Radiation‐Induced Defects in Uranyl Trinitrate Solids

• Published in: Chemistry : a European journal 2024-06, Vol.30 (35), p.e202400956-n/a
• Main Authors: Kruse, Samantha J., Rajapaksha, Harindu, LaVerne, Jay A., Mason, Sara E., Forbes, Tori Z.
• Format: Article
• Language: English
• Subjects: Actinides; Cations; characterization; computational; defects; Degradation products; Density Functional Theory; DFT; Electron paramagnetic resonance; Electron spin resonance; EPR; EPR spectroscopy; Free Radicals; Gamma irradiation; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Ionizing radiation; Irradiation; Metal ions; Nitrates; Radiation; Radiation effects; radicals; Raman; Raman spectroscopy; Redox properties; Rubidium; Ultraviolet radiation; Uranium; Uranium dioxide; vibrational analysis; γ Radiation
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202400956

Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO2(NO3)3] (where M=K+, Rb+, Cs+), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products. M[UO2(NO3)3] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO3• radical. Computational studies also highlight the need to include the second sphere coordination environment around the [UO2(NO3)3]0,1 species to gain agreement between the experimental and predicted EPR signatures. Uranyl trinitrate solid‐state materials are exposed to gamma radiation and characterized by electron paramagnetic resonance (EPR) and Raman spectroscopy. Density functional theory calculations confirm the spectroscopic signatures and the presence of a nitrate radical bound in a monodentate fashion to the uranyl cation. Including alkali cations in the theoretic models is crucial to accurate calculation of the g‐values.