MODEL CALCULATION OF THE CHARGE-TRANSFER IN LOW-ENERGY HE+ SCATTERINGFROM METALLIC SURFACES

Charge-transfer mechanisms in low-energy helium-scattering spectroscop y are analyzed by using an Anderson-like description of the time-depen dent collisional process, which allows us to include several electroni c bands of extended and localized nature in the solid. The Hamiltonian parameters are obtained from a Hartree-Fock self-consistent-field cal culation of the He-target atom dimeric system. We examine in particula r cases such as Ca and Ga linear chain substrates. We found that at ve locities large enough, the localized state in the solid contributes to the He+ neutralization, showing the characteristic oscillatory behavi or of the nonadiabatic charge exchange between localized states, in ag reement with other calculations. In the range of low velocities we fou nd 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' promote s the charge exchange between the Helium and the extended bandstates o f the solid.