Mechanisms of collision-induced desorption of a physisorbed atom at superthermal energy: a multiple scattering study

Abstract

A Faddeev-Watson multiple scattering approach to gas-surface collision-induced desorption is presented. The computational procedure is practical, yet allowing a fully quantum-mechanical treatment of gas-solid reactive scattering problems. The single plus double collision terms of the multiple collision series are included in the calculation, which provides a detailed description of the collision dynamics. The present study focuses on a simple model collision system: a heavy adsorbate on a rigid surface is ejected by a sufficiently energetic light projectile. Large differential cross sections are found when the amount of kinetic energy transferred from the projectile to the adsorbate coincides with that of a classical head-on elastic collision between two particles of the corresponding masses. In addition, when this energy transfer is a little over the binding energy of the bound state, double collisions analogous to classical off-center collisions, contribute significantly to the differential cross sections. Our results also show that qualitatively the differential cross sections reach their maxima when the incident energy is about twice the binding energy of the adsorbate, then stay approximately the same when the incident energy increases even further. In this work, the role of the form factor, which is the bound state wavefunction in momentum space, is investigated. It is found that the angular distributions of the scattered projectile and the ejected absorbate are very sensitive to the adsorbate form factor. Finally, a detailed comparison among the contributions to the differential cross sections from each of the multiple collision terms provides information about the relative importance of various collision-induced desorption mechanisms.