Direct and Inert-Gas-Sensitized Radiolysis and Photolysis of Methane in the Solid Phase

Abstract

The photolysis of CH4–CD4 mixtures has been briefly investigated at 20.4°K using the xenon and krypton resonance lines. From the isotopic composition of the hydrogen and ethane fractions, it could be derived that, in the solid phase, methylene and methyl radicals are produced. The methylene radicals, which are formed by the process CH4*→CH2+H2, insert into methane to form ethane. In the argon-sensitized radiolysis at 20.4° and 77°K, the hydrogen-molecule elimination process predominates, indicating that neutral excited-methane molecules are formed nearly exclusively. In the xenon-sensitized radiolysis, however, mainly hydrogen atoms and methyl radicals are observed. In all inert gas-sensitized radiolyses, there is a gradual decrease in the efficiency of the energy transfer with increasing dilution. In the direct radiolysis, hydrogen atoms play a more important role than in the photolysis at 1236 Å. Radiolysis of CD4−C2H4 (1:0.01) mixtures indicated that, at 77°K, hydrogen atoms react with ethylene and propylene to form higher saturated hydrocarbons while, at 20.4°K, hydrogen atoms disappear mainly by recombination with other free radicals. From the isotopic composition of the ethylene fraction formed in the radiolysis of Ar–CH4–CD4 mixtures, it is surmised that a fraction of the methylene recombines to form ethylene.