Luminescence Phenomena in Gamma-Irradiated Pure Alkanes at 77°K

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Abstract
Previous reports from this laboratory described the characteristic luminescence of γ-irradiated, pure 3-methylpentane glass and the influence of preirradiation standing time at 77°K on the luminescence intensity (annealing effect: decrease in intensity). In this paper it is shown: (a) that cracks in the annealed glasses are not necessarily required for the annealing effect to be observed, although they apparently accelerate the glass relaxation markedly, and (b) that the luminescence spectra of isopentane are different for the glassy and polycrystalline states. It is also shown, using a simple model, that the lowest charge-separated state can be stationary and lower in energy than the first excited state of the molecule; consequently, the charge-separated state can be the luminescent state for pure alkanes.