The interaction of He ϩ with a typical metal surface ͑Al or Pd͒ is described, analyzing in detail the different mechanisms that contribute to the neutralization of the projectile when backscattered from the surface. Auger and resonant neutralization processes are considered and analyzed including a detailed quantum-mechanical description of the He-metal interaction, for projectile energies between 100 eV and 3 keV. We show that the promotion of the He-1s level, due to its interaction with the metal-atom-core orbitals, is the crucial mechanism making resonant processes operative. We find, however, that resonant processes are much more important for Al than for Pd. In Al, both Auger and resonant processes are equally important for neutralization of the ion, while for Pd we find that Auger is the dominant mechanism, making the He/Pd system the ideal case for which Hagstrum's exponential law appears to be practically valid for all velocities. We also find qualitative agreement with experimental data, which we consider a satisfactory result in view of the fact that our theory is a complex ab initio calculation free of adjustable parameters.

A bond-pair model Hamiltonian developed previously for systems consisting of interacting atoms is applied to describe atom-surface interactions. By proposing a mixed basis set involving localized adatom orbitals ͕ ␣ ͖ and extended surface states ͕ k ͖, and by application of a mean-field approximation, the Hamiltonian is reduced to the form of the single-particle Anderson model. The resulting model Hamiltonian is free from adjustable parameters. These parameters include both the effects of electronic interactions between the atom and the solid and those arising from the lack of orthogonality between the adsorbate and substrate orbitals. The nonlocal exchange contributions are treated consistently within the Hartree-Fock method, while valencelike and corelike band states are also taken into account. This model is applied to consider the interaction of hydrogen with metals ͑Al, Li, and Na͒. The results for chemisorption are in good agreement with those obtained by other theoretical approaches based on either the density functional theory or embedding cluster methods, as well as with existing experimental data. In addition, the calculation of the shifts and widths of the adsorbate levels in an ample range of separation distances are also in good agreement with those obtained by using atomic physics techniques. ͓S0163-1829͑98͒10031-0͔

We develop a theory of the Auger neutralization rate of ions on solid surfaces in which the matrix elements for the transition are calculated by means of a linear combination of atomic orbitals technique. We apply the theory to the calculation of the Auger rate of He + on unreconstructed Al͑111͒, ͑100͒, and ͑110͒ surfaces, assuming He + to approach these surfaces on high symmetry positions and compare them with the results of the jellium model. Although there are substantial differences between the Auger rates calculated with both kinds of approaches, those differences tend to compensate when evaluating the integral along the ion trajectory and, consequently, are of minor influence in some physical magnitudes like the ion survival probability for perpendicular energies larger than 100 eV. We find that many atoms contribute to the Auger process and small effects of lateral corrugation are registered.