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 UO 2 Cl 2― 4 in binary mixtures of LiCl—KCl, LiCl—RbCl, and LiCl—CsCl was investigated. The spectrum of UO 2 Cl 2― 4 obtained was characterized by Raman active vibration modes, that is, totally symmetric stretching vibrations A 1g (v 1 : OUO) and A 1g (v 2 : UCl 4 ), and bending vibration Eg (v 8: UO 2 Cl 2 ). The dependence of polarizing power of solvent cations on the vibrational frequencies was clarified. The v 8 frequencies were insensitive to the change in the polarizing power. On the other hand, the v 1 and v 2 frequencies increased with the rise of polarizing power. The Raman shifts suggest that the square bipyramidal structure of UO 2 Cl 2― 4 is kept in various binary alkali chlorides, while O 2― and Cl ― around U(VI) are clearly polarized by the increase of polarizing power.