Probing the local coordination of hexavalent uranium and the splitting of 5f orbitals induced by chemical bonding.

We report here the first detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the M4 edge. We demonstrate the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. We show that for all local configuration analyzed, the main peak corresponds to non-bonding 5f orbitals, and the highest energy peak corresponds to anti-bonding 5f orbitals. Our findings are in agreement with the accepted interpretation of uranyl spectral features and embed the latter in the broader field of view where the spectra of a larger variety of U6+-containing samples are interpreted on the same theoretical ground.