Probing adsorbate state lifetime with low energy ions.

Charge transfer during back scattering of a H- ion from a Cu(111) metal surface with Cs adsorbates is studied theoretically within a wave packet propagation approach. We show that the long lifetime of the Cs-localized state in the Cs/Cu(111) system deeply modifies the nature of projectile-surface charge transfer, suppressing its irreversible character. Back and forth electron transfer between the projectile and the adsorbate during the collision results in characteristic oscillations in the H- yield as a function of projectile energy.