Velocity scaling of ion neutralization in low energy ion scattering

The ion fraction P+ is measured for He+ ions scattered by 129 degrees from a Cu surface. Both the primary energy and the angles of incidence and of exit are varied. From our results we conclude the following: along the incoming and outgoing trajectories, neutralization is due to Auger processes and depends on the normal velocity component v( perpendicular ) only. At higher energies, additional charge exchange is due to collision induced neutralization and reionization, both depending on the total ion energy only. Also in this regime P+ depends on v( perpendicular ), but via a two-valued function of the scattering geometry at fixed energy.