COLLISION-INDUCED DESORPTION AND DISSOCIATION OF O-2 ON PT(111)

We have studied desorption and dissociation of O-2 on Pt(111) induced by incident energetic Xe atoms. The collision induced (CI) desorption rate was measured directly with a quadrupole mass spectrometer whereas the CI dissociation was investigated indirectly in post-Xe exposure T PD. We report the kinetics together with the energy, coverage, Xe inci dence angle, and surface temperature dependences of the two processes; The cross sections for the two CI processes are determined via kineti c modeling, based on observed first-order CI desorption kinetics. Ther e is a threshold in Xe kinetic energy at about 1.1 eV, common for both CI desorption and dissociation at normal Xe incidence. The Xe energy dependence of the cross sections for the two processes are well descri bed by sigma(des) = 2.46.(E-Xe - 1.1) (Angstrom(2)) and sigma(diss) = 0.75.(E-Xe - 1.1) (Angstrom(2)), respectively, above the threshold at normal Xe incidence. A scenario where the O-2-Pt bond is mechanically excited by an incident Xe atom, and where energy is transferred to the intramolecular bond via electronic coupling is presented. Implication s of the results for the O-2/Pt(111) PES are also considered. (C) 1998 American Institute of Physics.