Radiolysis of methylcyclohexane. III. Pure vapor phase and effects of additives

Abstract

The radiolysis of methylcyclohexene (MCH) vapor was carried out under a variety of conditions. The G-values of the main products at 110°, extrapolated to 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 to G = 3.1 by each of the additives, N2O, SF6, and CCL4, and to 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(total ionization) = 4.4) resulted in hydrogen formation, whereas in the presence of DI or ND3, 75% 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(N+) = 1.0.The average ion lifetime with respect to neutralization was 10−3 s. The ion DI−was therefore stable with respect to decomposition to D + I− for a period greater than 10–3 s under the conditions of the experiments (~380 Torr MCH, 110°).The yield of methylcyclohexene isomers increased with increasing temperature and increased upon addition of ND3 or C2H4 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 methylcyclohexene and (or) methylcyclohexyl radicals in pure MCH.Approximately 85% of the methane is produced by methyl radicals abstracting hydrogen atoms from MCH.