Electron capture and loss in the scattering of oxygen atoms and ions on Mg, Al and Ag surfaces

We present the results of a study of collisions of 1 to 4 keV oxygen ions and atoms with Mg, Al and Ag surfaces. Formation of O- is in particular investigated. This is an interesting multichannel problem, since the ground state electronic configuration of oxygen 2p(4) corresponds to three states and electron capture processes involve three atom (P-3, D-1 and S-1)-metal continua. We report scattered ion fractions, measured in an angular range extending from 2 degrees to 40 degrees with respect to the surface plane. This allowed us to investigate the characteristics of the resonant charge transfer process for a large range of collision velocities normal to the surface, thus probing the charge transfer process in different atom-surface distance ranges. The ion fractions are found to increase with increasing angle and increasing energy. Similar fractions are obtained for Al and Ag, but significantly higher ones for Mg. Ionisation processes in hard collisions with surface atoms are observed. An electron spectroscopy study was performed and did not reveal any signs of autoionising state (O**2p(2)3s(2)) production.