Quasielastic helium atom scattering measurements of microscopic diffusional dynamics of H and D on the Pt(111) surface

The microscopic diffusional dynamics of H and D on Pt(111) have been studie d over length scales between 3 and 14 Angstrom by quasielastic helium atom scattering. Data taken over a wide range of parallel wave vectors (0.3 A(-1 )less than or equal to\Delta K\less than or equal to 3.1 Angstrom(-1)) in t he surface temperature range 140 K less than or equal to T(s)less than or e qual to 250 K and at coverages 0.05 ML less than or equal to Theta(H)less t han or equal to 0.66 ML, provide evidence for an isotropic single jump mech anism with an activation energy of 68+/-5 meV and a pre-exponential factor of D-0=1.1+/-0.5x10(-3) cm(2) s(-1) at low coverages. The diffusion coeffic ient is 2 to 3 orders of magnitude higher than found in an earlier laser in duced desorption experiment, whereas the dependence on coverage is similar. (C) 1999 American Institute of Physics. [S0021-9606(99)70325-9].