Theoretical studies of charge transfer in molecular ion-metal surface collisions

The collision of a molecular ion with a metal surface involves charge trans fer. The effects of charge transfer can be readily seen in the increase of dissociation of ionized molecules as compared to neutral molecule dissociat ion, and to detectable electron emission. In the present work we present th e results of a theoretical study of electron emission during the collision of hydrogen and nitrogen with an Al surface. In both cases the dominant ele ctron emission process for slow ions is the de-excitation of the H-2(+) and N-2(+) molecules formed by resonance neutralization of the molecular ion i n front of an Al surface. The de-excitation process is enhanced by the form ation of a negative ion, which corresponds to the free-molecule shape reson ances (2)Sigma(u)(+) and (2)Pi(g) for H-2 and N-2, respectively. The energy spectra of the emitted electrons are much broadened, making it difficult t o recognize the signature of a transient negative ion in the energy spectra of ejected electrons. Finally, the ubiquitous presence of negative ions in molecule-surface scattering is emphasized. (C) 1999 Elsevier Science B.V. All rights reserved.