The prediction of trapping probabilities for ethane by molecular dynamics simulations: scaling from Pt(111) to Pd(111)

The dynamics of ethane trapping on Pd(111) were investigated by supersonic molecular beam techniques and three-dimensional stochastic trajectory simulations. The initial trapping probability was measured over the range of incident energy, E-T, from 10 to 34 kJ/mol and incident angles, theta, from 0 degreesto 45degrees at a surface temperature of 95 K. The trapping probability scales with E(T)cos(0.9)theta, indicating a corrugated gas-surface potential. Stochastic trajectory simulations utilizing a Morse potential whose parameters were obtained experimentally from ethane trapping on Pt(111) [J. Chem. Phys. 104 (1996) 3134] predict the corresponding experimental values of the initial trapping probability of ethane trapping on Pd(111) to within 30%. Calculations of energy transfer for ethane after the first bounce on Pd(111) clearly indicate that vibrational excitation of the lattice phonons account primarily for the increase in trapping probabilities of ethane on Pd(111) compared with Pt(111). The enhancement in phonon excitation results from increasing the mass ratio of ethane to the metal atoms. (C) 2001 Elsevier Science B.V. All rights reserved.