The dynamical origin of non-normal energy scaling and the effect of surface temperature on the trapping of low molecular weight alkanes on Pt(111)

Molecular classical dynamical simulations of alkanes trapping on platinum surfaces were performed to examine the origin of non-normal energy scaling for molecular adsorption. Conversion of normal to parallel translational energy at normal incidence and conversion of parallel translational energy into normal translational energy at glancing angles are the primary mechanisms which produce non-normal energy scaling of alkanes trapping on cold Pt(lll). In addition, a tendency to convert rotational energy gained in the first gas-surface collision into normal translational energy for collisions at glancing incidence further increases the degree of non-normal energy scaling. Increasing surface temperature is shown to have little effect on energy transfer processes in the first bounce but increasing influence on subsequent bounces. Despite difficulties in defining trapping at high surface temperatures, simulations indicate that the initial trapping probability of ethane on Pt(lll) does not fall by more than a factor of two over the surface temperature range of 100-700 K. (C) 1997 Elsevier Science B.V.