Neutralization and electronic excitation during low-energy H and He scattering from LiF

Abstract

Low-energy H + and He + ions, together with their neutrals in the ground state, have been scattered from a polycrystalline LiF surface in order to investigate the mechanism of ion neutralization and electronic excitation. The surface peak of F obtained with He + incidence is composed of three subpeaks assignable to elastic scattering and inelastic scattering due to single and double electron-hole pair excitation. In the case of H + scattering, the surface peak of F consists only of the elastic peak, and a background due to multiple scattering from the deeper layers is remarkable. Almost the same H + spectrum without the surface peak is obtained for H 0 incidence. These results are analyzed on the basis of molecular-orbital energy calculations. It is found that the F 2p orbital has antibonding character with respect to the He 1s orbital during collision and, hence, one or two F 2p electrons can be excited preferentially. In the case of H + scattering from F −, on the other hand, the H 1s state appears in the band gap due to antibonding interaction with the F 2p orbital, leading to excitation of the H 1s electron rather than the F 2p valence electrons.