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

Abstract

The collision of a molecular ion with a metal surface involves charge transfer. The effects of charge transfer can be readily seen in the increase of dissociation of ionized molecules as compared to neutral molecule dissociation, and to detectable electron emission. In the present work we present the results of a theoretical study of electron emission during the collision of hydrogen and nitrogen with an Al surface. In both cases the dominant electron 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 in front of an Al surface. The de-excitation process is enhanced by the formation of a negative ion, which corresponds to the free-molecule shape resonances 2Σ u + and 2Π g for H 2 and N 2 , respectively. The energy spectra of the emitted electrons are much broadened, making it difficult to 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.