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The radiolysis of methylcyclohexane (MCH) vapor was carried out under a variety of conditions. The G-values of the main products a t 110°, extrapolated t o zero dose, are hydrogen (5.2), methylcyclohexene isomers (2.0), ethylene (1.5), methane (1.3), propylene (0.8), and total dimer (0.3). Other products were also measured.The hydrogen yield was reduced t o G = 3.1 b y each of the additives, NzO, SFB, and CC14, and t o G = 1.6 by C2H4. Both DI and ND3 increased the total hydrogen yield above the value in pure MCH. In pure MCH approximately 50% of the ions (G(tota1 ionization) = 4.4) resulted in hydrogen formation, whereas in the presence of D I or NDB, 75y0 of the ions are hydrogen precursors. Thus three different types of positive ions are distinguished in the system: G(M1+) = 2.1,. G(M2+) = 1.3, and G(NC) = 1.0.The average Ion lifetime with respect t o neutralization was s. The ion DI-was therefore stable with respect t o decomposition t o D + I-for a period greater than s under the conditions of the experiments ( N 380 Torr MCH, 110").The yield of methylcyclohexene isomers increased with increasing temperature and increased upon addition of hTD3 or CZH4 to the radiolysis system. The dimer yield was also enhanced by the addition of ND3. This effect was explained by the occurrence of an ionic secondary reaction that destroys methyl~~clohexene and (or) methylcyclohexyl radicals in pure MCH.Approximately 85Yo of the methane is produced by methyl radicals abstracting hydrogen atoms from MCH.

There is a radiation-induced chain reaction in methylcyclohexane (RICH) -CCla mixtures ill the vapor phase a t 110' and 380 Torr. The chain-propagation products are chloroform and n~eth~lcyclohexylchloride (G,,, = 40) and the chain-termination products are mainly methylcyclohexene (hlIC), bimethylcyclohexyl (CI4), and hexachloroethane, depending on the composition of the mixture. A t CC14 concentrations < 1 mole %, HC1 is formed mainly by reaction of C1-with positive ions, e.g. C1-+ C7H14+ + HC1 + C7H13. The value of the ratio G(%IC)/G(CI() is 8 1 1 in pure MCH and in the mixtures up t o 44 mole 7, CC14.There is a radiation-induced chain reaction in MCH-N2O mixtures in the vapor phase. &It 110' and 380Torr, G(N2) = 22, G(MC) = 16, and G(C14) = 1.6, independent of N20 concentration between 2 and 10 mole %. The G-values are independent of MCH pressure between 50 and 520 Torr. Product formation is inhibited by the addition of SF0 or DI. The half-life of the ion N20-with respect t o decomposition to N2 + 0-is 10-4-10-3 s under these conditions. I t is suggested that the mechanism contains the reactions

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