Energy Transfer in the Radiolysis of Neopentane-Alkane Mixture in the Solid Phase at 77 K

When neopentane containing a small amount of cyclohexane is γ-irradiated at 77 K, the cyclohexyl radical is mainly formed by the energy transfer from neopentane to cyclohexane. The addition of CCl4, which is an electron scavenger and an excitation acceptor, to the mixture suppresses the formation of the cyclohexyl radical. This fact indicates that the energy transfer is not due to an ion-molecule reaction. When CO2, which can capture an electron in the neopentane matrix to form CO2−, is added to the neopentane–cyclohexane mixture, scarcely any CO2 is formed by the irradiation. When ethyl chloride or nitrous oxide is added to the neopentane–cyclohexane mixture, the formation of the cyclohexyl radical is not suppressed, although these additives capture electrons effectively in the solid neopentane. The addition of tetramethylethylene (TME) to the neopentane–cyclohexane–carbon dioxide mixture does not affect the formation of the cyclohexyl radical, although an appreciable amount of TME+ is formed. These results show that the energy transfer is not due to the ionic process, but to a non-ionic process. The energy transfer is explained by two possible mechanisms, a selective abstraction reaction by the hydrogen atom and an excitation transfer via a highly-excited state.