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 studied over length scales between 3 and 14 Å by quasielastic helium atom scattering. Data taken over a wide range of parallel wave vectors (0.3 Å−1⩽|ΔK|⩽3.1 Å−1) in the surface temperature range 140 K⩽Ts⩽250 K and at coverages 0.05 ML⩽ΘH⩽0.66 ML, provide evidence for an isotropic single jump mechanism with an activation energy of 68±5 meV and a pre-exponential factor of D0=1.1±0.5×10−3 cm2 s−1 at low coverages. The diffusion coefficient is 2 to 3 orders of magnitude higher than found in an earlier laser induced desorption experiment, whereas the dependence on coverage is similar.