The photolysis of water vapor a t 1849 A has been investigated as a possible source of hydroxyl radicals for kinetic studies. At temperatures from 23 to 350' C and pressures from 1.3 t o 28 mm, H2 and H402 were the only detectable products. Experiments with added oxygen indicated that 0 2 ma37 have been present as a n intermediate a t a very low steady-state concentration, although this is not certain. Possible mechanisms are discussed. Ea2 -E C O = 4.0Zk0.3 kcal/mole, AH,/Aco = 3 1 f 5 , At temperatures below 200" C, hydroxyl radicals were not completely converted to COs, as the yield of Cop increased to a maximum, then decreased again, with increasing pressure of CO. The mechanism of this system is complex, but probably involves secondary reactions of HCO or COOH radicals.

No abstract

The apparatus used to study the photolysis contained a collimating region which minimized the effect of divergent light, and permitted the temperature of the cell and lamp to be controlled separately. Analytical sensitivity was such that conversions less than 0.2% were possible.Although CO and Oz were the only stable products, the CO/Oz ratios were higher than those required by mass balance. The product yields were found to be independent of COT pressure and to be linear with irradiation time a t 25 "C. At higher temperatures the quantum yields decreased and a t 200 OC were no longer linear functions of irradiation time. The 0 2 yields decreased when CO was added, the effect increasing with temperature. The overall quantum yield was less than ~~n i t y .Reactions were observed with CH.,, H Z , and N?O when these were added in small amount. These results indicated the presence of a reactive species, capable of promoting back reactions and of being adsorbed on the walls. A mechanism is suggested which best fits the results and which postulates COs as the reactive species.The ultraviolet photolysis of COz is of interest for a number of reasons. I t has been widely used as an actinometer for determining the quantum yields of other photolyses a t short wavelengths. Although it has generally been assumed that the CO quantum yield is unity, this has never been convincingly demonstrated. The photolysis also provides a potential source of metastable O(lD) atoins, which possesses advantages over alternate sources. Reactions of these metastable atoins play an important role in the chemistry of the earth's atmosphere but have received little study in the laboratory. The photolysis of COz is also of interest in understanding the photocheinistry of the atmospheres of Mars and Venus. However, the results obtained by previous investigators have not been satisfactorily interpreted by any mechanism thus far proposed.A number of investigators (1-3) have found that, although CO and Oz are the only products detected, oxygen is not recovered in the ainounts required for inass balance. Forillation of ozone has been postulated by Allahan (1) and by Warneck (3), although Warneck (4) recently claimed to have found evidence for incipient C03 formation.Although Juclier and Rideal (5) concluded that the primary photolytic product is electronically excited COZ, the consensus now seems to favor the initial production of CO and O(lD) atoms, in agreement with spectroscopic evidence (6, 7). Yamazalii and Cvetanovic (8-lo), however, found that O(lD) atoms are rapidly quenched by COz and should therefore have negligible lifetimes in systems in which they are generated by CO2 photolysis.Finally, no systen~atic study has yet been reported on the effect of temperature on the photolysis. The present I\-ork nTas undertaken as an attempt to clarify some of these problems. In particular, the results indicated the necessity for considering a back reaction.The essential features of all the glass and quartz apparatus are shown in Fig. 1. The light s...

Optical studies of the first positive system in the nitrogen afterglow were conducted in a conventional discharge -flow system. The vibrational level of v′=13 was observed readily at pressures up to 20 torr. For the first time, high-vibration levels of N2(B 3Πg) with v′≳13 were observed in the Lewis–Rayleigh afterglow under conditions of sufficiently high [N] and purity of N2. Bands from ΔV=4, 5, and 6 with v′ up to 26 have been identified. Based on the observed effects of pressure, temperature, atom concentration, and gas purity on the intensity of the emission bands, excitation processes responsible for the formation of these high-vibration levels are briefly discussed.

The homogeneous reaction between 0 atoms and CC14 was studied in a llow system under conditions of colnplete consurliption of atoms, in the presence ancl in the absence of ~liolecular oxygen. The only products of the reaction are CI:!, CO, CO:!, and COCI?. No conlpounds containing more than one carbon atom were detected. The dependence of the proclucts on CCld concentration suggests that the primary reactions arewhich are too slow to consume all the atoms. Carbon dioxide is produced by sccontlarp reactions which are fast enough to consume all the atoms, the rnost important of which is 0 + COCI? + co, + C1,. IHowever, the dependellce of the ratio (CO:! + COCI?)/CO on CCld concelrtratiot~ in the presence of 0 2 indicates other reactions also procluce CO?. The rapid disappearance of 0 atoms in the systems containing 0 2 s~rggests a chain mechanist11 it1 which CI:! is mainly converted to the aton~ic form. Carbon dioxide call then be produced by the sequellce co + C1 = COClThe rate constant for the pri~iiary process was found t o be independent of 0, 02, aild CC14 concentl-atiol~ and could be represcl~ted by the equation k = 3.3X10-l" esp ( -450D/RT) cm3 ~~~o l e c u l e -~ sec-I.