THE DYNAMICAL ORIGIN OF NONNORMAL 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 plati num surfaces were performed to examine the origin of non-normal energy scaling for molecular adsorption. Conversion of normal to parallel tr anslational energy at normal incidence and conversion of parallel tran slational energy into normal translational energy at glancing angles a re the primary mechanisms which produce non-normal energy scaling of a lkanes trapping on cold Pt(lll). In addition, a tendency to convert ro tational energy gained in the first gas-surface collision into normal translational energy for collisions at glancing incidence further incr eases the degree of non-normal energy scaling. Increasing surface temp erature is shown to have little effect on energy transfer processes in the first bounce but increasing influence on subsequent bounces. Desp ite difficulties in defining trapping at high surface temperatures, si mulations indicate that the initial trapping probability of ethane on Pt(lll) does not fall by more than a factor of two over the surface te mperature range of 100-700 K. (C) 1997 Elsevier Science B.V.