Phonon sudden theory of Debye–Waller attenuation. Temperature dependence of rotational energy transfer in molecule/surface scattering

Abstract

A model for the description of thermal attenuation in atom, molecule/surface scattering is presented. It is based on the energy sudden approximation for all degrees of freedom, i.e., phonons, diffraction, and rotation, and leads to a generalized Debye–Waller factor that depends on the rotational transition and is valid for arbitrary interaction potentials. The traditional Debye–Waller factor is recovered for a hard potential. Assuming a Debye frequency spectrum for the phonons we present two model calculations for molecule/surface scattering. In the first case we assume a pairwise interaction between the atoms of the molecule and the surface atoms and observe a temperature dependence of the rotational transition probabilities, which is due to both the rotational energy transfer and the rotational dependence of the Debye–Waller factor. In the second case we model NO/Ag(111) scattering and conclude that a variation of the surface temperature has only a slight influence on the final rotational state distribution which is in accordance with the experimental findings of Auerbach et al. The mean rotational energy transfer shows a slight linear increase with the temperature as recently observed by Kubiak et al.