Electronic structure and bonding properties of U6+ by high-resolution X-ray spectroscopy and computations

Understanding the chemistry of actinide compounds is crucial in many fields including medical research, energy, and radioactive materials disposal, and accordingly a number of in-depth studies have been conducted. [1] However, the electronic structures and bonding properties of actinides have not been studied as deeply as those for lanthanides or transition metals. In this work, we describe the use of high-energy resolution X-ray absorption/emission spectroscopy (HR-XAS and HR-XES, respectively) and resonant inelastic X-ray scattering (RIXS) techniques to probe the local atomic and electronic structures of the molecular [(UO2)F5] 3-, [(UO2)Cl4] 2-, and [(UO2)Br4] 2- complexes. In addition, we also detail the methodological approach for predicting the ligand K-edge high-energy resolution XANES, and U M4,5-edge core-to-core/valence band RIXS by means of first principles density-functional theory (DFT) calculations by using a time-dependent formalism and multiplet calculations, respectively, at the relativistic level (4-component Dirac Hamiltonian). [2] By comparing the theoretical and experimental spectra, our study also provides insight into the roles of the uranium 5f and 6d orbitals for the metal ligand bonding as a function of the equatorial ligand (fluoride, chloride, and bromide). ... mehrThe X-ray spectroscopic experiments were performed at the Karlsruher Research Accelerator (KARA) Light Source (Karlsruhe, Germany). The U M4-edge and Br K-edge high energy resolution X-ray absorption emission and resonant inelastic X-ray scattering data were recorded at the ACT station of the CAT-ACT beamline, [3a] the Cl K-edge XANES at the INE-Beamline, [3b] and the F K-edge XANES at the X-SPEC beamline. [3c] This work is supported by the ERC Consolidator grant “the Actinide Bond” (N° 101003292) under the European Union’s Horizon 2020 research and innovation program.
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