Dynamics of Resonant Electron Transfer in the Interaction Between an Atom and a Metallic Surface

Abstract

Resonant Charge Transfer (RCT) between an atom and a metal surface corresponds to a one-electron energy-conserving transition between a discrete atomic level and the continuum of metallic states. In a static system (fixed atom-surface distance), RCT can be efficiently described by attributing a width, inverse of a finite lifetime, to the atomic level. The RCT rate is then given by the atomic level width. The use of the same description, based on an adiabatic approximation, is not always valid in a collisional context, when the atom moves with respect to the surface. We review some recent results obtained on this problem using a wave-packet propagation approach to describe the dynamics of RCT. The nonadiabatic character of RCT is illustrated on three different situations. (1) For a free-electron metal surface, the adiabatic approximation is found to hold. (2) For more realistic metal surface descriptions, the presence of a projected band gap is found to deeply influence the static RCT. However, significant non-adiabatic transitions can appear even at moderate velocities, which wash out the effect of the metal electronic band structure. (3) In the case of metal surfaces partly covered with adsorbates, the possibility of electronic transitions between three objects (the atom, the adsorbate, and the substrate) deeply affects the RCT, leading to various dynamical behaviors, very different from the predictions of the adiabatic approximation.