Raman spectroscopic study of uranyl complex in alkali chloride melts

Raman spectra of alkali chloride melts containing 3 mol% U(VI) were measured at 823 K. The complexation of UO2Cl42- in binary mixtures of LiClKCl, LiClRbCl, and LiClCsCl was investigated. The spectrum of UO2Cl42- obtained was characterized by Raman active vibration modes, that is, totally symmetric stretching vibrations A1g (ν1: OUO) and A1g (ν2: UCl4), and bending vibration Eg (ν8: UO2Cl2). The dependence of polarizing power of solvent cations on the vibrational frequencies was clarified. The ν8 frequencies were insensitive to the change in the polarizing power. On the other hand, the ν1 and ν2 frequencies increased with the rise of polarizing power. The Raman shifts suggest that the square bipyramidal structure of UO2Cl42- is kept in various binary alkali chlorides, while O2− and Cl− around U(VI) are clearly polarized by the increase of polarizing power.