Relativistic Multiconfigurational Ab Initio Calculation 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. [1-3]). We employed the RASSCF/RASSCF 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 to different systems to address open unresolved questions: (1) Tc L3-Edge XANES of Tc(IV)-Gluconate complexes, (2) 3d4f RIXS map of Uranyl UO2 2+ , (3) Cl K-edge XANES of [UO2Cl4] 2− , (4) M4,5 XANES spectra of Np(VI)O2 2+ and Np(V)O2 2+ and 3d4f RIXS map of Neptunyl Np(V)O2 2+ .
(1) Tc L3-Edge XANES of Tc(IV)-Gluconate complexes: recently we found a considerable change of the Tc L3-Edge XANES from solid Tc(IV)O2 to Tc(IV)-Gluconate complexes [1]. With the help of new accurate multiconfigurational calculations we could completely understand the reason for this change in the XANES spectra. ... mehr(2) 3d4f RIXS map of Uranyl UO2 2+ [2]: The excellent agreement between our theoretical data and the measurements shows that the approach using the RASSCF/ RASPT2 methods followed by the inclusion of SO coupling is applicable to the accurate calculation of An M4,5 HR-XANES (in agreement with Sergentu et al. [3] ) and 3d4f RIXS maps and reproduces the multiplet structure of the uranyl spectra faithfully. We show that the multiconfigurational protocol, which is nowadays applied as a standard tool to study the X-ray spectra of transition metal complexes, can be extended to the calculations of RIXS maps of An compounds. With this theoretical data we are able to provide a full assignment and understanding of the experimental data [4]. (3) Cl K-edge XANES of [UO2Cl4] 2−: the results of the calculations provide detailed information about the 5f and 6d contributions to metal-ligand bonds. (4) M4,5 XANES spectra of Np(VI)O2 2+ and Np(V)O2 2+ and 3d4f RIXS map of Neptunyl Np(V)O2 2+ we show the first results for these systems which are theoretical considerable more challenging due to the additional 5f1 and 5f2 occupation of the 5f shell.
[1] K. Dardenne et al., Inorg. Chem. 2021, 60, 16, 12285–12298. [2] R. Polly et al., Inorg. Chem. 2021, 60, 24, 18764–18776. [3] D.-C. Sergentu et al., J. Phys. Chem. Lett. 2018, 9, 18, 5583–5591. [4] T. Vitova et al., Nat. Commun. 2017, 8, 1−9.