Ultrafast charge transfer and atomic orbital polarization

The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4x2)S/Ru(0001) the charge transfer times between the sulfur 2s(-1)3p(*+1) antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p(perpendicular to)(*) state along the surface normal and the 3p(parallel to)(*) state in the surface plane. The charge transfer times are determined as 0.18 +/- 0.07 and 0.84 +/- 0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap. (c) 2007 American Institute of Physics.