Paramagnetic Relaxation of Trapped Hydrogen Atoms in Irradiated Frozen Aqueous Solutions

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Abstract
The paramagnetic relaxation characteristics of trapped hydrogen atoms in γ‐irradiated acidic and oxyanion ices were studied by power‐saturation techniques. Relaxation times were measured as a function of radiation dose, deuteration, phase, and solute. The EPR linewidth of the trapped hydrogen atom was measured under various conditions. The EPR lineshape and power‐saturation response indicate that the linewidth is due to contributions from both homogeneous and inhomogeneous interactions. The changes in relaxation time with radiation dose indicate that hydrogen atoms are trapped with a uniform distribution near oxyanions in the ice and are not trapped within radiation‐produced spurs. The presence of phase effects on relaxation times supports an interstitial‐defect model for the hydrogen‐atom trapping site and suggests that the trap potential energy well is shallower in the polycrystalline phase than in the glassy phase. In polycrystalline ices the coupling between trapped hydrogen atoms and lattice phonons is modified by the type of oxyanion.