Time evolution of rate constant for tunneling reaction H2 + D → H + HD in solid D2-H2 mixtures at very low temperature

Time dependence of the amounts of H and D atoms, produced by γ-radiolysis of D2-H2 (1 mol%) mixture, was measured upon the storage of the sample at 4.5 K by ESR spectroscopy. The amount of D atoms gradually decreases up to 190 minutes, while that of H atoms increase in ten minutes and then become a plateau value. The results were interpreted in terms of competition of a tunneling reaction H2 + D → H + HD with combination reactions of D and H atoms. The results cannot be explained by a single value of a rate constant for the tunneling reaction used in homogeneous kinetics, but by time evolution of a rate constant. (author)