Chemical and spectroscopic characterization of plutonium tetrafluoride

Anhydrous plutonium tetrafluoride is an important intermediate in the production of metallic Pu. This historically important compound is also known to exist in at least two distinct, yet understudied hydrate forms, PuF₄·xH₂O(s) (0.5 ≤ x ≤ 2) and PuF₄·2.5H₂O(s). X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) are the most common tools used to characterize these materials, often in a context for studying structural and morphological changes that arise from aging or calcination. However, fundamental electronic and vibrational spectroscopic information is rather scarce. Here, we measured the visible and shortwave infrared (SWIR) diffuse reflectance, Fourier transform infrared (FTIR), fluorescence and Raman spectra of PuF₄(s) and PuF₄·xH₂O(s) to obtain a better electronic and vibrational fingerprint. Our work provides clear indication of the polymeric structure of anhydrous PuF₄, consistent with the Raman spectrum of UF₄(s) and its hydrates. This is supplemented with XRD, TGA and SEM analysis. Findings in this study indicate that the spectra are modified by particle size, which in turn is influenced by synthetic technique.