Time evolution of the rate constant for the tunneling reaction H2 + D → H + HD in solid D2H2 mixtures at very low temperature Original Research Article

The time dependence of the numbers of H and D atoms, produced by γ-radiolysis of a D2H2 (1 mol%) mixture, was measured upon storage of the sample at 4.5 K by ESR. The concentration of D atoms gradually decreases for up to 190 min, while that of H atoms increases in 10 min and then approaches a plateau value. The results were interpreted in terms of competition between the tunneling reaction H2 + D → H + HD with combination reactions of D and H atoms. The results cannot be explained by a single rate constant for the tunneling reaction used in homogeneous kinetics but by time evolution of the rate constant.