Pseudo-intramolecular behaviour of near-edge X-ray absorption fine structure from an atomic adsorbate

The polarization dependence of the Cl K-edge 'white-line' has been measured from Si(111)7*7-Cl and Si(100)2*1-Cl. In both cases it has the form expected on the basis of a pseudo-intramolecular sigma * -resonance model. This suggests that the near-edge X-ray absorption fine structure (NEXAFS) could provide a simple, incisive monitor of the surface structure for atomic adsorbates on semiconductors. Together with the corresponding surface extended X-ray adsorption fine structure (SEXAFS), the Si(100)2*1-Cl NEXAFS indicates that Cl bonds atop a buckled dimer with a Cl-Si bond length of 2.00+or-0.02 AA.