High-energy resolution X-ray spectroscopy studies of electron-electron interactions in actinide and lanthanide systems

Two new synchrotron-based techniques, high energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS), can now provide unprecedented detailed information about the electronic structure of actinide and lanthanide bearing materials. This includes information on the electron-electron interactions, hybridization between molecular orbitals, the nature of their chemical bonding, and the occupation and the degree of the f-electron localization.

We have studied the electronic structure of cerium, lanthanum, praseodymium, uranium and thorium systems by means of HERFD and RIXS at The European Synchrotron (ESRF). The recently upgraded Rossendorf Beamline (ROBL) at ESRF dedicated to actinide science provides now a unique opportunity to measure HERFD and RIXS with a novel X-ray emission spectrometer with ground-breaking detection limits.

The recorded experimental spectral features were evaluated using a variety of theoretical codes including the LDA+U approximation within DFT, atomic multiplet theory and full multiple scattering FEFF. We furthermore show that RIXS and HERFD can be used to assess the degree of the f-electron localization and the (rather unpredictable) covalent or ionic nature of the actinide and lanthanide bonds. The combined experimental and theoretical data provide a fundamental understanding of lanthanide and actinide chemistry significant for topics of high societal relevance.