Chemical shifts in the X-ray absorption near-edge structure spectra of UBr n ( n=3, 4, 5) and Cs 2LiUX 6 (X=F, Cl, Br, I)

Abstract

X-Ray absorption near-edge structure (XANES) spectra at the U–L I–III and Br–K thresholds were studied for a series of UBr n ( n=3, 4, 5) and Cs 2LiUX 6 (X=Cl, Br, I) compounds. It was found that the white line (WL) in the U–L III XANES spectra shifts to higher energies by ≅4 eV from UBr 3 to UBr 4 and further by ≅1.6 eV to UBr 5. This observation is in accord with increasing covalence when the valence increases. Chemical shifts were also studied in the Br–K XANES spectra, where the preedge peak was found to shift to lower energies with increasing valence of uranium. Furthermore, the WL at U–L III and the inflection point in the U–L I XANES spectra of the U III compounds Cs 2LiUX 6 and the U IV compounds UX 4 (X=F, Cl, Br, I) were found to shift to higher energies with increasing ligand electronegativity.