High energy resolution X-ray spectroscopy at actinide M4,5 and ligand K edges: what we know, what we want to know, what we can know

In recent years, scientists have progressively recognized the role of electronic structure in the characterization of chemical properties for actinide containing materials. High energy resolution X-ray spectroscopy at the actinide M4,5 edges emerged as a promising direction because this method can probe actinide properties at the atomic level through the possibility of reducing the experimental spectral width below the natural core-hole life time broadening. Parallel to the technical developments of the X-ray method and experimental discoveries, theoretical models, describing the observed electronic structure phenomena, have also advanced. In this feature article, we describe the latest progress in the field of high energy resolution X-ray spectroscopy at the actinide M4,5 and ligand K edges and we show that the methods are able to a) provide fingerprint information on the actinide oxidation state and ground state character b) probe 5f occupancy, non-stoichiometry, defects, ligand/metal ratio c) investigate the local symmetry and effects of the crystal field. We discuss the chemical aspects of the electronic structure in terms familiar to chemists and materials scientists and conclude with a brief description of new opportunities and approaches to improve the experimental methodology and theoretical analysis for the f-electron systems