DYNAMICS OF EXCITED-STATE PRODUCTION IN THE SCATTERING OF INERT-GAS ATOMS AND IONS FROM MG AND AL SURFACES

We present results of a detailed study of the production of electronic ally excited states in the scattering of ionic or neutral inert gas pr ojectiles in the keV energy range at Al and Mg surfaces. The complemen tary observation of scattered particles (neutrals or ions), secondary electrons and photons leads to a rather complete description of the su ccessive stages of inelastic scattering events. Efficient neutralisati on of the incident ions occurs, when they approach the surface. This i s clearly demonstrated by the strong similarities between results obta ined for incoming ions and incoming ground-state neutrals. The charact eristics of the scattered particle distributions, the observation of s cattered ions, and also of some excited states by electron and photon spectroscopy, delineates the decisive importance of short-distance bin ary collisions with atoms of the surface, in the production of these s pecies. A detailed comparison with the ''inverse'' collisional systems in the gas phase shows that the same kind of primary excitations as d escribed in the quasi-molecular orbital promotion model are operative and allows, for example, predictions about which of projectile and/or target atoms can be excited. Some very strong differences to gas-phase collisions are also demonstrated. They stress the importance of surfa ce-specific effects, such as the role of resonant or Auger electron tr ansfers between the metal surface and the receding particle in definin g the final state population. In particular, an interesting surface-in duced core rearrangement effect is emphasised, and different rearrange ment mechanisms are presented and discussed.