Excitation Transfer in the Radiolysis of Solid Alkane Mixtures at 77 K

Abstract

Abstract The radiolysis of isobutane-propane (less than 5 mol %) or neopentane-alkane (5 mol%) mixtures has been studied at 77 K by means of ESR spectroscopy. When these alkane mixtures are γ-irradiated, the solute radicals are mainly formed by energy transfer from γ-irradiated isobutane or neopentane to the solutes. It is discussed whether the energy transfer is due to a proton transfer, a positive-charge transfer, or an excitation transfer, and it is concluded, for the following reasons, that the energy tranfser is probably due to the excitation transfer and that the excitation transfer may occur via highly-excited states of isobutane or neopentane; (i) The ionization potentials and the energies of the first singlet-excited states of the some additives are higher than those of isobutane or neopentane. (ii) The decrease in the solvent radical yields and the increase in the solute radical yields upon the addition of the solutes to the isobutane or neopentane amount approximately to 2–2.5 G-units. (iii) The yields of hydrogen increase sharply upon the addition of cyclopentane in the radiolysis of solid neopentane. (iv) It was concluded in previous studies that the formation of the solvent radical in the radiolysis of solid isobutane is due to the fragmentation of excited isobutane produced directly by γ-irradiation.