Embedded cluster Δ-XANES modeling of adsorption processes on Pt

Full multiple scattering models of X-ray absorption near edge spectra of Pt Janin clusters, with atop and bridge bound oxygen, were systematically improved by increasing the number of cluster atoms contributing X-ray photoelectrons from unity (limited-absorber model), to all six Janin cluster Pt atoms, and finally embedding the Janin cluster into a larger Pt reservoir with photoelectron contributions from all atoms. The simulated XANES of the adsorbate modified clusters were subtractively normalized to their respective clean clusters to yield Δ-XANES signatures. The sequential analysis of previously published limited-absorber model, and the isolated and embedded all atoms models provide insights concerning the relative contribution of surface vs. subsurface atoms to adsorbate induced ligand effects and charge compensation provided by the bulk lattice. Limitations to the application of Δ-XANES signatures to interpretation of Δ-XANES data obtained from an air-breathing fuel cell are discussed.