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0893-JJ03-07.1

Studies of Structural and Electronic Properties of Uranium Compounds, by XANES Spectroscopy C. Fillaux1, C. Den Auwer1, D. Guillaumont1, E. Simoni2, N. Barré2, D. K. Shuh3 and T. Tyliszczak3 1 CEA Marcoule, DEN/DRCP/SCPS, 30207, Bagnols sur Cèze cedex, France 2 Institut de Physique Nucléaire d’Orsay, 91405, Orsay cedex, France 3 Lawrence Berkeley National Laboratory, Berkeley, CA, USA ABSTRACT X-ray absorption near edge structure (XANES) is a sensitive probe of the electronic structure, and can provide information about the valency, the unoccupied electronic states and the effective charge of the absorbing atom. In this paper, near edge x-ray absorption fine structure spectra are reported at the L3, M5 and N5 thresholds and used to determined structural and electronic properties of U(VI) within uranyl nitrate (UO2(NO3)2.6H2O) and perovskite (Ba2ZnUO6). Experimental data analysis by simulating the absorption edge allows to compare the coordination polyhedrons, identify the electronic transitions and calculate the density of states associated with the absorption spectra. Moreover, a coupling between simulations of the experimental spectra and quantum chemical calculations is performed, in order to improve the model describing the final states and better understand the bonding properties of the cation with the ligand. INTRODUCTION Both structural and electronic properties of the actinide cations are of fundamental interest in order to describe the intramolecular interactions. The 5f and 6d orbitals are the first partially or totally vacant states of these elements and their properties reflect the nature of the actinide-ligand bond. Because of its chemical and orbital selectivities, XANES spectroscopy is useful to probe the actinides’ frontier orbitals and then understand the cation reactivity towards chelating ligands. The L3-edge x-ray absorption spectroscopy of uranium (formal 2p-6d transition in the dipolar approximation) has been the most reported one in the literature because of its convenient energy (17.2 keV). Although significant structural information on the coordination polyhedron can be obtained from these electronic transitions because of the important shape resonances [1,2], the very short core-hole lifetime broadens the edge signal (~7 eV) resulting in very little extractable electronic information. On the other hand, the M5 (3d-5f transition) and N5 (4d-5f transition) edges provide a better resolution (~4 eV for M5 and N5 core holes) and allow to achieve quantitative information. Thus a multiple-edge approach has been chosen to study both structural and electronic properties of actinides compounds. In this paper, we discuss, in a preliminary work, the influence of the uranium effective charge as well as the uranium polyhedron on the edge position and edge features. For this purpose, the data are compared to energy levels and population analysis obtained by quantum chemical calculations. The studied compounds have been chosen in order to enhance the effect of the uranyl group (UO22+) on th