PACS 61.10.Hb, 78.70.Dm In-situ X-ray absorption spectroscopy at the Re L 1 and L 3 edges was used to study a modification of the local atomic and electronic structure around rhenium in perovskite-type ReO 3 upon hydrogen intercalation. The analysis of both EXAFS and XANES parts of the X-ray absorption spectra shows an evidence of the charge disproportionation phenomenon in hydrogenated rhenium trioxide. and explaining the metallic conductivity of ReO 3 . These conduction electrons play also the main role in the stabilization of the cubic structure of ReO 3 [3]. While many perovskites, as for example SrTiO 3 , BaTiO 3 and KNbO 3 , show upon temperature change a series of phase transitions, caused by condensation of one or more optical modes [4] and accompanied by the electronic and atomic structure changes, the structure of ReO 3 remains non-distorted at atmospheric pressure down to liquid-helium temperature [3]. However, a number of phase transitions can be induced in ReO 3 by applying external pressure [1,5,6] or by hydrogen insertion, that results in the formation of hydrogen rhenium bronzes H x ReO 3 [7][8][9].X-ray and neutron diffraction [1,5,6] and X-ray absorption spectroscopy (XAS) [10] studies has revealed that pressure effect results in a rotation (the Re-O-Re angle changes from 180° to 160°) of ReO 6 octahedra, but the octahedra remain regular with the Re-O bond length about 1.88±0.01 Å. Neutron diffraction study [9] of the hydrogen rhenium bronze D 1.36 ReO 3 showed that the hydrogen insertion produces similar effect on the ReO 3 structure. In particular, for x=1.36 the bronze structure is composed of tilted regular ReO 6 octahedra with the Re-O-Re angle equal to 169° and the Re-O distance of about 1.90 Å [9]. More accurate information on the local atomic and electronic structure of the bronzes can be obtained using XAS, which is a structural method complimentary to diffraction. To our knowledge, no such works have been performed until now.In this work, we present the first results of the in-situ XAS study of hydrogen intercalation into ReO 3 . The analysis of both extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) allowed us to reconstruct changes of the local environment around rhenium ions occurring upon hydrogen intercalation and provides an evidence of charge ordering at rhenium sites.X-ray absorption spectra were recorded at the Re L 1 and L 3 -edges in transmission mode at the LURE DCI storage ring on the EXAFS-3 beam line, located at the bending magnet. The storage ring DCI oper-

X-ray absorption near-edge structure (XANES) signals at the oxygen K edge in polycrystalline α-MoO 3 and amorphous a-MoO 3 thin film were analysed within the full-multiple-scattering (FMS) formalism. Significantly different XANES signals were found for non-equivalent oxygen atoms in low-symmetry layered-type α-MoO 3 structure. The obtained results are in agreement with the experimental data and allow us to interpret all XANES peaks for α-MoO 3 . Besides, the FMS XANES simulations, performed for several fragments of α-MoO 3 structure, allowed us to explain the O K-edge XANES in amorphous a-MoO 3 thin film. We found that although the crystallographic structures of α-MoO 3 and a-MoO 3 are strongly different, a cluster consisting of six MoO 6 octahedra joined by vertices produces the main contribution to both XANES signals.

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