Systematic studies of actinide systems by resonant inelastic X-ray scattering and high energy resolution X-ray spectroscopy

The unique behavior of 5f electrons plays a central role in shaping the intriguing physics and chemistry of actinide systems, influencing their bonding, reactivity, and technological applications. Probing the behavior of these electrons requires experimental techniques that are element-specific and chemically sensitive, in combination with theoretical analysis. In this thesis, high energy resolution fluorescence detected X-ray absorption (HERFD XANES) at the actinide M₄ edge and 3d–4f resonant inelastic X-ray scattering (RIXS) are used to probe the 5f electronic states in actinide systems. A series of systematic studies are presented, focusing on: (i) the influence of different halide ligands on tri- and tetra-valent uranium, (ii) the M₄-edge spectral features of tetravalent Th, U, Np, and Pu in isostructural complexes, and (iii) the corresponding Cl K-edge XANES as a probe of ligand contributions. The results demonstrate the sensitivity of HERFD XANES and RIXS to subtle changes in bonding, oxidation state, and electronic interactions, offering a detailed picture of 5f-electron behavior. This work establishes an experimental–theoretical framework for studying complex actinide systems and f-electron materials more broadly.