Surface microstructure effects: Molecular ethane adsorption dynamics on Pt(110)-(1x2)

The molecular adsorption probability of ethane on clean Pt(110)-(1 x 2) at a surface temperature of 95 K was measured as a function of incident translational energy, E(T), incident polar angle, theta(i), and azimuthal angle, phi. At normal incidence the adsorption probability decreases with incident translational energy from near unity at an incident kinetic energy of 10 kJ/mol to 0.5 at 40 kJ/mol. For molecules incident with the tangential velocity component directed along the [1(1) over bar0$] (smooth) direction, the initial adsorption probability increases with increasing theta(i), scaling with E(T) cos(0.6)theta(i); however, the adsorption probability decreases with theta(i) for molecular beams directed along the [100] (rough) direction, indicating the effects of corrugation. Stochastic trajectory simulations employing ethane-Pt Morse potential parameters previously developed from measurements of the adsorption probabilities of ethane on Pt(111) give quantitative predictions of the initial trapping probability of ethane on Pt(110)-(1 x 2) for both azimuthal angles at all energies and polar angles of incidence. The simulations suggest that interconversion of normal and parallel momenta due to the surface corrugation governs the adsorption process and serves as an effective mechanism which facilitates trapping. Excessive parallel momentum, however, can cause ethane to scatter on subsequent bounces because of the reconversion of large amounts of parallel energy into normal energy. Analysis of a large number of trajectories illustrated that collisions on the ridges of Pt(110)-(1 x 2) mitigate against trapping of ethane while collisions within the troughs facilitate trapping. Finally, the simulations show that the trapping probability is determined to within 12% by the fate of the first bounce.