Optical vibrational spectra of β-U3O8

Technogenic uranium oxides are ubiquitous in the nuclear fuel cycle. Identifying the chemical composition of these oxides is frequently done with optical vibrational spectroscopy (infrared and Raman spectroscopy). The α phase of U3O8 is the most stable and common uranium oxide, but a β phase of U3O8 can be produced via very slow cooling of the α phase from elevated temperatures or the application of small shear forces. However, optical spectra of this compound have not been reported. Here, we use high-resolution attenuated total reflection infrared spectroscopy and Raman spectroscopy to collect the optical vibrational spectra. Despite similarities in the crystal structure of α and β−U3O8, the optical spectra of these compounds differ substantially, with additional Raman active modes in β−U3O8 that are likely originating from differences in the U–O coordination units. Measurements presented here provide spectral characterization that can be used for chemical identification in future studies of uranium oxides.