ELECTRON AND PHOTON-STIMULATED DESORPTION FROM PHYSISORBED CO FILMS

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