O- FORMATION IN GRAZING SCATTERING FROM AN AL(111) SURFACE

We report on the results of a joint experimental and theoretical study on the formation of O- ions in grazing scattering from an Al(111) sur face. The O- fractions in the scattered beam are studied over a wide r ange of collision energies. This allows us to observe a resonance stru cture for the O- formation probability as a function of the collision velocity component parallel to the surface (V-parallel to). Such a cha racteristic V-parallel to dependence is the signature of a kinematical ly induced charge-transfer process between the O- ion and the Al surfa ce. The theoretical treatment of charge transfer is based on the coupl ed angular mode method. The multistate aspect of the problem originati ng from the open-shell structure of the O- ion is taken into account.