Uranyl fluoride, the product of the hydrolysis of UF6, has previously been shown to undergo structural changes in the presence of gas phase water. Water sorbs between the layers of the anhydrous crystal, resulting in a stable, partially-hydrated state with a distinct spectroscopic signature. Another stable hydrate form, [(UO2)7F14(H2O)7]*4H2O, is produced via further hydration and subsequent desiccation, but has not been fully characterized previously. Clarifying how these structural and chemical changes can be induced by environmentally relevant perturbations is important for the detection of uranyl fluoride, i.e. in nuclear forensics applications. Raman spectroscopy with humidity and temperature control was used to conduct a time-dependent analysis of the induced structural and chemical changes in uranyl fluoride. A complementary computational study was also undertaken to help interpret the Raman spectra. Static DFT calculations were previously shown to accurately predict vibrational frequencies of the “pristine” anhydrous state. Expanding on this work, Born-Oppenheimer molecular dynamics simulations were performed to show how the predicted vibrational states change with temperature and the introduction of water. These simulations show hydrogen bonding interactions that provide insight into the water-phonon coupling previously observed with inelastic neutron scattering.

Structural and chemical changes in uranyl fluoride: A complementary spectroscopic and computational study

253rd National Meeting (2017)

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