Pt L-edge XANES as a probe of Pt clusters

The sensitivity of Pt L-edge XANES to local geometric and electronic struct ure in various Pt-n clusters is investigated using the ab initio self-consi stent FEFF8 code. Calculations based on FEFF8 are found to be in good agree ment with experiment. For pure Pt clusters the XANES can distinguish betwee n 2- and 3-dimensional clusters. Self-consistency is important in determini ng the variation of XANES with cluster size. The effect of a support is als o studied. In Pt-Cl-x clusters the presence of a Cl-Pt bond leads to a "hyb ridization peak," i.e., a peak in the Cl d-density of states (d-DOS) mixed with Pt d-states. For Pt-H clusters hydrogen addition is well correlated wi th the growth of a broad shoulder on the white line. This change is attribu ted largely to AXAFS, i.e., to a corresponding change in the atomic backgro und absorption.