Multiple Scattering Approach to Pt L3-edge X-Ray Absorption near Edge Structure Spectra of Small Pt Clusters with Hydrogen Adsorption

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Abstract
Recent experimental studies on the Pt L-edge X-ray absorption near edge structure (XANES) spectra of Pt clusters show that the spectra are greatly influenced by hydrogen adsorption. In this paper the full multiple scattering method, which we developed, is applied to study the difference in measured XANES spectra before and after the hydrogen adsorption. Hydrogen atoms are more plausible on adsorbed sites out of the cluster than on absorbed sites inside the cluster though the calculated spectra are not so sensitive to the adsorption sites. The adsorbed hydrogen atoms have rather negative charge due to the charge transfer from Pt atoms. In the charge transfer process Pt 6s (or 6p) electrons play a more important role than 5d electrons. Furthermore the small difference in the XANES spectra for Pt foil and small cluster is studied, and we find that it is due to the large fraction of surface Pt atoms in the latter system.