Low-energy H+, He+, N+, O+, and Ne+ scattering from metal and ionic-compound surfaces: Neutralization and electronic excitation.

Abstract

Neutralization and electronic excitation during low-energy ion-surface scattering have been investigated from a combination of experiments and molecular-orbital energy calculations based on the discrete variational X\ensuremath{\alpha} method. It is found that a variety of electronic transitions are mediated by the molecular orbitals during the violent collision or the short-lived chemisorption state of the ions, which may not be inferred from the atomic orbitals of the isolated projectiles. The rare-gas ions, such as ${\mathrm{He}}^{+}$ and ${\mathrm{Ne}}^{+}$, capture a valence electron mainly via the Auger neutralization process, whereas resonant tunneling can also play an important role in neutralization of the reactive ions (${\mathrm{H}}^{+}$, ${\mathrm{N}}^{+}$, ${\mathrm{O}}^{+}$). The occurrence of resonant tunneling is related to the open-shell structure of the reactive ions. The probability for resonance neutralization is sensitively dependent upon the nature of the valence band (band effect) and is largely enhanced at the metal surface relative to the ionic-compound surface. The valence-band electron can be excited in scattering of reactive ions as a sequence of neutralization/ionization along the promoted antibonding molecular orbital. In scattering of the rare-gas ions, not only the valence electron but also the semicore electron can be excited for specific ion-target combinations in which sufficient promotion of the antibonding molecular orbital can take place during collision.