The Radiolysis of Water Vapor and a Surface-Catalyzed Isotope-Exchange Reaction

Article abstract of DOI:10.1021/ja00407a033

The steady-state radiolysis of deuterium oxide vapor has been examined using protium, perprotiopropane, or mixtures of these two as free-radical scavengers.Tritiated water was used as an internal radiation source, and glass irradiation vessels were imployed.D atoms are produced in the radiolytic decomposition of D2O, and HD is formed by reaction of this species with the added radical scavengers.It was assumed previously that the yield of HD molecules could be equated with the yield of radiolytically produced D atoms.However, the experimental results of the present investigation demonstrate conclusively that when H2 is used as a radical scavenger there are two pathways for HD formation: (1) homogeneous scavenging of the radiolytically produced D atoms by H2, as expected, and (2) heterogeneous combination of H atoms produced in the scavenging reaction (D + H2 -> HD + H) with D atoms adsorbed on the vessel surface, where the adsorbed D atoms are generated by a surface-catalyzed isotope-exchange reaction between H atoms adsorbed from the volume and D2O.From the results of this investigation, it appears that the yield of D atoms produced in the radiolysis of D2O is G_D = 7.0 atoms/100 eV absorbed energy, i.e., the G(HD) found in experiments using propane as the radical scavenger.G_D2 is shown to be 0.65 molecules/100 eV.