Resonant charge transfer in ion–metal surface collisions: Effect of a projected band gap in the H^--Cu(111) system

A wave-packet propagation method is applied to the treatment of the resonant charge transfer (RCT) process in the interaction between an H^- ion and a Cu(111) surface. Using a model description of the Cu(111) electronic structure, it is shown that the RCT efficiency is deeply influenced by the presence of the Cu(111) projected band gap, that partially blocks the electron transfer in the direction normal to the surface. The differences between the RCT process on a free electron metal surface and on a Cu(111) surface are discussed. The two cases are associated with very different pictures of the electron transfer. In particular, the importance of the Cu(111) surface state for the decay of the H^- ion is demonstrated. The effect of the band gap is also shown to strongly depend on the interaction time. For short interaction times (large collision velocities), the electron wave packet does not have enough time to probe the metal band structure and the RCT on a Cu(111) surface is very similar to that on a free electron surface. For long interaction times (low collision velocities), the RCT efficiency is drastically reduced by the presence of the band gap. The wave-packet propagation method is also used to discuss the validity of the rate equation approach in the case of a free electron metal target.