E.s.r. of γ-irradiated single crystals of ice at 77°K. Identification of the hydroxyl radical and its trapping site

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Abstract
The e.s.r. spectra of γ-irradiated single crystals of ice and heavy ice at 77°K have been studied. Analysis shows the complex spectrum to be consistent with OH or OD radicals trapped at 24 sites which differ in orientation but are otherwise indistinguishable. It is suggested that the radical is in a relaxed substitutional site roughly parallel to any one of the perpendicular bisectors of the faces of the two non-equivalent tetrahedra formed by the oxygen atoms in the crystal lattice. The experimentally derived tensors: [graphic omitted] are consistent with theory for OH radicals in the proposed trapping site. Annealing studies show the radicals to disappear according to first-order kinetics; this finding is discussed in terms of the proposal for a substitutional radical site.