Quantifying Covalency and Environmental Effects in RASSCF-Simulated O K-Edge XANES of Uranyl.

A RASSCF approach to simulate the O K-edge XANES spectra of uranyl is employed, utilizing three models that progressively improve the representation of the local crystal environment. Simulations successfully reproduce the observed three-peak profile of the experimental spectrum and confirm peak assignments made by Denning. The [UOCl] model offers the best agreement with experiment, with peak positions (to within 1 eV) and relative peak separations accurately reproduced.

Bounding [AnO] (An = U, Np) covalency by simulated O K-edge and An M-edge X-ray absorption near-edge spectroscopy.

Restricted active space simulations are shown to accurately reproduce and characterise both O K-edge and U M-edge spectra of uranyl in excellent agreement with experimental peak positions and are extended to the Np analogue. Analysis of bonding orbital composition in the ground and O K-edge core-excited states demonstrates that metal contribution is underestimated in the latter. In contrast, An M-edge core-excited states produce bonding orbital compositions significantly more representative of those in the ground state.