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UBC Theses and Dissertations

Studies on the afterglow of nitrogen and oxygen discharges Ashford, Robert D. 1970

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STUDIES ON THE AFTERGLOW OF NITROGEN AND OXYGEN DISCHARGES • by ROBERT D. ASHFORD B.Sc. (Hons), University of London, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1970 In presenting th i s thes i s in p a r t i a l f u l f i lment of the requirements fo r an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make i t f r e e l y ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th i s thes i s fo r scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t i on of th i s thes i s f o r f i nanc i a l gain sha l l not be allowed without my wr i t ten permiss ion. Department The Un ivers i ty of B r i t i s h Columbia Vancouver 8, Canada ABSTRACT The reactions: and O^C1! +) + wall + 0„(1A ) + wall have been studied here i n a discharge flow system. Using two tempera-2 tures, the rate constant for wall deactivation was found to be 3.8 x 10 -330 -1 exp ( -^-) sec . I t was concluded that the deactivation was not d i f f u s i o n K l controlled as previously suggested but controlled by the surface deacti-vation process on the walls. The rate constant for production of O^i.^^^) was found to be 6.7 x 10^ exp ( p^2^) l i t r e s mole ^sec i n reasonable agreement with the room temperature value determined by-Arnold. An upper l i m i t of 1.6 x 10^ l i t r e s mole *sec ^ was obtained for the rate constant of the'reaction: ' N + 0_( 1A ) NO + 0 showing that the reaction i s considerably slower than expected from comparison with the analogous reaction of ground state oxygen. This i s r a t i o n a l i z e d by showing that the two reactions require d i f f e r e n t t r a n s i t i o n states. Whilst studying the above reaction several surface catalysed glows from molecular nitrogen and n i t r i c oxide were seen. These glows were found to require 0 9(*A ) for t h e i r production and not atomic oxygen as previously thought. Several q u a l i t a t i v e and spectroscopic experiments were performed and i n the l i g h t of the information gained various possible mechanisms are discussed. STUDIES ON THE AFTERGLOW OF NITROGEN AND OXYGEN DISCHARGES. - i -:CONTENTS PAGE Abstract. i i i L i s t of Tables. i v L i s t of I l l u s t r a t i o n s . . v i Acknowledgements. i x Preface. x Part I. Production and Deactivation of ° 2 ^ g + ^ a t T w 0 T e m P e r a t u r e s • Introduction - Spectroscopic studies. 1 - Singlet oxygen from discharge systems. 3 - Energy pooling processes. 7 Experimental - Measurement of the absolute i n t e n s i t y 0 of the 6340 A emission as a function of the 0 o(*A ) concentration. 18 2 S j + - Measurement of the relaxation of 0„( I ) to steady state conditions as a function of temperature. 22 - Measurement of the I(7619)/!(6340) r a t i o as a function of temperature. 24 Results - The rate constant for 'dimol' emission o at 6340 A. 26 - The temperature dependence of the rate of wall deactivation of 0_( 1Z + ) . 29' 2 g 1 + - The temperature dependence of O 2 ( Eg ) production from energy-pooling of O ^ A g ) . 35 Discussion - The 0„(^Z +) surface deactivation co-e f f i c i e n t y and the deactivation-con-t r o l l i n g process. 43 PAGE Conclusion Energy pooling of two 0„(. A ) molecules 1 + g to form 0.( £ ) . 48 2 . 8 50 Part I I . A K i n e t i c and Spectroscopic Investigation of the  N + Q 2( 1Ag) system. Introduction - Gas phase recombination of nitrogen atoms. 51 - Radiative recombination of n i t r i c ox-ide. 55 - The homogeneous reaction between N(^s) and 0 o ( 1 A ). ' 5 5 - The surface catalysed emission of and NO. 59 Experimental Results - The homogeneous reaction between N and O ^ A g ) . 69 - The red f i r s t p o s i t i v e glow of cobalt. 77 - The blue NO 6 band glow. 87 - The blue copper glow. 94 - Summary of r e s u l t s . 95 Discussion - The rate constant of the N + 0_(*A ) reaction. 101 - The mechanism of the red f i r s t p o s i t i v e emission. 103 - The mechanism of the blue NO 8-band glow. 109 - The blue copper glow. I l l Conclusion 113 - i v -LIST OF TABLES TABLE PAGE I The rate constants for quenching of 0„(*E +) and O-C^A ) by nitrogen and oxygen i n l i t r e s mole * -1 , sec . 6 II Observed double-molecule tr a n s i t i o n s i n oxygen. 8 o III The i n t e n s i t y of emission at 6340 A for d i f f e r -ent concentrations of including c a l i b r a -t i o n data. 28 o IV The in t e n s i t y of 7619 A emission as a function -of distance along the tube at diff e r e n t temper-atures and pressures. 31-34 V The r a t i o of I(7619)/I (6340) at diff e r e n t temper-atures and pressures. 1 - 41 VI P r i n c i p l e band spectra seen i n molecular nitrogen. 56 VII P r i n c i p l e band spectra seen i n n i t r i c oxide. 58 VIII Detection equipment. 67 IX Data showing the relevant conditions for the N + 0 o ( 1 A ) reaction. 71-72 X ^ The v a r i a t i o n of the cobalt catalysed f i r s t posi-t i v e emission with the usual Lewis-Rayleigh emission. 85 XI Data showing the v a r i a t i o n of the ni c k e l NO 8 band glow and i t s background glow an addition of n i t r i c oxide. 88 - V -TABLE PAGE XII The v a r i a t i o n i n the i n t e n s i t y of the NO 8 bands produced by di f f e r e n t methods. 93 XIII The copper I lines seen i n the blue glow. 99 - v i -LIST OF ILLUSTRATIONS  FIGURE PAGE I The oxygen potential energy diagram as compiled by Gilmore (1). 2 o II The spectrum of single t oxygen between 8000 A o and 3500 A as obtained by Gray and Ogryzlo (2). 9 III Diagram of the apparatus used to measure the o absolute i n t e n s i t y of the 6340 A emission as a 1 13 function of the 0_( A ) concentration. IV The c i r c u i t of the isothermal calorimeter. 16 V The r e l a t i v e i n t e n s i t y of the continuum as a function of wavelength as given by Fontijn, Meyer and S c h i f f (3) compared with the r e l a t i v e inten-s i t y of the N O 2 continuum as seen by the photo-m u l t i p l i e r through the f i l t e r . - 19 o VI The effect of the f i l t e r on the 6340 A band emission. 21 VII Diagram of the apparatus used to measure the change 1 + 0 i n 0 of £ ) emission at 7619 A as a function of 2 8 time at d i f f e r e n t temperatures. 23 o VIII The r e l a t i v e i n t e n s i t y of the 7619 A emission of 0^(^Z^~) as a function of distance along the tube at (a) 20°C and (b) -69°C. 36-37 IX Plot of i o g i o ^ s s " 2 ) against time at (a) 20°C and (b) -69°C. 39-40 -VI1-FIGURE X A diagramatic comparison (to scale) of possible t r a n s i t i o n energies i n an unperturbed state. XI The nitrogen potential energy diagram as compiled by Gilmore (1). XII The n i t r i c oxide potential energy diagram as com-p i l e d by Gilmore (1). XIII The flow apparatus used to measure the decay of atomic nitrogen as a function of time. XIV Plot of the nitrogen atom concentration against the distance along the tube. XV Plot of l o g ^ t N ] against time. XVI Spectrum of the cobalt catalysed f i r s t p o s i t i v e o o emission between 8000 A and 5600 A. XVII Spectrum of the usual Lewis-Rayleigh f i r s t posi-o o t i v e emission between 8000 A and 5600 A. XVIII Spectrum of the cobalt catalysed f i r s t p o s i t i v e emission between 1.8u and 0.6u. XIX Spectrum of the usual Lewis-Rayleigh f i r s t p o s i t i v e emission between 1.8u and 0.6u. XX Graph of the cobalt catalysed emission against the usual Lewis-Rayleigh f i r s t p o s i t i v e emission show-ing d i r e c t dependence. XXI Graph showing the effect on the n i c k e l catalysed and normal gas phase emission of the NO 8 bands, - V l l l -FIGURE PAGE of addition of n i t r i c oxide to the N + 0 o ( 1 A ) stream. 89 XXII Spectrum of the nickel-catalysed emission from the NO 8 bands. 91 XXIII Spectrum of the emission produced by conventional n i t r i c oxide recombination. 92 o o XXIV Spectrum of the copper glow between 3200 A and 5000 A. 96 o XXV Spectrum of the copper glow between 4250 A and o 5600 A at higher dispersion. 97 XXVI The r e l a t i v e population of the v i b r a t i o n a l levels 3 of the B IT state of nitrogen. 105 ACKNOWLEDGEMENTS The author wishes to express his gratitude to: - Dr. E.A. Ogryzlo for his continued patience and guidance throughout t h i s work. - my colleagues i n the laboratory f o r many helpful and in s t r u c t i v e discussions. - the University of B r i t i s h Columbia for a Teaching Assistant ship. - the many members of the technical s t a f f i n the Department. - Mrs. V. Mottershead for typing the thesis. -X-PREFACE Three major subjects, only s l i g h t l y i n t e r r e l a t e d , are dealt with i n t h i s thesis. The f i r s t i s concerned with the ki n e t i c s of various production and deactivation reactions taking place i n a stream of 'singlet' oxygen; the second i s a k i n e t i c study of the reaction between atomic nitrogen and singlet oxygen and the t h i r d i s a s p e c t r o -scopic study of surface catalysed and homogeneous gas phase glows found i n mixtures of atomic nitrogen and 'singlet' oxygen gas streams. These three subjects have been divided and placed i n two d i f f e r -ent sections i n an ef f o r t to provide some organization to the d i v e r s i t y of material. Part I contains only the f i r s t subject, sing l e t oxygen k i n e t i c s , with very l i t t l e reference to nitrogen chemistry. Part II contains both the second and t h i r d subjects, which have been placed together i n a separate section i n order to introduce the subjects of recombination and radi a t i o n i n nitrogen and n i t r i c oxide. In f a c t , very l i t t l e s i n g l e t oxygen chemistry i s required i n Part I I , thus making each part v i r t u a l l y autonomous. A d i v i s i o n of the two major subjects of Part II has not been made since the subdivision of each main section i n a p a r a l l e l manner should enable the reader to pick out any p a r t i c u l a r topic. An examination of the 'contents' should make th i s clear. ~ P A R T I. Production and Deactivation of 09(*£ +) at Two Temperatures. INTRODUCTION Spectroscopic Studies. Singlet oxygen i s a term which tends to be used rather loosely, but generally refers to a mixture of the f i r s t two e l e c t r o n i c a l l y excited states of molecular oxygen. These are the af^A^) state and 1 + 1 + the b( E ) state. The upper, b( £ ) state l i e s 0.65 eV above the 1 3 -a( A ) state which, i n turn, l i e s 0.98 eV above the ground X ( E ) s . . s state as shown i n Fig. I (1). The existence of the O^^^^) state was f i r s t predicted by Mulliken i n 1928 (4) and l a t e r detected by Herzberg (5) i n the infra-red solar spectrum where the atmospheric oxygen absorbs weakly i n the 1.27u region. Further confirmation of the presence of t h i s band was pro-vided by E l l i s and Kneser (6) i n absorption through l i q u i d oxygen and by Van Vleck (7) i n emission from a gaseous discharge. Later Harrison and Vallance-Jones (8) observed anomolous enhancement of the (2,3) Meinel band i n the nitrogen nightglow that was probably due to 1 3 - -the (0,1), ( A - E ) "infra-red atmospheric' band at 1.58u. The g g . (0,0) t r a n s i t i o n at 1.27u was not observed at ground l e v e l due to reabsorption by the oxygen i n the lower atmosphere. The t r a n s i t i o n was characterized by i t s nine branches - two R, two P, three Q, and 1 3 -one each of 0 and S branches which are ch a r a c t e r i s t i c of a ( A - E ) g g magnetic dipole t r a n s i t i o n . Vallance-Jones and Gattinger (9) have -4 -1 determined an Einstein A c o e f f i c i e n t of 1.5 x 10 sec for the (0,0) t r a n s i t i o n . Fig. I . Oxygen potential energy diagram as compiled by Gilmore (1). -2--3-The 0~ b( E +) state was f i r s t observed by the atmospheric oxygen absorption i n the 'red* region of the solar spectrum. The o (0,1) t r a n s i t i o n at 8645 A was observed by Meinel (10) i n the airglow, 1 3 -the (0,0) band being reabsorbed as for the ( A - E ) t r a n s i t i o n . The spectrum has also been observed i n emission from the aurora (11) and from discharged oxygen (12). The bands consist of two P and two R branches as expected for a magnetic dipole ( 1Z + - 3E ") t r a n s i t i o n . Childs and Mecke (13) obtained a value f o r the Einstein A c o e f f i c i e n t of the (^ E - *E +) t r a n s i t i o n and subsequent determination (14) gave A = 0.145 sec 1, i n good agreement with the e a r l i e r work. Recently, however, Wallace and Hunten (15), on the basis of t h e i r own work together with the results of an unpublished report by Burch and Gryvnak, have suggested a value of 0.085 sec" 1 for A. Singlet Oxygen from Discharge Systems. The discharge flow technique for studying the k i n e t i c s of fast reactions consists b a s i c a l l y of a uniform flow tube with a controlled gas i n l e t at one end and a rapid pumping system at the other. The gases are regulated to flow at a uniform rate producing a l i n e a r time axis along the length of the tube. By observation at d i f f e r e n t points along the tube the v a r i a t i o n of the reaction with time can be followed. Metastable species, for which the technique i s usually used, can be produced by passing the p a r t i c u l a r gas through an electrodeless d i s -charge. Other reactant gases can then be added to the stream p r i o r to observation along the tube. By varying the flowrate the time d i s -placement can be varied over a considerable range, the only l i m i t a t i o n being that the flowrate must be large compared with the d i f f u s i o n rate through the gas (16). A discharge through oxygen produces a r e l a t i v e l y large quantity of atomic oxygen as well as excited molecular oxygen (17). Because of interference of t h i s atomic oxygen i n reactions of singl e t oxygen, i t s s e l e c t i v e removal by some means i s necessary. I t was found that by recombination of the atomic oxygen on a surface of mercuric oxide, a stream of ground state oxygen containing about 10% excited molecular oxygen could be produced (18) (19). This recombination process i s achieved by placing a heated bead of mercury either before or after the microwave discharge causing mercuric oxide to form as a hot layer on the wails of the tube downstream of the discharge region. The precise function of the mercuric oxide i s not well understood. A 20% increase i n the C> (*A ) concentration on introduction of the mercuric oxide into the stream has been reported by Cairns and Samson (20) using photoion-i z a t i o n techniques to measure the (^(^A^) concentration. This value has been confirmed by Whitlow and Findlay (21) by d i r e c t observation 1 3 -of the (0,0),( A - £ ) band at 1.27y. The 14-fold enhancement of o the 7619 A band on removal of the atoms reported by March et a l (22) has not been confirmed by other workers. In the present work a discharge flow system was used i n which the s i n g l e t oxygen was produced by removal of the atomic oxygen with mercury 0,( 1A ) concentrations of about 10% and 0_(1£ + ) concentrations of about -5-0.1% are formed i n such systems (23). The concentration of other excited molecular states of oxygen i s n e g l i g i b l e . I t i s possible to study a few quenching reactions of 0 ( A ) and O^i ^ g +) without the presence of mercuric oxide to recombine the atomic oxygen provided the oxygen atoms do not react with the quencher. In order to minimize quenching by the atomic oxygen very small flowrates of discharged oxygen have been used, requiring special techniques for the detection of the low O^^A^) concentrations. Clark and Wayne (24) have used a photoionization technique employing the argon resonance lines at 11.70 eV and 11.61 eV to achieve a monochromatic l i g h t source. They compensated for absorption by 0„(1Z + ) by comparison with the ion-current produced using the krypton l i n e at 10.69 eV, since ra d i a t i o n of t h i s energy cannot ionize the 0 9(*A )(see Fig. I ) . Since there i s also some absorption by ground state oxygen a further correction, determined by measurement at various oxygen pressures, must be made. Using t h i s technique Clark and Wayne (24) have determined quenching constants for deactivation of Q^}~t\^) by several gases. Their value 3 f o r quenching by 0£(X 2^ ) agrees well with that obtained by Findlay et a l . (25) using i r r a d i a t i o n of benzene-oxygen mixtures to obtain 0 9(*A ). g Values for the deactivation of both 0 2( 1A ) and 0_( 1Z +) by oxygen and nitrogen are shown i n Table I. The values used are those suggested i n the recent reviews by Wayne (26) and Zipf (27). -6-Table I. Rate constant for quenching of 0^C^I^*) and 0^(*Ag) by N,, and 0 2 i n l i t r e s mole "^sec Quenching Molecule Rate constant i n l i t r e s mole '''sec * °2 N2 1.4 x 10 3 (24) . <40 (24) 6 x 10 4 (27) 1.5 x 10 6 (35) -7-Energy Pooling Processes. . Of p a r t i c u l a r interest i n s i n g l e t oxygen chemistry are the double molecule 'energy pooling 1 processes which give r i s e to emission i n the v i s i b l e region of the spectrum. The c o l l i s i o n of two O^^A^) molecules can produce, not only c o l l i s i o n induced'radiation at 1.27u, but also 0 1 + emission at twice that energy (6340 A). Bands involving both 0„( £ ) and 0^{}L\^ have been seen together with tra n s i t i o n s from various v i b r a t i o n a l l y excited l e v e l s . These bands are l i s t e d i n Table II to-gether with t h e i r r a d i a t i v e l i f e t i m e s and wavelengths. The tra n s i t i o n s were f i r s t seen by absorption i n l i q u i d oxygen (28) and l a t e r , by ab-_ . sorption i n high pressure oxygen (29) and i n emission from both chemical (30)(31) and discharge sources (32)(2). A l l bands are broad and lack r o t a t i o n a l structure. A complete spectrum of discharged s i n g l e t oxygen i s shown i n Fig. I I . Two values have been quoted for the rate constant, k j , of emission o at 6340 A: , 1(6340) = k ^ O ^ A g ) ] 2 (1) The f i r s t determination was by Browne (33)(34) who determined the 0 9(^A ) concentration using an isothermal calorimeter and calibrated the absolute o emission at 6340 A by comparison with the known i n t e n s i t y of the emission from the N0 2 continuum produced by the recombination (3): 0 + NO N0 2 + hv (2) -8-Table II Observed double molecule t r a n s i t i o n s i n oxygen. Excited State 3 Transition to ground ( £ + J£ ) g state. V e x c i t e d " vground Wavelength 0 (A) * Lifetime (sees) A + E 0 12700 4 sees. g g -1 15800 •h + + 3 E " 0 7619 15 sees. g g -1 8345 A + A 0 6340 1.5 sees. g g -1 7030 +1 5800 * A ^ *v + A + E 0 4800 1.7 sees. g g -1 5200 h + + h + 0 4000 0.3 sees. g g 3800 calculated from integrated absorption c o e f f i c i e n t s (2). 6 o Fig. I I . Spectrum of s i n g l e t oxygen between 8000 A and 3500 A as obtained by Gray and Ogryzlo (2). Taken using an RCA IP21 photomultiplier and uncorrected for spectral response. The dotted l i n e shows the r e l a t i v e spectra at 300°K and the s o l i d l i n e at 150°K. Both spectra were taken at 10 t o r r . -9-A11SN31N! -10-He obtained a value of 0.09 l i t r e s mole *sec * for k^. F a l i c k and Mahan (35) also made a determination i n which they found a value for k^ of 0.03 l i t r e s mole ^"sec They determined the O^C^h ~) concentration by observation of the AMj = 1 t r a n s i t i o n of the J = 2 t o t a l angular momen-tum state, using a paramagnetic resonance spectrometer. . The cavity was calibrated using a known pressure of ground-state oxygen. Since, i n the work to be described, the 0_(*A ) concentration was o determined by monitoring i t s emission at 6340 A, the present work also includes an independent determination of k 1 Under normal conditions i n a discharge flow system the +) concentration i s i n a steady state (32) between i t s production by the reaction: k o 2 ( 1 y + o2 c ly - ^ v V * + °2 ( 3V ) (3) and i t s deactivation on the walls of the reaction tube: 0_ ( 1 E +) + wall - 4 - * - o ( 3 E ") + wall (4) ^ g ^ g or O^Ag) Reaction (3) i s an example of a non-radiative energy-pooling process, which has been c a l l e d an energy dispropriation reaction (36). I t was f i r s t pro-posed by Young and Black (37) to account for the steady state concen t r a t i o n of 0 2( 1S + ) . By determining the possible l i m i t s of k^ and from a knowledge of the 0 ( 1Z +) and 0_( 1A ) concentrations they obtained an 2 g g 7+0 5 - I -1 estimate f o r k j of 2 x 10 " ' l i t r e s mole sec . This value, however, was found to be high by several orders of magnitude (38). A determination -11-by Arnold and Ogryzlo (23) using non-stationary conditions gave a value 3 - 1 - 1 for kj of 1.4 x 10 litres mole sec . Under these conditions the Op^Eg*) concentration is governed by: = k 3 t 0 2 ( \ ) ] 2 - M ° 2 C \ + ) ] (5) Since, under usual flow conditions, the [0_(1A )] is approximately constant 8 the first term on the right hand side of the above equation can also be taken as constant., can then be' obtained from a knowledge of the rate of change of the 0„(1E +) concentration. At steady state when 8 d__[*E +] = 0, equation (6) holds: dt g > 3 [ 0 2 ( 1 A g ) ] 2 = k 4 [ 0 2 ( 1 E g + ) ] s s (6) and a knowledge of the O^^E +) and O-^A ) concentrations gives k_. 2 g 2 g 3 In the experiments to be described here a similar analysis is carried out. The temperature dependence of the change in the 0 2( 1E g +) concentra-tion with time under non-stationary conditions, together with the vari-ation of [0„(1E +)]/[0«(1A ) ] 2 with temperature allows the temperature ^ 8 ^ 8 variation of both k^ and k4- Determination of the [0 2( E g +)]/[0 2( A g)] o o ratio was by comparison of the 7619 A and 6340 A bands, necessitating the o determination of the absolute emission rate at 6340 A mentioned earlier. -12-EXPERIMENTAL The three experiments described here require, in each case, control and measurement of certain specific parameters, necessitating the use of three different flowtubes designed to meet the particular require-ments of each experiment. The design of the gas inlets, controls, flow detectors, pressure gauges and pumping system, however, remained essen-ti a l l y the same since the flowtube design was altered only between conveniently placed ground glass joints. The general design of a flow system is shown in Fig. III. The particular variations on this design will be dealt with later. The main oxygen flow through the system was controlled using an Edward's needle valve and the flowrate was determined from the pressure difference across a capillary measured using a differential manometer f i l l e d with dibutyl phthalate. This manometer was calibrated on known flowrates determined by collecting the quantity of gas passing through the system in a given time. The added gas was contained in a 2 litre bulb and admitted to the flowtube by a similar system to that employed for the mainstream oxygen. It was found, however, that unless P, the pressure in the storage bulb, could be kept constant the flowrate could not be monitored using the familiar Poiseuille relationship: F = r4IIAP(2P - AP) 16nLRT where F = flowrate in mole sec Fig. I I I . Diagram of apparatus used f o r measuring the emission i n t e n s i t y along the tube using a photomultiplier and the absolute concentration of an excited species using an isothermal calorimeter. DISCHARGE ( LIGHT TRAPS, *- QUARTZ Hg (7mm. O.D.) REFLECTOR REACTANT • MULTIPLE JETS T7 / / CALORI METRIC DETECTOR Co FILTER W 1 R E SLITS TO TRAPS AND PUMP PHOTOMULTIPLIER -14-AP = pressure difference across c a p i l l a r y i n dynes.cm r,L = radius, length of c a p i l l a r y i n cms. l") = v i s c o s i t y of gas i n poise. T = temperature (°K) This d i f f i c u l t y was overcome by determining dP_ using a pressure gauge dt made by Texas Instrument Co. which could l i n e a r l y measure pressure of up to one atmosphere to an accuracy of 0.02 t o r r . The decrease i n pres-sure with time was then measured over a period of about 5 minutes and, using the volume of the storage bulb, the flowrate could be determined d i r e c t l y . The oxygen was Matheson extra-dry grade which was used without further p u r i f i c a t i o n . The nitrogen dioxide was made from n i t r i c oxide, obtained from Matheson Co. and p u r i f i e d as described i n Part I I . The bulb was f i l l e d to about 200 t o r r with n i t r i c oxide and then to a pressure j u s t below one atmosphere with pure oxygen. The gas was then s o l i d i f i e d to 77°K, pumped on.to remove excess oxygen and n i t r i c oxide and eventually allowed to warm up to room temperature. This procedure was repeated several times u n t i l a pure white f l a k y s o l i d was produced ( 3 6 ) . The three d i f f e r e n t flowtubes had s i m i l a r s i n g l e t oxygen production systems. The discharge was maintained by power supplied through a 214L gas discharge cavity from an Electromedical Supplies 'Microtron' micro-wave generator with a continuous 2450 MHz output. The cavity could be tuned to resonance which, as well as producing a steadier discharge, -15-a l s o minimized d e s t r u c t i v e i n t e r f e r e n c e w i t h power r e f l e c t e d back along the l e a d s . Although the u n i t had a maximum, output of 200 watts, i t was found t h a t the s i n g l e t oxygen c o n c e n t r a t i o n increased only s l i g h t l y w i t h i n c r e a s i n g power above 75 watts. In order to e l i m i n a t e s t r a y l i g h t produced by the d i s c h a r g e , the gas was passed through two conventional l i g h t t r a p s b e f o r e being admitted to the flowtube. The whole discharge area as w e l l as the l i g h t t r a ps were covered w i t h f l a t , b l a c k p a i n t . The atomic oxygen was removed from the discharge products by d i s t i l -l a t i o n of a l i t t l e mercury to form a surface of mercuric oxide on the w a l l s o f the tube. I t was found t h a t i f the mercury was placed near the d i s c h a r g e , i t could be maintained at a s u f f i c i e n t temperature to be e f f e c t i v e by simply a l t e r i n g the p o s i t i o n of the c a v i t y along the tube. The absolute 0 of^A ) c o n c e n t r a t i o n was determined by the isothermal c a l o r i m e t e r technique (19). This c o n s i s t s of d e a c t i v a t i o n of a l l the 0„(*A ) on an e l e c t r i c a l l y heated wir e known as a d e t e c t o r . The heat l i b e r a t e d by the C^t^A^) i s then matched by an a p p r o p r i a t e decrease i n the c u r r e n t through the w i r e , the d i f f e r e n c e p r o v i d i n g an accurate measure-ment o f the (^(^Ag) c o n c e n t r a t i o n . In p r a c t i c e the d e t e c t o r c o n s i s t s of a h e l i c a l l y wound s p i r a l o f platinum w i r e , e l e c t r o p l a t e d w i t h c o b a l t . The c i r c u i t i s shown i n F i g . IV. In the absence o f C> (*A ) , the b r i d g e * g i s balanced a l l o w i n g the r e s i s t a n c e , R, of the d e t e c t o r to be determined and the c u r r e n t , i , i s measured usi n g a potentiometer. The 0 9 ( 1 A ) O £• g i s then passed over the d e t e c t o r and the b r i d g e rebalanced by decreasing the c u r r e n t . Thus by e q u a l i z i n g R before and a f t e r the 0_(*A ) a d d i t i o n , Fig. IV. C i r c u i t for isothermal calorimeter. -16-P p o t e n t i o m e t e r t e r m i n a l C c o m m o n G galvanometer " T ..tapping key -17-t h e t e m p e r a t u r e o f t h e d e t e c t o r i s m a i n t a i n e d a t a c o n s t a n t v a l u e . The c u r r e n t ( i ) i s a g a i n mea su red . The 0 „ ( 1A . ) f l o w r a t e i s g i v e n b y : S d_ [0 {h ) ] =• A ( i ) 2 - R d t g K.E 2 2 2 whe re A ( i ) = i - i J o E = e n e r g y l i b e r a t e d p e r mo l e = 23 k c a l s . mo le 1 f o r C^C^A ) K = 4 .18 c a l . s e e s , w a t t s - 1 o The e f f i c i e n c y o f t h e d e t e c t o r was- c h e c k e d by d e t e c t i o n o f t h e 6340 A b a n d downs t ream o f t h e d e t e c t o r . I n each c a s e i t was o b s e r v e d t h a t >95% o f t h e 0 o ( 1 A ) was removed f r o m t h e s t r e a m . o o The 7619 A and 6340 A bands were d e t e c t e d i n a l l c a s e s u s i n g an RCA 7265 p h o t o m u l t i p l i e r ( S 20 ) . The s i g n a l was chopped , a m p l i f i e d by a T e k t r o n i x 122 p r e a m p l i f i e r and t h e n f e d i n t o a PAR J B - 5 l o c k - i n a m p l i f i e r whe re b o t h pha se and f r e q u e n c y were compared w i t h a s i m i l a r l y chopped r e f e r e n c e s i g n a l . S p e c t r a were t a k e n u s i n g a low r e s o l u t i o n f / 6 . 5 Bausch and Lamb g r a t i n g manochromato r w i t h a s l i t w i d t h o f about 1 mm. V e r y weak s i g n a l s were i s o l a t e d u s i n g i n t e r f e r e n c e f i l t e r s t o s e l e c t t h e wave -0 l e n g t h . F o r t h e 7619 A band a Bausch and Lomb 337876 f i l t e r was u sed i n c o n j u n c t i o n w i t h a C o r n i n g 2424 f i l t e r t o e l i m i n a t e t h e l a r g e f i r s t o r d e r o o ' w i n d o w ' a t 3800 A. F o r t h e 6340 A band a Bausch and Lomb 337863 f i l t e r was u s e d , t h e f i r s t o r d e r b e i n g i n a r e g i o n o f low p h o t o m u l t i p l i e r r e s p o n s e a s w e l l as b e i n g w e l l removed f r o m any s i n g l e t oxygen bands o r UO^ e m i s s i o n w i t h w h i c h t h e a p p a r a t u s was c a l i b r a t e d . The l i g h t cone c o l l e c t e d was a l w a y s abou t 30° w h i c h was e a s i l y s u f f i c i e n t f o r t h e p u r p o s e s o f t h i s wo r k . -18-Measurement of the absolute i n t e n s i t y of the 6340 A emission as a function of the O ^ f ^ A ) concentration. Apparatus s i m i l a r to that shown i n Fig. I l l was used i n t h i s ex-periment. The t o t a l 0 2 ( * A ^ ) concentration was measured using an i s o -thermal calorimeter which was placed at the end of a 25 cm. long, 3.5 cm. o diameter flowtube. The 6340 A emission was viewed across the tube with an RCA 7265 photomultiplier together with a suitable f i l t e r . The absolute o i n t e n s i t y of the 6340 A band was determined by comparison with the N0 2 continuum produced by the addition of N0 2 to atomic oxygen: 0 + N0 2 -*• NO + 0 2 (7) 0 + NO + N0 2 + hv (continuum) (2) The o r i g i n a l atomic oxygen concentration was found using the end point of the 0 — N0 2 t i t r a t i o n - when [N0 2] ^ [0] no green continuum i s seen. The actual atomic oxygen concentration for reaction (2) i s given by: ^ = ^ t i t r a t i o n "Padded and [NO] = [ N 0 2 ] a d d e d F o n t i j n , Meyer and S c h i f f (3) have determined an absolute value f o r the t o t a l emission i n the N0 2 continuum and have calculated a rate constant 4 - 1 - 1 for reaction (2) of 3.8 x 10 l i t r e s mole sec . This value, however, represents the t o t a l N0 2 emission and since here only part of that emission i s being observed, the rate constant must be reduced accordingly. This was done by taking the r a t i o of the shaded area to the t o t a l area under the continuum i n Fig. V. The shaded area i s the r a d i a t i o n of the continuum Fig. V. Relative intensity of the NC^ continuum as a function of wavelength as given by Fontijn, Meyer and Schiff (3) compared with the relative intensity of the NG^  continuum as seen by the photomultiplier through the f i l t e r . -20-modified by the f i l t e r transmission and adjusted to allow for the change i n phototube response with wavelength. The curve i s increased i n height to match the continuum at i t s peak. Thus the change i n f i l t e r transmission with wavelength i s being used as a weighing factor with o r a d i a t i o n at 6340 A being a given weight of 1. The second factor which had to be considered was whether a l l the o o l i g h t i n the 6340 A band would pass through the f i l t e r and how the 6340 A band was modified by the f i l t e r transmission. This i s i l l u s t r a t e d i n Fig. VI. The transmission curve of the f i l t e r was obtained using a p a r a l l e l beam of l i g h t incident on the f i l t e r at 90°. The increased transmission to longer wavelengths due to the fact that a 30° cone of l i g h t was collected o by the f i l t e r was found to be neg l i g i b l e . The t o t a l 6340 A emission was thus given by: +oo +oo 1(6340) = k 2[0][N0] Mx f F s(A)f(X)dXr F 6 3 4 0 (X)dX V r f ' - O O \J-CO +oo +00 M 2 ] F 6 3 4 0 ( X ) f ^ d A f V A ) d X •v-oo \J _00 4 - 1 - 1 where k 2 = rate constant for reaction (2) = 3.8 x 10 l i t r e s mole sec o Fg(^)> ^ 6 3 4 0 ^ = f u n c t i o n representing N0 2 continuum and 6340 A band respectively. f(X) = function representing f i l t e r transmission. o M^,M2 = recorded i n t e n s i t i e s of 6340 A band and N0 2 continuum respectively. o Fig. VI. Effect of f i l t e r on the 6340 A band emission. -21-Wavelengfh (//) -22-From Fig. V using the integrated areas under the curves: /1+co -CO F (X)f (X)dX/~+«> F c(X)dX = .0145 and from Fig. VI: _ 0 0 6340 (A)f(X)dA 6340 (X)dX = .458 The atomic oxygen was produced by a microwave discharge of oxygen i n the absence of mercuric oxide. A s l i g h t a i r afterglow was seen due to traces of nitrogen i n the oxygen but t h i s zero error was found to be n e g l i g i b l e . To produce si n g l e t oxygen the atomic oxygen was recombined by simply d i s t i l l i n g mercury through the discharge u n t i l the c h a r a c t e r i s t i c red glow was seen. Measurement of the relaxation of O^^Z +) to steady state conditions as a function of temperature. A diagram of the flowtube used i n t h i s experiment i s shown i n Fig. VII. The uniform t r i p l e - w a l l e d tube was about 1 metre long and 1.'9 cms. i n diameter. The r e l a t i v e 0_(*E + ) concentration was measured by observa-2 V g *  J . • 1 + 3 - ° t i o n of the (0,0)( Z - Z ) t r a n s i t i o n at 7619 A using an RCA 7265 photomultiplier together with a suitable f i l t e r . Opposite the photo-m u l t i p l i e r was placed a polished aluminium r e f l e c t o r which not only increased the l i g h t input to the tube but also provided a constant back-..Fig. VII. Diagram of the apparatus used to measure the rate of change 1 + 0 i n the 0_C Z ) emission at 7619 A as a function of temperature. Thermocouple to McLeod gauge Photomultiplier Filter Chopper Silver J L _ z 2 <-/ / / / / / / / / / / / / / / / / / / A/ / / / / h 1 K^u^y ///////////////// { - U ) j Vacuum jacket to pump Coolant 0 2 from discharge i to I -24-ground for the emission. A rotating sectored disc was placed i n front of the photomultiplier to chop the l i g h t input. The whole detection system was mounted on a platform which was moveable along the length of o the tube. This arrangement allowed v a r i a t i o n i n the 7619 A band int e n s i t y to be monitored as a function of distance along the tube. The temperature i n the flowtube was lowered by means of l i q u i d n i t r o -gen vapour, produced by placing a heating c o i l i n a dewar of l i q u i d nitrogen. The vapour was passed between the inner two walls of the t r i p l e -walled reaction vessel, the space between the outer two walls being evacuated. The temperature was measured with a copper-constantan thermo-couple which was moveable along the inside of the tube i n order to check f o r the uniformity of the gas temperature. This was found to vary by about 5% along the tube. The potential difference across the thermocouple was continuously monitored by means of a 10 mV s t r i p chart recorder which was calibrated against a low temperature thermometer supplied by Fisher S c i e n t i f i c Co. by placing a thermometer and thermocouple i n a series of s t i r r e d low temperature baths. The uniformity of the O^C^A ) was checked o using i t s emission at 6340 A and found to be reasonably constant along the tube. Measurement of the I (7619)/l(6340) r a t i o as a function of temperature. For this experiment the flowtube consisted of a tube 1.9 cms. i n diameter and 10 cms long surrounded by a jacket through which cold l i q u i d nitrogen vapour could be passed, as i n the previous experiment. A copper--25-constantan thermocouple, placed i n the gas stream was again used to measure the temperature. Spectra were taken using a Bausch and Lomb f/6.5 mono-chromator viewing the emission along the length of the tube. Scan times were about 1 minute/200 A. Some d i f f i c u l t y was encountered with f r o s t i n g of the observation window at low temperature, but i t s effect was reduced by simply cleaning the .window before each scan and then scanning the wave-length range i n both directions. The mean of the two scans was then taken. o o The r e l a t i v e i n t e n s i t i e s of the 7619 A band and the 6340 A band were de-termined by comparison of the region with the NC^ continuum which was produced i n the c e l l by simply passing a i r through the discharge instead of pure oxygen. The spectrum obtained was compared with the absolute spectrum published by Fontijn, Meyer and Sch i f f (3). Thus any non-linearity, such as phototube response, was eliminated. -26-RESULTS o The r a t e constant f o r ' d imo l ' emission at 6340 A. As mentioned e a r l i e r there have been two previous determinations o o f the r a te constant f o r absolute emission at 6340 A: 1(6340) = k ^ O ^ A g ) ] 2 (1) These determinat ions were made by Brown (33)(34) us ing an isothermal ca lo r imeter and by F a l i c k and Mahan (35) using paramagnetic resonance to M e a s u r e the 0„ ( *A ) concentrat ion. Because the previous values d i f f e r e d 2 V g by .a f a c t o r o f th ree , the present determinat ion was performed to provide an independent t e s t o f k^ and to po s s i b l y al low a choice between the two va lues to be made. 0„( *A ) concentrat ions were measured us ing an isothermal ca lor imeter . 2 V g J & p The absolute emission at 6340 A was obtained by comparison with the N0 2 continuum produced by: 0 + NO -> N0 2 + hv (2) o The data i s g iven i n Table III. Absolute emission at 6340 A was obtained by s u b s t i t u t i o n i n equation (8): 1(6340) = k 2 [0][NO] MjA W2 4 -1 where k 2 = r a te constant f o r r e a c t i o n (2) = 3.8 x 10 mole sec o M^ ,M2 = recorded i n t e n s i t i e s o f 6340 A band and N0 2 continuum r e s p e c t i v e l y . -27-o A = parameter a d j u s t i n g t r a n s m i s s i o n of 6340 A band and NO2 continuum through f i l t e r =0.032. S u b s t i t u t i o n o f 1(6340), together w i t h the 0 9(*A ) concentrations i n t o g equation (1) allowed an average value of 0.12 ± 0.04 l i t r e s mole '''sec to be obtained f o r k^. The p r i n c i p a l ' e r r o r was due to the u n c e r t a i n t y i n the a b s o l u t e i n t e n s i t y o f the N O 2 continuum (3). This i s i n good agreement w i t h the v a l u e of 0.09 l i t r e s mole ''sec * r e p o r t e d by Brown (33) (34). Mahan (35) has suggested t h a t the discrepancy between the r e s u l t s o f the two determinations could be due to incomplete d e a c t i v a t i o n of a l l v i b r a t i o n a l l y e x c i t e d oxygen on the i s o t h e r m a l c a l o r i m e t e r . Assuming a mean time f o r d i f f u s i o n o f the 0„(*A ) to the isothermal c a l o r i m e t e r of 2 g -3 1 10 sees and assuming d e a c i v a t i o n at c l l i s i o n fr quency, the A^ would be expected to be c o l l e c t e d i n about 1 cm. w i t h a f l o w r a t e of 2 - 1 5 x 10 cms. sec used here. Further v i b r a t i o n a l d e a c t i v a t i o n might r e q u i r e anything up to 5 cms. In these l a b o r a t o r i e s i t has been conventional to use i s o t h e r m a l c a l o r i m e t e r s forming c o i l s about 2 cms. long. I t i s thus c o n c e i v a b l e t h a t e l e c t r o n i c a l l y d e a c t i v a t e d 0 2(*Ag) might escape 3 1 the d e t e c t o r as v i b r a t i o n a l l y e x c i t e d 0„( 1 ). The 0~( A ) concentra-1 2 V g 2 V g J o t i o n would then appear f a l s e l y low even though a l l the 6340 A emission had been quenched,-suggesting complete removal of the 0„(*A ) by the ^ g d e t e c t o r . The d e t a i l e d experiments of E l i a s , Ogryzlo and S c h i f f (19) u s i n g two i s o t h e r m a l c a l o r i m e t e r s , however, show that t h i s i s c e r t a i n l y not the case f o r recombination of atomic oxygen, which would presumably have Lg 3 a s i m i l a r 0_( £ ) v i b r a t i o n a l d e a c t i v a t i o n process. -28-Table I I I Intensity of emission at 6340 A for dif f e r e n t concentrations of 0_(*A ) and absolute emission c a l i b r a t i o n data. 2 — g-C^C^Ag) concentration expressed as a flowrate i n moles, sec o Recorded int e n s i t y of 6340 A emission as seen by the photo-m u l t i p l i e r (arbitrary units) 5.97 x 10" 6 48/.02 5.67 x 10" 6 39/.02 7.03 x 10" 6 55/.02 Cal i b r a t i o n conditions: Flowrate of atomic oxygen Flowrate of n i t r i c oxide Recorded i n t e n s i t y of N0 2 continuum as seen by the photomultiplier. -7 -1 2.45 x 10 mole, sec - 8 -1 4.96 x 10 mole, sec" 13/.002 (arbitrary units) As far as Mahan's experiment i s concerned,Westerberg (40) has c r i t i -sized the use of the magnetic dipole transitions of oxygen for c a l i b r a t i o n of e l e c t r i c dipole t r a n s i t i o n s such as exhibited by O^k^). He states that the magnetic and e l e c t r i c f i e l d vectors of the microwave radiation are oriented at ri g h t angles to each other and even though they may be related i n p r i n c i p l e , i n practice distortions of the f i e l d i n the cavity for various reasons cause the theoretical calculations to be some-what unreliable. Thus the question of which of the two values for i s correct, remains unanswered. The value of k^ found i n t h i s work w i l l be used here. The temperature dependence of the rate of wall deactivation of 0 2 (^g +)• I t has already been mentioned that the 0 o ( ^Z +) concentration i s 2 g governed by the two reactions: ° 2 ( 1 V + - ° 2 C \ + ) + 0„(3I ~) 2 V g (3) o 2 ( \ + ) + wall (4) or O^A ) This gives: dt 1 2 1 + k_TA r - M z J 3 L g J 4 L g J (5) At steady state: 4 L g J s s (6) -30-Th e f i r s t term on the ri g h t hand side of equation (5) i s taken as constant since the O-C^ A. ) concentration i s approximately constant along the tube. In order to independently vary the O-C^E +) concentration without changing the O ^ & g ) concentration i t i s necessary to disrupt the O^^E +) pro-duction-deactivation balance. This was achieved by chance i n the previous work of Arnold and Ogryzlo (23). Unfortunately, l i t t l e i s known of the reason why the necessary conditions were obtained i n t h e i r apparatus. Great d i f f i c u l t y was encountered i n trying to repeat t h e i r conditions i n a normal glass apparatus which suggested that other factors might be involved apart from the i n i t i a l formation of non-stationary concentrations i n the discharge. (A decrease i n the deactivation rate by a change i n the s l i g h t mercuric oxide deposit on the walls, for instance). Other methods of producing non-stationary conditions were thus t r i e d . These included a temperature drop (500°K •+ 200°K) and introduction of glass wool into the flow system to increase the surface deactivation area, both of which were unsuccessful. I t was eventually found that p a r t i a l deactivation of the O^i^^^) on s i l v e r wire produced the required con-ditions which were optimum with about 50 cms. of s i l v e r wire (10 gauge) forming a g r i d across the tube. o The increase i n the 7619 A emission with distance along the tube af t e r the s i l v e r wire i s tabulated i n Table IV for eight pressures and two temperatures. This data i s plotted i n Fig. V I I I . Combining equations (5) and (6) gives: -31-Table IV o Intensity of 7619 A emission as a function of distance along  the tube at diff e r e n t pressures and temperatures. 1. Pressure = 2.90 t o r r 2. Pressure = 3.22 t o r r Temperature = 20°C Temperature = = 20°C Distance along tube (cms.) 1(7619) arbi t r a r y units Distance along tube (cms.) 1(7619) ar b i t r a r y units 0 0.0 0 -1.9 1 1.0 1 -0.2 2 2.1 2 +1.8 3 3.4 3 3.2 4 5.4 4 4.7 5 6.9 5 6.2 6 8.0 6 7.2 7 9.2 7 8.0 8 10.2 8 8.9 9 11.2 9 9.9 10 11.8 10 10.4 12 12.8 12 11.4 14 13.8 14 12.0 16 14.4 16 12.2 18 14.7 .18 12.2 20 14.9 20 12.2 25 15.0 25 12.1 30 15.0 30 12.1 -32-Table IV (continued) 3. . Pressure = 4.16 torr 4. Pressure =4.98 t o r r Temperature = 20°C Temperature = 20°C Distance along tube (cms.) 1(7619) ar b i t r a r y units Distance' along tube (cms.) 1(7619) ar b i t r a r y units 0 • 2.4 0 1.6 1 4.6 1 '3.9 2 6.6 2 5.9 3 8.5 3 7.8 4 10.2 4 9.5 5 12.0 5 10.8 6 13.2 6 11.9 7 14.4 7 13.0 8 15.2 8 13.8 9 16.0 9 14.6 10 16.5 10 15.2 12 17.4 12 16.2 14 18.0 14 16.8 16 18.5 16 17.3 18 18.9 18 17.5 20 19.0 20 17.8 25 19.4 25 17.9 30 19.4 30 17.9 -33-Table IV (continued) 5. Pressure = 2.48 tor r 6. Pressure = 3.04 tor r Temperature = -69°C Temperature = -69°C Distance along: tube (cms.) 1(7619) ar b i t r a r y units Distance along tube (cms.) 1(7619) arbitrary units 0 2.0 0 -1.7 1 13.5 1 +0.3 2 6.2 2 3.8 3 8.5 3 ,5.9 4 10.4 4 8.0 5 12.5 5 10.0 6 14.0 6 10.5 7 14.5 7 12.0 8 16.0 8 14.1 9 17.0 9 14.6 10 18.0 10 15.4 12 19.8 12 17.0 14 21.2 !4 18.7 16 22.5 16 1.9.4 • 18 24.0 18 20.1 20 24.5 20 20.6 25 '26.0 25 21.4 30 27.8 30 21.6 -34-Table IV (continued) 7. Pressure = 4.20 tor r 8. Pressure = 5.00 torr Temperature = -69°C Temperature = -69°C . Distance along tube (cms.) 1(7619) ar b i t r a r y units Distance along tube (cms.) 1(7619) ar b i t r a r y units 0 0.3 0 -2.3 1 2.0 1 -1.0 2 4.5 2 +1.0 3 6.2 3 3.4 4 8.8 4 6.0 5 9.6 5 7.0 6 11.0 6 9.4 7 12.2 7 10.4 8 13.9 8 12.0 9 14.8 9 13.0 10 15.6 10 13.4 12 17. 2 12 15.6 14 18.4 14 17.4 16 19.4 16 18.6 18 20.0 •'. 18 19.6 20 20.6 20 20.4 25 22.0 25 22.0 30 22.2 30 23.0 -35-which on integration gives: 2.3 l o g 1 0 ( [ 1 E g + ] s s - t 1 ^ * ] ) = " V + constant (9) Thus a plot of 2 .3 log 1 0(I(7619) s s - 1(7619)) against time w i l l have a slope of -k^. The use of relative instead of absolute values of the H Oji^I. +) concentration w i l l only effect the constant of equation (9). This plot i s shown in Fig. IX. The value of is 215 ± 20 sec 1 at 20°C and 170 ± 20 sec" 1 at -69°C, which combined in an Arrhenius equation 2 f-33&\ -1 gives 3.8 x 10 exp ^ — — J s e c . These values represent a direct deter-mination of k^ and are thus independent of any other constant. :.k4 can be seen from Fig. IX to be independent of the total pressure of the system. The values given here actually represent a l l pressure independent loss mechanisms, including radiative deactivation. These latter processes, however, are negligible with lifetimes of 0.15 sec 1 .for the ( 1 E + - 3 Z " ) transition (13) (21) and 2.6 x 10 - 3 sec" 1 for the ( 1 E + - XA ) transition (18). g g The temperature dependence of 0 2 ^ g + ) production from energy-pooling of 0 2 ( 1 A g ) . From reaction (6) at steady state: h * = k, A 4 g Using the rate constants that govern emission: 1(7619) = k [OjC 1^*)] (11) 1(6340) = k 1 [ 0 2 ( 1 A g ) ] 2 (1) 1 + Fig . V I I I ( a ) . Relative i n t e n s i t y of 7619 A emission of 0„( I ) as a function of distance along the tube at 20°C. ° 1 + Fig. V I I I ( b ) . Relative i n t e n s i t y of 7619 A emission of 0 ( £ ) S as a function of distance along the tube at -69°C -36--38-th e r a t i o of k^/k^ can be determined: IC3 = ^1(7619) ( 1 2 ) k 4 k nI(6340) . The experimentally determined I (7619)/I(6340) r a t i o under d i f f e r i n g con-dit i o n s i s shown i n Table V. In order to measure the temperature va r i a -t i o n of kg the temperature dependence of the other constants i n equation (12) must be known. The only one that does not vary i s k^^ since t h i s represents the Einstein c o e f f i c i e n t f o r spontaneous emission. Child and Mecke's value of 0.145 sec * w i l l be used here. The v a r i a t i o n of k^ with temperature has been previously determined by Arnold, Brown and" Ogryzlo (34). By combining t h i s temperature dependence with the room -2 temperature value of 0.12 found here, k^ was calculated to be 7.3 x 10 l i t r e s , mole. *sec * at -79°C. This, together with the r e s u l t s of Table V gave a mean value of 10.8 l i t r e s , mole *sec * for k^/k^ at 293°K and 2.34 l i t r e s . mole - 1sec 1 for k^/k^ at 194°K. Thus, using the value for 2 /-330^ -1 k^ determined here of 3.2 x 10 exp I — ^ 1 sec , k^ was found to vary as 6.7 x 10 4 exp ( ~ 2 ^ R T ] l i t r e s . mole~ 1sec 1, giving a value of 2.3 x 10 3 l i t r e s mole *sec * at room temperature, k^ i s known to vary with d i f f e r -ences i n wall surface. The j u s t i f i c a t i o n f o r using the results of the determination of k^ i n t h i s experiment i s that l i t t l e v a r i a t i o n would be expected. This i s because the same b o r o s i l i c a t e glass of the same inte r n a l diameter, and cleaned i n the same fashion, was used i n each case. Arnold and Ogryzlo obtained a value of 1320 l i t r e s , mole *sec * for Fig. IX(a). Plot of l o g i n ( Z -£) against time at 20°C. Fig. IX(b). Plot of loglft(£ -£) against time at -69°C. -69 C -41-Table V. Ratio of I(7619)/!(6340) at dif f e r e n t pressures and temperatures. Temperature (°C) Pressure (torr.) 1(7619) u 1(6340) o b s e r v e d 1(7619) corrected for 1(6340) non-linearity. 20 1.44 9.7 2.10 10.0 15.7 2.85 10.0 -79 1.72 2.92 2.67 3.00 4.65 3.30 2.94 -42-at room temperature. Thus some agreement between these results is obtained which, with uncertainties of ±35% in their values, is not un-reasonable. -43-DISCUSSION The O -f^E + ) surface deactivation c o e f f i c i e n t Y and the deactivation 2-—g-^ • — J co n t r o l l i n g process. The rate constant for wall activation of 0„(^Z +) i s dependent on 2 g the dimensions of the flowtube and i s better expressed as a surface deactivation c o e f f i c i e n t , y, defined by: rate of wall deactivation Total number of c o l l i s i o n s with wall per sec. = N VK .. = 2r K o 1 , o wall — wall h N cA C o where N = number of molecules per unit volume o 2 V = volume of flowtube = IIr I wall = rate constant for wall deactivation (k^) = 215 s e c - 1 at 20°C and 170 s e c - 1 at -69°C A •-= surface area of flowtube = 2nr£ ' oo c = mean molecular v e l o c i t y = \ c d-Nc = ~>o ~^c7~ k /8RT . ., ..47T -1 ^ n M - = 1 , 4 6 x 107M C M S - S E C M = molecular weight of oxygen. Using the K w a l j values found here for b o r o s i l i c a t e glass walls cleaned with 50% HN03, water and acetone, y = 9.3 x 10" 3 at 20°C and 8.9 x 10" 3 at -69°C giving a value which i s only s l i g h t l y temperature dependent. The -3 room temperature value can be compared with 3.7 x 10 obtained by Arnold _ 2 and Ogryzlo (23) and 1.0 x 10 obtained by Izod and Wayne (41). -44-The value of y i s large enough to require a check to see whether i t i s governed by the actual surface deactivation process at the wall or by the rate of d i f f u s i o n of the gas to the wal l . This i s usually de-termined i n a rather crude fashion by comparing the expected mean time of d i f f u s i o n to the walls, t , with the observed l i f e t i m e for the deactiva-t i o n , t i f t > t the reaction can be regarded as d i f f u s i o n ' wall wall & controlled. Einstein's equation for the displacement x executed by a p a r t i c l e during time t i n a medium of s e l f d i f f u s i o n c o e f f i c i e n t , D, i s given by: x 2 = 2Dt d (13) D i s given by: D = 1/3X<T where X i s the mean free path i n cms. and c i s the mean molecular v e l o c i t y . Taking the mean distance traversed by any molecule before s t r i k i n g any wall to be r (37), equation (13) gives, on substitution: t _ 3 r ^ (14) d 2X.c X varies inversely with pressure and thus, using a standard value for X at room temperature and one atmosphere of 9.93 x 10 ^  cms. (42), equation _3 (14) gives: t ^ = 4.1 x 10 P for P i n t o r r . Typical pressures are about _2 2.5 t o r r . for which t ^ i s about 1.3 x 10 sees. This has to be compared - 2 - 2 with values of t „ (= 1/k , J of 0.5 x 10 sees at 20°C and 0.6 x 10 wall v w a l l ' sees at -69°C, which gives t ^ > t w a u suggesting that the process i s d i f -fusion controlled. There i s , however, i n th i s p a r t i c u l a r case an alternative mechanism -45-by which the 0-(*E +) energy can be transfered to the walls. This i s by .2 an energy exchange mechanism. Because of exact resonance with a neigh-bouring oxygen molecule, the 0_(.*£ +) exchange process should be f a i r l y l g e f f i c i e n t . The low t r a n s i t i o n p r o b a b i l i t y of the (*£ + - 3E ~) t r a n s i t i o n , however, would be expected to r e s t r i c t t h i s exchange to a rate not much greater than c o l l i s i o n frequency. Treating t h i s exchange as a t y p i c a l •random-walk' problem, the rate of energy transfer to the walls at c o l l i -sion frequency can be expressed by a normal d i s t r i b u t i o n curve. Thus i f r i s the mean distance for a molecule to t r a v e l before reaching the walls (37): • r (15) where n = mean number of c o l l i s i o n s for the energy to t r a v e l a distance r. Expressing the time required to reach the walls by: t _ number of c o l l i s i o n s required to transfer energy to walls ex c o l l i s i o n frequency and substituting i n with equation (15), gives: t = - ^ - = "4 (16) e X (c/X) 8Xc Comparing equation (16) with equation (14) i t can be seen that transfer of energy to the walls by t h i s exchange mechanism i s 4 x faster than by a _3 d i f f u s i o n mechanism. This gives values of t of about 3.2 x 10 sees 6 ex and thus t ^ > t^-Q > t e x implying that 1 S n o t governed by the rate of transfer of O-f^E +) to the wall but by the actual surface deactivation 2^ g / process at the wall. -46-Support for the fact that k i s controlled by the surface deacti-vation process i s given by the lack of i t s pressure and temperature de-pendence. Energy exchange and d i f f u s i o n mechanisms would be expected to show a considerable v a r i a t i o n with both temperature and pressure, whereas the lack of pressure dependence and small temperature dependence of a surface deactivation mechanism are i n keeping with the results of both atomic oxygen (19) and nitrogen (44) wall recombination. Further support i s given by the o r i g i n a l experiments of Young and Black (45) i n which they compared d i r e c t l y the quenching rates of N^ O, N and C0„ against k ^ 1. A change i n reaction tube diameter by a factor of 2.2 produced a s i m i l a r change i n the value of k JJ. This direct de-pendency on r would be expected for a surface deactivation process but not for an energy exchange (equation (16)) or d i f f u s i o n controlled (equation (14)) process. Young and Black also concluded that deactivation was con-t r o l l e d by a surface quenching mechanism. The rate constant for deactivation of the 0o(*£ +) on the wall i s 2 V g about 215 sec * at room temperature. This corresponds roughly to 1 c o l l i s i o n i n 100 which i s comparable to methanol or ammonia i n i t s quenching a b i l i t y (38) . The presence of water adsorbed to the surface of the glass might-account for t h i s . The s i m i l a r i t y of quenching rate on the wall with that involving normal quenching molecules suggests the p o s s i b i l i t y of a s i m i l a r mechanism being used i n each case. The relaxation of the 0_("^ Z +) to 0 o(*A ) or 6 2 V g 2 V g J 3 0„( Z ) can thus be represented by the general expressions: -47-O j C 1 ^ ) + M + O^ 1^ + M (17) 0 2 ( 1 E g + ) + M+ 0 2 ( 3 E g " ) + M (18) where M represents the quenching molecule or w a l l . Information on which of the two processes i s taking place could be gained by observing the effect of using a paramagnetic molecule as the quencher. The paramagnetism should eff e c t the spin change i n reaction. (18), but have l i t t l e effect on reaction (3.7). This i s conveniently done by comparison of the quenching rates of oxygen and nitrogen shown i n Table I. In the case of 0 9(*A ) quenching, 2 g which must be by a spin change mechanism s i m i l a r to reaction (18), oxygen 1 + i s a better quencher than nitrogen. The reverse i s true for 0„( E ), g implying no change i n spin m u l t i p l i c i t y and consequently quenching v i a reaction (17). The evidence i s not foolproof but i t seems l i k e l y that a spin allowed mechanism would be preferable to a spin forbidden mechanism requiring a greater conversion of electronic energy into v i b r a t i o n a l energy. This also agrees with the t h e o r e t i c a l l y predicted mixing of the *E + and *A states upon perturbation of the molecule with a component at r i g h t angles to the internuclear'axis (46) f a c i l i t a t i n g t h i s *E + - *A interconversion. Using t h i s mechanism, however, i t i s very d i f f i c u l t to say what the s l i g h t a c t i v a t i o n energy of the wall deactivation process would represent. I t i s possible that the observed temperature dependence i s t o t a l l y unconnected with the wall deactivation process but i s simply due to a slowing up i n the rate of transfer of the O-^E + ) from the gas phase to g the w a l l at lower temperature. Thus a s l i g h t contribution to the reaction -48-rate from the transfer process (using either the d i f f u s i o n or energy ex-change mechanism) at the lower temperature might result i n a small temper-ature dependence without the corresponding pressure effect being noticed. Energy pooling of two O^ C^ A,) molecules to form C^C^ +) • The energy pooling reaction: 0 o (*A ) + 0_ (*A ) + 0o(h +) + 0 o( 3Z ") (3) 2 g J 2K g J 2 g 2 S provides a conceptually rather simpler case than wall deactivation of C" (*£ + ) . I t can be regarded as an energy transfer i n which one oxygen ^ g 1 3 -molecule loses energy i n a ( A - I ) t r a n s i t i o n while the other gains energy by e x c i t a t i o n from the ''"A state to the *T + state. This s i t u a t i o n i s i l l u s t r a t e d i n Fig. X. Energy transfer has been treated for large molecules as a resonance transfer process involving either long-range or coupled interactions (47) (48). In t h i s case a c o l l i s i o n a l perturbation would be required to give the levels the exact resonance energy. Again l i t t l e can be said about the magnitude of the observed temperature de-pendence of t h i s reaction. Fig. X. A diagramatic comparison (to scale) of possible t r a n s i t i o n energies of unperturbed molecules. - 4 9 -<3 C M — O CM -50-CQNCLUSION The rate constant for deactivation of the 0 „ + ) on the wall of 2 -330 -1 the reaction vessel was found to be 3.8 x 10 exp( r , ^ ) sec . I t was K i concluded that t h i s represented the actual process on the wall and not . any d i f f u s i o n controlled mechanism as previously suggested. The rate constant for formation of 0O(*E +) from a bimolecular reaction 2 g involving 0„(^A ) was found to be 6.7 x 10 4 exp( l i t r e s , mole *sec I % K l The controversy over the value of the absolute emission rate at 6340 A was not resolved. Both Browne's and Falick and Mahan's values s t i l l stand. An independent method of measuring the C^C^A^) concentration i s r e a l l y required. However, for a l l such methods known to date a c a l i -bration on an absolute standard i s needed. This necessarily involves an isothermal calorimeter or a calibrated EPR cavity unless some other method can be devised. P A R T I I . A Kinetic and Spectroscopic Investigation of the N + 0„( A ) System, -51-INTRODUCTION Of considerable interest to the study of chemical aeronomy i s a knowledge of the rate constant for the homogeneous reaction between atomic nitrogen and 0„C^A ) to form n i t r i c oxide. Experiments performed to determine t h i s rate constant w i l l be described here, together with some work on the o r i g i n of various glows seen near the surface of certain metals exposed to these species. These glows involve the excited states of both molecular nitrogen and n i t r i c oxide. Because of i t s direct bear-ing on the present work, a b r i e f summary of the theories of radiative recombination of these molecules w i l l be given. More extensive reviews can be found i n the l i t e r a t u r e . (44)(49) Gas-phase recombination of nitrogen atoms giving r i s e to the f i r s t p o sitive  emission of molecular nitrogen. The well known Lewis-Rayleigh afterglow of nitrogen produced by the action of a high frequency electrodeless or condensed electrode discharge of the gas, has the c h a r a c t e r i s t i c yellow colour of the f i r s t p o sitive emission of nitrogen N^B 3]! ) -»- N 2(A 3£ u +) (see Fig. XI). The spectrum o stretches from 5000 A to l . l u i n the infrared and consists of emission from a l l v i b r a t i o n a l levels up to v 1 = 12 which i s just below the dis s o c i a t i o n energy of the nitrogen ground state at 9.76 eV. When two N( 4S) atoms recombine to form molecular nitrogen, they can form any of the following states (50): 1Z +, 3£ +, 5£ +, 7Z +. The l a s t state i s b g u . g ' u repulsive. The B^ state cannot be populated d i r e c t l y necessitating involvement of the three lowest lying states. Mechanisms based on both Fig. XI. N_ potential energy diagram as compiled by Gilmore (1). - 5 2 --53-3 + 5 + the A r.^  and Eg states have been proposed. One of the f i r s t attempts to provide a possible mechanism for the f i r s t p o s i t i v e emission was by Kistiakowsky and co-workers (51) (52) who, on the basis of a study of the va r i a t i o n i n vib r a t i o n a l l e v e l population d i s t r i b u t i o n of the B\ state with temperature and with added foreign gases, suggested that the B^I • state was populated by a collision-induced t r a n s i t i o n from the ^ £ + state, thus: g N?( 5£ C T +) + M "*" ^ ( ^ J ^ = 12,11,10 + M (19) . g g The rate of population of the B3JT state required the ^ £ + state to be g g i n equilibrium with atomic nitrogen: N( 4S) + N(4 S) + M — ^ N 9( 5£ c t +) + M (20) In order to explain the smaller maximum i n emission for the B f^i , V = 6 vi b r a t i o n a l l e v e l and the increase i n emission from the V = 4 0 vibra-t i o n a l levels i n the f i r s t p o s i t i v e systems, Kistiakowsky et a l proposed a series of cascade processes involving other intermediate species: 5£ + > B' 3E " v'= 8,7,6 -v B f^l -,v'' = 4,3,2 (21) 3A B^ V' = 7,6,5 (22) They also maintained that emission from the lower levels could be maintained by a direct collision-induced radiationless t r a n s i t i o n from the N„fA3£ +) 2 v u i f state around the v =8 l e v e l . 3 Harteck, Reeves and Manhella (53) suggested that the B n state was populated i n v 1 = 6 region from highly v i b r a t i o n a l l y excited N 2(A 3£ U +) -54-molecules. They gave as evidence the fact that the f i r s t p o sitive spectrum observed near the surface of certain metals involves only v i -brational levels of t h i s v' = 6 region which, because of the crossing of the potential curves, i s the region of maximum overlap of the two wave functions. Campbell and Thrush (54) endorsed t h i s view by determining a rate 8 2 -2 -1 constant of 6.2 x 10 l i t r e s , moles sec : t h i s , they maintain, i s incompatible with population of the B^ H state from the * * E g + state, because the s t a b i l i z a t i o n of t h i s state i s not high enough to provide a s u f f i c i e n t equilibrium population (reaction (20).) They therefore pro-posed that the B^il state i s populated by a collision-induced radiation-less t r a n s i t i o n from the A 3 E U + and that the v a r i a t i o n i n population d i s t r i b u t i o n with v i b r a t i o n a l energy le v e l r e f l e c t s the ease with which crossing can take place at that p a r t i c u l a r l e v e l . Some evidence for t h i s ( A 3 E + - B^I ') crossing i s provided by the breaking o f f of the forbidden u g 3 + Vegard-Kaplan emission from the A E u state above the v" = 6 l e v e l (55). Benson (56) has recently treated t h i s system from a point of view of production v i a the ^£„+ state. He shows that since the p r o b a b i l i t y of the curve crossing ( 5 E + ->• B ^ ) i s about 10 _ 1 - 1 0 - 2 per c o l l i s i o n there i s an equilibrium set up between r o t a t i o n a l l y hot members of the 12th v i b r a t i o n a l l e v e l of the B ^ state and free nitrogen atoms, without t h e intervention of a t h i r d body. Rotational quenching then populates t h e 12th v i b r a t i o n a l level and t h i s i s followed by v i b r a t i o n a l quenching populating the 11th, 10th and 9th levels i n competition with emission. -55-Since neither Campbell and Thrush or Benson can s a t i s f a c t o r i l y exclude the p o s s i b i l i t y of each other's mechanism taking place the question of the recombination path to produce the f i r s t p o s itive emission i s s t i l l open. The p r i n c i p l e emission spectra seen i n molecular nitrogen are l i s t e d i n Table VI. Radiative recombination of n i t r i c oxide. Young and Sharpless (49) and Callear and Smith (57) have extensively studied the kin e t i c s and mechanism of the recombination process: N( 4S) '+• 0( 3P) + M > NO* + M - (23) 4 3 They have concluded that the mechanism for recombination of N( S) and 0( P) atoms involves formation i n i t i a l l y into the N0(a4IT) state (see Fig. XII) followed by a 'pre-association' crossing into the C^JT v = 0 state, giving r i s e to the 6 bands (C^ EI - X^II). The A 2£, v = 0 state i s then excited by both cascade ra d i a t i o n (the (0*0) (C^ TI - A^Z) band being at 1.22 u) and by c o l l i s i o n a l crossing from the C^ JI and a \ states. The a4JI state spon-taneously populates the b 4Z state which, i n turn, populates the BTI state by means of a collision-induced t r a n s i t i o n . The various emission spectra seen from NO are l i s t e d i n Table VII. 4 1 The homogeneous reaction between N( S) and 0 ?( A ). ^ g The f i r s t estimate for the rate of the reaction: N + O ^ A ) -^-> NO + 0 (24) was made by Hunten and McElroy (58) who were interested i n th i s reaction as a possible source of NO i n the 90.Km region of the upper atmosphere. -56-. Table VI P r i n c i p l e band spectra seen i n molecular nitrogen. Emission Transition Approximate spectral region Type of t r a n s i t i o n F i r s t p ositive B \ -0 5000 - 25000 A e l e c t r i c dipole system '.Y* bands B ,V* 3n g 0 6000 - 10800 A e l e c t r i c dipole Vegard-Kaplan bands 0 2100 - 5000 A forbidden by AS = 0 approximation Lyman-Birge-Hopfield bands 1 Y l + a n - X y 1200 - 2600 A magnetic dipole and e l e c t r i c quadropole Second positive system c 3 n - B3H u u u g 0 2800 - 5450 A e l e c t r i c dipole Birge-Hopfield system b f Y - x V u 0 930 - 1650 A e l e c t r i c dipole 3A - \ u g 3. 3 - • A u " n g o 22500 - 7700 A e l e c t r i c dipole system Fig. XII. NO potential energy diagram as compiled by Gilmore (1). -57--58-Table VII P r i n c i p l e band spectra seen i n n i t r i c oxide Band Transition Wavelength 3 bands B2]! - X ^ 0 5000 - 2000 A y bands A 2E + - Xii o 2250 - 2800 A 6 bands c\ - X ^ o 1900 - 2400 A Ogawa bands b 4Z - a4!! o 7500 - 9000 A For the reaction: k 2 5 N + 0 2 > NO + 0 + 1.42 eV (25) the experimental data could be adequately reproduced using k = 1.2 x 8 2 /3000 V -1 -1 lO.T.expl—Y ~ J l i t r e s , mole .sec. . Since reaction (24) has 0.98 eV more energy at the beginning and the ac t i v a t i o n energy of reaction (25) i s only 0.28 eV, a f i r s t approximation to the rate constant was made by 9 se t t i n g the exponential factor to unity giving K = 1.8 x 10 l i t r e s . mole." 1sec." 1 at 200°K. From the concentrations of the constituents of the 90 Km region of the upper atmosphere and assuming steady state k i n e t i c s i t was found that to successfully account for the NO concentration at that height a value 8 -1 1 fo r ^ 4 of 1.8 x 10 l i t r e s , mole. sec. was required. Since no dir e c t laboratory determination of t h i s rate constant had been previously made, the present work was done i n an attempt to v e r i f y these values. Surface catalysed emission of N,, and NO. About 1960, there appeared i n the l i t e r a t u r e a series of three papers by Harteck, Reeves and Mannella (57) (58)(51) concerned with surface cata-lysed e x c i t a t i o n of molecular nitrogen and n i t r i c oxide produced with mixtures of the flowing afterglows of nitrogen and oxygen discharges. They observed three glows: (A) A red glow consisting of the nitrogen f i r s t p o s i t i v e emission bands, seen i n the gas phase near surfaces of Co, Cu, Ni and Ag i n the presence of the combined products of nitrogen and oxygen discharges. Emission i s maximum from the B^ II v' = 6 le v e l and no emission was seen for v 1 >8. The glow extended 10-15 nun-into the -60-gas phase. (B) A blue glow consisting of the NO 8 bands, seen near the surface of n i c k e l i n the presence of the combined products of the nitrogen and oxygen discharges. (The red glow (A) was also present.) No NO Y or 6 bands were seen. The glow extended only a few millimetres into the gas phase. (C) A weak blue glow consisting of the N 2 second p o s i t i v e system (C^II.. - B^fl ) observed near copper maintained at 15-20°C i n a n i t r o gen afterglow only. It extended about 2 mm. into the gas phase. In t h e i r f i r s t paper (59), Harteck et a l . proposed the following mechanism for the formation of the red (A) and blue (B) glows over n i c k e l : N( 4S) + 0( 3P) — NOfB^n) (26) formed on surface and goes into gas phase. N O ^ ) — > NOfX^) + hv(B bands) (27) N + NO(B^I) "> N„(B3JI ) + 0( 3P) (28) *• g N 2(B 3tI g) > N 2(A 3E U +) + hv ( f i r s t p o sitive bands) (29) This mechanism i s successful i n explaining the fact that the nitrogen f i r s t p o s i t i v e emission of the red glow:was only from v i b r a t i o n a l levels with v.* < 8. since the maximum energy produced by reaction (28) i s just s u f f i c i e n t to excite the N-fB3!! ) to the v' = 8 l e v e l . 2 V gJ Harteck et a l . pointed to the s l i g h t l y greater i n t e n s i t i e s of the tr a n s i t i o n s from the NO ) v' = 0 v i b r a t i o n a l l e v e l for corroboration. The d i f f i c u l t y with t h i s mechanism i s that i t i s necessary to evoke some unique property of the metal i n order to account for the absence of y a n d 6 bands i n the blue glow. -61-Harteck et a l . l a t e r became doubtful of this theory when they found that the red glow produced over cobalt was rather more extensive than over -3 n i c k e l , giving a l i f e t i m e for the metastable species of 10 sees. This i s incompatible with the upper l i m i t for the NOCB^ IT) l i f e t i m e of 10 ^ sees, set by Keck et a l . (61). Thus Harteck (53) proposed the idea of recom-bination of the nitrogen atoms into the N 2(A 3E U +) state on the surface of the metal followed by d i f f u s i o n into the gas phase where conversion to the B^fig state with v' < 8 takes place by a collision-induced radiationless t r a n s i t i o n . Harteck relegated the function of the atomic oxygen to some sort of 'conditioning' process on the metal surface. The blue glow from nick e l was then produced by the reverse of reaction (28): N 2(A 3E u +) + 0( 3P) N0(B2H) + N( 4S) (30) The concentration of N 2(A 3E U +) state would probably be controlled by the f a s t reaction: N 2 ( A 3 E U + ) + N( 4S) T- N 2 C x l E g + ) + N C 3 1 ) Rate constants of 3 x 10^ l i t r e s mole. *sec. * (62) and 3 x 10*^ l i t r e s mole. ^sec. * (63) (64) have been determined for t h i s deactivation process. From measurements on the i n t e n s i t y of the glow as a function of distance away from the cobalt surface, Weinreb and Mannella (65) have set an upper 8 -1 -1 l i m i t of 3 x 10 l i t r e s mole. sec. for k^, which, i f Harteck i s correct, involves high v i b r a t i o n a l levels of the A 3 £ u + state. The discrepancy between values quoted for high and low v i b r a t i o n a l levels has then to be explained. -62-The weak blue glow (C) seen near the surface of copper i n the n i t r o -gen afterglow, Harteck (59) attributes to the nitrogen second positive 3 3 system (C H - B II ) . The extent of t h i s glow into the gas phase, about ^ g 2 mm., eliminates the p o s s i b i l i t y of the metastable species being the 3 C II state since i t s radiative l i f e t i m e i s too short (66). Some recent u K J work by Stedman and Setzer (67) provides a possible excitation process: N 2 ( A 3 I u + ) + N 2(A 3E u +) ^ > N 2 ( cV ) + N ^ Z g * ) (32) They quote a value of 1.25 x l O 1 ^ l i t r e s mole. '''sec. 1 for k^2 which i s based on a value for the N 2(A 3E^ +) rad i a t i v e l i f e t i m e of 2.0 sees given by Shemansky (68). I f the metastable species i s i n fact the N 2(A 3E u +) state, then the production of the red glow on addition of discharged oxygen to th i s system i s unexplainable using Harteck's theories. The present work describes a re-examination of these glows i n an attempt to c l a r i f y some of the confusion surrounding t h e i r production. EXPERIMENTAL The rate constant for the N + 0„ f^ A. ) reaction was determined i n a conventional discharge-flow apparatus i l l u s t r a t e d i n Fig. XIII. The tube was about 1 metre long and 2.5 cms. i n diameter with a quartz window attached to the downstream end of the tube through which spectra of the gaseous emission could be obtained. Two main i n l e t s provided the discharged oxygen and nitrogen flows and four smaller i n l e t s supplied n i t r i c oxide for t i t r a t i o n of the atomic nitrogen at different points along the tube. The flowrate control and measuring systems for both the main and added gases are i d e n t i c a l to those described i n Part I. Both discharges were o p t i c a l l y isolated from the flowtube by means of blackened l i g h t traps. The nitrogen used was u l t r a high puri t y grade obtained from Matheson Co. I t s t i l l contained s u f f i c i e n t impurity to produce reasonable con-centrations of nitrogen atoms (43) and was thus used without further p u r i f i c a t i o n . N i t r i c oxide was also obtained from the Matheson Co. and contained nitrogen dioxide, water and nitrogen as the main impurities. These were removed by passing the gas through soda lime followed by successive d i s t i l l a t i o n at -78°C with the i n i t i a l and f i n a l fractions being discarded each time. The resultant was a pure white s o l i d . The s i n g l e t oxygen was produced by a mercury contaminated discharge as described e a r l i e r . Power to maintain the discharges was supplied through 214L gas discharge c a v i t i e s from standard 2450 MHz microwave power supplies. Both c a v i t i e s were cooled by blowing a i r through them. I t was found that the atomic nitrogen concentration was roughly propor-XIII. Flow apparatus used to measure decay of atomic nitrogen as a function of time. Nitric oxide Silica window Monochromaton 1 l \l o: to McLeod gauge f to pump Nitrogen from discharge 4^  Oxygen from discharge -65-tional to the discharge power. To stop rapid recombination of the atomic nitrogen, the walls of the tube were 'poisoned' with orthophosphoric acid. This was then pumped on overnight, followed by several hours of exposure to atomic nitrogen before any attempt was made to measure experimental value. Between runs the apparatus was constantly under vacuum and the discharges were always run for about 1 hour before use. The method of switching on the apparatus always followed the same procedure: first the singlet oxygen discharge was switched on and the 0_(*A ) detected by its <- g characteristic red glow. The molecular nitrogen was added through the other inlet and the apparatus left to check for the stability of the 0„(*A ) production system. Finally the nitrogen discharge was switched on. * g These precautions eliminated the possibility of incomplete recombination of the atomic oxygen by the mercury. The flowrate of O^ f^ A ) was measured g using an isothermal calorimeter and the total pressure was measured with a McLeod gauge which was usable between 0.1 torr and 5.0 torr. The heterogeneous glows were first seen on the cobalt-plated platinum isothermal calorimeter situated at the downstream end of the above appar-atus. The spectra of the cobalt and nickel glows in the visible and infra-red were obtained by viewing the metal sideways across the tube. For the copper glows and the glows in the ultraviolet the metal was placed in a short cell, about 5 cms. long and 3 cms. in diameter, fitted with a sil i c a window of about 1 mm. in thickness, through which the spectrum was obtained. Products of the nitrogen and oxygen discharges were mixed before entering the cell and were passed through several blackened light traps in order to eliminate stray light from the discharge. Entrance and exit ports in -66-t h i s c e l l were made as wide as possible to stop streaming of the gases. This c e l l was f a i r l y successful i n minimizing the contribution to the spectrum of the Lewis-Rayleigh afterglow, except i n the case of the blue copper glow which was p a r t i c u l a r l y weak. The spectra were taken i n a l l cases using a Hilger-Watts f/4.5 mono-chromator. This instrument contains interchangeable quartz and glass prisms, the l a t t e r being used i n the v i s i b l e and infra-red because of the higher dispersion i n those regions. Spectra were calibrated using an Ar/Ne lamp for the red end of the spectrum and a medium pressure mercury o lamp for the blue end. Scan speeds were generally about 100 A/minute. Detection devices varied according to the spectral region. Those used are l i s t e d i n Table VIII. 'Photon-counting' techniques (69)(70) were found to give a d e f i n i t e improvement i n signal-to-noise r a t i o using RCA IP28 and IP21 phototubes, but were about equal with phase sensitive detection techniques using an RCA 7265 phototube. For the l i q u i d nitrogen cooled RCA 7102 phototube phase sensitive detection techniques were d e f i n i t e l y superior. The RCA i n t r i n s i c germanium detector was a photoconductive device and thus could not be handled by the pulse discrimination techniques of 'photon-counting 1. The electronics used for t h i s 'photon-counting' apparatus were constructed of components supplied by Hamner Co. and con-s i s t e d of a preamplifier, followed by a l i n e a r amplifier, an analyser and f i n a l l y a l i n e a r ratemeter. The output of the ratemeter was recorded on a conventional s t r i p chart recorder. Phase sensitive detection techniques have already been described. -67-\ Table VIII Detection equipment Phototube (RCA) Response Approximate spectral range (A) Amplification system IP28 S5 t 2500 - 6000 photoncounting IP21 S4 - 3200 - 6500 pho t oncount ing 7265 S20 . 3200 - 8000 photoncounting P.S. detection 7102 cooled to 77°K Sl 5000 - 11000 phase sensitive detection i n t r i n s i c . germanium photo-diode cooled to 77°K S25 8000 - 17000 phase sensitive detection -68-Th e surfaces of the cobalt and ni c k e l were cleaned before use with 50% hydrochloric acid although cleaning was found to have l i t t l e effect on the i n t e n s i t y of the glow. Both metals were of 'technical' grade and were i n either wire or p e l l e t form. More attention was paid to the sur-face of the copper since the glow was so weak. 'Analar'. sheet copper was used and the surface cleaned with steel wool and an organic solvent. Of the methods t r i e d , including cleaning with 50% n i t r i c acid and depositing and removing layers by e l e c t r o l y s i s , t h i s was the only one that produced a reasonable glow. The copper sheet was aligned p a r a l l e l to the entrance s l i t of the monochromator. -69-RESULTS The homogeneous reaction between N and O^C^A^). Using the discharge-flow techniques, the predicted (58) rate constant for reaction (24) should produce an e a s i l y measurable change i n the n i t r o -gen atom concentration along the tube: N + 0,(1A ) 5> NO + 0 (24) Atomic nitrogen concentrations were determined by t i t r a t i o n with n i t r i c oxide: N + NO N 2 + 0 (33) which i f [N] > [NO], gives r i s e to blue emission from n i t r i c oxide: N + 0 + M > NO* + M (23) NO* >N0 + hv(8, y and 6 NO bands) or, i f [N] < [NO] the green a i r afterglow i s obtained: NO + 0 zp- N0 2 + hv (continuum) (34) At [N] = [NO] no emission i s seen. The end point i s very sharp and i t was found that detection by eye was as good as using photoelectric methods. The O^ C^ A ) was determined by isothermal calorimeter. . Preliminary ex-periments using EPR to detect the 0 2(*Ag) showed an i n s i g n i f i c a n t change i n the 0 2(*A g) concentration on addition of atomic nitrogen to the system. I t was therefore taken as constant along the tube. Typical data .is shown -70-i n Table IX and a plot of atomic nitrogen concentration against distance along the tube i s shown i n Fig. XIV. I t can be seen that very l i t t l e change i n the atomic nitrogen decay i s apparent on addition of 0_C*A ). This indicates that the rate constant for reaction (24) i s considerably slower than expected and allows only an upper l i m i t , set by the s e n s i t i v i t y of the apparatus, to be placed on the rate constant. To determine t h i s upper l i m i t i t i s convenient to change the results of Fig. XIV into a s t r a i g h t - l i n e p l o t , enabling comparison of slopes to be made. A k i n e t i c analysis i s thus required. The main atomic nitrogen decay process i n the presence of molecular oxygen i s : N + 0 2 NO + 0 (25) followed by: N + NO >^ N 2 + 0 . (33) Reactions (25) and (33) have rate constants of 10 3 l i t r e s mole. ^ e c . 1 and l O 1 ^ l i t r e s mole. ^sec. 1 respectively at room temperature (71). Removal of the atomic nitrogen by wall recombination and t h i r d order gas phase recombination i s small compared with removal by reaction (25). Thus: 4 M l = k 2 5 [ 0 2 ) 1 [ N ] 1 + k 3 3 [ N] 1[N0] which for a steady state concentration of NO gives: = 2 k 2 5 [ N ] 1 [ 0 2 ] 1 _ (34) -71-Table IX Variation of atomic nitrogen concentration with  distance along tube. Distance along tube (cms.) [N] with 02(.\) moles, litre-1(±0.1) [N] without 0 2 ( 1 A g ) moles, litre-1(±0.1) 0 1.45 x 10" 7 1.71 x 10" 7 10 0.94 x 10" 7 1.03 x 10" 7 30 0.52 x 10" 7 0.55 x 10" 7 50 0.20 x 10" 7 0.00 Conditions: [0 2] = 4.2 x 10~ 5 moles, l i t r e " 1 [N 2] = 1.3 x 10" 5 moles, l i t r e " 1 [0 2( 1A )] = 1.6 x 1 0 m o l e s . l i t r e 1 (assumed constant along tube) Total pressure = 2.00 t o r r . - 7 2 -Table IX (cont.'d.) Distance along tube (cms.) [Nl with 0 o( A ) moles. l i t r e _ 1 ( 0.1) [N] without 0 o( 1A ) moles, l i t r e 1( 0.1) -7 -7 0 2.1 x 10 2.1 x 10 - 7 -7 10 1.2 x 10 1.3 x 10 30 0.6 x 10" 7 0.7 x 10" 7 50 0.4 x 10" 7 0.6 x 10" 7 Conditions: [0 2] = 3.5 x 10 3 moles, l i t r e 1. [N2] = 2.3 x 10" 5 moles, l i t r e " 1 . [ 0 2 ( 1 A )] = 1.2 x 10 ^ moles, l i t r e 1 (assumed constant . along the tube.) Total pressure = 2.20 t o r r . F i g . XIV. Plot showing decay of atomic nitrogen along tube. The points represent the data i n Table IX. -73-^aiijisaiouj^oiX Distance along tube (cms) -75-S i m i l a r l y : . 2 [ N ] 2 ( k 2 5 [ 0 2 ] 2 • k 2 4 [ 0 2 C 1 A g ) ] ) (35] The subscripts 1 and 2 refer to the absence and presence of 0 2(^Ag) re-spectively. On integration equation (34) and (35) become: l o g 1 Q [ N ] 1 =--2k 2 5[0 2] ]t + constant. _ l o g 1 0 [ N ] 2 = - 2 ( k 2 5 [ 0 2 ] 2 + k 2 4 [ 0 2 ( 1 A g ) ] ) t + constant. A plot of log^g[N] against time thus gives straight lines of slope - 2 k 2 5 [ 0 2 ] 1 a n d - 2 ( k 2 5 [ 0 2 ] 2 + k ^ f O ^ A )]).. This plot i s shown i n Fig. XV. For a change i n slope which i s too small to be observed: k o c [ 0 _ ] o + k_.[0_( 1A )] , . '•... 25 L 2 J2 24 L 2 V gJ J. :maximum possible slope. k 2<-[0 2]j v mean slope Where the maximum possible slope refers to the l i m i t at which the d i f f e r -ence i n the two slopes would become noticeable. Taking t h i s to be twice the possible error i n the slope, the mean value of the two runs gives: 1.8 > k 2 5 [ 0 2 ] 2 + k ^ t o / A g ) ] k 2 5 [ o 2 ] l wh ich using the approximation [0-,]^ = [ ^ 2 ] 2 becomes: 0.8 > fc24[02(1Ag)] k25^°2h giving k 2 4. 41.6 x 10^ l i t r e s mole. *sec. Fig. XV. Plot of log i n[N] against time. -76-In a recent paper, Clark and Wayne (72) determined a value of 1.7 x 10^ l i t r e s mole. *sec. * for the deactivation of (^ (''"Ag) by atomic nitrogen, which they state represents an upper l i m i t for t h i s reaction. By comparison with deactivation rates of other species they state that the main deactivation process i s probably reaction (24), which gives good agreement with the upper l i m i t determined i n t h i s study. The red f i r s t p o s i t i v e glow from cobalt. The red glow seen near cobalt was f i r s t discovered by Reeves, Mannella and Harteck (59) i n 1960. They found that the presence of discharged oxygen as well as discharged nitrogen was required for the formation of the glow and from t h i s assumed that atomic oxygen played a necessary part i n the formation mechanism. A series of q u a l i t a t i v e experiments were performed here to study t h i s p a r t i c u l a r aspect of the glow i n more d e t a i l . The following observations were noted:-(1) With molecular oxygen and discharged nitrogen, no glow was seen over the cobalt. Only on addition of.discharged oxygen to the stream was the glow produced. Removal of the discharged oxygen by switching o f f the discharge or by closing a tap caused the immediate disappearance of the glow. (2) D i s t i l l a t i o n of mercury through the oxygen discharge causing complete removal of the atomic oxygen had very l i t t l e effect on the i n t e n s i t y of the glow. (3) Addition of n i t r i c oxide to a stream of discharged nitrogen.producing atomic oxygen by the rapid reaction: N + NO + 0 (33) -4 resulted i n only a very weak glow (~10 of the i n t e n s i t y of the glow i n the presence of discharged oxygen.) (4) A large flow of water vapour (~10% of the t o t a l flow) diminished the glow only s l i g h t l y (< 50%). Experiment (1) immediately suggests error i n Harteck's assumption of small quantities of atomic oxygen being necessary for the formation of the glow, t h i s i s because of the absence of a glow with atomic oxygen produced by the reaction: N + 0 2 -»• NO + 0 (25) The lack of atomic oxygen p a r t i c i p a t i o n i s further indicated by the resu l t s of Experiment (3). Here atomic oxygen, produced by: N + NO •»• N 2 + 0 (33) also results i n an absence of strong emission. Some constituent of discharged oxygen, however, i s necessary for production of the glow. Experiment (2) indicates that the active product of the oxygen discharge i s also present i n si n g l e t oxygen. This l i m i t s the range of possible active species to 0 2(*A ), 0'(*£ +) or v i b r a t i o n -3 -a l l y excited 0 ( Z ). In Experiment (4), the water added was s u f f i c i e n t 2 to t o t a l l y quench 0 2(^E + ) v i b r a t i o n a l l y excited 0 2 ( 3 E ). The only remaining p o s s i b i l i t y i s 0„(*A ). The formation of the very weak glow i n Experiment (3) can be a t t r i -buted to 0_(*A ) production by energy transfer to ground state oxygen or, -79-more l i k e l y , to t h i r d order recombination from atomic oxygen; 0 + 0 + M -> O^A. ) + M (36) A s i m i l a r l y weak glow which could be produced by an analogous mechanism was occasionally seen i n the presence of molecular oxygen, and discharged nitrogen. Mercury vapour was shown to be unimportant since i t s concentration was varied i n the stream without producing an effect on the glow. I t can therefore be concluded that C> (^A ), not atomic oxygen as o r i g i n a l l y assumed by Harteck, was necessary for the production of the red cobalt glow. o o The spectrum of th i s glow i n the region 5000 A - 8000 A was obtained and i s shown i n Fig. XVI. Harteck's characterization was checked by comparison with the normal Lewis-Rayleigh afterglow f i r s t p o sitive emission shown i n Fig. XVII. The peaks of the B 3n v" '= 12,11,10 v i b r a t i o n a l levels ©" i n Fig. XVI are probably due to some normal Lewis-Rayleigh emission which was always present. The spectrum of the red glow i n the infrared was also recorded and shown i n Fig. XVIII. Resolution i s not good since wide s l i t s had to be used. A comparison spectrum of the normal Lewis-Rayleigh afterglow i s shown i n Fig. XIX. The homogeneous gas-phase effect of ground state and singlet oxygen on the normal Lewis-Rayleigh afterglow was checked. It was found that i n 3 - 1 a system 'poisoned' with orthophosphoric acid both 0„( 1 ) and O^ C A ) had no effect on the glow. However, i n an 'unpoisoned' system the spectrum 1 3 i n the presence of 0 o ( A ) showed an increase i n emission from the B n , . 2 V gJ g' v 1 = 6 region. Later a red glow, s i m i l a r to that observed over cobalt Fig. XVIII. Spectra of cobalt catalysed f i r s t p o sitive emission between 1.8 y and 0.6 y. Taken with a Hilger-Watts f/4.5 monochromator i n conjunction with an i n t r i n s i c germanium detector. S l i t s 250 y. Fig. XIX. Spectra of Lewis-Rayleigh f i r s t p o sitive emission between 1.8 y and 0.6 y. Taken with a Hilger-Watts f/4.5 mono-chromator i n conjunction with an i n t r i n s i c germanium detector. S l i t s 250 y. F i g . XVI. Spectrum of cobalt catalysed f i r s t p o sitive emission between o o 8000 A and 5600 A. Taken with a Hilger-Watts f/4.5 mono-chromator i n conjunction with an RCA 7265 photomultiplier. S l i t s 100 u. F i g . XVII. Spectrum of usual Lewis-Rayleigh f i r s t p o sitive emission between / o o / 8000 A and 5600 A. Taken with a Hilger-Watts f/4.5 monochromator i n conjunction with an RCA 7265 photomultiplier. S l i t s 100 u. c — 2 r 0 ) 7500 7000 6500 Wavelength (A) 6000 5600 The cobalt catalysed f i r s t p o sitive glow.. -84-was seen near the surface of the glass w a l l . The only effect on the gas-3 1 phase infrared spectrum upon addition of Q^l 2^ ) or 0 2 ( A ) to the Lewis-Rayleigh afterglow was the appearance of the strong N O - A2£+)(0,0) t r a n s i t i o n at 1.22 u. The dependency of the red cobalt glow on the nitrogen atom concentration was obtained by monitoring the in t e n s i t y of the surface-catalysed (6,3) band at 6600 A and comparing i t with the int e n s i t y of normal Lewis-Rayleigh f i r s t p o s i t i v e (11,7) band. Since the 0 ?( 1A ) was found to have no effect on the population d i s t r i b u t i o n of the f i r s t p o sitive glow, the 2 in t e n s i t y of t h i s band can be taken as proportional to [N] . The results of t h i s are shown i n Table X and a plot of the cobalt glow i n t e n s i t y against the Lewis-Rayleigh afterglow i n t e n s i t y i s shown i n Fig. XX. An attempt was made during these studies to determine whether the 0„(*A ) was involved i n reaction at the surface of the metal or i n the gas phase. This was done by moving the cobalt upstream of the mixing region of the nitrogen and oxygen afterglow. The r e s u l t , however, was rather inconclusive since the extent of O^^A ) d i f f u s i o n equalled that of the glow and estimates of the d i r e c t i o n of the in t e n s i t y gradient were d i f f i -c u l t . As well as on cobalt and glass, the glow was also seen on copper, s i l v e r and n i c k e l . When a new piece of metal was placed i n the gas stream, the glow required about half an hour to reach maximum in t e n s i t y , which could then be maintained indefinately. -85-Table X Variation of cobalt catalysed first positive  emission with normal gas-phase Lewis-Rayleigh emission. Cobalt catalysed (6,3) f i r s t positive emission (arbitrary units) Lewis-Rayleigh (12,7) first positive emission (arbitrary units) 12 ± 2 11 ± 2 20 22 28 38 48 49 36 45 30 39 20 23 42 46 * Fig. XX. Graph of cobalt catalysed emission against Lewis-Rayleigh f i r s t p o s i t i v e emission showing d i r e c t dependence. -87-The blue NO g band glow. This glow was first seen by Harteck et al (60) over nickel. It has not been seen over any other metal. Similar tests (Experiments (l)-(4)) to those of the previous section were performed on this glow and similar results were obtained, showing that the reactive species from the oxygen discharge was not atomic oxygen as originally thought by Harteck et al, but 0 (*A ). The effect of NO addition on the intensity of the nickel catalysed glow is shown in Table XI and plotted in Fig. XXI. For comparison purposes the effect of NO addition on the NO B bands produced by reaction (23) is also shown; N + 0 + M->N0*+M (23) Since both glows were obtained under exactly the same conditions the gas-phase recombination glow can be regarded as the background radiation of the nickel-catalysed glow. In practice this was achieved by moving the nickel (magnetically) away from the entrance s l i t of the monochromator and repeating the NO addition. Little screening of the gas-phase glow from the monochromator s l i t by the nickel wire would be expected. It can be seen that, unlike the gas-phase glow, the nickel catalysed glow appears independent of the atomic oxygen concentration and directly dependent on the atomic nitrogen concentration. Harteck (60) states that there is a complete absence of y a°d 5 bands in the nickel-catalysed glow. This conclusion was not definitely verified in the present studies because of the difficulty in removing the gas--88-Table XI Variation of nickel NO 3 band glow and its background  glow on addition of nitric oxide. Nitric oxide concentration (Arbitrary units) Intensity of (0,7)NO 3. band in gas phase + nickel catalysed glow (Arbitrary units) Intensity of (0,7)NO 3 bands in gas phase (Arbitrary units) 0 8.8 4.3 2 8.4 4.7 3 8.0 4.9 4 7.6 5.05 5 7.2 5.1 6 6.7 5.05 7 5.7 4.8 8 4.8 4.1 9 2.6 2.3 * 0 0 Nitrogen atom titration point. Fig. XXI. Graph showing effect on n i c k e l catalysed and normal gas-phase emission of NO 3 bands, of addition of n i t r i c oxide to the N + O^ C A^ ) stream. The t i t r a t i o n point i s a r b i t r a r i l y put at 10 units of [NO]. -89-Nifric oxide concentration (arbitrary units) -90-phase emission. However, a d e f i n i t e reduction i n these bands compared with the i n t e n s i t i e s obtained i n the normal recombination reaction (23) was apparent. o o The spectra of the NO g bands between 5000 A and 4000 A obtained over n i c k e l and by gas-phase recombination are shown i n Figs. XXII and XXIII. 3 - 1 The effect of both O^ C £ g ) and 0 2 ( A ) on individual NO g bands produced by gas-phase recombination was checked. Intensities of the bands were seen to vary s l i g h t l y between spectra. The band i n t e n s i t i e s are l i s t e d i n Table XII. Molecular oxygen was also found to cause ov e r a l l quenching of the NO 8 bands. This was observed by addition of oxygen to the NO g bands pro-duced by: N + NO N 2 + 0 (33) N + 0 + M -> NO* + M (23) A comparison of equal flowrates of argon and oxygen showed a considerable decrease i n NO g band emission with oxygen. This could possibly be due to competition with reaction (23) from the reaction sequence: N + 0 2. -»• NO + 0 (25) N + NO •> N 2 + 0 (33) However, with an oxygen concentration of about 10^ l i t r e s mole. *sec. the h a l f l i f e for atomic nitrogen decay by reactions (25) and (33) ( k 2 5 = 1 x 10^ l i t r e s mole. 1 s e c . ~ 1 = 1.5 x l O 1 ^ l i t r e s mole. *sec. *) would Fig. XXII. Spectrum of n i c k e l catalysed emission from NO 0 bands. Taken with a Hilger-Watts f/4.5 monochromator i n conjunc-t i o n with an RCA IP21 photomultiplier. The f r a c t i o n of the glow produced by background rad i a t i o n (Fig. XXIII) i s un-known. S l i t s 150 u. Fig. XXIII. Spectrum of emission produced by conventional n i t r i c oxide recombination. Taken with a Hilger-Watts f/4.5 monochromator i n conjunction with an RCA IP21 photomultiplier. S l i t s 150 u. -91-( 3; l 6 )(2,i5) J ll„, I I f « I « • ' ' I f 1 ' • ' 1 1 5 5 0 0 5 0 0 0 4 5 0 0 4 0 0 0 Wavelength (&) Nickel catalysed emission from the NO 8 bands -92-NO g band emission from nitric oxide recombination -93-Table XII Variation i n the i n t e n s i t y of the NO g bands produced  by d i f f e r e n t methods. Peak of NO 3 band Intensity from N + NO (arbitrary units) Intensity from N + 0 2 (arbitrary units) Intensity from N + 0 2 + 0 2 ( l A g ) (arbitrary units) (0,12) 2.3 2.3 3.3 (1,13) 0.8 1.3 2-4 (2,14) 0.6 0.5 0.95 (0,13)(3,15) 1.1 0.9 ,1.65 (1,14) 0.5 0.7 1.45 (2,15) 0.4 0.7 1.5 (0,14)(3,16) 0.6 0.8 1.45 (1,15) 0.2 0.3 0.6 (2,16) 0.4 0.5 0.9 (3,17) 0.6 0.8 1.3 (2,17 0.4 0.4 0.7 -94-be about 0.5 seconds. On t h i s mechanism a t r i v i a l decrease i n the NO 3 2 -1 band i n t e n s i t y would be expected (flowrate = 5 x 10 cms. sec . - obser-vation within 20 cms.) - c e r t a i n l y not of the order of a factor of 10 observed here. I t was also found that the 3 band i n t e n s i t y increased s l i g h t l y on discharging the oxygen to form 0 9(*A ), the complete recom-bination of atomic oxygen i n the Q^^^^) stream being checked by addition of excess n i t r i c oxide. The NO 3 band glow over n i c k e l was always seen i n the presence of the f i r s t p o s i t i v e red glow also seen near other surfaces. A v a r i a t i o n i n the r e l a t i v e i n t e n s i t i e s of the two glows could be made by varying the r a t i o of the atomic nitrogen concentration to the 0 9(*A ) concentration. Pre-* g dominance of the n i c k e l catalysed NO 3 band glow required a smaller [N]/ [ 0 9 ( 1 A )] r a t i o , g The blue copper glow. This glow was very weak and was produced with discharged nitrogen alone. The copper was not maintained at room temperature as i n the spec-trum recorded by Harteck et a l (53) but was allowed to be heated by the atom recombination. The effect of cooling the copper was t r i e d but no obvious change i n the colour or i n t e n s i t y of emission could be seen. The glow consisted of a blue emission extending about 2 mm. away from the copper surface under usual conditions. The spectrum was taken at lower pressure to eliminate as much of the gas phase Lewis-Rayleigh emission as possible. Under these conditions the glow was s l i g h t l y more extensive. The spectrum - 9 5 -of this glow is seen in Fig. XXIV and the region between 5 0 0 0 A and o 4 0 0 0 A is shown in more detail in Fig. XXV. Less resolution was possible in Fig. XXIV since a quartz prism was used instead of the glass prism employed for Fig. XXV. The strongest features of the spectrum were at o o 3 2 4 7 A and at 3 2 7 4 A, consisting of the Cul resonance lines. The Cul lines seen in the spectra are listed in Table XIII. Summary of the experimental results on the surface-catalysed glows. I. Surface catalysed red first positive emission. ( 1 ) Glow seen over a variety of metals and from 'unpoisoned' glass walls. ( 2 ) 0„(*A ) required for production of glow. *• g 2 ( 3 ) Glow varies as [N] ( 4 ) Increased population from the v' = 8,6 levels relative to the v J = 1 2 - 9 levels compared with population distribution of Lewis-:_ Rayleigh emission.* ( 5 ) Decreased population towards the v' = 0 level. _3 ( 6 ) Lifetime of glow ~ 2 x 1 0 sees (calculated for a diffusion distance of 1 .5 cms. into gas phase)* II. (a) Nickel catalysed nitric oxide 8 band glow. ( 1 ) Glow seen only over nickel* ( 2 ) O-C'A ) required to produce glow. ^ g ( 3 ) Glow varies as [N]. Independent of [ 0 ] . (4) Glow favoured by higher [Nj/fO-f1^ )] ratio than required for *• g red first positive glow. Fig., XXIV. Spectrum of the copper glow between 3200 A and 5000 A. Taken with a Hilger-Watts f/4.5 monochromator (quartz prism) i n conjunction with an RCA IP28 photomultiplier. S l i t s 250 u. o o Fig. XXV. Spectrum of the copper glow between 4250 A and 5600 A. Taken with a Hilger-Watts f/4.5 monochromator (glass prism) i n conjunction with an RCA IP21 photomultiplier. S l i t s 170 u. 6 5 2 I 0 Cul NO p band - i 1 1 1 1 1 1 i i i i i _ i _ 3200 3300 3400 3500 3600 3700 3800 3900 Wavelength (A) rls 6 5 4 3 2 I 4000 4200 4400 4600 4800 5000 Wavelength (A) v. -99-Table XIII' Copper I li n e s seen i n blue glow. Wavelength of Cul 0 lines (A) Approximate i n t e n s i t y corrected for detection response. (Arbitrary units) 2745 2 2766 5 2824 15 2961 10 3070 7 3094 4 3248 100 3274 58 5219 11 -100-(5) Spectrum suggests a more.even d i s t r i b u t i o n through the v i b r a t i o n -a l energy levels than i n the glow produced by ra d i a t i v e recombination of n i t r i c oxide. (6) Absence of y and 6 bands.* -4 (7) Lifetime of glow ~ 10 sees (calculated for a d i f f u s i o n distance of 0.2 cms. into the gas phase).* 11(b) N i t r i c oxide B band glow produced i n gas phase by normal n i t r i c - oxide recombination. (1) Glow quenched by ground state oxygen. (2) Glow produced by 0„(*A ) addition. I I I The blue copper glow. (1) The spectrum shows a band emission and copper l i n e emission. -4 (2) Lifetime of glow ~ 10 sees (calculated for a d i f f u s i o n distance of 0.2 cms. into the gas phase). Results f i r s t obtained by Harteck et a l . (53)(59)(60) and confirmed here. -101-DISCUSSION The rate constant for the N + O.^A ) reaction. An upper l i m i t of 1.6 x 10^ l i t r e s mole. *sec. * was obtained here for ^ 2 4 , t n e r a t e constant for the reaction: N + 0 ( 1A ) -> NO + 0 (24) This should be compared with l^s' the rate constant for the analogous reaction with ground state oxygen: N + 0 2 ->• NO + 0 (25) which has a rate constant of 1.0 x 10^ l i t r e s mole. *sec. * at room -3 temperature (71). Thus i s less than 16 x faster than l^^, n o t ^ faster as required by Hunten and McElro'y (58) to explain the concentration of NO i n the 90 km region of the upper atmosphere. They calculated that 8 -1 -1 a rate constant of 1.8 x 10 l i t r e s mole. sec. would be required for k24 i n order to account for the NO concentration found by Barth (73) using rocket observation of the NO y bands. These bands are emitted by a f l u o r -escence mechanism of n i t r i c oxide that i s excited by absorption of sun-0 14 l i g h t around 2500 A. He deduced a column density of 1.7 x 10 molecules -2 cm above 85 km which i s considerably greater than that o r i g i n a l l y pre-dicted by Nicolet and Aiken (74) and Barth (75) using as the p r i n c i p l e production and removal reactions: N + 0 2 + NO + 0 (25) N + NO •*• N 2 + 0 (33) -102-Two reactions have so far been proposed to explain the increased steady state concentration of NO found experimentally. The f i r s t was the reaction: °2 + + N2 * N 0 + N 0 + " ^37) o r i g i n a l l y proposed by Nicolet (76). Upper l i m i t s for the rate of reaction (37) have been determined, however, showing that the reaction i s too slow to explain the observed concentration (77) (78). The second reaction was reaction (24) proposed by Hunten and McElroy, which has already been dis-cussed. The present work rules out reaction (24) as the major n i t r i c oxide production process, again leaving the whole question of an explan-ation for the high oxide concentration unanswered. The unexpected slowness of reaction (24) compared with the rate expected from comparison with reaction (25) (see e a r l i e r ) can be ration-a l i z e d by consideration of the t r a n s i t i o n states involved i n the two processes. The reactions can be written: N( 4S) + 0 2 ( \ ) NOf2!!) + 0( 3P) (24) S: 3/2 O 6 1/2 1 N( 4S) + 0 2( 3Z ~) -*• NC-tfl) + 0( 3P) (25) S: 3/2 . 1 g 1/2 1 The spin quantum numbers are written below each separate component i n the reaction. I f i t i s assumed that there i s no change i n the t o t a l spin state reaction (24) must proceed v i a a quartet (S = 3/2) and reaction (25) v i a a doublet or quartet (S = 1/2 or 3/2). Thus: -103-N( 4S) + O.^A ) 4 [ N — - 0 = ^ 0 ] + NO A ) + 0C 3P) (38) N( 4S) + 0 2 ( 3 E ~) -»• 2 ° r 4 [ N 0 — 0 ] •*• NO A ) + 0( 3P) (39) where [N Q----0] represents the t r a n s i t i o n state. By comparison with the i s o e l e c t r o n i c O-N-O molecule, the f i r s t doublet state would be expected to be below the f i r s t quartet state i n [N 0*- 0] r e s u l t i n g i n d i f f e r e n t reaction paths for the two processes. Hunten and McElroy's prediction of the reaction rate depended on the same t r a n s i t i o n state being used i n both cases. The above argument shows that t h i s i s probably not true i f the t o t a l spin i s conserved throughout the reaction. For the opposite s i t u a t i o n i n which a spin change does take place (quartet doublet i n reaction (38),) other considerations would be required and Hunten and McElroy's argument s t i l l would not stand. The mechanism of the red f i r s t p o s i t i v e emission. I t was shown e a r l i e r that both atomic nitrogen and 0_(*A ), as well as 3 a surface, are necessary for the formation of the N_(B n ) state giving r i s e to the red nitrogen f i r s t - p o s i t i v e glow. Since no new or increased emission i s seen near the surface i n the absence of O^^A^), the 0 2(^A g) must be involved i n an actual formation process and not i n selective re-moval of p a r t i c u l a r v i b r a t i o n a l l e v e l s . Any mechanism proposed for the red glow must be able to explain not only t h i s p a r t i c i p a t i o n of the atomic 1 nitrogen, 0 9( A ) and the surface, but also the spectral d i s t r i b u t i o n , _3 the l i f e t i m e of the glow (2 x 10 sees using the data of Weinr&b and -104-Mannella (.65)) and the [N] dependency shown i n Fig. XX. The populations of the v i b r a t i o n a l energy levels of the' B^ JI state are compared i n Fig. XXVI. The r e l a t i v e population d i s t r i b u t i o n of the d i f f e r e n t v i b r a t i o n a l levels i n the normal Lewis-Rayleigh glow i s taken from Fig. VII of reference (52). This diagram should be treated with some caution since i n several cases there i s divergence between the theoreti-c a l l y predicted (79)(80) and the experimentally determined t r a n s i t i o n p r o b a b i l i t i e s for di f f e r e n t bands of one p a r t i c u l a r v i b r a t i o n a l l e v e l . Bayes and Kistiakowsky (52) have suggested that t h i s i s due to an under-lying band system (B1 3 Z y ~ — B^g-'' a n d has calculated the B^JI^ state population accordingly. I t i s t h i s population d i s t r i b u t i o n which i s used i n Fig. XXVI. The r e l a t i v e populations of the cobalt red glow v i b r a t i o n a l levels are determined from the heights of the peaks i n Figs. XVI and XVIII compared with Figs. XVII and XIX. Harteck et a l (53) suggested that surface catalysed recombination of atomic nitrogen to produce the red glow was v i a the N 2(A 3E u +) state, followed by collision-induced transfer to the B3]! state, which then emitted. This i s also the route suggested by Campbell and Thrush (54) for gas phase recombination of atomic nitrogen giving r i s e to Lewis-Rayleigh emission. I f the mechanism of Campbell and Thrush i s correct, the N 2(A 3E U +) state would be expected to have a f a i r l y steady change i n population through i t s v i b r a t i o n a l l e v e l s , because of i t s formation by a termolecular c o l l i s i o n process. In order to explain the B^ H population of the red glow a large increase i n population of the V = 10-15 levels Fig. XXVI. The r e l a t i v e population of v i b r a t i o n a l levels i n the 3 B II state of nitrogen. Shaded areas denote the cobalt -catalysed glow. Unshaded bars denote the normal Lewis-Rayleigh emission. Populations are a r b i t r a r i l y equalized at v 1 = 6. - 1 0 5 -\Qh9\ f&JBUB |DU0ij£)jqj/\ -106-of the A 3 E u + state would have to be proposed as well as rather e r r a t i c population d i s t r i b u t i o n s i n the v" = 7 and v" > 20 regions (correspond-3 ing to B n v 1 = 12-9 respectively). A population d i s t r i b u t i o n s i m i l a r to that for gas phase recombination would seem more l i k e l y . Harteck's mechanism would fare better i f i t were proposed that the v 1 =12-9 levels of the B3n state were populated v i a the 3E + state as discussed by Benson (56), the v' = 8-0 levels by s i m i l a r mechanisms to that of Harteck involving the A 3E + state with the lower v 1 = 2-0 levels u 3 enhanced by population from the B' E^ state as o r i g i n a l l y proposed by Bayes and Kistiakowsky (52). The p a r t i c u l a r v i b r a t i o n a l d i s t r i b u t i o n could then be produced by allowing formation of the A 3 E y + state but not the E^ + state on the surface of the metal, g Both these mechanisms require the 0 2(*Ag) to be of l i t t l e importance i n the reaction and relegate i t s effect to a 'conditioning' process of the surface. The appearance of the glow over a wide variety of surfaces and the complete and immediate removal of the glow on switching o f f the 0 2(^Ag) stream imply the contrary. Because of i t s s p e c i f i c r o l e i n t h i s reaction the most l i k e l y function of the 02(*A ) i s i n the spin-change energy transfer process. A possible mechanism using the N 2(A 3E u +) state requires i t s production i n high v i b r a t i o n a l levels on a surface followed by d i f f u s i o n into the gas phase where i t forms the a*n and W*A states by an energy-pooling g u c o l l i s i o n with 0»(1A ). V i b r a t i o n a l deactivation to the v' = 0 v i b r a t i o n -3 a l levels and then c o l l i s i o n a l transfer to the B n state might be expected -107-t o p r e f e r e n t i a l l y p o p u l a t e t h e v ' = 6 and 8 l e v e l s w i t h o u t s i g n i f i c a n t p o p u l a t i o n o f t h e v ' = 12-9 l e v e l s . Thu s : N + N + c o b a l t s u r f a c e *^ N„ (A E ) + c o b a l t s u r f a c e 2 u ' N 2 ( A 3 E u + ) + 0 2 ( 1 A g ) — ^ N ^ a ^ g ) * + 0 2 ( ^ g " ) . N 2 ( w l A u ) * N 0(a 1n ) * . , N 0(a 1n ) v = 0 w N 0(B 3n ) 2 ngJ V i b r a t i o n a l 2 , g M • . 2*-. gJ N2(w\?* d e a c t i v a t i o n N 2 ( w V v = .0 - ^ v 1 = 6,8 where t h e a s t e r i s k d e n o t e s v i b r a t i o n a l e x c i t a t i o n . The s t r o n g e s t e v i d e n c e so f a r a g a i n s t t h e A 3 £ u + s t a t e as t h e m e t a -s t a b l e i s t h e e f f e c t o f a t o m i c n i t r o g e n on t h e g l o w . We in reb and M a n n e l l a (65) have shown t h a t t h e r a t e c o n s t a n t f o r t h e d e a c t i v a t i o n 8 - 1 o f t h e m e t a s t a b l e s p e c i e s by a t o m i c n i t r o g e n i s < 3 x 10 l i t r e s m o l e . -1 3 + s e c . . The r a t e c o n s t a n t f o r d e a c t i v a t i o n o f t h e N„(A E ) s t a t e , how-2 V u J e v e r , a p p e a r s t o be abou t 3 x 10^ l i t r e s m o l e . ' ' ' s ec . * (63) (64). O t h e r m e t a s t a b l e s p e c i e s a p a r t f r o m t h e ^ ( A 3 E^ ) s t a t e c a n be p r o -3 p o s e d as i n t e r m e d i a t e s o f t h e s t a t e s b e l o w 9.76 eV, t h e B n w i t h a f i r s t p o s i t i v e r a d i a t i v e l i f e t i m e o f 6 x 10 ^ s e e s . (81) and t h e a * n s t a t e w i t h - s a r a d i a t i v e l i f e t i m e t o t h e g r ound s t a t e o f 2.5 x 10 ^ (82) c an b o t h be 3 e l i m i n a t e d as w e l l as t h e B' E s t a t e , t h e r a d i a t i v e l i f e t i m e o f w h i c h u w o u l d be e x p e c t e d t o be c o m p a r a b l e w i t h f i r s t p o s i t i v e r a d i a t i o n . O f t h e r e m a i n i n g w-A , a ' ^E^ and A^ s t a t e s , t h e l a s t ha s been e x t e n s i v e l y s t u d i e d u s i n g n i t r o g e n c o n t a m i n a t e d e l e c t r i c a l d i s c h a r g e s t h r o u g h a r g o n . (83)(84). - 1 0 8 -Th e r e s u l t s obtained agree with those expected from a recent determination ( 8 5 ) o f i t s p o s i t i o n on the potential energy diagram by observation of the ( V - B \ ) t r a n s i t i o n i n the infrared. By comparison with, the (B\ 3 + 3 A E u ) t r a n s i t i o n and only compensating for the smaller v factor i n the Ei n s t e i n A c o e f f i c i e n t , a l i f e t i m e of the order of seconds would-be ex-3 pected for the v' = 0 A l e v e l , making i t a suitable metastable species. 3 Unfortunately mechanisms involving the A u state have been found to produce a considerable increase i n the f i r s t p o s i t i v e v'= 0 emission ( 8 2 ) . I t can be seen from Fig. XVIII, that t h i s i s not so i n the present case. The a l(^'E u ) state has a l i f e t i m e of about 0 . 1 sees ( 8 6 ) and i s thus a possible metastable species. The W(*A U) state would be expected to have a very fast r a d i a t i v e l i f e t i m e to the a(TI ) state. g One attempt was made to gain some insight into a possible intermediate by producing a stream of N 2 ^ ^ u + ^ u s^ nS a l o w P° w e r ed hollow cathode d.c. 3 3 discharge to produce metastable Ar atoms i n th e i r P^, PQ. states with about 11.6 eV of energy ( 6 7 ) . This i s enough to excite nitrogen to the C 3 n u s t a t e , producing a small flame about 1 cm long consisting of the second p o s i t i v e (C^IIy - ^^g) a n d f i r s t p o s i t i v e emission on addition of molecular nitrogen to the argon stream. The resul t of t h i s r a d i a t i v e cascade process i s the production of the ^ (A^E +) state i n the absence of atomic nitrogen, which allows the A 3 E u + state to l a s t along the length of the tube. The 3 + 0 N 2(A E u ) state was detected by the presence of the 2 5 3 7 A resonance l i n e formed by energy transfer from the ^ (A^E +) state on addition of mercury vapour to the stream ( 8 7 ) . No emission could be seen near the surface of -109-a cobalt plug placed i n a stream of N (A E + ) and 0„( A ), although. z u z g emission was e a s i l y detected when a small quantity of atomic nitrogen was added to the stream. Since ^(A^E +) appears to.be rapidly quenched by ground state oxygen (88), the cobalt was moved to the mixing zone of the two streams. Again no emission was detected. The absence of a p o s i t i v e r e s u l t does not necessarily disprove that the metastable species was the ^(A^Z + ) - v = 0 v i b r a t i o n a l l e v e l . This experiment i l l u s t r a t e s the d i f -f i c u l t y involved i n testing possible mechanisms as well as the d i f f i c u l t y i n interpreting the results of these tests. The mechanism of the blue NO g band glow. In connection with the reaction between atomic nitrogen and 0»(^A ) ^ g to form the NO $ bands, two processes have to be considered - the surface catalysed emission and the gas phase effect of oxygen on the NO recombin-ation process. The l a t t e r i s the simpler system and w i l l therefore be treated f i r s t . 2 I t was found that emission from the N0(B IT) state was quenched by ground state oxygen and produced by addition of 0?(''"A ). This can be ex-^ g 1 4 plained by an energy-pooling reaction between the 0„( A ) and the NO(a n) ^ g state formed i n the f i r s t step of the recombination process producing the state: N0(a 4n) N O ( b V ) N0(B 2n) (40) N0(a 4n) + o 2 C 1 A g ) + N0(B 2n) + vX"3 m The quenching effect of ground state oxygen on the ^ ( B ^ ) state emission -110-i s presumably due to the reverse of reaction (41). The absence of any marked selective quenching of the NO 3 bands b y oxygen (see Table XII) would be expected since the B^il and a4II potential curves appear to run almost p a r a l l e l , suggesting that the (0,0), (1,1), (2,2) etc. Franck-Condon factors and energy differences are a l l approximately the same. This, unfortunately, cannot be calculated exactly since there i s some uncertainty i n the p o s i t i o n of the a^ II state. The p o s s i b i l i t y of energy-pooling by the reaction: NOCa^1). + O J ^ ) N O ( b V ) + 0 ( 3E ") (42) cannot be neglected. Similar arguments to those for the B^ TI state would apply except that, from the positions of the potential curves, a greater population i n the B^ JT v 1 = .0 state might be expected. For the n i c k e l catalysed glow, the d i f f u s i o n distance of a few m i l l i --4 meters into the gas phase suggests a l i f e t i m e of 10 sees for the metastabl species. Thus th i s metastable species can not be the NO ( B ^ ) state with a r a d i a t i v e l i f e t i m e of 10 ^ sees (61). By analogy with the gas phase process the metastable species would be expected to be the a^il state which would 3 require removal at a rate of 1 c o l l i s i o n i n 5 x 10 to explain the extent of the glow. This i s about 1 c o l l i s i o n i n 20 with 0„(*A ), which i s not 6 2 V g " unreasonable.. One major difference, however, exists between the surface catalysed and gas phase glows and t h i s i s the effect of addition of n i t r i c oxide i l l u s t r a t e d i n Fig. XXI. I t can be seen that the normal gas phase curve peaks at about halfway to the t i t r a t i o n end point, i . e . when [N] = [0] as expected from the k i n e t i c analysis. The surface catalysed glow does not follow t h i s curve but appears d i r e c t l y dependent on the atomic nitrogen concentration and independent of the atomic oxygen concentration. A possible mechanism which would explain t h i s would be a surface catalysed reaction between atomic nitrogen and ground state or singlet oxygen: + "1 T T . N ( 4n) N : I f either h a l f of the reaction i s rate c o n t r o l l i n g direct dependence on the atomic nitrogen concentration would r e s u l t . Campbell and Thrush (54) suggested, from a consideration of the required surface coverage f o r the recombination of nitrogen atoms, that the process followed neither a Hinshelwood nor a Rideal type mechanism but that the atomic nitrogen must have considerable m o b i l i t y on the surface of the walls. I t i s possible that such a mechanism i s taking place here and f a c i l i t a t i n g the seemingly rather d i f f i c u l t reaction. Mechanisms involving energy transfer from metastable molecular nitrogen can not be proposed, because the glow would then be seen over cobalt and copper as well as over n i c k e l . The copper blue glow. The copper blue glow seen i n these studies i s c e r t a i n l y not the n i t r o -gen second p o s i t i v e glow seen by Harteck et a l (53). Its o r i g i n i s un-known. No comparison with the glow obtained by Harteck et a l over copper could be made since they did not publish a diagram of th e i r spectrum. A systematic search to i d e n t i f y the present band system was made using the N . . N 0 = 0 N •0 = 0 data listed in references(89-92). The method of checking a particular band system was to find a transition which had its wavelength within o o o ±20° A of the wavelength of the two most intense peaks at 4957 A and 4852 A and then to search for other expected transitions from the same vibrational level. The spectrum appears to consist of at least two groups of bands, which show a definite resemblance, suggesting a progression with to = 2345 ± 10 cm This co value is unusually large, being comparable in spacing to the vibrational levels of ground state nitrogen. This suggests either k, the vibrational force constant is large or y, the reduced mass, is small, as in a hydride. The appearance of the spectrum suggests that the emission is either from a polyatomic molecule or from several closely spaced different electronic states in a diatomic molecule. There are several overlapping bands and this presents difficulty even in picking out a progression involving the two stronger bands. For the progression shown in Fig. XXV, co = 410 cm The existence of Cul lines is not surprising; they have been seen many times in active nitrogen (44). -113-CONCLUSION The rate constant for the reaction: N + 0 o ( 1 A ) •+ NO + 0 (24) 2 . g was found to have an upper l i m i t of .1.6 x 10^ l i t r e s mole. ''sec. * which i s too slow to account for the concentration of n i t r i c oxide i n the 90Km. region.of the upper atmosphere. The red glow seen over cobalt was found to require Q^^^^) for i t s 2 production and vary as [N] . Its v i b r a t i o n a l l e v e l population d i s t r i -bution d i f f e r e d from that obtained i n the normal Lewis-Rayleigh after-glow. The nickel-catalysed blue glow also required O^^A ) for i t s production and varied as [N]. A more even d i s t r i b u t i o n of population 2 through the v i b r a t i o n a l levels of the B n state was obtained than i n the normal ra d i a t i v e recombination of n i t r i c oxide. Variations i n the gas phase NO 6 band emission could be attributed to the reaction: N0(a 4 n ) + 0 2( 1A ) ^ N 0 ( B 2 n ) + 0 ( 3 E ") (41) The copper blue glow was d e f i n i t e l y not the second po s i t i v e emission as o r i g i n a l l y stated by Harteck et a l (53). The testing of mechanisms suggested for indivdual glows i s made ex-tremely d i f f i c u l t by both the lack of method of obtaining isolated states as well as the lack of s p e c i f i c detection methods. One mechanism for the production of the red f i r s t p o s i t i v e glow, however, can be tested. This i s the mechanism requiring production of the a*ttg state from the N 2 ( A 3 E u + ) -in-state by energy-pooling with CL ( A ). The a II state can be produced by absorption of radiation i n the 1300 A region (Argon lamp). The production of the B n state i n the v' = 6 l e v e l can then be checked. The success g o of the experiment depends on applying s u f f i c i e n t i n t e n s i t y at 1300 A without masking the f i r s t p o s itive emission with stray v i s i b l e l i g h t . This might just be possible. -115-REFERENCES 1. Gilmore F.R. J.Q.S.R.T; 5_ 369 (1965) 2. Gray E.W. and Ogryzlo E.A. Chem. Phys. Letters .3 698 Q969) 3. Fontijn A., Meyer C.B. and Sc h i f f H.I. J. Chem. Phys. 40 64 (1964) 4. Mulliken R.S. Phys. Rev. (2) 3_2 880 .(1928) 5. Herzberg G. and Herzberg L. Nature 133 759 (1934) 6. E l l i s J.W. and Kneser H.O. Publ. Astron. Soc. Pac. 46 106 (1934) 7. 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Wallace L. Astrophysical J. Suppl. 1_ 165 (1962) 92. Herzberg G. Molecular Spectra and Molecular Structure. Vols. 1 and 3 VanNostrand Co. Inc. N.Y. 93. Weinreb M. and Mannella J . Chem. Phys. 50 3129 (1969) -120-POSTSCRIPT A paper (93) by Weinreb and Mannella has been recently published dealing with the red f i r s t p o s itive glow. They agree with the present work i n that they also f i n d the presence o£.0„(^A ) necessary for the glow. They also show that the O^^Ag) does not react at the surface of the metal but on a metastable species (which they assume i s the ^ ( A ^ E ^ ) state) d i f f u s i n g into the gas phase. They then vary the quantity of di s -charged oxygen flowing into the system and obtain an estimate of the rate of reaction between the metastable nitrogen and the discharged oxygen, by measuring the v a r i a t i o n of the glow with distance away from the surface. Assuming 20% 0^(^A^) i n the discharged oxygen and a dir e c t v a r i a t i o n of the 0„(*A ) concentration with the t o t a l oxygen concentration they obtained 9 - 1 - 1 3 x 10 l i t r e s mole. sec. for the reaction of the metastable nitrogen with 0„(*A ) giving r i s e to the glow. They assume that quenching by ground state oxygen i s n e g l i g i b l e , an assumption which i s not necessarily v a l i d . This might account for the good correla t i o n between the half-l i f e of the glow and the reciprocal of the t o t a l oxygen concentration. 

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