Some properties of trapped electrons, radicals and H atoms in glassy hydrocarbons

Abstract

This autoreview summarizes studies made in the author's laboratory of the properties and reactions of electrons, radicals and hydrogen atoms produced in organic glasses at 77 K and below by γ-radiolysis and photolysis. The goal of the work has been to advance understanding of the mechanisms of formation, trapping and reaction of these intermediates. Optical and E.S.R. spectrometry, electrical conductivity and differential thermal analysis have been the techniques of analysis. The work has included selective wavelength bleaching of the I.R. spectra of trapped electrons in organic glasses: investigation of electron capture by free radicals and subsequent photodetachment from the carbanions; and determination of the heats of reaction of trapped electrons, ions and radicals when the glass is photobleached or warmed to permit diffusion. The effects of γ dose on the yield of trapped electrons, and of light intensity on the photobleaching of the e t − are considered. The data on electrons are discussed with respect to the evidence which they give on the electron trapping mechanism, the variety of trap depths, electron tunneling and multiple retrapping without neutralization. Evidence is given on the fraction the radicals produced by γ-irradiation of a hydrocarbon glass which decay by random diffusive encounters as compared to intraspur reaction. CH 3 radicals produced from methyl halides in 3-methylpentane glass by dissociative electron capture are shown to decay by abstraction of H from the C 6H 14 molecules, whereas in C 6D 14 the decay is attributable to geminate recombination (CH 3+I −→ CH 3I −). An example is given of the use of radical decay kinetics in hydrocarbon glasses to determine diffusion coefficients of small molecules which can react with the radicals. Hydrogen atoms are shown to be absent in the radiolysis of glassy hydrocarbons. These and related observations are discussed with respect to the information they give on the properties of the intermediates and on the total radiolytic process in the glasses.