Wave-packet study of hyperthermal alkali ion neutralization at metal surfaces

Resonant neutralization of 50 eV Na+ ions impinging on Cu(100) surfaces is studied, focusing on events where the incident particle undergoes multiple collisions within the first surface layers of the samples. Specific trajectories are generated, via molecular dynamics simulations, in which the projectile comes out interacting, on long time scales, either with a single surface atom or with the valence band of the solid. The resulting three-body problem is modelled by a semi-empirical, one-electron potential that incorporates: (i) the effect of a plane metal surface, with projected band gap, and (ii) the contributions of the projectile, whose charge state will be eventually investigated, as well as of the substrate atom. On this basis, a wave-packet propagation algorithm is constructed to establish the reverse evolution of the affinity orbital of the projectile. The calculated neutralization probability is compared with the results of a model Hamiltonian of the Anderson-Newns type (Nucl Instr Meth 2009;B267:578) and is found in good agreement with the angle resolved neutral fraction measured by Keller et al. (Phys Rev Lett 1995;75:1654).