CHAOTIC DYNAMICS IN THE PREDESORPTION OF CO MOLECULES FROM THE NACL(100) SURFACE

In this paper the rotational predesorption of a CO molecule from the N aCl(100) surface at very low substrate temperature is studied by using methods of classical Hamiltonian dynamics. The system is described by a two-dimensional model in which the relevant degrees of freedom are the non-linearly coupled molecule-surface distance and the polar angle between the molecular axis and the normal to the surface. By studying the properties of the chaotic trajectories in the Poincare sections o f the phase space of the system, spanned by the molecule-surface bond coordinates, one is able to calculate: (i) the desorption rates; and ( ii) the asymptotic momentum and energy distributions and the time-of-f light spectra. In particular the latter, depending on the initial cond itions, display different maxima which are related to the properties o f the multi-dimensional molecule-surface potential. (C) 1997 Elsevier Science B.V.