Quantum size effect in the resonant electron transfer between an ion and a thin metal film

The resonant charge transfer (RCT) process between an ${\mathrm{H}}^{-}$ ion and a thin Al film is studied using a wave-packet propagation method. Both the static situation, with a fixed ion surface distance, and the dynamical situation, with a moving ion, are investigated. The RCT on a thin metal film is found to exhibit quantum size effects due to the finite thickness of the film. The way the case of the semi-infinite metal is recovered for thick films is discussed in detail. The conditions for observing quantum size effects in the RCT process are defined and discussed in terms of the various characteristic times of the system. In particular, it is shown that the quantum size effects disappear in the case of fast collisions, where the RCT on a thin metal film becomes basically identical to that on a semi-infinite metal surface.