ASYMPTOTIC ENERGY-DISTRIBUTIONS IN ROTATIONAL AND VIBRATIONAL PREDESORPTION

The predesorption processes of CO and CH3F molecules from the NaCl(100 ) surface at very low coverage and substrate temperature are described by classical models with two non-linearly coupled degrees of freedom. The analysis of the phase space structure of these systems from the P oincare sections spanned by the canonical coordinates of the molecule- surface bond allows one to calculate the desorption rates and the asym ptotic energy distributions of the desorbed molecules. It is shown tha t these quantities clearly reflect the presence of dynamical barriers in the phase space induced by the chaotic behaviour of the desorbing t rajectories.