Nature of the ns-derived states for an isolated alkali atom on a surface

It has recently been shown (for K/graphite) that experimental core level sp ectroscopy data for adsorbed Ar combined with calculations is a most valuab le tool in order to obtain information about the alkali-derived unoccupied density-of-states [A. Sandell et al,, Phys. Rev. Lett. 78 (1997) 4994]. We present experimental results for Ar on various metallic substrates and disc uss them in terms of adsorption properties of an isolated K adatom. We find a clear tendency for increased 4s-substrate mixing as the substrate work f unction decreases, in accordance with a simple extension of the Gurney mode l. It is also shown that core level spectroscopy data for Ar coadsorbed wit h K can be used to investigate the effects on the 4s resonance of increasin g K coverage. (C) 1999 Elsevier Science B.V. All rights reserved.