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D. B. PETERSON AND GILBERTJ . ~ I A I N S
Vol. 81
a t an energy input rate of 1.6 X 101j e.v. per g. sec. ( Ilo5 rep. per hr.), [MI = 1 atm., and a t 25”. For this estimation
Since energy requiredz0 to produce an ion pair in methane by a-particle irradiation is 31 e.v., their estimation corresponds to a G(H) = 2.8, in agreement with our result of 3.2. ki2 = 3.4 X lo1*esp( -6SOO/RT) cm mole-’sec: Iodine probably is better than nitric oxide to was used. l8 Concentrations of other radicals are identify individual free radicals21; but its use to probably of the same order of magnitude or less. estimate radical G-values is not advisable. Iodine Hence, a t the experimental conditions employed does not inhibit the formation of hydrogen in in our work, the rate of reaction 12 is approximately methane radiolysis.fi Since 41y0 of the hydrogen lo4 and lo7 times faster than the rate of reactions formed arises from radical processes, the above 13 and 14, respectively, even if a steric factor of 1 observation suggests that iodine cannot inhibit the is assumed for the latter processes.lg Thus, the type of reaction 7. Hence, the iodine method gives aforementioned approximation that all radicals ambiguous energy yields for hydrogen atom and for undergo hydrogen abstraction reactions seems those radicals produced by the interaction of hyreasonable. Using this approximation and the drogen atom with the reactants. Hydrogen iodide nitric oxide inhibition data, G-values for various accelerates the formation of hydrogen in methane radiolysisj6 and its use involves similar uncerFree radicals are calculated tainties. Ethylene and propylene produce hydrocarbons such as methane, ethane and propane by .If \Radical €1 CHa CzHa reacting with hydrogen atoms and hydrocarbon CH4 2.8 .. free radicals produced by y-irradiation. 22 For this C2H6 2.8 0.3 reason, their use is also not advisable. Therefore, C3Hs 3.4 0.5 0.6 i t appears that nitric oxide is one of the few radical scavengers which is satisfactow to estimate the a Not able t o estimate with the present method. energy yield of radicals, as well as the contributions Due to the probable uncertainty arising from the of free radical reactions to the over-all radiolysis contribution of radical recombination in chain of gaseous hydrocarbons. Acknowledgments.-The authors are indebted to lengthening processes, G-values for the radicals having a larger carbon number than the reactant Mr. A. B. Care1 for gas chromatographic analysis of the samples. Drs. L. 0. Morgan and F. H. Dickey are not estimated. hieisels, Hamill and Williams6 reported an ion offered valuable discussions for the preparation of this manuscript. pair yield of 1 for H in the radiolysis of argon methane system, using both an isotopic exchange (20) W. P. Jesse and J. Sadanokis, P h y s . Rea., 97, 1668 (1955). (21) L. H. Gevantman and I
