The prediction of trapping probabilities for ethane by molecular dynamics simulations: scaling from Pt(1 1 1) to Pd(1 1 1)

The dynamics of ethane trapping on Pd(1 1 1) 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, ET, from 10 to 34 kJ/mol and incident angles, θ, from 0° to 45° at a surface temperature of 95 K. The trapping probability scales with ETcos0.9θ, indicating a corrugated gas–surface potential. Stochastic trajectory simulations utilizing a Morse potential whose parameters were obtained experimentally from ethane trapping on Pt(1 1 1) [J. Chem. Phys. 104 (1996) 3134] predict the corresponding experimental values of the initial trapping probability of ethane trapping on Pd(1 1 1) to within 30%. Calculations of energy transfer for ethane after the first bounce on Pd(1 1 1) clearly indicate that vibrational excitation of the lattice phonons account primarily for the increase in trapping probabilities of ethane on Pd(1 1 1) compared with Pt(1 1 1). The enhancement in phonon excitation results from increasing the mass ratio of ethane to the metal atoms.