Counting the 5f Electrons of the Actinides

The actinides have a complex electronic structure and, as a result, are amongst the elements with the least understood chemical and physical properties in the periodic table. The occupation and role in covalency of the 5f and 6d orbitals is central to understanding the electronic structure of actinides. Advanced experimental tools, able to obtain deep insights into the electronic structure and binding properties of the actinides, are highly desirable. Here, we present two highly sensitive spectroscopic tools.¹ The first is capable of ‘counting’ the number of 5f electrons localized on an actinide element. The second is sensitive to the level of covalent character of the actinide-ligand bonding. Both tools are based on the multiplet structure present in actinide M₄ edge core-to-core resonant inelastic X-ray scattering (CC-RIXS) maps.² The spectral intensity of different many-body final-state multiplets directly depends on the local many-electron ground-state symmetry including the local 5f spin configuration and electron occupation. By comparing U M₄ edge CC-RIXS data for total of 21 U, Np, Pu and Am compounds, we theoretically and experimentally demonstrate how this type of spectroscopy can be used to compare the number of 5f electrons across the actinide series or bond covalency for different ligands bound to one actinide element.<br/>Acknowledgement: This presentation is based on the study referenced in [1], and I would like to acknowledge all co-authors. I also acknowledge funding from the European Research Council (ERC) Consolidator Grant 2020 under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 101003292).<br/>References:<br/>[1] Bianca Schacherl, Michelangelo Tagliavini, Hanna Kaufmann-Heimeshoff, Jörg Göttlicher, Marinella Mazzanti, Karin Popa, Olaf Walter, Tim Pruessmann, Christian Vollmer, Aaron Beck, Ruwini S. K. Ekanayake, Jacob A. Branson, Thomas Neill , David Fellhauer, Cedric Reitz, Dieter Schild, Dominique Brager, Christopher Cahill, Cory Windorff, Thomas Sittel, Harry Ramanantoanina, Maurits W. Haverkort , Tonya Vitova , “Counting the 5f electrons of the actinides”, under review<br/>[2] T. Vitova, I. Pidchenko, D. Fellhauer, P. S. Bagus, Y. Joly, T. Pruessmann, S. Bahl, E. Gonzalez-Robles, J. Rothe, M. Altmaier, M. A. Denecke, and H. Geckeis, "The role of the 5f valence orbitals of early actinides in chemical bonding", Nat Commun 8, 16053 (2017).