . o 1 1 atm. . 8 1 1 atm. 1.1 1 1 atm. 1 . 0 5 1 1 atm. . 8 avg. 1 . 0 6 6 x IO " 9 A 1 1/2 atm. . 5 5 x 1 0 " 9 A 1 1/2 atm. . 4 2 1 1/2 atm. . 6 2 1 1 /2 atm. . 6 4 5 1 1/2 atm. . 5 4 1 1/2 atm. . 3 9 1 1 /2 atm. . 5 6 •avg. . 5 3 2 x I O - 9 A 1 1/4 atm. . 2 x IO "9 A 1 1/4 atm. . 1 6 1 1/4 atm. . 2 1 1 /4 atm. . 1 2 avg. . 1 7 x I O - 9 A 1/2 1 atm. . 6 2 x IO "9 A 1 /2 1 atm. 1 . 0 5 1/2 1 atm. 1 . 5 1 / 2 1 atm. 1 . 3 2 5 1/2 1 atm. 1 . 3 1 / 2 1 atm. 1 . 1 5 avg. 1 . 1 5 x IO " 9 A 1/2 1 / 2 atm. . 6 3 x 1 0 ~ 9 A 1/2 1 /2 atm. . 9 1 /2 1 /2 atm. . 8 7 avg. .80 x IO" 9 A 1/2 1 /4 atm. . 3 0 5 x IO"9 A 1/2 1 / 4 atm. . 2 6 5 1/2 1/4 atm. . 2 9 avg. . 2 8 6 x 1 0 - 9 A 152.. [MSM]/Cell Atmospher ic I n t e n s i t y of Max. x 1 0 - 6 J l /Ce l l P ressure Emiss ion 1/4 1 atm. .9 x 1 0 "9 A 1/4 1 atm. 1.11 1/4 1 atm. 1.0 1/4 1 atm. 1.16 avg . 1.04 x 1 0 - 9 A 1/4 1/2 atm. .38 x 1 0 -9 A 1/4 1/2 atm. .29 1/4 1/2 atm. .25 avg. .306 x 10- 9 A 1/4 1/4 atm. .08 x l O "9 A 1/4 1/4 atm. .08 1/4 . 1/4 atm. .18 1/4 1/4 atm. .12 1/4 1/4 atm. .08 1/4 1/4 atm. .14 avg .113 x 10" 9 A 1/8 1 atm. .47 x l O "9 A 1/8 1 atm. .42 1/8 1 atm. .61 1/8 1 atm. .35 1/8 1 atm. .40 avg .505 x 1 0 - 9 A 1/8 1/2 atm. .22 x 1 0 "9 A 1/8 1/2 atm. .24 1/8 1/2 atm. .36 1/8 ' 1/2 atm. .20 .255 x l O " 9 A 1/8 1/4 atm. .00 1/8 1/4 atm. .05 x 1 0 - 9 A 1/8 1/4 atm. .08 1/8 1/4 atm. .10 1/8 1/4 atm. .00 1/8 1/4 atm. .00 avg . .0383 x 10- 9 A 153. APPENDIX G DEPENDENCE OF INTENSITY OF EMISSION FROM DIMETHYL SULPHIDE AEROSOL UPON ATMOSPHERIC PRESSURE OF DRY NITROGEN [MSM]/Cell x IO " 6 5,/Cell Atmospheri c P ressure (N 2 ) I n t e n s i t y o f Max. Emiss ion j 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 3.51 x IO " 9 A 3.85 2.40 2.05 4.45 2.45 3.9 2.95 4.15 3.35 2.85 avg. 3.26 x IO" 9 A 1 1/2 atm. 1/2 atm. 1/2 atm. 1/2 atm. 1/2 atm. 2.23 x IO" 9 A 3.4 2.68 2.78 2.88 avg. 2.81 x 10~ 9 A 1 1 1 1 1/4 atm. 1/4 atm. 1/4 atm. 1/4 atm. .98 x IO " 9 A .93 .73 .73 avg. .84 x 1 0 " 9 A 1/2 1/2 1/2 1/2 1 atm. 1 atm. 1 atm. 1 atm. 2.8 x 10 - 9 A 2.43 2.74 2.35 avg . 2.58 x 10~ 9 A 154. [MSM/Cell x l O " 6 Jo/Cell Atmospher ic Pressure (N 2 ) I n t e n s i t y o f Max. Emiss ion 1/2 1/2 1/2 1/2 1/2 atm. 1/2 atm. 1/2 atm. 1/2 atm. .73 x 1CT 9 A .69 .85 .68 avg. .737 x 10" 9 A 1/2 1/2 1/2 1/2 1/4 atm. 1/4 atm. 1/4 atm. 1/4 atm. .16 x 1 0 " 9 A .26 .17 .28 avg. .217 x 10~ 9A 1/4 1/4 1/4 1/4 1/4 1 atm. 1 atm. 1 atm. 1 atm. 1 atm. 1 .45 x l O " 9 A 1.52 .79 1 .04 .76 avg. 1.112 x 10" 9 A 1/4 1/4 1/4 1/4 1/4 1/2 atm. 1/2 atm. 1/2 atm. 1/2 atm. 1/2 atm. .21 x l O " 9 A .475 .35 .20 .18 avg. .283 x 10" 9 A 1/4 1/4 1/4 atm. 1/4 atm. .04 x l O " 9 .03 avg. .035 x 10~ 9A 1/8 1/4 atm. 02 x l O " 9 A 155 APPENDIX H E S T I M A T I O N O F R A T E C O N S T A N T S F O R R E A C T I O N S ( 3 - 7 ) A N D ( 3 - 1 5 ) (A) Es t imat ion of the CH3S Ox ida t i on Rate Constant The o x i d a t i o n ra te constant f o r r e a c t i o n (3-7) may be est imated r e l a t i v e to the r a t e constant f o r recombinat ion o f the CH 3S r a d i c a l ( 3 -9 ) . From experiment 73% o f su lphur atoms formed d i s u l p h i d e and 16.8% o x i d i z e d . Thus the recombinat ion p roceeds 'a t a ra te 4.3 t ha t o f o x i d a t i o n . Now R c = k c [ C H 3 S ] 2 molecu les d i s u l p h i d e produced = 2 k c [ C H 3 S ] 2 r a d i c a l s CH3S reac ted R = k [CH 3 S] [ 0 2 ] ox ox L and R = 4.3 R^  c ox k. = 2.5 x 1 0 1 0 M" 1 s " 1 Thus 2 k c [ C H 3 S ] 2 = 4.3 k Q x [CH 3 S] [ 0 2 ] 2 k c [ C H 3 S ] kox " 4 .3[0 2F The r a t e o f combinat ion o f methyl t h i y l r a d i c a l s i s a l s o known from which we may c a l c u l a t e the concen t ra t i on o f methyl t h i y l spec ies i n the r e a c t i o n atmosphere. R = 73% of. CH 3S produced from CH3SH f rora.F igure 22 f o r a photon c abso rp t i on r a t e of 3 x 1 0 1 7 photons • h r - 1 . Then d[CH 3SHl = 4 1 7 x 1 0 i 8 m o 1 e c u i e s • h r " 1 dt Thus d t CH 3 SSCH 3 ] = 3 x 1 0 1 8 , m o l e c u 1 e s . h r - i dt c. 18 3 x 1 0  (2) (6 .02 x 10^ J ) 40 3600 10 3 1 M s - ! 1.755 x 1 0 - 8 M s _ i Now R = 2k [ C H 3 S ]2 = 1.755 x l O " 8 M s " 1 c c Thus [CH 3 S] 2k N 1.755 x I P " 8 2(2 .5 x 1 0 1 U ) = 5.9 x 1 0 " 1 0 M 157 2 k c [CH 3 S] T h e n k o x = 4 .3 L02J 2(2 .5 x I O 1 0 ) (5.9 x I O " 1 0 ) 4 .3 (8.17 x 1 0 - 3 ) 8.39 x IO 2 M s _ 1 (B) Es t ima t i on o f the Me ta the t i c a l Rate Constant f o r React ion (3-15) I f r e a c t i o n (3-15) i s to occu r , i t must proceed a t a ra te g rea te r , than the mutual i n t e r a c t i o n o f HOO (k r f = 1.5 x 10 9 M - 1 s _ 1 ) . I f the metathes i s d id not occu r , the HOO i s produced by CH3S a t one r a d i c a l per absorbed photon ( v i a r ea c t i on s 3-1, 3-7, 3-12) . For an absorbed photon ra te o f 3 x 1 0 1 7 photon • h r " 1 3 x 1 0 1 7 10 3 1 R d = 2 k d [HOO] 2 - I a = 6 > 0 2 x 1 0 2 3 • 4 Q • 3 6 Q 0 3.46 x I O - 9 e i n JT 1 s •9 Wl ~ 9 T , „ r u n r n _ 3.46 x 10"^ M s " . Thus [HOO] 3 X 10 9 M - ^ - 1 = = 1 * 0 x 1 0 M Now i f we assume the metathes is to be a f a c t o r o f 10 g rea te r than the mutual i n t e r a c t i o n then R^  = 10 R^. 158 R k [HOO] [CH 3SH] So m _ m _ - I Q R^  2 k d LHOOJ^ Thus 20 k d [HOO] cm = [CH 3SHJ Now when I = 3 x 10 a 1 7 [CH 3SH] = 250 - i i i / c e l l 13.4 x 1 0 _ b g/ml = 2.79 x 10" 1 20(1.5 x 1 0 9 U 1 . 0 7 x I P " 9 ) Thus k m = — [2779 X 10-*) = 1.15 x 10 5 M _ 1 s " 1 For [CH 3SH] = 1.53 x 10"1* M Then R 1 5 = (1.15 x 1 0 5 M - 1 s ^ H l ^ x 1 0 " 4 M) [HOO] = 17.5 [HOO] s -1 

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