Abstract
Ultraviolet radiation absorbed by radicals trapped in γ-irradiated 3-methylpentane (3MP), 3-ethylpentane (3EP), and 3-methylheptane (3MHp) glasses and in polycrystalline n-hexane at 77 K causes a major improvement in resolution of the ESR spectra without change in the radical concentration, indicating that the energy of the absorbed photons changes the nature, the configuration, or the environment of the radicals. The new spectral shape slowly reverts to the old in the dark at a rate which is dependent on the matrix and the temperature. Ultraviolet irradiation also accelerates the decay of paired radicals and other radicals which are removed by intraspur processes, but not of those which react by random encounter after diffusion. This effect is attributed to localized heating of the matrix in the immediate vicinity of a radical which has absorbed a photon. Secondary 3-ethylpentyl radicals in glassy 3EP undergo spontaneous conversion to an isomer or change to a new rotamer configuration in the dark and the process is reversed by exposure to uv light. The ΔMs=2 ESR spectrum of radical pairs in γ-irradiated 3MHp has been observed.
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