Electronic structure of uranyl compounds: an XPS study

X-ray photoemission spectroscopy (XPS) measurements are reported for a series of uranyl compounds in which the primary uranium--oxygen (U--O/sub I/) separation varies substantially. Crystal field splittings of the U 6p$sub 3$/ $sub 2$ core electron energy levels were observed. These splittings are explained with the point charge crystal field model when both first and second near uranium neighbors are considered. The systematics of charge migration (observed by monitoring electron core level shifts) associated with bonding in the uranyl series were also investigated. Core level shifts for compounds with different U--O/sub I/ separations are large, but essentially no relative shifts of uranium and oxygen core levels were observed within the uranyl group. Thus charge appears to flow between the uranyl group (as a unit), and the secondary uranium ligands as U--O/sub I/ is varied. The U 5f electron participation in covalent bonding was also studied by systematically measuring XPS line intensities; U 5f electron occupation appears to be minimal. (auth