Raman and infrared spectra of plutonium (IV) oxalate and its thermal degradation products

For over 80 years, plutonium dioxide has been routinely produced via thermal decomposition of hydrated plutonium(IV) oxalate. Despite the longstanding utility of this process, the chemical structures of starting materials and intermediates produced during this thermal conversion remain ill-defined. To help resolve this uncertainty, we measured high-resolution Raman and infrared spectra of Pu(C2O4)2·6H2O that was heated to 25, 100, 220, 250, 350, and 450 °C in air. Our measurements show that Pu(C2O4)2·6H2O has a rich vibrational spectrum with at least 15 Raman bands between 180 cm−1 and 1900 cm−1 and 9 infrared bands between 800 cm−1 and 4000 cm−1. As Pu(C2O4)2·6H2O is heated, water is liberated, and the oxalate ligand decomposes to produce plutonium oxycarbide species. When heated to 350 °C or higher, vibrational spectra are consistent with PuO2 with some residual carbon-containing species. Full vibrational spectra, powder X-ray diffraction, and scanning electron microscopy measurements of Pu(C2O4)2·6H2O and its thermal degradation products are presented herein along with approximate assignments for observed spectral bands. These data can be used to validate and potentially improve existing computational models that describe the chemical structure of compounds produced during thermal degradation of plutonium (IV) oxalate. Given the utility of plutonium (IV) oxalate in synthesizing plutonium dioxide, these results are expected to provide value in the fields of nuclear fuel processing, nuclear nonproliferation, and nuclear forensics.