X-Ray Spectroscopies with Increased Resolution—A Powerful Tool to Characterize 5f Systems

Characterizing the electronic structure of actinide materials, and in particular of the 5<i>f</i> electrons, is of fundamental importance to advance our understanding of 5<i>f</i>-systems. X-ray absorption near-edge structure (XANES) is a well-established technique to probe the electronic structure of a selected chemical species. The M_4,5 edges are of particular relevance for actinide science, since they probe the 5<i>f </i>states through the excitation of a 3<i>d</i> core-electron. However, due to the large core-hole lifetime broadening of the 3<i>d</i> core-hole, the XANES is poorly informative and structureless.<br/>The use of an X-ray emission spectrometer allows recording XANES in the high-energy-resolution fluorescence detected mode (HERFD). By integrating the maximum of the characteristic fluorescence with a bandwidth smaller that the core-hole lifetime broadening, spectral features are better resolved and sharper. The gain in resolution is very high in the case of actinides M_4,5 edges and since its introduction in the actinide field, HERFD-XANES has revolutionized the study of 5<i>f</i> electronic structure.<br/>In this talk, I will present the basics, the capabilities and the applications of HERFD-XANES for actinide systems. I will also show how theoretical calculations help the interpretation of data and provide information beyond the determination of the actinide oxidation state. I will finally discuss challenges and perspectives of HERFD-XANES applied to 5<i>f</i> systems.