Energy dependence of resonant charge transfer from adsorbates to metal substrates

We have investigated the resonant charge transfer from an adsorbed Ar atom in an electronically excited 2p⁵_3/24s¹ state into different metal substrates, i.e., Ag(111), Ni(111) and Cu(111). Using the so-called core hole clock method we have been able to determine the resonant charge transfer times for the three systems. They differ roughly by a factor of two with the fastest transfer time being observed for Ni(111) and the slowest for Ag(111). Furthermore we observe strong energy dependences of the charge transfer times across the resonances which are opposite to the expectations from a simple tunneling model, or from a detuning induced shortening of the interaction time. Possible reasons for the observed behavior are discussed.