Investigation of Pu Bonding Properties using X-ray Spectroscopic and Computational Methods

The understanding of the electronic structure and bonding properties of actinides (An) is still limited, detailed quantum chemical calculations of An compounds even more so. At the same time, an in-depth understanding of the structural properties of An and their compounds is fundamental for comprehending their chemical behaviour, which is of great importance for nuclear waste disposal, fuel reprocessing, applications in nuclear medicine and the general handling of An. Over the last decade, a combination of high energy resolution X-ray absorption and emission spectroscopy in combination with theoretical quantum chemical calculations has shown promise in unravelling new insights into the structural properties of An.[1]
In this study, these methods are applied to several different Pu compounds. For this, solid PuO2 and the four most relevant aqueous ions Pu3+, Pu4+, PuO2+ and PuO22+, were prepared and analysed using Pu M3- and M5-edge high energy resolution X-ray absorption near edge spectra (HR-XANES) and core-to-core resonant inelastic X-ray scattering (CC-RIXS). Additionally, CC-RIXS maps were calculated with ab initio ligand field density functional theory calculations (LF-DFT). ... mehr
Depending on the oxidation state, a significant shift of the white line (WL) and a characteristic shape of the HR-XANES/CC-RIXS spectra can be observed in the experiment. If the Pu coordination environment is properly taken into consideration, the calculations accurately reproduce the main features of the experimental spectra. This showcases the importance of an accurate description of the Pu-ligand bond, including covalent contributions. The Pu bonding properties in the different oxidation states are correlated to the HR-XANES and RIXS spectral features. Further, this work provides a valuable contribution to the correct treatment of 5f electrons and their influence on oxidation states and bonding.
This work benefitted from financial support from the European Research Council (ERC) Consolidator Grant “The Actinide Bond” (N°101003292) under the European Union’s Horizon 2020 program.
[1] aA. Bajaj, et al., Inorg. Chem. 64, 24 (2025) 12297-12312. bA. Schacherl, et al. Nat. Commun. 16 (2025) 1221. cT. Vitova, et al., Nat. Commun. 8 (2017) 16053.