Model calculation of the charge transfer in low-energy He+ scattering from metallic surfaces

Charge-transfer mechanisms in low-energy helium-scattering spectroscopy are analyzed by using an Anderson-like description of the time-dependent collisional process, which allows us to include several electronic bands of extended and localized nature in the solid. The Hamiltonian parameters are obtained from a Hartree-Fock self-consistent-field calculation of the He-target atom dimeric system. We examine in particular cases such as Ca and Ga linear chain substrates. We found that at velocities large enough, the localized state in the solid contributes to the He+ neutralization, showing the characteristic oscillatory behavior of the nonadiabatic charge exchange between localized states, in agreement with other calculations. In the range of low velocities we found that if the hybridization between the He orbital and the localized states in the solid is able to produce the formation of an antibonding state having a predominant weight of the He-1s orbital, this promotes the charge exchange between the Helium and the extended bandstates of the solid