A THEORETICAL-STUDY OF THE VIBRATIONAL-EXCITATION OF NO AG(111)/

We present a model study of the vibrational excitation of NO molecules scattering from a Ag(111) surface using time-dependent wave packet me thods. The molecule-surface interaction is described by a two-dimensio nal potential energy surface in the vibrational and center-of-mass coo rdinates. Surface motion is modeled by a single atomic oscillator This model reproduces the experimentally observed increase in the vibratio nal excitation as a function of both increasing initial translational energy of the molecule and surface temperature. The surface temperatur e only enters via the Boltzmann weighting of initial surface vibration al states. We simplify the simulation to a two-dimensional surface-mas s model, where the gas-surface interaction is analogous to a classical ''cube'' model. It is shown that the relative velocity of the incomin g molecule, with respect to the surface, causes the observed dependenc e of the vibrational excitation on surface temperature. The savings in computational time achieved with this model allows a study of the eff ect of the potential topology and surface mass on the temperature depe ndence of the vibrational excitation.