Inelastic Collision Processes of Methane and Ethane Molecules at a Pt(111) Surface Studied by Molecular Beam Scattering Techniques

Despite distinct differences in molecular structures and chemical bonds of various alkanes, the inelastic collision processes of CH 4 and C 2 H 6 on a Pt(111) surface have been found to be very similar. Both processes can be explained qualitatively by a simple classical binary collision model. Angular intensity distributions of reflected molecules of both species indicate that direct inelastic collision is primarily governed by the molecular mass, the incident kinetic energy of the molecule and the surface temperature of the Pt(111). Other factors such as the molecular structure and chemical bond play minor roles in the process. However, the degree of inelastic collision, that is, the energy transfer rate per collision, increases with the molecular mass. Helium atom scattering has revealed that the dissociation process on the surface is identical for both molecules depending on the incident energy and the surface temperature, as methyl moiety, ethylidyne moiety and complete decomposition into carbon and hydrogen atoms, successively. At elevated surface temperatures, however, thermally assisted hydrogen tunneling appears to dominate ethane dissociation.