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

Uranium trichloride (UCl) 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, at both ambient condition and high temperatures up to 871 K. The frequencies of five of the Raman-active vibrational modes () of UCl exhibit a negative temperature derivative ((∂ν/∂)) with increasing temperature. This red-shift behavior is likely due to the elongation of U-Cl bonds. The average isobaric mode Grüneisen parameter (γ = 0.91 ± 0.02) of UCl was determined through use of the coefficient of thermal expansion published in Vogel et al. (2021) and the (∂ν/∂) values determined in this study. These results are in general agreement with those calculated here by density functional theory (DFT+). Finally, a comparison of the ambient band positions of UCl to those of isostructural lanthanide (La-Eu) and actinide chlorides (Am-Cf) has been made.