Ab initio calculations of XANES spectra and RIXS maps of radionuclide compounds

X-Ray Absorption Near Edge Structure (XANES) spectroscopy and Resonant Inelastic X-ray Scattering (RIXS),
combined with relativistic multiconfigurational ab initio Wave Function Theory (WFT) calculations including spin-
orbit (SO) interactions, are a preferred combination of experimental and theoretical tools to explore the electronic
structure of radionuclide compounds in different chemical environments (see e.g. 1–5). This approach has been
recently extended to calculate XANES spectra and RIXS maps of actinide compounds. 3–5
We employed the RASSCF/RASPT2 methods with ANO-VTZ/VQZ basis sets and included spin-orbit
interaction via a mean-field SO operator using RASSI as available in OpenMolcas. We apply this powerful
theoretical method in several different research projects to allow for the assignment of the observed spectral
transitions and to characterize the core-excited states of XANES spectra and RIXS maps:
(1) Tc L 3-edge XANES of Tc(IV)-gluconate complexes,
(2) core excited states of U M4-edge XANES of Uranyl UO22+
,
(3) core-to-valence (3d5f) RIXS map of Uranyl UO 22+
.
(1) Tc L 3-edge XANES of Tc(IV)-gluconate complexes: we applied our theoretical approach to Tc L 3-edge
... mehr
XANES. 1,2 We observed a considerable change of the Tc L 3-edge XANES from solid Tc(IV)O 2 to aqueous Tc(IV)-
gluconate complexes, while the corresponding Tc K-edge spectra exhibits similar transition features for both
substances. 1 With the help of accurate multiconfigurational ab initio calculations we were recently able to accurately
simulate the significant change in the Tc L 3-edge XANES spectra and, hence, to explain the reason for this initially
puzzling observation.
(2) U M 4 -edge XANES of Uranyl UO 22+ shows three very pronounced peaks which are assigned to excitation
into core excited states with a hole in the 3d shell and different valence orbitals |5fδθ>, |5fπ> and |5fσ> of Uranyl
occupied. The peak splittings between these three very pronounced features are frequently used to gain information
about the composition of the U-O bonds. We present a detailed calculation of the relevant core-excited states which
allow a clear understanding of the observed behavior of the variationof the peak splitting in different Uranyl
compounds and how they are related to the composition of the U-O bonds.
Second International Workshop on Theory Frontiers in Actinide Science: Chemistry & Materials
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(3) The core-to-valence (3d5f) RIXS map of Uranyl UO 22+ provides information about the bonding Uranyl σu
and πu orbitals. We present the first calculations of such a RIXS map with ab initio methods and give a detailed
assignment of the observed features which are very relevant for many experimental studies of Uranyl.
References:
(1) K. Dardenne et al., Inorg. Chem. 60 (16), 12285–12298 (2021)
(2) D. Badea et al., CHEMISTRY-A EUROPEAN JOURNAL 28 (63), e202201738 (2022)
(3) D.-C. Sergentu et al., J. Phys. Chem. Lett. 9 (18), 5583–5591 (2018)
(4) R. Polly et al., Inorg. Chem. 60 (24), 18764–18776 (2021)
(5) D. C. Sergentu and J. Autschbach, CHEMICAL SCIENCE 13(11), 3194-3207 (2022)