Counting 5f electrons in actinide compounds

Due to their complex electronic structure, the physical and chemical properties of actinides are still less understood compared to other elements in the periodic table. In order to achieve a better under-standing of the physical properties of actinide compounds, advanced spectroscopic tools can be used to provide a deeper insight into the electronic structure, occupation and the role of covalency in acti-nide bonding. Twenty-one different samples including U, Np, Pu and Am compounds in solid and liquid form were investigated to determine a clear trend. The X-ray experiments were performed at the ACT station at the CAT-ACT beamline and the SUL-X beamline at the KIT Light Source (KLS) in Karlsruhe, Germany.

In this work, a novel highly sensitive spectroscopic tool is investigated, which originates from the exchange interaction between the 4f core hole and 5f electrons present during the actinide M4 edge core-to-core resonant inelastic X-ray scattering (CC-RIXS) process. The satellite peak gives insight into the number of 5f electrons localized at the investigated actinide atom. Compared to clas-sical tools for the determination of the oxidation state like the chemical shift of the absorption edge in X-ray absorption near edge structure spectra,[5] the satellite peak is barely influenced by the delocal-ized electron density distributed between metal and ligand but only by electrons localized on the met-al atom. ... mehrFor a 90° π scattering geometry an upward trend was observed from 5f0 to 5f4 with a break and following decrease in intensity for 5f5 and 5f6. Additionally, at 180° π scattering geometry the satellite peak also appeared to be sensitive to the total metal-ligand bond covalency. This work intro-duces a new tool to probe the 5f electron configuration as well as the bond covalency of actinides, which can be used to further advance the understanding of chemical and physical properties of actinide compounds.