SCATTERING OF HE AND NE ATOMS AND IONS ON A NA SURFACE

Results of measurements of angular distributions of neutrals and ions in low-keV Ne+ and Ne-0 collisions with a Na-covered surface are prese nted. These results are supplemented by time of flight measurements. M easurements of angle-resolved energy spectra of electrons are presente d for He+ and Ne+ collisions on Na. These results are compared with th ose obtained on other systems (Mg, Al and Si). Ion fraction measuremen ts show that the incident ionic projectiles are neutralized during the approach towards the surface, and then reionized due to inelastic pro cesses occurring during binary collisions with surface atoms. Our elec tron spectroscopy measurements show the existence of two-electron exci tation processes. These results compared with previous gas-phase resul ts indicate the involvement of similar primary excitation mechanisms. These are well described within a diatomic quasi-molecular model. Seve ral marked differences observed between the gas-phase measurements and our electron spectra are explained by surface specific mechanisms due to charge transfer between the projectile and the surface. (C) 1998 E lsevier Science B.V. All rights reserved.