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The formation of O₂(a¹Δg̳) by O-atom recombination Ali, Ayoub Azam 1986

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THE FORMATION OF 0,(aA ) BY 0-ATOM RECOMBINATION 2 " g BY AYOUB AZAM ALI B . S c , THE UNIVERSITY OF TORONTO, 1983 A THESIS SUBMITTED IN PARTIAL FULFILLEMNT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA MAY 1986 (c) Ayoub Azam A l i , 1986 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of vJ^\<P\fv\\ s4/lA  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 E-6 (3/81) ABSTRACT The formation of 0 2 ( a ) by the recombination of 0-atoms was s t u d i e d i n a d i s c h a r g e - f l o w system. The r a t e of formation of 02(a) by the homogeneous recombination of 0-atoms i n the absence of 0 2 was found to be second-order in [0] and f i r s t - o r d e r i n [M]. When 0 2 was added the r a t e of formation i n c r e a s e d l i n e a r l y with i n c r e a s i n g [ O 2 ] . The f o l l o w i n g mechanism was presented as being the sim p l e s t which i s c o n s i s t e n t with the data: 0 + 0 + M s - 0 2 + M f k 1 ° 2 * + N 2 ?-0 2(a) + N 2 f 2 k 2 ° 2 * + ° 2 > - 0 2(a) + 0 2 f 3 k 3 where, " f " repr e s e n t s the f r a c t i o n a l y i e l d of the s p e c i f i e d 0 2 product i n the r e a c t i o n s , and M i s mainly N 2 > A n a l y s i s of the experimental data i n terms of t h i s mechanism gave the f o l l o w i n g r e s u l t s : f j f j = 0.071 (+/-0.007) f ] f 3 k 3 / k 2 = 5.0 (+/-0.5) T h i s mechanism i s c o n s i s t e n t with the 02(a) nightglow and with the experimental data when the f o l l o w i n g c o n d i t i o n s are s a t i s f i e d : a) k 2 / / k 3 = 0 , 1 2 b) f 3 / f 2 = 8.5 c) f t f 3 = 0.6 The y i e l d of 02(a) by O-atom recombination on g l a s s wool, with a s u r f a c e recombination c o e f f i c i e n t of 6(+/-1)x10~ 5, was found to be 0.08(+/-0.02). ACKNOWLEDGEMENTS I w o u l d l i k e t o t a k e t h i s o p p o r t u n i t y t o p u b l i c l y r e c o g n i z e t h e c o n t r i b u t i o n s o f some p e o p l e t o t h e c o m p l e t i o n o f t h e work d e s c r i b e d i n t h i s t h e s i s and t o t h e c o m p l e t i o n o f t h e a c a d e m i c r e q u i r e m e n t s f o r my M a s t e r ' s d e g r e e . F i r s t l y , I am g r a t e f u l f o r t h e e f f i c i e n t s e r v i c e s r e n d e r e d by t h e E l e c t r i c a l and M e c h a n i c a l s h o p s . I n p a r t i c u l a r , I w o u l d l i k e t o t h a n k B i l l H e n d e r s o n , P h i l C a r p e n d a l e , J o e S h i m , C h a r l i e Mc C a f f e r t y , and Ron M a r w i c k f o r t h e i r e f f o r t s . S e c o n d l y , I am g r a t e f u l t o P a u l Y o n H i n and Kong Hung S z e f o r t h e i r a s s i s t a n c e i n c o m p l e t i n g t h e a c a d e m i c r e q u i r e m e n t s f o r my d e g r e e . T h i r d l y , I w o u l d l i k e t o t h a n k P r o f e s s o r R. E . P i n c o c k f o r t h e s u p p o r t w h i c h I r e c e i v e d f r o m h i m . F i n a l l y , I am g r a t e f u l f o r t h e s u p e r v i s i o n and s u p p o r t o f P r o f e s s o r E . A . O g r y z l o d u r i n g t h e t i m e r e q u i r e d t o c o m p l e t e t h e M a s t e r ' s p r o g r a m . TABLE OF CONTENTS SECTION 1: INTRODUCTION 1 . Introduction to the night airglow. page 2 2. Introduction to the 02(a) component of the nightglow. page 3 3 . Spectroscopic characteristics of the 0_(a) emission at 1270 nm. page 10 4. Possible excitation mechanisms for the 02(a) nightglow. page 14 SECTION 2: APPARATUS AND EXPERIMENTAL METHOD 1 . Description of the flow system. page 19 2. Description of the detection system. page 24 3 . Calibration of the detection system. page 26 4. Measurement of reaction time. page 29 5. Surface recombination studies. page 42 SECTION 3 : RESULTS AND DISCUSSION 1 . Experimental data for the formation of 02(a) by the homogeneous recombination of 0-atoms. page 47 2. Determination of the rate law for the formation of 0„(a) by the homogeneous recombination of O-atoms. page 55 3 . Tne proposed mechanism for the formation of 02(a) by • the homogeneous recombination of 0-atoms. page 82 4. Analysis of the 02(a) nightglow in terms of the proposed mechanism. page 86 5. Comparison of the proposed mechanism with the existing literature. page 9 3 6 . Experimental data for the formation of 02(a) by the heterogeneous recombination of 0-atoms. page 94 Calculation of the yield of ©2(a) by the recombination 98 of 0-atoms on glass wool. page Discussion of the significance of the homogeneous recombination of 0-atoms to the surface recombination studies. page 101 Comparison of the results from the surface recombination studies with the existing literature. page 103 1 0 . Determination of the surface recombination coefficient. page SECTION 4: CONCLUSION page 1 0 9 REFERENCES page 111 2/ LIST OF FIGURES 1. The bound electronic states of 0^  correlating with two ground state 0-atoms. page 4 2. Nomenclature of some o p t i c a l t r a n s i t i o n s i n molecular oxygen. page 6 3. Some important o p t i c a l transitions for 0-atoms i n the atmosphere. page 8 4. The calculated spectrum for the 0^(a) emission near 1270 nm. page 12 5. The flow system and the detection system used i n the experiments. page 20 6. The observed spectrum for the 02(a) emission near 1270 nm. page 30 7. The observed emission intensity of the NO 2 afterglow as a function of [NOJ. page 32 8. The wavelength-dependent p r o f i l e of the rate constant for the NO+0 reaction. page 34 9. The observed NO^ spectral d i s t r i b u t i o n . page 36 10. The apparatus used to measure reaction time. page 39 11. The effect of increasing [ojon the formation of 0 2(a). page 48 12. The effect of increasing [MJon the formation of 0 2(a). page 51 13. The effect of increasing j^02]on the formation of 0 2(a). page 53 14. Determination of the rate of formation of 0 2(a). page 56 15. Determination of the rate of formation of 02(a) at several [o] . page 64 16. Determination of the order of the dependence of the rate of formation of 02(a) on £ OJ . page 66 17. Determination of the rate of formation of 02(a) at several [M]. page 70 Vi 18. Determination of the order of the dependence of the rate of formation of 0^(a) on [ M ] . page 72 19. Determination of the rate of formation of 02(a) at several [O2]. page 78 20. The rate of formation of 02(a) as a function o f [ 0 ] • page 80 21. The calculated y i e l d of 0„(a) as a function of [ 0 2 ] / [ N 2 ] . 2 page 88 22. The calculated rate of formation of 02(a) as a function of a l t i t u d e . page 91 23. Measurement of the N0 2 afterglow and [02(a)] i n the surface recombination studies. page 95 LIST OF TABLES 1. The formation of 02(a) at several [ o j . . page 60 2. The formation of 02(a) at several [M], page 68 3. The formation of 02(a) at sevaral [o ] . page 75 A. The yield of 0 (a) by the recombination of 0-atoms on glass wool. page 99 D i l i SECTION 1: INTRODUCTION 1. I n t r o d u c t i o n t o t h e n i g h t a i r g l o w . page 2 2. I n t r o d u c t i o n to t h e 0 2 ( a ) component o f t h e n i g h t g l o w . page 3 3 . S p e c t r o s c o p i c c h a r a c t e r i s t i c s o f t h e 0 2 ( a ) e m i s s i o n a t 1270 nm. page 10 4 . P o s s i b l e e x c i t a t i o n mechanisms f o r t h e 0 2 ( a ) n i g h t g l o w . page 14 1 SECTION 1.1 INTRODUCTION TO THE NIGHT AIRGLOW The night a i r g l o w i s a f a i n t glow i n the atmosphere that has i t s o r i g i n s i n photochemical p r o c e s s e s . Astronauts on re t u r n voyages from outer-space see the nightglow as an envelope sheathing the nig h t s i d e of the E a r t h . In the l a t t i t u d e s of the Temperate Zones, Earth-bound observers see i t as a f a i n t , m u l t i c o l o u r e d glow almost uniform i n b r i g h t n e s s over the e n t i r e night sky; but in A r c t i c and A n t a r c t i c l a t t i t u d e s the glow i s o f t e n overpowered by the l i g h t of the a u r o r a . The most d i s t i n g u i s h a b l e c o l o u r s i n the nightglow are green and blue; these r e s u l t from e x c i t e d O-atoms and e x c i t e d O2, r e s p e c t i v e l y . In a d d i t i o n to the v i s i b l e component, the nightglow c o n s i s t s of UV r a d i a t i o n and IR r a d i a t i o n . The st r o n g e s t f e a t u r e s of 1 2 3 the nightglow are i n the near IR. ' ' The nightglow c o n s i s t s of atomic and molecular l i n e s , bands, and continuum, systems of n e u t r a l and i o n i z e d atmospheric c o n s t i t u e n t s . T h e r e f o r e , rocket probe and s a t e l l i t e i n v e s t i g a t i o n s of the nightglow provide i n s i g h t i n t o the composition of the atmosphere. 2 In addition, laboratory study in support of these investigations a s s i s t in interpretations of the photochemistry and dynamics of the atmosphere. SECTION 1.2  INTRODUCTION TO THE Q 2(a) COMPONENT  OF THE NIGHTGLOW Excited states of 0 2 make important contributions to the nightglow of the Earth. Figure 1 shows the bound electronic states of 0 2 c o r r e l a t i n g with ground-state O-atoms, and Figure 2 shows the t r a n s i t i o n s which have been observed for e l e c t r o n i c a l l y excited 0 2 in the nightglow. In making subsequent reference to these states the alphabetical prefixes shown in Figure 1 w i l l be used for i d e n t i f i c a t i o n . Therefore, the e l e c t r o n i c a l l y excited state of 0 2 l a b e l l e d 0 2(a 1Ag) in Figure 1 w i l l be i d e n t i f i e d as 0 2 ( a ) . In addition, Figure 3 shows some of the atmospherically important t r a n s i t i o n s for 0-atoms. Emission from 0 2(a) in the nightglow i s stronger than the emission from any other state of 0 2« The (0,0) component of this band system l i e s in the near IR at 1270 nm, and the (0,1) component l i e s at 1580 nm. 3 FIGURE 1 The bound e l e c t r o n i c s t a t e s o f 0 2 c o r r e l a t i n g w i t h two g round-s t a t e O-atoms (from re fe rence Potential Energy (I04cm1) FIGURE 2 Nomenclature of some optical transitions in molecular oxygen (from reference 2). 6 Energy (wavenumbers) o o o o o o o o o o o o o o o o O o o o llerzberg II Atmospheric H • o t» z o x o « • M o M e I Chamberlain M Herzbergl > w M c + 00 w M c I Schumann- Runge Energy (eV) FIGURE 3 Some i m p o r t a n t o p t i c a l t r a n s i t i o n s o f 0 -a toms i n t h e a tmosphe re ( f rom r e f e r e n c e 2). 8 Although the (0,0) component i s 80 times more intense that the (0,1) component, ground-based measurements of 0 2 ( a ) are r e s t r i c t e d to the 1580 nm emission. T h i s i s because there i s resonance a b s o r p t i o n of the 1270 nm r a d i a t i o n i n the atmosphere below the 0 2 ( a ) e m i t t i n g l a y e r , whereas the 1580 nm r a d i a t i o n i s t r a n s m i t t e d . However, the more intense 1270 nm emission i s p r e f e r a b l e f o r l a b o r a t o r y s t u d i e s , rocket probe i n v e s t i g a t i o n s , and s a t e l l i t e i n v e s t i g a t i o n s of the O-(a) emission i n the nightglow. SECTION 1.3  SPECTROSCOPIC CHARACTERISTICS OF THE Q 2(a) EMISSION AT 1270 NM The e x i s t e n c e of the 0 2 ( a ) s t a t e was f i r s t 5 p r e d i c t e d by M u l l i k e n a f t e r studying the lowest e l e c t r o n c o n f i g u r a t i o n of 0 2. The f i r s t experimental evidence f o r t h i s s t a t e was obtained by E l l i s and Kneser^ in the IR a b s o r p t i o n spectrum of l i q u i d 0 2, where i t g i v e s r i s e to a p r o g r e s s i o n of bands from 1261 nm to s h o r t e r wavelengths. H e r z b e r g 7 photographed t h i s r e g i on of the s o l a r spectrum and concluded that i t r e s u l t s from the 0_(a) to 0 o ( X ) t r a n s i t i o n . 10 The 0 2 ( a ) to 0 2(X) t r a n s i t i o n i s e l e c t r i c d i p o l e forbidden by both the s p i n s e l e c t i o n r u l e and the angular momentum s e l e c t i o n r u l e . T h e r e f o r e , r a d i a t i o n may appear only as a r e s u l t of t r a n s i t i o n s allowed by the magnetic d i p o l e s e l e c t i o n r u l e s or magnetic quadrupole s e l e c t i o n r u l e s . Using the s e l e c t i o n r u l e s 8 f o r magnetic d i p o l e r a d i a t i o n , Herzberg and Herzberg were able to f i n d good agreement between t h e i r observed spectrogram f o r the 0 2 ( a ) emission and t h e i r p r e d i c t e d . 9 spectrum. Subsequently, Gush and B u i ] S were able to use a balloon-borne Michelson i n t e r f e r o m e t e r to o b t a i n the 0 2 ( a ) spectrum near 1270 nm. Using the f r e q u e n c i e s measured by Herzberg and Herzberg and the l i n e s t r e n g t h s t a b u l a t e d by Van V l e c k 1 ^ , Gush and B u i j s were a b l e to c o r r e l a t e t h e i r observed spectrum with a c a l c u l a t e d p r o f i l e (see F i g u r e 4). 11 FIGURE 4 A c o m p a r i s o n o f t h e s p e c t r u m o b s e r v e d by Gush and B u i j s (a) w i t h t h e p r o f i l e t h e y c a l c u l a t e d f o r t h e 02 (a) t o 0 0 ( X ) t r a n s i t i o n (b) ( f r o m r e f e r e n c e 9 ) . 12 7800 7900 6000 7800 F r e q u e n c y , c m * ' 1 3 SECTION 1.4  POSSIBLE EXCITATION MECHANISMS FOR THE Q 2(a) NIGHTGLOW Thomas and Young 1 1 have measured the a l t i t u d e p r o f i l e f o r the 0 2 ( a ) nightglow i n t e n s i t y and the 0-atom c o n c e n t r a t i o n s i m u l t a n e o u s l y . They found that the 0 2 ( a ) p r o d u c t i o n r a t e peaks near an a l t i t u d e of 90 km, at a value of 8x10 4 molec cm ^ sec 1 , and [0] peaks at 1 1 -3 a value of 6.0x10 atoms cm near t h i s a l t i t u d e . Since [O] and the 0 2 ( a ) production r a t e both peak near the same a l t i t u d e i t i s p o s s i b l e that O-atom recombination can account f o r . the ®2^a^ p r o d u c t i o n r a t e . The simplest r e p r e s e n t a t i o n of t h i s mechanism i s r e a c t i o n 1.1: (1.1) 0 + O + M = ~ 0 2 ( a l l s t a t e s ) + M k 1 where, M i s any sp e c i e s i n the atmosphere, but near 90 km i t i s u s u a l l y N 2 or 0 2 because of t h e i r presence i n l a r g e c o n c e n t r a t i o n s . Since a l l of the bound s t a t e s of 0 2 c o r r e l a t e with two ground-state O-atoms 0 2 ( a ) can be formed by O-atom recombination. u I f * s ^ o r m e ( ^ O-atom recombination and emits r a d i a t i o n a c c o r d i n g to r e a c t i o n 1.2, (1.2) 0 2 ( a ) - ^ 0 2 ( X ) + h^ > then the 0 o ( a ) p r o d u c t i o n r a t e (I ) i n the absence of £ a quenching i s given by the f o l l o w i n g e quation: (1.3) I = f k.[0] 2[M] a a i where: a) I = 8x10 molec cm sec near 90 km. a b) f i s the f r a c t i o n a l y i e l d of 0,(a) by O-atom recombination. c) [ O]=6.0X10 1 1 atoms cm" 3 near 90 km. 1 1 d) [N 2]=3.6x10 1 3 molec cm" 3 and [ 0 2]=9.4x10 1 2 molec -3 12 cm near 90 km. — 32 6 - o — 1 e) k 1=1.12x10 cm molec sec at a temperature of 200 K, 1 3 and near 90 km the temperature i s 200 K. 1 2 S u b s t i t u t i o n of these values f =0.4; that i s , 40% of a recombination must be 0~(a) i n t o equation 1.3 g i v e s the products of O-atom to account f o r the O-(a) 15 nightglow i n t e n s i t y measured by Thomas and Young. An a l t e r n a t i v e mechanism f o r the e x c i t a t i o n of the 0 2 ( a ) nightglow near 90 km by O-atom recombination i s the " p r e c u r s o r " mechanism. T h i s type of mechanism was 1 4 f i r s t proposed by Barth and Hi l d e b r a n d t to account fo r the 0 ( 1 S ) emission at 557.7 nm i n the atmosphere. The i n i t i a l step i n t h i s type of mechanism i s the formation of an e l e c t r o n i c a l l y e x c i t e d s p e c i e s of 0 2 (the " p r e c u r s o r " ) by O-atom recombination. Subsequent quenching of the p r e c u r s o r can r e s u l t i n the formation of 0 2 ( a ) . In the succeeding s e c t i o n s of t h i s t h e s i s the p r e c u r s o r s p e c i e s of 0 2 i n v o l v e d in a r e a c t i o n i s * 1 denoted by 0 2 . Ogryzlo has proposed that p r e c u r s o r mechanisms can account f o r the formation of 0 2 ( c ) , 0 2 ( b ) , and 0 ( 1 S ) i n the atmosphere, although the i d e n t i t y of the p r e c u r s o r (or p r e c u r s o r s ) i s unknown. P r e l i m i n a r y r e s u l t s r e p o r t e d by O g r y z l o 1 g i v e the y i e l d of 0 2 ( a ) by O-atom recombination i n the absence of 0 2 as about 0.1. T h i s i s only 1/4 of the y i e l d r e q u i r e d to account f o r the 0 2 ( a ) nightglow i n t e n s i t y measured by Thomas and Young. However, Ogry z l o r e p o r t s that the a d d i t i o n of 0 2 to a stream of recombining 0-atoms d r a m a t i c a l l y i n c r e a s e s the r a t e of formation of 16 02(a). Ogryzlo and co-workers found a s i m i l a r e f f e c t of 0 2 on the r a t e of formation of O-atom recombination, and presented a p r e c u r s o r mechanism f o r the formation of 02(b) which i s c o n s i s t e n t with t h e i r experimental data. In the work d e s c r i b e d i n t h i s t h e s i s the formation of 0 2(a) by O-atom recombination was s t u d i e d i n a d i s c h a r g e - f l o w system to determine whether a simple, d i r e c t mechanism can account f o r i t s formation, or whether, as was the case with 02(b), a p r e c u r s o r mechanism i s r e q u i r e d . 17 SECTION 2: APPARATUS AND EXPERIMENTAL METHOD 1. D e s c r i p t i o n o f t h e f l o w s y s t e m . page 19 2. D e s c r i p t i o n o f t h e d e t e c t i o n s y s t e m . page 24 3 . C a l i b r a t i o n o f t h e d e t e c t i o n s y s t e m . page 26 4 . Measurement o f r e a c t i o n t i m e . page 29 5 . S u r f a c e r e c o m b i n a t i o n e x p e r i m e n t s . page 42 18 SECTION 2.1 DESCRIPTION OF THE FLOW SYSTEM In order to study the recombination of O-atoms i n t o the 0 2 ( a ) s t a t e the flow system and the d e t e c t i o n system shown i n F i g u r e 5 were used. A small percentage of N 2 flowing through the d i s c h a r g e tube was d i s s o c i a t e d to give N-atoms. D i s s o c i a t i o n energy was provided by microwaves as the gas flowed a c r o s s the microwave c a v i t y . An E l e c t r o M e d i c a l S u p p l i e s Microton 200 was used to generate microwaves. The inner s u r f a c e of the d i s c h a r g e tube was coated with syrupy phosphoric a c i d to minimize subsequent N-atom recombination on the Pyrex w a l l . In a d d i t i o n , p r i o r to l e a v i n g the di s c h a r g e tube the gas flowed through a g l a s s wool p l u g . The plug p r o v i d e d a s u r f a c e on which v i b r a t i o n a l l y e x c i t e d N 2 formed by the di s c h a r g e c o u l d be c o l l i s i o n a l l y d e a c t i v a t e d . The presence of N-atoms in the flow tube c o u l d be re c o g n i z e d by the yellow 3 a f t e r g l o w which comes from the B ff s t a t e of N 2 formed when N-atoms recombine. Oxygen atoms were generated i n the neck of the flow tube by adding NO to the stream of N-atoms. The 19 FIGURE 5 The flow system and the detection system used to study the formation of 02(a) in the present experiments. l=microwave c a v i t y 2=capacitance manometer 3=connector 4=light chopper 5=monochromator 6=Ge detector 7=bias supply 8=lock-in a m p l i f i e r 9=chart recorder 20 Vacuum Pumps 6 4 A f o l l o w i n g r e a c t i o n r e s u l t e d i n the removal of N-atoms. and t h e i r replacement by O-atoms: (2.1) N + NO >-N2 + 0 At the p o i n t where the [ N O ] added i s e q u a l t o the i n i t i a l [N ] ( [ N ] Q ) the f l o w tube appears b l a c k . At t h i s p o i n t a l l of the N-atoms have r e a c t e d w i t h N O , and the i n i t i a l [0] ( [ 0 ] Q ) i s e q u a l t o the [ N O ] added. The f u r t h e r a d d i t i o n of N O beyond t h i s e q u i v a l e n c e p o i n t r e s u l t s i n r e a c t i o n 2.2, and the o b s e r v a t i o n of a g r e e n i s h - y e l l o w a f t e r g l o w . T h i s a f t e r g l o w i s c h a r a c t e r i s t i c of e l e c t r o n i c a l l y e x c i t e d N0 2. (2.2) 0 + N O + M =-N02 + hV The e x p e r i m e n t s were performed w i t h the a d d i t i o n of a v e r y s m a l l e x c e s s of N O beyond the e q u i v a l e n c e p o i n t . T h i s r e s u l t e d i n a g r e e n i s h - y e l l o w background f o r the 0 2 ( a ) e m i s s i o n . However, i t p r o v i d e s a c o n v e n i e n t method f o r m o n i t o r i n g the r e l a t i v e [0] a l o n g the f l o w tube, and e n s u r e s t h a t N-atoms a r e c o m p l e t e l y absent from the body of the f l o w t u b e . T h e r e f o r e , upon emerging from the neck of the f l o w tube the r e a c t a n t m i x t u r e c o n s i s t e d of N ~ , 0-atoms, a s m a l l [ N O ] , and 22 only a t r a c e [NO,,] because of the very f a s t r e a c t i o n which i s shown below. ( 2 . 3 ) NO + 0 2 A l l of the gases used i n the experiments were minimum p u r i t y f o r N 2 was 99.998%. A s p e c i a l l y -requested mixture of 10% NO i n N 2 was used to pr o v i d e NO f o r g e n e r a t i n g O-atoms. For some experiments 0 2 was r e q u i r e d . Lindes' "dry" 0 2, with a l i s t e d minimum p u r i t y of 99.995% was used. The gases were used d i r e c t l y from " T - s i z e d " c y l i n d e r s . P r i o r to entry i n t o the flow tube the pressure of the compressed gas was reduced by a r e g u l a t o r a t t a c h e d to the c y l i n d e r , and then a Nupro s h u t - o f f v a l v e . F i n e - c o n t r o l of the gas flow was obtained by u s i n g an Edwards needle v a l v e immediately preceding e n t r y of the gas i n t o the flow tube. obtained from Linde S p e c i a l t y Gases. The l i s t e d 23 SECTION 2.2 DESCRIPTION OF THE DETECTION SYSTEM The d e t e c t i o n system used to monitor the 02(a) emission i s d e p i c t e d i n F i g u r e 5. I t c o n s i s t e d of the f o l l o w i n g components: a) A combination l i g h t - c h o p p e r and 200 Hz o s c i l l a t o r assembly from American Time Products. b) A Bausch and Lomb model 33-06-03 g r a t i n g monochromator. T h i s i s o p e r a t i o n a l between 700 nm and 1600 nm. c) A North Coast model E0-817 i n t r i n s i c germanium d e t e c t o r and b i a s supply u n i t . d) A P r i n c e t o n A p p l i e d Research C o r p o r a t i o n model 5101 l o c k - i n a m p l i f i e r . e) A BBC Goerz Metrawatt Servogor 120 dual sample c h a r t r e c o r d e r . An e x t e n s i o n at the f r o n t of the monochromator was used to l i m i t i t s f i e l d of view to a 6 mm h o r i z o n t a l d i s t a n c e at the f a r w a l l of the flow tube. The c a l i b r a t i o n of t h i s d e t e c t i o n system to y i e l d the a b s o l u t e [0,(a)] from observed peak h e i g h t s i s 24 described in the following section. For some experiments i t was useful to monitor the r e l a t i v e [0] along the flow tube. The intensity of the N0 2 afterglow from reaction 2.2 i s proportional to [0] and [NO]. 1^ However, there i s no net change in [NO] along the length of the flow tube because of reaction 2.3. Therefore, any change in the N0 2 emission intensity along the flow tube must result from changes in [0]. A Hamamatsu IP28 photomultiplier tube was used to monitor the greenish-yellow N0 2 afterglow. The photomultiplier was fastened to the 0 2^ a^ detection assembly; th i s allowed for the simultaneous measurement of the 0 2(a) emission and the N0 2 emission. Ah Ortec system consisting of a model 9349 l o g / l i n ratemeter, a model 9301 fast preamplifier, and a model 9302 amplifier/discriminator was used in conjunction with the photomultiplier. A Hamner model NV-19 high voltage power supply was used to provide power for the Ortec system. 25 SECTION 2.3 CALIBRATION OF THE DETECTION SYSTEM The presence of 0 2(a) in the flow system was inferred from an emission peak centered at 1270 nm. This peak was superimposed on a broad N0 2 emission band. For the resolution l i m i t of the 0 2(a) detection system the N0 2 emission appeared as a continuous band. The N0 2 afterglow provided a baseline from which the observed 0 2(a) emission peak height was measured. Cal i b r a t i o n of the detection system to y i e l d the absolute [0 2(a)] was based on the method of Fontijn and 1 7 co-workers, who developed the NO+O chemilummescence reaction as a standard. However, the c a l i b r a t i o n could not be performed at 1270 nm because of the presence of 0 2(a) in the system under the required conditions. Instead the c a l i b r a t i o n was performed at 1150 nm, where the purity of the N0 2 emission was assured. In order to ensure the accuracy of subsequent measurements the c a l i b r a t i o n of the detection system was frequently repeated. In addition, once the detection system was ca l i b r a t e d i t s dimensions were kept constant. A t y p i c a l c a l i b r a t i o n is outlined 26 below. The f o l l o w i n g i s a l i s t of d e f i n i t i o n s used i n the c a l i b r a t i o n of the 02(a) d e t e c t i o n system: ( 1 ) g = i a / i a -( 2 ) 9' " ^ . i s ^ i . i s ' ( 3 ) 5" = I 1 . 2 7 ^ 1 . 21 (4) I K 1 5 ' = k K l 5 ' B P [ N 0 ] [ 0 ] = slope [NO] (5) I 1 > 1 5 = k 1 > 1 5 B P [ N O ] [ 0 ] (6) l u 2 1 = k K 2 7 B P [ N 0 ] [ 0 ] where: a) I and I ' are the a b s o l u t e and observed 0 o ( a ) a a 2 emission i n t e n s i t i e s at 1270 nm, r e s p e c t i v e l y . b) I, , c and I, ( I , , c ' and I, -,-,') are the a b s o l u t e I . I O \ . C I 1,10 \ m £. I and observed (bracketed) N0 2 emission i n t e n s i t i e s at 1150 nm and 1270 nm, r e s p e c t i v e l y . c) k, 1 C and k. 0-, (k. 1 C ' and k. -•,') are the 1.1D 1 .2. I 1.10 1 . I. I a b s o l u t e and observed (bracketed) r a t e c o n s t a n t s f o r the NO+O r e a c t i o n at 1150 nm and 1270 nm, r e s p e c t i v e l y . 2 7 d) BP i s the monochromator bandpass. e) slope i s the slope of a plot of I 1 1g' versus NO] for NO added to a stream of O-atoms. The c a l i b r a t i o n was performed in the following steps: Step 1: From d e f i n i t i o n s 4 and 5 i t follows that: (2.4) ^ . i s ^ L I B ' = k 1 . 1 5 B P [ 0 ] / s l ° P e Step 2: From d e f i n i t i o n s 1 and 2, and equation 2.4 i t follows that: (2.5) l a = U K 1 5 B P [ 0 ] / s l o p e ) ( g / g ' ) l a ' Step 3: Since g and g" both measure the s e n s i t i v i t y at 1270 nm, g=g". Therefore, by using d e f i n i t i o n s ' 2 and 3, and then 5 and 6, i t can be shown that: (2.6) g/g' = U,.27/*,., 5><I,., 5'/I K 2 7'> Step 4: From reaction 1.2 i t can be shown that I =k [ 0 o ( a ) ] . Therefore, substitution of equation 2.6 28 into equation 2.5 gives the following expression for the absolute [02(a)]: (2.7) [0 2(a>] = k l . 2 7 B P [ 0 ] ( I 1 . l 5 , / I 1 . 2 7 , ) I a ' slope k a where: a) k = 2.54x10 4 sec 1 (from reference 18) a b) BP = 12.8 nm (see Figure 6). c) slope = 1.95X10"13 cm/(molec cm"3) and [O]=3.70x10 1 4 atoms cm (see Figure 7). - 2 0 — 1 3 d) k 1 2 7 = 2 « 3 x 1 0 (molec cm /sec)/nm (see Figure 8). e) I 1 ^ ' / I , 2 7 ' = 1 , 3 ( s e e F i 9 u r e 9 ) « SECTION 2.4  MEASUREMENT OF REACTION TIME The 0 2(a) detection system and the photomultiplier assembly were mounted on a movable plate. An underlying track allowed for the movement of the plate along the horizontal axis of the flow tube (see Figure 5). Therefore, the detection systems could be positioned at any distance along the length of the flow 29 FIGURE 6 S p e c t r u m f o r t h e 0^(a) e m i s s i o n a t 1270 nm. T h e s p e c t r u m 19 o b t a i n e d by Evans and c o - w o r k e r s i s i n d i c a t e d by " B " , and t h e s p e c t r u m drawn f o r t h e 13 nm b a n d p a s s u s e d i n t h e p r e s e n t e x p e r i m e n t s i s i n d i c a t e d by " A " . 30 5 12400 12500 12S00 12700 12100 12900 WAVELENGTH (JO 3 1 FIGURE 7 Observed emission intensity of the NO., aft glow at 1150 nm as a function of [NO] for [M]=1.88xl017 molec cm"3. 32 3 33 FIGURE 8 Wavelength-dependent p r o f i l e of the rate constant for the NO+0 chemiluminescence reaction (from reference 20). 34 FIGURE 9 T h e o b s e r v e d NO., s p e c t r a l d i s t r i b u t i o n . T h e b a s e l i n e i s l a b e l l e d " A " , and t h e o b s e r v e d i n t e n s i t y p r o f i l e i s l a b e l l e d " B " . 36 9 tube. In order to convert the distances to reaction time i t was necessary to determine the volumetric flow rate in the system. A large o r i f i c e valve between the flow tube and a Welch S c i e n t i f i c duo seal vacuum pump was used to t h r o t t l e the flow rate as required. The time per centimeter along the flow tube was obtained by measuring the rate of vacuum pump exhaust throughput. The rate of vacuum pump exhaust throughput was measured by channelling the exhaust into an inverted volumetric flask. I n i t i a l l y the flask was f i l l e d with water and inverted in a w a t e r - f i l l e d bucket. Once submerged, the water in the flask was maintained by atmospheric pressure. However, as the exhaust pressure in the flask steadily increased, the volume of water in the flask steadily decreased. This continued u n t i l the water-level inside the flask was equal to the l e v e l outside the flask (see Figure 10). At thi s point the exhaust pressure in the volumetric flask i s equal to the atmospheric pressure, and the volume of exhaust co l l e c t e d i s equal to the volume of the flask. The time required to c o l l e c t the equivalent of one atmosphere of exhaust in the volumetric flask was measured. 38 FIGURE 10 Apparatus used to measure the volumetric flow rate, "p " refers to the pressure of the vacuum pump exhaust, and "P a t m" refers to the atmospheric pressure. 39 exhaust A O For an ideal gas the pressure (P) in the volumetric flask i s related to the volume (V) of the flask by the ideal gas law. Therefore, PV=nRT, where n is the number of moles of gas collected at a temperature T, and R i s the gas constant. If the rate of vacuum pump exhaust throughput (F) i s defined as the number of moles of gas col l e c t e d in a given time t, then F may be expressed in terms of the ideal gas law: (2.8) F = PV/tRT The flow of the gas in the flow tube may be treated as a series of discrete, concentric discs flowing horizontally along the body of the flow tube. Since the body is c y l i n d r i c a l l y shaped, and has radius 2 r, the area of these discs isyTr . If a term V is cm defined as the volume per unit centimeter length of the 2 flow tube, then V = ifr . The volumetric flow rate in cm the system (F') at pressure P' and temperature T i s equal to the rate of vacuum pump exhaust throughput measured simultaneously. By using the ideal gas law for the gas in the flow tube an expression for F' i s obtained which is similar to equation 2.8, and the time per centimeter along the flow tube is given by the 4 1 following equation: (2.9) time/cm = P'V /F'RT cm SECTION 2.5  SURFACE RECOMBINATION EXPERIMENTS 2 1 It has been proposed by Slanger and Black that the recombination of 0-atoms on a Pyrex surface i s a large contributor to the formation of 0 2(a) in flow systems. Using conditions thought to be favourable for wall-recombination, Slanger and Black found that between 18% and 36% of the recombinations of 0-atoms on a Pyrex surface results in the formation of 0 2 ( a ) . In order to determine the r e l a t i v e e f f i c i e n c i e s for the formation of 0 2(a) by the homogeneous recombination of 0-atoms and by the heterogeneous recombination of 0-atoms, a set of experiments to determine the y i e l d of 0 2(a) by the recombination of 0-atoms on a glass surface was undertaken. The experimental conditions established to study the heterogeneous recombination of O-atoms were di f f e r e n t from those used for the homogeneous 42 recombination studies. In the homogeneous recombination experiments the conditions favoured gas-phase recombination r e l a t i v e to surface recombination. F i r s t l y , the inner wall of the flow tube was coated with phosphoric acid, which has the e f f e c t of reducing . . . 22 the e f f i c i e n c y of wall recombination. Secondly, by using a large-diameter flow tube the large volume to surface area r a t i o favours gas-phase recombination r e l a t i v e to surface recombination. F i n a l l y , the t o t a l pressure maintained in the flow system for the homogeneous recombination experiments was three times larger than that used for the surface recombination experiments, and t h i s favours termolecular processes. A l l of the experiments described in t h i s thesis were ca r r i e d out 300 K. To study the heterogeneous recombination of 0-atoms in t h i s flow system the surface area to volume r a t i o was increased by the insertion of a glass wool plug in the body of the flow tube. The plug provides a very large surface area on which recombination can occur. The glass wool was spread out over a distance of 11 cm along the length of the flow tube. It covered the entire diameter of the flow tube. In order to minimize channelling of the flow the glass wool was A3 evenly d i s t r i b u t e d over the region i t occupied. The pressure drop across the plug was measured to determine the extent of c o n s t r i c t i o n of the flow. A pressure drop of only 1% of the t o t a l pressure in the flow tube was found, suggesting that the flow was not constricted. By measuring the weight of the glass wool plug and the diameter of the individual threads (using a microscope), the surface area of the plug was determined. The following equations were used to calculate the surface area of the glass wool plug: (2.10) V = W/p (2.11) SA/V = 2/r where: a) V i s the volume of the glass wool. b) W i s the weight of the plug (W=0.8901 g). c) y i s the density of the glass wool (P = 2.2 g cm ). d) r i s the radius of the glass wool threads (r=5x10~ 4 cm). e) SA i s the surface area of the glass wool threads. Therefore, the surface area provided by the glass wool 2 is 1618 cm . Since the radius of the flow tube i s 3 cm, the surface area of the 11 cm region of the flow 2 tube in the absence of the glass wool i s 207 cm , and hence, the surface area of the 11 cm region of the flow tube i s 7.8 times larger with the glass wool than without i t . 45 SECTION 3 : RESULTS AND DISCUSSION 1 . Experimental data for the formation of 02(a) by the homogeneous recombination of 0-atoms. page 47 2 . Determination of the rate law for the formation of 02(a) by the homogeneous recombination of 0-atoms. page 5 5 3 . The proposed mechanism for the formation of 02(a) by the homogeneous recombination of 0-atoms. page 82 4 . Analysis of the 02(a) nightglow in terms of the proposed mechanism. page 86 5 . Comparison of the proposed mechanism with the existing literature. page 93 6 . Experimental data for the formation of 02(a) by the heterogeneous recombination of 0-atoms. page 94 7 . Calculation of the yield of 0 (a) by the recombination of 0-atoms on glass wool. page 98 8 . Discussion of the significance of the homogeneous recombination of 0-atoms to the surface recombination studies. page 101 9. Comparison of the results from the surface recombination experiemnts with the existing literature. page 103 1 0 . Determination of the surface recombination coefficient. page 105 46 SECTION 3.1 EXPERIMENTAL DATA FOR THE FORMATION OF 0 ;(a) BY THE HOMOGENEOUS RECOMBINATION OF O-ATOMS The data for studying the formation of 0 2(a) by the homogeneous recombination of O-atoms was obtained from three types of experiments. The f i r s t type determined the dependence of the rate of formation of 0 2(a) on [0] by varying the i n i t i a l [0] ([0]Q) while keeping the t o t a l pressure ([M]) constant. For these experiments only N 2 and NO were d i r e c t l y added to the flow tube, and N 2 accounted for over 9 9 % of the t o t a l pressure. In Figure 11 i s shown, the effe c t of increasing [0] on the formation of 0 2 ( a ) . It can be seen that the rate of formation of 0 2(a) increases with increasing [0], as wouLd be expected i f 0 2(a) i s formed by O-atom recombination (reaction 1 . 1 ) . ( 1 . 1 ) 0 + 0 + M 5 - 0 2 ( a l l states) + M k1 1 2 Campbell and Gray have found that the rate constant — 3 3 6 for O-atom recombination ( k ^ at 300 K i s 4.8x10 cm molec 2 sec 1 . Ul FIGURE 11 The effect of increasing [0] on the formation of 0 2(a) for [M]=1.88xl017 molec cm'3. The 14 -3 alphabetical labels Tefer to [OjxlO atoms cm . A=2.27 B=5.57 C=1C24 D=14.32 E=16.98 48 The second type of experiment determined the dependence of the rate of formation of 0 2(a) on [M] by varying [ N 2 J while keeping [0]Q constant. For these experiments only N 2 and NO were d i r e c t l y added to the flow tube, and N 2 accounted for over 99% of the t o t a l pressure. In Figure 12 i s shown the eff e c t of increasing [M] on the formation of 0 2 ( a ) . It can be seen that the rate of formation of 0 2(a) increases with increasing [M], as would be expected i f 0 2(a) i s formed by O-atom recombination. The t h i r d type of experiment determined the dependence of the rate of formation of 0 2(a) on [0 2] by varying [0 2] while keeping [0]Q and [M] constant. For these experiments 0 2 was added through an i n l e t into the body of the flow tube. In Figure 13 i s shown the effe c t of adding 0 2 at the front of the flow tube ( i . e . near t=0). It can be seen that for low [0 2] the rate of formation of 0 2(a) increases with increasing [0 2J (lines A, B, and C). However, for very large [0 2] the rate of formation of 0 2(a) appears to decrease ( l i n e D). This i s due to the competition for 0-atoms between O-atom recombination and reaction 3.1. 50 FIGURE 12 The effect of increasing [M]on the formation of 0 2(a) for [O]=4.54xl014 atoms cm"3. The 17 -3 alphabetical labels refer to [M]xlO molec cm . A=0.91 B=1.24 02.21 D=2.94 51 15 FIGURE 15 T h e e f f e c t o f t h e a d d i t i o n o f 0^ on t h e f o r m a t i o n o f 0 2 ( a ) f o r [uj = 3 . 3 4 x l 0 1 4 atoms c m " 3 and [ M ]=1 .88x10 m o l e c cm" . T h e a l p h a b e t i c a l l a b e l s 15 - 3 r e f e r t o [ 0 2 ] x l 0 molec cm . A=0 B=0.13 C=1.59 D=2.88 53 (3.1) 0 + 0„ + M =~0 3 + M Kaufman and Kelso have found that the rate onstant for reaction 3.1 is 6.0x10 3 4 cm^ molec ^ sec 1 . In this reaction O-atoms are removed by reaction with 0 2, and hence, increasing [02]/tO] w i l l favour ozone formation over O-atom recombination. This has the ef f e c t observed for l i n e D in Figure 13, where at high [0 2] the rate of O-atom recombination appears to decrease because of the removal of O-atoms by reaction with 0 2. Therefore, the most favourable conditions for studying O-atom recombination are at large [0]/[0 2] and at short reaction times. SECTION 3.2 DETERMINATION OF THE RATE LAW FOR THE FORMATION OF Q 2(a) BY THE HOMOGENEOUS RECOMBINATION OF Q-ATOMS The data obtained for a t y p i c a l homogeneous recombination experiment i s shown in Figure 14. The data was analyzed by drawing the " l i n e - o f - b e s t - f i t " ( l i n e A) through the or i g i n and at least one experimental point. The slope of thi s l i n e i s denoted by d[0 9(a)]/dt, and i t i s defined as the i n i t i a l rate 55 FIGURE 14 Determination of the rate of formation of 02(a) by measuring the slope of l i n e A. 56 57 of formation of 0 2 ( a ) . The [0] corresponding to t h i s slope was taken to be the average over the time during which the slope was measured. The order of the dependence of the rate of formation of 0 2(a) on [0] and [M] can be determined using the general rate law expression (equation 3.2) i f the dependencies are simple. (3.2) d[0 2(a)]/dt = k[0] a [M] b  where: a) "a" i s the order of the dependence on [0]. b) "b" i s the order of the dependence on [M]. c) "k" i s some constant of proportionality. By taking the logarithm of both sides of t h i s equation the following expression r e s u l t s : (3.3) ln d [ 0 2 ( a ) ] / d t = ln k + a ln [0] + b ln [M] Therefore, i f the dependencies are simple, then "a" i s the slope of a plot of ln d[0 2(a)]/dt versus ln [0] and "b" i s the slope of a plot of ln d [ 0 5 ( a ) ] / d t 58 versus In [M]. In Table 1 is compiled the data for [02(a)] formed as a function of time for several [0], and in Figure 15 i s shown the data used to determine d [ 0 2(a)/dt for these [0] . In Figure 16 is shown a plot of In d [ 0 2(a)]/dt versus In [0] for the data in Table 1. A straight l i n e with a slope of 1.9(+/-0.2) can be f i t t e d to the points ( i . e . a=2); therefore, i t can be concluded that the rate of formation of °2^ a^ ^ s second-order in [0] , as would be expected i f 02(a) i s formed by O-atom recombination. In Table 2 i s compiled the data for [ 0 2(a)] formed as a function of time for several [M], and in Figure 17 i s shown the data used to measure d [ 0 2(a)]/dt for these [M], In Figure 18 is shown a plot of In d [ 0 2(a)]/dt - 2 1 n [ 0 j versus In [M] for the data in Table 2. A straight l i n e with a slope of 1.0(+/-0.1) can be f i t t e d to the points ( i . e . b=1); therefore, i t can be concluded that the rate of formation of 0 2(a) i s f i r s t - o r d e r in [M], as would be expected i f 0 2(a) i s formed by O-atom recombination. The simplest representation of the formation of ©2(a) by 0-atom recombination i s the following reaction: (3.4) 0 + 0 + M ° 2 ( a ) + M k i 59 TABLE 1 Measurement of the rate of formation of (^(a) at several [o] f o r [M]=1.88X1017 molec cm"3. 60 [0]Qx 10 atoms cm 2.27 2.27 2.27 2.27 2.27 3.24 3.24 3.24 3.24 3.24 3.24 3.24 4.21 4.21 4.21 4.21 4.21 4.21 4.21 time sec 0.28 0.55 0.74 0.93 1.11 0.18 0.28 0.37 0.55 0.74 0.93 1.11 0.18 0.28 0.37 0.55 0.74 0.93 1.11 [o 2 ( a ) ] x 10 molec cm 0.12 0.26 0.34 0.38 0.43 0.18 0.29 0.38 0.47 0.57 0.61 0.66 0.33 0.47 0.61 0.71 0.81 0.90 0.95 61 [0] Qx 10 atoms cm 5.57 5.57 5.57 5.57 5.57 5.57 5.57 5.57 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 10.24 10.24 10.24 10.24 10.24 10.24 10.24 time sec 0.09 0.18 0.28 0.37 0.55 0.74 0.93 1.11 0.07 0.14 0.21 0.29 0.41 0.65 0.89 1.11 0.09 0.18 0.37 0.55 0.74 0.93 1.11 [ o 2 ( a ) ] x 10 molec cm 0.29 0.52 0.81 0.86 1.04 1.13 1.27 1.42 0.29 0.52 0.72 0.90 1.38 1.79 2.08 2.17 0.75 1.04 1.90 2.31 2.60 2.83 3.08 62 [o] x 1 0 1 4 t i m e [o 2(a)]x 1 0 1 3 - 3 - 3 atoms cm s e c , m o l e c cm .. 14 .32 0 .09 ' 1 .38 14 .32 0 .18 1.70 14 .32 0 .28 2 .42 14 .32 0 .55 3 .78 14 .32 0 .83 4 .12 14 .32 1.11 4 . 3 9 16.98 0 .09 1.61 16.98 0 .18 2 .22 16.98 0 .28 3 .08 16 .98 0 .55 4 . 3 9 16 .98 0 .83 5 .25 16.98 1.11 5 . 4 9 63 FIGURE 15 D e t e r m i n a t i o n o f t h e r a t e o f f o r m a t i o n o f 0^(a) a t s e v e r a l [o] f o r [ M.] = l . 8 8 x l 0 * 7 m o l e c cm 3 . The a l p h a b e t i c a l l a b e l s r e f e r t o [ o j x l O ^ 4 atoms cm 3 . A=2.27 B=3.24 C=4.21 D=5.57 E=8.00 F=10.24 6=14.32 H=16.98 6 4 0 0.2 (W 0.6 t i m e ( s e c ) 65 FIGURE 16 D e t e r m i n a t i o n o f t h e o r d e r o f t h e d e p e n d e n c e o f t h e r a t e o f f o r m a t i o n o f 0 2 <a) on [ o ] f o r [ M ] = 1 . 8 8 x l 0 1 7 m o l e c cm 3 . 66 3 3 I 67 TABLE 2 Measurement of the rate of formation of 0 (a) at several [M] for [o]=4.54x10 atoms cm . 68 [ M ] X 1 0 molec cm 0 . 9 1 0 . 9 1 0 . 9 1 0 . 9 1 1 . 2 4 1 . 2 4 1 . 2 4 1 . 2 4 1 . 8 8 1 . 8 8 1 . 8 8 1 . 8 8 2 . 2 1 2 . 2 1 2 . 2 1 2 . 2 1 2 . 9 4 2 . 9 4 2 . 9 4 2 . 9 4 time sec 0 . 2 5 0 . 5 0 0 . 7 5 1 . 0 0 0 . 2 1 0 . 4 8 0 . 7 4 1 . 0 0 0 . 1 0 0 . 2 0 0 . 3 0 0 . 5 1 0 . 1 6 0 . 4 4 0 . 7 1 1 . 0 0 0 . 1 6 0 . 4 0 0 . 7 2 1 . 0 5 [o 2(a)]x 1 0 molec cm 0 . 2 3 0 . 3 9 0 . 5 1 0 . 5 9 0 . 2 6 0 . 4 5 0 . 6 6 0 . 7 8 0 . 1 6 0 . 2 7 0 . 4 3 0 . 6 2 0 . 2 7 0 . 6 6 0 . 8 2 0 . 9 9 0 . 3 5 0 . 6 6 0 . 9 5 1 . 1 4 69 FIGURE 17 D e t e r m i n a t i o n o f t h e r a t e o f f o r m a t i o n o f 0 2 ( a ) a t s e v e r a l [M] f o r [ 0 ] = 4 . 5 4 x 1 0 * ^ atoms cm 3 . T h e a l p h a b e t i c a l l a b e l s r e f e r t o [ M J X I O ^ m o l e c cm 3 , A=0.91 B=1.24 C - 1 . 8 8 D=2.21 E=2.94 70 t i m e ( s e c ) 71 FIGURE 18 D e t e r m i n a t i o n o f t h e o r d e r o f t h e d e p e n d e n c e o f t h e r a t e o f f o r m a t i o n o f 0 2 ( a ) on [ M ] f o r [o ]=4 .54x10 - 3 atoms cm 72 In [M] 73 For t h i s simple reaction to be consistent with the experimental data presented in t h i s thesis i t must explain the increase in rate of formation of 02(a) with added 0 2• In Table 3 i s compiled the data for the formation of 02(a) at several [O2], and in Figure 19 i s shown the data used to determine d [ 0 2(a)]/dt for these [ 0 2 ] . In Figure 20 i s shown a plot of d [ 0 2(a)]/dt versus [ ° 2 ^ * A straight l i n e with a slope of 1.1(+/-O . D x l O " 2 sec" 1 and a y-intercept of 2.8 (+/-0. 3 )x 1 0 1 3 -3 -1 molec cm sec can be f i t t e d to the points. The - 3 2 6 — 2 slope of t h i s l i n e gives k 1'=2.4xl0 cm molec sec 1 for O2 as the third-body in reaction 3.4, and i t s y-intercept gives k1'=3.4x10 3 ^ cm^ molec 2 sec 1 for N2. This means that the third-body effectiveness of O2 must be 71 times larger than that for N 2 i f reaction 3.4 i s to be consistent with the experimental data. However, the third-body effectiveness of 0 2 and N 2 in other termolecular reactions have been found to be 24 si m i l a r , as would be expected because of their similar molecular weights. Therefore, i t i s unreasonable to conclude that 0 2 i s 71 times more e f f e c t i v e as a third-body than N 2 in reaction 3.4, and hence, i t i s unreasonable to conclude that the simple termolecular recombination of O-atoms can account for 74 TABLE 3 Measurement o f t h e r a t e o f f o r m a t i o n o f 0^(a) a t s e v e r - . l [o 2 ] f o r j^ o] = 6 . 6 3 x l 0 1 4 atoms c m " 3 and [ MJ = 1 . 8 8 x l 0 1 7 molee cm 75 [ o j x 1 0 1 5 t i m e [ 0 2 ( a ) ] x 10 m o l e c cm 3 s e c , m o l e c cm 0 0 . 0 7 1 0 . 2 8 0 0 . 1 4 3 0 . 5 0 0 0 . 2 1 4 0 . 7 1 0 0 . 2 8 6 0 . 9 0 0. 0 . 3 5 7 1.08 1.35 0 . 1 5 3 0 . 5 7 1.39 0 . 2 0 4 0 . 8 0 1.39 0 . 2 5 5 0 . 9 9 1.39 0 . 3 0 6 1.23 1.39 0 . 3 5 7 1.47 3 . 1 1 0 . 1 5 3 0 . 5 7 3 . 1 1 0 . 2 0 4 0 . 8 5 3 .11 0 . 2 5 5 1.13 3 . 1 1 0 . 3 0 6 1.42 3 . 1 1 0 . 3 5 7 1.70 4 . 8 9 0 . 1 5 3 0 . 6 6 4 . 8 9 0 . 1 8 4 0 . 8 0 4 . 8 9 0 . 2 1 4 0 . 9 5 4 . 8 9 0 . 2 4 5 1.09 4 . 8 9 0 . 2 7 6 1.23 6 .51 0 . 1 5 3 0 . 7 6 6 . 5 1 0 . 2 0 4 0 . 9 9 6 . 5 1 0 . 2 5 5 1.18 6 .51 0 . 3 0 6 1.42 6 .51 0 . 3 5 7 1.60 76 [o ]x 10 1 5 time [0 2(a)]x 10 1 3 -3 , -3 molec cm sec molec cm 8.13 0.153 0.80 8.13 0.184 0.99 8.13 0.214 1.13 8.13 0.245 1.28 8.13 0.276 1.47 77 FIGURE 19 D e t e r m i n a t i o n o f t h e r a t e o f f o r m a t i o n o f 0 2 ( a ) a t s e v e r a l [ o j f o r [o ] = 6 . 6 3 x l 0 1 4 atoms c m " 3 a n d [M]=1 . 8 8 x l 0 1 7 m o l e c cm 3 . The a l p h a b e t i c a l l a b e l s r e f e r t o [o I x l O * " * m o l e c _3 cm . O2 was a d d e d a t a d i s t a n c e e q u i v a l e n t t o 0 . 1 3 3 s e c . A=0 B=1.39 C=3.11 D=4 .89 E=6.51 F=8.13 78: FIGURE 20 The e f f e c t o f t h e a d d i t i o n o f 0^ on t h e r a t e o f f o r m a t -i o n o f O^Ca) f o r [o]= 6 . 6 3 x 1 0 * 4 atoms cm 3 and [M ]=1 .88x10 m o l e c cm . 80 the experimental data presented in th i s thesis. SECTION 3.3 THE PROPOSED MECHANISM FOR THE FORMATION OF Q 2(a) BY THE HOMOGENEOUS RECOMBINATION OF O-ATOMS Since i t i s unreasonable to conclude that the increase in rate of formation of 0 2(a) by the recombination of O-atoms in the presence of 0 2 i s simply due to a greater third-body effectiveness of 0 2 r e l a t i v e to N 2 in reaction 3.4, a precursor mechanism may be proposed. The simplest precursor mechanism which is consistent with the experimental data is that in which O-atoms i n i t i a l l y recombine into some high energy it state of 0 2 (0 2 ), and 0 2(a) i s formed by the quenching of 0 2 by 0 2 and N 2. This i s shown in the following mechani sm: (3.5) 0 + 0 + M °2* + M f1 k1 (3.6) 0 2* + N 2 s-0 2(a) + N 2 f 2 k 2 (3.7) ° 2 * + °2 = - 0 2 ( a ) + 0 2 f 3 k 3 This mechanism assumes that 0 2 i s formed d i r e c t l y by O-atom recombination with a f r a c t i o n a l y i e l d of f ^ Subsequent quenching of 0 2 by N 2 and 0 2 produces 0 2(a) 82 with f r a c t i o n a l y i e l d s of f 2 an& ^3' respectively. For these reactions "k" i s the ove r a l l rate constant, and the product of " f " and "k" i s the observed rate constant for the formation of the spe c i f i e d 0 2 product. * If the steady state assumption i s made for 0 2 , then the rate of formation of 0 2(a) by the proposed mechanism i s given by the following equation: (3.8) d[0 2(a)]/dt = ( f 2 k 2 [ N 2 ] + f 3 k 3 [ 0 2 ] ) f 1 k 1 [ 0 ] 2 [ M ] k 2[N 2]+k 3[0 2] When [O 2]=0 equation 3.8 reduces to the following equat ion: (3.9) d[0 2(a)]/dt = f 2 f 1 k 1 [ 0 ] 2 [ M ] This equation shows that the rate of formation of 0 2(a) by the proposed mechanism is second-order in [0] and f i r s t - o r d e r in [M] in the absence of 0 2. This i s consistent with the experimental data and with reaction 3.4 for M=N2< However, the precursor mechanism can incorporate the eff e c t of 0 2, whereas reaction 3.4 cannot. The proposed mechanism i s consistent with the 83 l i n e a r i t y shown in Figure 17 when k ^ ^ J ^ k ^ t C ^ l and f-jk-jtC^] is comparable to f 2 k 2 [ N 2 ] ; t h i s can be seen from equation 3.10, which r e s u l t s from equation 3.8 when these conditions are s a t i s f i e d . (3.10) d[0 2(a)]/dt = f 2 f 1 k 1 [ 0 ] 2 [ M ] + f 3 f 1 k 1 k 3 [ 0 ] 2 [ 0 2 ] [ M ] k 2[N 2] Equation 3.10 shows that the rate of formation of 0 2(a) w i l l have a linear dependence on [C^], and f j ^ k ^ can be obtained from the y-intercept of a plot of d[0 2(a)]/dt versus [ 0 2 ] , and f 1 f 3 k 1 k 3 / k 2 can be obtained from the slope of thi s p l o t . Analysis of the data shown in Figure 17 in terms of the proposed mechanism gives the following r e s u l t s : a) f 2 f 1 k l = 3« 4( +/-0.3)xl0~ 3 4 c m 6 molec - 2 sec" 1 b) f 1 f 3 k 1 k 3 / k 2 = 2.4(+/-0.2)x10~ 3 2 cm6 molec" 2 sec" 1 c) f 3 k 3 / f 2 k 2 = 71 These results mean that for the proposed mechanism to be consistent with the experimental data the observed rate constant for the formation of 00(a) by the 84 quenching of that for N 2. 300 K, the those above: a) f f 2 = 0.071 (+/-0.007) b) f 1 f 3 k 3 / k 2 = 5.0 (+/-0.5) A value of f 1f 2=0.07l means that only 7.1% of the 0 2 products of O-atom recombination in the absence of 0 2 are 0 2 ( a ) . At the opposite extreme, where k 3[0 2]>>k 2[N 2] and f 3 k 3 [ 0 2 ] > > f 2 k 2 [ N 2 ] , equation 3.8 reduces to the following equation: (3.11) d[0 2(a)]/dt = f 1 f 3 k 1 [ 0 ] 2 [ M ] This equation shows that when [0 2]/[N 2] i s large the rate of formation of 0 2(a) w i l l reach a maximum value. In a plot of d[0 2(a)]/dt versus [0 2] th i s w i l l appear as a plateau at large [ 0 2 J . As [0 2] approaches the saturation l i m i t for d[0 2(a)]/dt t h i s plot w i l l show a downward curvature. This i s important for * 0 2 by 0 2 must be 71 times larger than — 33 6 —2 —1 Since k 1=4.8xl0 cm molec sec at following results can be calculated from 85 understanding the shape of the curve to be presented in the following section of t h i s t h e s i s . SECTION 3.4  ANALYSIS OF THE 0 2(a) NIGHTGLOW IN TERMS OF THE PROPOSED MECHANISM Recall that for the 0 2(a) nightglow near 90 km the following conditions have been found (see Section 1.4): 1 1 -3 a) [0] = 6.0x10 atoms cm b) [0 2] = 9.4xl0 1 2 molec cm"3 c) [N 2] = 3.6X 1 0 1 3 molec cm"3 d) k 1 = 1.12X10~ 3 2 cm 6 molec - 2 sec" 1 e) I = d[0 0(a)]/dt = 8X10 4 molec cm"3 s e c - 1 3 ^ Since f 1 f 2 = 0.07l and f . j k ^ / f 2 k 2 = 47 substitution of the nightglow data into equation 3.8 gives k2/k3=0.12 and hence, f 3/f 2=8.5 and £^^-0.6. This means that for the proposed mechanism to be consistent with the experimental data and with the 0 2(a) nightglow data the rate constant for the quenching of 0 2 by 0 2 must be 8.5 times larger than that for N 2, and the y i e l d of * 0 2(a) by the quenching of 0 2 by 0 2 must be 8.5 times larger than that for N 2. 86 From equation 3.8 i t can be shown that the y i e l d of 02(a) (Y) by the homogeneous recombination of 0-atoms i s given by the following equation: f 1 f 2 k 2 [ N 2 ] + f 1 f 3 k 3 [ 0 2 ] y = . k 2[N 2] + k 3 [ 0 2 ] The analysis of the experimental data and the C ^ 3 ) nightglow data in terms of the proposed mechanism gave f 3 k 3 / f 2 k 2 = 7 l and k 2/k 3=0.12. If these values are substituted into the above equation, and for r= [ 0 2]/[N 2], the following equation can be obtained: Y = f 1 f 2 ( l / r + 71)/(1/r + 8.5) where, £^2=0.071 from the analysis of the experimental data. In Figure 21 i s shown a plot of the y i e l d of 02(a) (Y) calculated from the above equation as a function of [ 0 2]/[N 2]. It can be seen that the y i e l d approaches a l i m i t of 0.071 as [ 0 2]/[N 2] approaches zero and a l i m i t of 0.6 at large [ 0 2 ] / [ K 2 ] , The l i m i t of 0.071 i s consistent with the observed y i e l d of 0 9(a) in the 87 FIGURE 21 The y i e l d of 02(a) calculated from equation 3.8 as a function of [0 ] / [ N ] 88 89 absence of 0 2 which has been found experimentally; and the value of 0.6 corresponds to the maximum y i e l d of 0 2 ( a ) , which i s attainable only when [0 2]/[N 2] i s very large. The darkened c i r c l e in Figure 21 shows the position of the °2^ a^ nightglow data, where [0 2]/[N 2]=0.2. The calculated y i e l d of 0 2(a) at t h i s point i s 0.4. This i s consistent with the value of 0.4 calculated in Section 1.4 for the y i e l d of 0 2(a) which i s required for O-atom recombination to account for the 0 2(a) nightglow intensity measured by Thomas and Young 1 1. It can also be seen that for the low [0 2]/[N 2] used in the experiments ([0 2]/[N 2]<0.045) the plot can be approximated to a straight l i n e . This i s consistent with the l i n e a r i t y in the plot of d[0 2(a)]/dt versus [0 2] shown in Figure 20. In Figure 22 i s shown the rate of formation of 0 2(a) calculated from equation 3.8 as a function of a l t i t u d e . The data for t h i s Figure was taken from reference 12. The peak 0 2(a) emission i s seen to be at 93 km. This compares favourably with the a l t i t u d e for the peak C ^ 3 ^ emission measured by Thomas and Young. 90 FIGURE 22 The calculated rate of formation of 0 2(a) (from equation 3.8) as a function of a l t i tude. 91 1 0 1 851 1 1—= ' ' « 1 0 1 2 3 d [ 0 2 ( a ) ] / d t ( x l O ^ m o l e c c m ^ s e c - 1 ) 92 SECTION 3.5 COMPARISON OF THE PROPOSED MECHANISM WITH THE EXISTING LITERATURE The large y i e l d of 0 2(a) by O-atom recombination which the proposed mechanism provides suggests that either a l l of the bound states of 0 2 can act as the precursor for the formation of 0 2(a) or that some individual state, which i s formed in very high y i e l d in O-atom recombination, i s the precursor. Only the yields of 0 2(b) and 0 2(A) by O-atom recombination have been obtained in the laboratory. Ogryzlo and co-1 5 workers have found that the maximum y i e l d of 0 2(b) by O-atom recombination i s 0.04, and Ogryzlo 1 has interpreted the experimental results of Young and 2 5 Black as meaning that the maximum y i e l d of 0 2(A) by O-atom recombination i s 0.01. These yie l d s are i n s u f f i c i e n t for either of these species to be considered as candidates for the precursor for the formation of 0 2 ( a ) . An obvious candidate for the precursor i s the 5 26 weakly-bound 7i state of 0,. Wraight , in a 5 theoreti c a l c a l c u l a t i o n , found that 00{ ff ) i s formed 93 in over 70% of the recombinations of O-atoms at 200 K and in over 50% of the recombinations at 300 K. However, t h i s species has not been detected spectroscopically, and spectroscopic i d e n t i f i c a t i o n w i l l be very d i f f i c u l t because of unfavourable Franck-Condon factors and the absence of allowed t r a n s i t i o n s . Therefore, i t i s important that theor e t i c a l chemists determine the exact location of 0 2 ( Iig) in the spectrum so that i t s role in the nightglow can be better assessed. SECTION 3.6 EXPERIMENTAL DATA FOR THE FORMATION OF 0 ;(a) BY THE HETEROGENEOUS RECOMBINATION OF 0-ATOMS The results from a t y p i c a l surface recombination experiment is shown in Figure 23. The alphabetical labels contained in t h i s paragraph and in the succeeding one refers to Figure 23. In the experiment from which Figure 23 draws i t s contents the 0 2^ a^ emission was monitored before and after the glass wool plug. The conditions used were such that the [0 2(a)] formed before the plug was negl i g i b l e (point A). It was observed that after the plug the additional formation of 0 0(a) was also ne g l i g i b l e (points B, C, 94 FIGURE 23 Measurement of [ ^ ( ^ J C^Pty circles) and the NO^  afterglow (darkened circles) before and after the glass wool plug for [O] q=2.36xl0* 4 atoms cm 3 and [M]=8.06x10 molec cm" . The alphabetical labels are defined in the text. 95 D I S T A N C E ( cm ) 96 and D). In a d d i t i o n , i n t h i s experiment the r e l a t i v e [0] before and a f t e r the plug was monitored using the N0 2 a f t e r g l o w . The observed i n t e n s i t y of the N0 2 a f t e r g l o w was measured at three p o i n t s a f t e r the plug ( p o i n t s E, F, and G). A s t r a i g h t l i n e ( l i n e H) was drawn through these p o i n t s and e x t r a p o l a t e d to the f r o n t face of the plug ( p o i n t I ) . The observed i n t e n s i t y of the N0 2 a f t e r g l o w was a l s o measured i n f r o n t of the plug (point J ) . A s t r a i g h t l i n e ( l i n e K) with the same slope as l i n e H was drawn through t h i s p o i n t , and e x t r a p o l a t e d to the f r o n t face of the pl u g ( p o i n t L ) . L i n e K was a l s o e x t r a p o l a t e d to the f r o n t of the flow tube ( p o i n t M) . 97 SECTION 3.7  CALCULATION OF THE YIELD OF 0 2(a) BY THE RECOMBINATION OF O-ATOMS ON GLASS WOOL The y i e l d of 0 2(a) was calculated from the following equation: [°2 ( a )]obs 2 [ 0 2 ( a ) ] O b s (3.12) y i e l d l / 2 [ 0 ] r e c ( A I / I 0 ) [ O ] 0 where: a) [°2^ a^obs * s t h e f ° 2 ^ a ^ m e a s u r e d at point B. b) A I i s the difference between the intensity of the N0 2 afterglow at points L and I. c) I Q i s the intensity of the N0 2 afterglow at point M. d) [0] i s the [0] removed on the glass wool. rec In Table 4 are shown the y i e l d s of 0 2(a) by the recombination of O-atoms on the glass wool for a series of experiments with d i f f e r e n t [0], f°2^' a n a " • T h e weighted average of the y i e l d s in this Table i s 0.09(+/-0.02). 98 TABLE 4 Measurement of the y i e l d of 02(a) by the recombination of 0-atoms on glass wool. 99 [O] 0xl0 1 4 -3 atoms cm [MfxlO 1 6 molec cm"3 [O 2]xl0 1 4 molec cm"3 [O 2(a)]xl0 1 2 molec cm"3 Yield •/-o.c 2.27 4.83 2.7 0.07 2.30 9.69 3.9 0.11 2.36 3.21 2.5 0.07 2.36 6.48 2.6 0.07 2.36 8.06 3.5 0.09 2.40 6.48 3.5 0.09 2.49 7.45 12.31 3.9 0.10 2.53 7.45 6.16 3.9 0.10 2.53 7.45 9.72 3.9 0.10 2.56 7.45 2.59 3.9 0.10 2.66 6.48 3.4 0.08 3.11 6.48 3.4 0.07 100 SECTION 3.8 DISCUSSION OF THE SIGNIFICANCE OF HOMOGENEOUS RECOMBINATION OF Q-ATOMS TO THE SURFACE RECOMBINATION STUDIES The decay of O-atoms before the glass wool was by reactions 1.1, 2.2 and 2.3. (1.1) 0 + 0 + M =-02 + M k1 (2.2) 0 + NO + M >-N02 + M k 4 (2.3) 0 + N0 2 >-NO + 0 2 27 Whytock and co-workers have found that ~31 6 —2 —1 k^=1.0xl0 cm molec sec . If the steady state assumption i s made for N0 2, and the f i r s t - o r d e r approximation i s made for the decay of O-atoms, then [0] at any time t can be calculated from equation 3.13. (3.13) [0] = [0] ( )exp{-2t[M](k 1 [0] + k 4[N0])} In order to get a usuable N0 2 afterglow i t was necessary to have a s u f f i c i e n t l y large excess of NO, and t y p i c a l l y for the surface recombination experiments [N0]=7%[0] n. For Figure 19 [0] n=2.36x10 1 4 atoms cm - 3, 1 0 1 and hence, [NO]=1.6X10 molec cm , and [M]=8.06x10 - 3 molec cm . Since t=0.18 sec at the front face of the glass wool plug, only 6% of the i n i t i a l [0] i s removed by reactions 1.1, 2.2, and 2.3 in front of the plug. In contrast, on the glass wool 32% of the [0] is removed in only 0.11 sec by surface recombination. Therefore, the decay of 0-atoms by recombination on the glass wool i s 8 times faster than the gas-phase decay, and hence, the gas-phase decay of O-atoms i s only a minor correction in c a l c u l a t i n g the [ O ] removed by surface recombination. S i m i l a r l y , the contribution of homogeneous recombination of O-atoms to the formation of 0 2(a) in the surface recombination experiments can be assessed. Since in the absence of 0 2 0 2(a) i s formed by the homogeneous recombination of O-atoms with an observed rate constant ( f ^ ^ ) of 4.0x10 3 4 cm^ molec 2 sec 1, [0 2(a)] at any time t can be calculated from the following equation: (3.14) [0 2(a)] = f 2 f 1 k 1 [ M ] [0] 2dt If [0] i s assumed to be constant and equal to the 102 average [0] between points M and E in Figure 19, then t h i s equation reduces to the following: [0 2(a)] = f 1 f 2 k 1 t [ M ] [ 0 ] 2 where, [O]=1.8x10 1 4 atoms cm 3 . 16 — 3 For point B in Figure 23 [M]=8.06x10 molec cm and t=0.34 sec, and hence, from the above equation [0 2(a)]=3.0x10 1 1 molec cm - 3. This i s 8% of the [0 2(a)] measured at point B. Therefore, i t follows that the "true" y i e l d of 0 2(a) by O-atom recombination on glass wool i s 0.08(+/-0.02), and not 0.09. SECTION 3.9  COMPARISON OF RESULTS FROM THE SURFACE  RECOMBINATION STUDIES WITH THE EXISTING LITERATURE 2 1 Slanger and Black studied the recombination of O-atoms on a Pyrex surface and found a random v a r i a t i o n in the y i e l d of 0 2(a) from 0.18 to 0.36. In their experiments the formation of 0 2(a) and 0 2(X) were monitored by their absorptions at 128.5 nm and 149.5 nm, respectively. Slanger and Black calculated the 103 y i e l d of 02(a) from the r a t i o of the 0 2(a) produced to the sum of the 0 2(a) and the 0 2(X) produced by the recombination of O-atoms. The y i e l d of 0 2(a) by the recombination of O-atoms on glass wool was found to be 0.09 in the surface recombination studies described in th i s thesis. Therefore, these experiments cannot reproduce the high y i e l d of 0 2(a) found by Slanger and Black. One c r i t i c i s m of the work reported by Slanger and Black i s that an appreciable fractio n of the recombination of O-atoms in their system occurred in the gas-phase. It can be shown that i f the results presented in this thesis are correct, then homogeneous recombination accounted for 20% to 60% of the decay of O-atoms in the experiments of Slanger and Black. Therefore, the values which they reported are those for the cumulative y i e l d of 0 2(a) by the heterogeneous and homogeneous recombination of O-atoms. A second c r i t i c i s m of the work reported by Slanger and Black i s the large random var i a t i o n which they observed in the fraction of O-atoms recombined. In the surface recombination studies described in t h i s thesis 104 the fracti o n of atoms which recombined on the glass wool was found to be constant, as would be expected i f the decay was mainly on the surface. However, the fraction recombined in the experiments of Slanger and Black varied randomly from 0.44 to 0.79. This large, random va r i a t i o n i s most l i k e l y a measure of the r e p r o d u c i b i l i t y of their r e s u l t s , and hence, the r e p r o d u c i b i l i t y i s poor. SECTION 3.10  DETERMINATION OF THE SURFACE RECOMBINATION COEFFICIENT Since the decay of O-atoms by gas-phase reactions in the glass wool was corrected for, the observed decay is due only to surface recombination (reaction 3.15). (3.15) 0 + wall =-1/2 0 2 ( a l l states) + wall k w The O-atom decay due to surface recombination can be calculated from equation 3.16. 1 0 5 (3.16) [ 0 ] j / [ 0 ] L = I j / I L = exp {-kwt} where: a) [0]j and Ij are the observed [0] and the observed NC>2 emission intensity at point I, respectively. b) [ ° ] L a n c * I L a r e fc^e o l 3 S e r v e c ; C0] and observed NC>2 emission intensity at point L, respectively. c) t i s the reaction time across the 11 cm region occupied by the glass wool. From Figure 23 Ij/I L=0.6(+/-0.1), and t=0.11 sec. Therefore, k =5(+/-l) sec 1. The surface recombination c o e f f i c i e n t (?f ) for the glass wool can be calculated 21 from the following equation: 4k w(V/S) (3.17) /= (4k w/c)(V/S) = (8RT/#M) 1 / 2 where: a) V/S i s the ra t i o of the volume of the region occupied by the glass wool to the surface area i t provides. 1 0 6 b) c i s the mean vel o c i t y of the O-atoms. c) M i s the atomic weight of O-atoms (M=16.00 g). d) R i s the gas constant. e) T i s the temperature (T=300 K). Since the volume to surface area r a t i o in the absence of the plug i s 1.5 cm, and the surface area was increased by a factor of 7.8 by the glass wool, V/S=0.19. Therefore, / = 6(+/-1)x10~ 5. This result i s consistent with the value of t =7.7x10 ^ for a Pyrex 28 surface reported by Schiff and co-workers. 1 0 7 SECTION 4 CONCLUSION 1 0 8 CONCLUSION In the experiments described in this thesis the formation of 02(a) by O-atom recombination in the gas phase and on glass wool was studied. It was found that in the gas phase the rate of formation of 0 2(a) i s second-order in [0] and f i r s t - o r d e r in [M] in the absence of 0 2. A plot of the rate of formation of 0 2(a) as a function of [0 2] for [0]=6.63x10 1 4 atoms — 3 17 — 3 cm and [M]=1.88x10 molec cm gave a straight l i n e - 3 -1 with a slope of 1.1(+/-0.1)x10 sec and a y-intercept of 2.8(+/-0.3)x10 1 3 molec cm"3 sec" 1. The following mechanism was presented as being the simplest which i s consistent with the experimental data: 0 + 0 + M = ~ ° 2 * + M f1 k1 0 2* + N 2 =-0 2(a) + N 2 f 2 k 2 °2* + °2 =-0 2(a) + 0 2 f 3 k 3 Analysis of the experimental data in terms of th i s mechanism gave the following r e s u l t s : a) f 1 f 2 = 0.071 (+/-0.007) b) f 1 f 3 k 3 / k 2 = 5.0 (+/-0.5) c) f 3 k 3 / f 2 k 2 = 71 (+/-7) 1 0 9 The atmospheric data f o r the G ^ a ) nightglow was analyzed i n terms of the proposed mechanism and i t was found that the proposed mechanism i s c o n s i s t e n t with the atmospheric data and the experimental data presented i n t h i s t h e s i s i f k ^ / k ^ O . ^ , ^ ^ = 0 . 6 and f 3 / f 2 = 8 . 5 In the s u r f a c e recombination experiments i t was found that the y i e l d of 02(a) by O-atom recombination on g l a s s wool, with a s u r f a c e recombination c o e f f i c i e n t of 6 ( + / - 1 ) x 1 0 ~ 5 , i s 0 . 0 8 ( + / - 0 . 0 2 ) . 110 REFERENCES 1. E.A. Ogryzlo. (1985) Chemiluminescent association reactions in the upper atmosphere, in Gas-Phase Chemiluminescence and Chemi-Ionizat-ion. A. Fontijn (editor). Elsevier Science Publishers, B.V. p 289. 2. R.P. Wayne. (1985) Chemistry of Atmospheres. Clarendon Press, U.S.A. p 257. 3. R.A. Young. (1966) Scientific American (March), p 103. 4. Haslett, J.C. and F.C. Fehsenfeld. (1969) J. Geophys. Res. 7_4, 1878. 5. R.S. Mulliken. (1928) Phys. Rev. 32, 186, 880. 6. E l l i s , J.W. and H.O. Kneser. (1933) Zeits fur Physik. 86, 583. 7. G. Herzberg. (1934) Nature' (London). 133, 759. 8. Herzberg,L. and G. Herzberg. (1947) Astrophya. J. 105, 353. 9. Gush, H.P. and H.L. Buijs. (1964) Can. J. Phys. 42, 1037. 10. J.H. Van Vleck. (1934) Astrophys. J. 80, 161. 11. Thomas, R.J. and R.A. Young. (1981) J. Geophys. Res. JB6, 7389. 12. U.S. Standard Atmosphere, 1976. (1977) National Oceanic and Atmospheric Administration. N.A.S.A. 13. Campbell, I.M. and C.N. Gray. (1973) Chem. Phys. Lett. 18, 607. 14. Barth, CA. and A.F. Hildebrandt. (1961) J. Geophys. Res. 66, 985. 15. Ogryzlo, E.A.; Shen, Y.Q.; and P.T. Wassel. (1984) J. Photochem. 125, 389. 16. F. Kaufman. (1958) Proc. Roy. Soc. A247, 123. 17. Fontijn, A.; Meyer, C.B.; and H.I. Schiff. (1964) J. Chem. Phys. 40, 64. 18. Badger, R.M.; Wright, A.C.; and R.F. Whitlock. (1965) J. Chem. Phys. 43, 4345. 19. Evans, W.F.J.; Wood, H.C.; and E.J. Llewellyn. (1970) Can.J. Phys. 48, 747. 20. Sutoh, M.; Morioka, Y.; and M. Nakamura. (1980) J. Chem. Phys. 72_, 20. 111 21. Slanger, T.G. and G. Black. (1981) J. Chem. Phys. 74, 6517. 22. F. Kaufman. (1961) Prog. Reaction. Kinetics. _1, 1. 23. Kaufman, F. and J.R. Kelso. (1967) J. Chem. Phys. 46, 4541. 24. Hampson, R.F. and D. Garvin (eds). (1978) Reaction Rate and  Photochemical Data for Atmospheric Chemistry, 1977. National Bureau of Standards Special Publication 513. 25. Young, R.A. and G. Black. (1966) J. Chem. Phys. 44, 3741. 26. P.C. Wraight. (1982) Planet. Space Sci. 30, 251. 27. Whytock, D.A.; Michael, J.V.; and W.A. Payne. (1976) Chem. Phys. Lett. U2, 466. 28. Schiff, H.I.; Ogryzlo, E.A.; and L. Elias. (1959) Can. J. Chem. 37, 1690. 112 

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