Excited states in the alkali/noble metal surface systems: A model system for the study of charge transfer dynamics at surfaces

The low coverage adsorption of alkalis on metal surfaces induces excited states localised on the adsorbate. In the case of noble metal substrates, these excited states can exhibit a very long lifetime, up to tens of fs in the Cs/Cu(1 1 1) system. We review recent experimental and theoretical investigations of alkalis adsorbed on noble metal surfaces, with emphasis on the characteristics of the alkali-induced excited states, the origin of their long lifetimes, and the consequences for the adsorbate dynamics. The possibility of long-lived resonances in other adsorbate/substrate systems is also discussed.