Desorption induced by electronic transitions. Some recent progress

In analogy to electron impact or photon-induced dissociation of molecules, electronic excitation of adsorbate complexes leads to desorption of ions and neutrals. Both processes require a primary excitation to a repulsive potential curve, by which conversion of electronic excitation to nuclear motion can occur. However, in the surface case strong competition with the desorptive process occurs by transfer of the excitation away from its primary location, because of strong coupling to the many modes of surface layer and substrate; this leads to very strong dependence of cross sections on bonding mode, excitation energy, isotope mass, and coverage. Recently, considerable progress has been made in the understanding of primary, secondary, and tertiary processes by detailed investigations of energy and polarization dependencies of cross sections, and of angle and energy distributions of products, for primary valence as well as core excitations, and for neutral and ionic products. The importance of localization of the excitation and its dependence on many-body interactions becomes obvious. These aspects are reviewed, and some applications sketched.