Isotope Effects in Eley-Rideal and Hot-Atom Abstraction Dynamics of Hydrogen from Tungsten (100) and (110) Surfaces

The influence of isotopic substitutions on the recombination dynamics of molecular hydrogen under normal incidence scattering of hydrogen isotopes on H(D,T)-precovered W(100) and W(110) surfaces is investigated. Quasiclassical trajectory simulations on density functional theory based potential energy surfaces are first performed within the single adsorbate limit, thus focusing on the Eley-Rideal abstraction. Significant isotope effects show up regardless of surface symmetry. Homonuclear recombinations (H-on-H, D-on-D, and T-on-T) lead to very similar cross sections, whereas for heteronudear processes (H-on-D, D-on-H, ...), cross sections are ordered by the mass ratio between the impinging atom and the adsorbate. The diatom energy partitioning is also affected by isotopic substitution. Similar effects, though less pronounced, appear for hot-atom abstraction on W(110) at theta = 0.25 ML surface coverage.