Stochastic simulations of the trapping of ethane on Pt(111) from a realistic potential: The roles of energy transfer processes and surface corrugation

Classical three dimensional stochastic trajectory simulations using an empirical pairwise additive Morse potential were employed to model the molecular adsorption of ethane on cold Pt(111). A single set of parameters was found which quantitatively represents the dependence of the initial adsorption probability on incident energy and angle and accurately reproduces scattering distributions of ethane from Pt(111). The simulations suggest that, on average, rotational excitation serves as an effective temporary energy storage mechanism which facilitates trapping. Excess rotational excitation into cartwheel motion, however, can cause ethane to scatter by a chattering collision. At moderate translational energies trapping is determined primarily by energy transfer from translational energy to cartwheel rotation and surface phonons for molecules incident along the surface normal, whereas cartwheel rotation combined with parallel translational energy retention determine trapping at glancing angles of incidence. As the incident translational energy is increased, trapping becomes more dependent on the excitation of cartwheel rotational excitation at normal incidence. Finally, the trapping probability of ethane on Pt(111) was found to be determined to within 10% by the fate of the first bounce. (C) 1996 American Institute of Physics.