Gas-Phase Radiolysis of Propane

Abstract

The radiolysis of CH3CD2CH3 and of equimolar C3H3—C3D8 mixtures in the presence of radical scavengers has been investigated as a function of pressure from 0.35 to 6000 mm and as a function of temperature from 40° to 220°C. In the presence of scavengers, hydrogen and methane are mainly produced by molecular elimination. Values for the ratio CH3D/CH4 were found to increase with pressure and with surface to volume ratio of the irradiation vessel. Ethane is mostly formed by a hydrogen transfer reaction such as C2H5++C3H8→C2H6+C3H7+.From the distribution of the isotopic ethanes formed in the radiolysis of CH3CD2CH3, it can be concluded that the hydrogen atoms in the CH3CD2+ ion undergo a rapid randomization prior to reaction with propane. Ethylene can be accounted for by the occurrence of the following processes: (a) decomposition: C3H8*→CH4+C2H4, (b) ion molecule reactions, (c) decomposition of vibrationally excited propyl and/or ethyl radicals. From a comparison of the radiolysis results with the mass spectral cracking pattern of propane and recent photochemical studies, it can be deduced that the decomposition of propane ion and of neutral excited propane molecules are responsible for the products. The relative importance of these two modes of decomposition depends on the pressure and the size of the reaction vessel.