Ar scattering on Ru (0001): A comparison to the washboard model

The scattering of Ar atoms on a Ru (0001)surface has been studied by applying supersonic molecular beam techniques. Variation of the incidence energy (E _i)results in a rich variety of angular and energy distributions. At a low energy,clear zero-order di.raction has been identifed. At higher energies (> 1 eV), argon scattering of Ru (0001), however,seems to be dominated by a totally different mechanism, which appears to be almost quantitatively reproduced by the washboard model, developed by Tully (J.C.Tully, J. Chem. Phys., 1990,92, 680, ref.1).This is surprising since his comparison of the washboard model to a reference of classical trajectory calculations for the Ar/Pt (111) system showed essential deviations. Our attempt to reproduce the experimental Ar/Ru (0001)data by similar simulations was unsuccessful, most likely due to shortcomings in the description of the solid state.