Effect of the projected band gap on the formation of negative ions in grazing collisions from Cu surfaces

The formation of negative ions (H-, O-, S-, F-, Cl-) is studied for grazing scattering of fast ions from Cu(110) and Cu(111) surfaces. In a detailed e xperimental and theoretical investigation we reveal that the projected L-ba nd gap of the Cu metal affects charge transfer in a specific manner. From t he analysis of the negative ion fractions as functions of projectile veloci ty we conclude that, for the Cu(111) surface the electronic 2D surface stat e continuum plays an essential role in the projectile-surface electron tran sfer.