Stanistreet-Welsh Kurtis, Kerridge Andrew
Department of Chemistry, Lancaster University, Lancaster, LA1 4YB, U.K.
Inorg Chem. 2024 Aug 12;63(32):15115-15126. doi: 10.1021/acs.inorgchem.4c02144. Epub 2024 Aug 1.
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. Establishing a direct link between a specific electronic transition and peak intensity is complicated, as a large number of possible transitions can contribute to the overall peak profile. Furthermore, a relationship between oxygen character in the antibonding orbital and the strength of the transition breaks down when using a variety of orbital composition approaches at larger excitation energy. Covalency analysis of the U-O bond in both the ground- and excited-state reveals a dependence on the crystal environment. Orbital composition analysis reveals an underestimation of the uranium contribution to ground-state bonding orbitals when probing O K-edge core-excited states, regardless of the uranyl model employed. However, improving the environmental model provides core-excited state electronic structures that are better representative of that of the ground-state, validating their use in the determination of covalency and bonding.
采用一种RASSCF方法来模拟铀酰的O K边X射线吸收近边结构（XANES）光谱，利用三种逐步改进局部晶体环境表示的模型。模拟成功再现了实验光谱中观察到的三峰轮廓，并证实了丹宁所做的峰归属。[UOCl]模型与实验结果最为吻合，峰位置（在1 eV范围内）和相对峰间距都能准确再现。由于大量可能的跃迁会对整体峰轮廓有贡献，因此建立特定电子跃迁与峰强度之间的直接联系很复杂。此外，在较大激发能量下使用各种轨道组成方法时，反键轨道中的氧特征与跃迁强度之间的关系会失效。对基态和激发态的U - O键进行共价性分析，揭示了其对晶体环境的依赖性。轨道组成分析表明，在探测O K边芯激发态时，无论采用何种铀酰模型，铀对基态成键轨道的贡献都被低估。然而，改进环境模型可提供更能代表基态的芯激发态电子结构，验证了它们在确定共价性和键合方面的用途。
