TIME EVOLUTION OF THE RATE-CONSTANT FOR THE TUNNELING REACTION H-2-]H+HD IN SOLID D-2-H-2 MIXTURES AT VERY-LOW TEMPERATURE(D)

The time dependence of the numbers of H and D atoms, produced by gamma -radiolysis of a D-2-H-2 (1 mol%) mixture, was measured upon storage o f the sample at 4.5 K by ESR. The concentration of D atoms gradually d ecreases 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 t erms of competition between the tunneling reaction H-2 + D --> H + HD with combination reactions of D and H atoms, The results cannot be exp lained by a single rate constant for the tunneling reaction used in ho mogeneous kinetics but by time evolution of the rate constant.