Improving understanding of NpO₂ and Np₂O₅ through vibrational spectroscopy

Raman spectra of three NpO₂ samples and two samples produced from a modified direct denitration (MDD) process were collected. The spectral features of the NpO₂ samples were consistent and indicated only NpO₂. The spectra of the MDD samples indicated the presence of NpO₂ and an additional phase attributed to the neptunium binary oxide Np₂O₅. These Raman spectra are the first reported of Np₂O₅, and the proportions of these neptunium oxide phases varied within the samples, suggesting significant sample inhomogeneity. Peaks in the Raman spectra of Np₂O₅ at 569 and 782 cm^–1 were tentatively assigned to concerted, symmetric stretches of the neptunyl cations. Finally, laser-induced heating of regions in the MDD samples that were rich in Np₂O₅ showed spectral features that indicated conversion to NpO₂.. Authors: Gilson, Sara E. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0009000706842064); Sadergaski, Luke R. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000302482114); Parkison, Adam J. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)]. DOE Contract: AC05-00OR22725. Subjects: 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Actinyl-actinyl interactions; Neptunium oxide; Np2O5; Raman spectroscopy; cation-cation interactions