No abstract

Ethylene photolysis was investigated at 147, 163, 185 and 193 nm. The following three primary processes were observed at all wavelengthsCCC(1) was independent of all experimental parameters tested: temperature, pressure, wavelength, scavenger, and light intensity. (2) decreases with increasing pressure and increases with increasing photon energy. (3) shows almost no pressure dependence at 185 nm and decreases in importance with increasing photon energy. A kinetic analysis shows that participation of at least three different states of ethylene must be invoked to explain the results. A tentative correlation of these states with the spectroscopic states of ethylene is given.

Irradi a tion of CC I4 , CFCI3 , a nd CF2C1 2 in the prese nce of C2 H6 in vesse ls co ntaining s ilica sa nd or fused qua rt z tubing results in th e formati on of chl orine-cont aining produ cts. The form ation of these compounds occurs at wavelength s ex tending up to a pproximately 400 nm, that is, at wavele ngths wel l beyond the a bsorpti on threshold of the ch lo romethanes in the gas p hase . It is s uggested that CCI, adsorbed on silica surfaces ph otod issociates to yield CCI" and CCl2 s pec ies. The poo r mate ri a l ba la nce obtained in these experim ents ind ica tes that several of the chl orine -co ntaining fragme nts are strongly adsorbed o n the su rface. At a CCI, pressure of 13 Pa (0.1 torr), ph otolys is with 366 nm light in th e prese nce of sa nd resu lt s in the decomposit ion of one mo lec ule for every 10' photo ns stri king th e sudace. Under oth erw ise id e nt ical co ndit ions, the photon-induced breakdown of CFC I3 and CF2CI2 is res pectively o nl y JO pe rce nt ur 3 pe rc e nt as effi c ie nt.Key words: Chl oron1etha nes, photoche mist ry; q ua ntum yields; q ua rtz; sa nd; surface reacti ons; tropospheri c s ink. . IntroductionIn a recent study [1 r from this laboratory, it was shown th a t in th e gas phase, the photodecompositi on c ross secti on of CC14 at 313 nm was ~ 3 .7 ± 0 .4 X 10-26 cm 2 mo lec ul e-I at 300 K. Because sun l ight reach ing sea level consists mainly of wa velengths a bove 320 nm , thi s laboratory result suggests tha t in th e troposphe re gaseous CC14 will not be di ssociated by light. Th e p hotodi ssoc iation cross section of f1u orines ubst ituted meth a nes a t th e wavele ngth s whi ch reach the ear th's surface s hou ld be eve n smalle r th a n th at [or CC14 , s ince th e abso rpti on s pec tra of th e f1u orin e-substituted compounds are shifted to shorter wavele ngth s [2]. The refore, c hloromethanes and fluorochloromethanes released to the a tmospher e would be expected to diffuse to the stratosph ere, unless s ome mec hanism for their re moval other th an p hotodecomposition exists. As Molina and Rowland [2] suggested , th ese compounds in the stratosphere would absorb h igh ene rgy ph otons and undergo photodissociation to produ ce chlorin e atoms , which in turn would be expected to unde rgo a c ha in re ac tion resulting in the re moval of ozone molec ules .Howe ve r, the re were available two pi eces of evide nce whi ch ind icated that possibly CCl4 wh en adsorbed on cel·tain sltl-faces d oes undergo photodecomposition at wavelength s as long as th ose wh ich reach the earth's surface . Th e first such observa ti o n was that the cross section for ph otodeco mpos iti on of CC I4 showed a n appare nt increase by a facto r of fi ve wh e n the measure ments were made in quartz ra th er th an Pyrex 2 vessels. Second ly, measurements of the co ncentra ti on of CCl4 in th e tro pos phere in the e astern he mis ph ere as a functi on of la titude fro m 50 N to 3 0 S have shown th at there is a pro nou nced minimum in the CC14 concentrati on in the...

The Reaction of Hydrogen Atoms with Silane; Arrhenius Parameters and Kinetic Isotope Effect Relative rate constants were measured for the systems H + C2H4/SiD4 and D + C2D4/SiH4 over a wide temperature range. From the known arrheniusparameter for the reaction H + C2H4 the activation energy EA and the preexponential factor A of the abstraction reaction H + SiD4 → HD + SiD3 may be calculated. Values of EA = 3.2 kcal/Mol and A = 4.92 • 1013 cm3 Mol-1 sec-1 were obtained. Upper limits for the kinetic isotope effects are given in the paper