A microscopic theory of desorption induced by electronic transitions

Abstract

Desorption induced by electronic transitions (DIET) in two cases is investigated from a microscopic point of view. In case A, where a single electron in a state of the localized kind (localized around adsorbates) is excited into a state of the extended kind (extended into the bosom of the substrate), the shape of the excited-state potential-energy surface (PES) may differ markedly from that of the ground-state PES for adsorbate motion. The Franck-Condon factor then takes a finite value, giving rise to a finite desorption probability. In case B, where a single electron in a state of the extended kind is excited into another state of the extended kind, the shape of the excited-state PES is practically the same as that of the ground-state PES. The Frank-Condon factor is then zero. In such a case, one should take DIET as a single-step (coherent) process and take into account the adsorbate-position dependence of the matrix element for state transitions of the electron system in order to obtain a finite desorption probability.