A MODEL CALCULATION FOR PHOTO-STIMULATED DESORPTION

A model calculation is presented for photo-stimulated desorption of ad sorbates from a metal surface. In the model, the electron system of th e material is described by a two-band tight-binding Hamiltonian. Inter band electronic excitation is induced by laser pulse irradiation and c auses a change in adsorbate trajectory. Close investigations are made of the dependence of the adsorbate trajectory on the photon energy and the time-width of laser pulse within one-photon process. For that pur pose, an effective excited-state potential for adsorbate motion is int roduced tentatively When the electronic excitation is spatially locali zed in the neighborhood of the surface, substantial deviation of shape from the ground state potential can be seen in the effective excited- state potential, and gives rise to adsorbate desorption. It can be exp ected from the obtained results that the desorption probability increa ses as the photon energy is increased and as the time-width of laser p ulse is decreased.