Spectroscopic tools for characterization of bonding properties of actinides

Understanding the electronic structure and chemical bonding properties of the actinide (An) elements poses a great challenge and frontier in fundamental chemistry and physics. The An4,5 absorption edge core-to-core and valence band resonant inelastic X-ray scattering (CC/VB-RIXS) and high energy resolution X-ray absorption near edge structure (HR-XANES) techniques probe the occupied and unoccupied parts of the valence band of the actinide elements with extraordinary energy resolution and thus unique information on the chemical bond can be obtained. A deep insight into the An electronic structures is for example essential to understand actinide environmental behaviour. All An M4,5 edge RIXS and HR-XANES studies are performed at the ACT station of the CAT-ACT beamline at the KIT Light Source.

Spectroscopic and computational tools for probing in detail the An-ligand (U, Np, Pu or Am) bond covalency will be discussed. Examples of applications describing the link between covalency and stability/reactivity of different actinide materials will be presented. We will address questions like for example: 1) how Fe(II) influences the electronic structure U(V)O21+ and thus increases the U(V) stability in the environment; 2) how the binding properties of equatorial ligands influence the electronic structure and stability of U, Np or Pu in solutions or solids.