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We report on electron-stimulated desorption (ESD) of O- ions from δ phase O2 physisorbed on graphite. A production of energetic O- ions is observed with an onset at about 13 eV. The measured onset of the yield of O+ ions is however found at about 20 eV. O- ions yields obtained at different ion kinetic energies and kinetic energy (KE) measurements lead us to postulate a substrate mediated ESD mechanism following direct electronic excitation of physisorbed O2.

We report a high-resolution electron-energy-loss study of the ${\mathit{X}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathit{a}}^{1}$${\mathrm{\ensuremath{\Delta}}}_{\mathit{g}}$ electronic excitation of ${\mathrm{O}}_{2}$ molecules physisorbed on Ag(110). Three resonances are observed to occur at incident electron energies of \ensuremath{\approxeq}6, 8.5, and 12 eV in the monolayer regime. These features shift to higher energies by about 1\char21{}1.5 eV with increasing coverage. The relative intensities of these peaks also change dramatically as a function of coverage. This allows us to explore the appearance of resonant states which are not seen in the gas-phase molecule, and which can be compared with similar features observed in electron-stimulated desorption studies of condensed ${\mathrm{O}}_{2}$. \textcopyright{} 1996 The American Physical Society.

We report an experimental and theoretical study of resonance electron scattering by physisorbed ${\mathrm{O}}_{2}$/Ag(110). The cross sections for molecular vibrational excitation, obtained from high-resolution electron-energy-loss spectra, reveal changes in both the energy and the lifetime of the \ensuremath{\sigma} shape resonance of the ${\mathrm{O}}_{2}$ molecule as the coverage is increased from the monolayer to the multilayer regime. With the aid of a layer--Korringa-Kohn-Rostoker calculation of the resonance parameters, which embodies a proper treatment of the unoccupied electronic band structure of the surface, we find that the shift in resonance energy can be attributed to the image potential of the surface, whereas the observed reduction in resonance lifetime in the monolayer is primarily due to the interaction between the molecular resonance state and the unoccupied electronic states of the surface.

This article gathers together a collection of recent experimental studies of the adsorption of oxygen on (001), (110) and (111) crystal surfaces of silver with special emphasis on the negative ion states of this model system for oxygen adsorption. These investigations were performed in a network entitled `Negative ion resonances of adsorbed molecules' supported financially by the European Union within the `Human capital and mobility programme'. The kinetics and thermodynamics of adsorption are investigated by measuring the sticking coefficient and by thermal desorption spectroscopy (TDS). The vibrational spectra provided by high-resolution electron energy loss spectroscopy (HREELS) are used to analyse the adsorbed species (physisorbed and chemisorbed) in the case of O2 on Ag(110) and on Ag(111). The mechanisms of inelastic electron scattering by adsorbed O2 are further investigated with special reference to the negative ion resonances (NIRs), formed by electron capture, which are involved in the electron-molecule collision process.