Flash Desorption and Isotopic Mixing of Hydrogen and Deuterium Adsorbed on Tungsten, Iridium, and Rhodium

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Flash desorption of hydrogen from tungsten, iridium, and rhodium dosed at 100° and 300°K was investigated together with isotope mixing in coadsorbed mixtures of hydrogen and deuterium. The desorption of hydrogen from tungsten, iridium, and rhodium dosed at 300°K proceeds by a second-order process with an activation energy of desorption well represented by ΔH=ΔH0—αn. At low surface coverages, values of 35, 24, and 18 kcal/mole, respectively, were obtained for ΔH0; the parameter α was determined from desorption curves at higher initial coverages and was found to be 28±2, 14±1, and 24±2 kcal/mole (1015 molecules/cm2)−1, respectively. The desorption spectrum of hydrogen from these metals dosed at 100°K contains two peaks, α and β. The distribution of the isotopes in the desorbed phase formed from coadsorbing H2 and D2 indicates that the α peak is due to an atomic species in the case of iridium and rhodium and a molecular species in the case of tungsten.