X-ray photoemission spectroscopy study of hexavalent uranium compounds

Abstract

The electronic structure of the outer occupied levels of a series of hexavalent uranium (predominately uranyl) compounds was studied using x-ray photoemission spectroscopy (XPS). The changes in the spectral features of the outer occupied levels with the variation of the uranium-oxygen bond lengths (1.7-2.1 Å) are systematically investigated. Previously unexplained spectral structure has been found to result from ligand-field splitting of the occupied $\mathrm{U}6p_{\frac{3}{2}}$ levels. The XPS results are compared with predictions of a relativistic molecular-cluster calculation and with the results of a simple point-charge crystal-field model. When the crystalline electric fields generated by both the primary and secondary ligands are taken into consideration, excellent quantitative agreement is obtained between the XPS data and the molecular-cluster results with no parameter adjustment.