Resonant x-ray emission across the L3 edge of uranium compounds

A narrow bandwidth x-ray beamline and a multi-crystal von Hamos spectrometer were used to record x-ray absorption and x-ray emission (XES) across the uranium L3 edge of UO2, UO3, Cs2UO2Cl4, and Cs2UCl6. Measurements were made over 17150-17250 eV with an instrumental resolution of similar to 2 eV. This resolution allowed the use of Lorentzian peak fits to the L3N4 and L3N5 characteristic x-ray fluorescence lines that have similar to 12-13 eV lifetime widths. The fluorescence yields of the four compounds display strong white lines near threshold and multiple scattering features at higher energies. The XES spectra were fit with three Lorentzians, two for the L3N4 and L3N5 lines and one for inelastic scattering by 2p-6d excitations and 4d-6d final states. The intensities of the white lines were largely due to the inelastic scattering component. To support the measurements, relativistic equation-of-motion coupled-cluster and restricted active space configuration interaction calculations were performed for uranium core-excitation energies in Cs2UO2Cl4 and Cs2UCl6. These calculations with rigorous treatments of relativistic effects are shown to provide accurate uranium L3-edge binding energies, L3N5 emission energies, as well as the energy losses in the inelastic scattering process. The measured and calculated results show variations between compounds with U(IV) oxidation states that contain 6d05f2 electrons in their ground configurations (UO2 and Cs2UCl6) compared with U(VI) compounds (UO3 and Cs2UO2Cl4) with empty 5f and 6d configurations.