ELECTRON AND PHOTON-STIMULATED DESORPTION FROM PHYSISORBED CO FILMS

We have investigated photon stimulated desorption (PSD) and electron stimulated desorption (ESD) from CO films physisorbed on graphite and Pt(111) at monolayer coverages, with photon and electron energies in the range 13-35 and 0-70 eV, respectively. The C+ ion yields in PSD from the two substrates show remarkable similarities. Therefore, we conclude that the CO dissociation proceeds mainly via direct molecular excitation processes. In ESD from CO/graphite the energy dependences of the C-, O-, C+ and O+ signals exhibit a variety of distinct thresholds and enable us to identify the desorption processes involved. A comparison of the PSD and ESD results provides further evidence for the direct nature of the desorption process in this model system.