Vibrationally excited products after the photodesorption of NO from Pt(111): a two-mode open-system density matrix approach

The experimentally observed vibrational excitation of NO molecules photodesorbing from a Pt(111) surface is investigated numerically with the help of open-system density matrix theory. We extend Gadzukʹs jumping wave packet model to treat DIET processes (desorption induced by electronic transitions, single-excitation limit) which is equivalent to a one-channel open system Liouville-von Neumann equation with coordinate-independent quenching, to cases when the electronic relaxation becomes coordinate-dependent. This allows for a more realistic but still economic and, hence, systematic study of DIET within a two-state, two-degrees of freedom model. Adopting “reasonable” Antoniewicz-type model potentials, we find that the experimental observations can semi-quantitatively be rationalized if an electronic quenching rate decreasing with increasing NO separation, is assumed. Preliminary two-mode DIMET simulations (desorption induced by multiple electronic transitions, multiple-excitation limit) within a stochastic wave packet approach are also presented.