In Situ High-Temperature Raman Spectroscopy of UCl 3 : A Combined Experimental and Theoretical Study.

Uranium trichloride (UCl 3 ) has received growing interest for its use in uranium-fueled molten salt reactors and in the pyrochemical processing of used fuel. In this paper, we report for the first time the experimentally determined Raman spectra of UCl 3 , at both ambient condition and in situ high temperatures up to 871 K. The frequencies of five of the Raman-active vibrational modes ( v i ) of UCl 3 exhibit a negative temperature derivative ((∂ν i /∂ T ) P ) with increasing temperature. This red-shift behavior is likely due to the elongation of U-Cl bonds. The average isobaric mode Grüneisen parameter (γ iP = 0.91 ± 0.02) of UCl 3 was determined through use of the coefficient of thermal expansion published in Vogel et al. (2021) and the (∂ν i /∂ T ) P values determined in this study. These results are in general agreement with those calculated here by density functional theory (DFT+ U ). Finally, a comparison of the ambient band positions of UCl 3 to those of isostructural lanthanide (La-Eu) and actinide chlorides (Am-Cf) has been made.