Bagus Paul S, Schacherl Bianca, Vitova Tonya
Department of Chemistry, University of North Texas, Denton, Texas 76203-5017, United States.
Karlsruhe Institute of Technology (KIT), Institute for Nuclear Waste Disposal (INE), P.O. Box 3640, D-76021 Karlsruhe, Germay.
Inorg Chem. 2021 Nov 1;60(21):16090-16102. doi: 10.1021/acs.inorgchem.1c01331. Epub 2021 Oct 11.
Plutonium is used as a major component of new-generation nuclear fuels and of radioisotope batteries for Mars rovers, but it is also an environmental pollutant. Plutonium clearly has high technological and environmental importance, but it has an extremely complex, not well-understood electronic structure. The level of covalency of the Pu 5f valence orbitals and their role in chemical bonding are still an enigma and thus at the frontier of research in actinide science. We performed fully relativistic quantum chemical computations of the electronic structure of the Pu ion and the PuO compound. Using four different theoretical tools, it is shown that the 5f orbitals have very little covalent character although the 5f() a orbital with the highest orbital energy has the greatest extent of covalency in PuO. It is illustrated that the Pu M edge high-energy resolution X-ray absorption near-edge structure (Pu M HR-XANES) spectra cannot be interpreted in terms of dipole selection rules applied between individual 3d and 5f orbitals, but the selection rules must be applied between the total wavefunctions for the initial and excited states. This is because the states cannot be represented by single determinants. They are shown to involve major redistributions on the 5f electrons over the different 5f orbitals. These redistributions could be viewed as shake-up-like excitations in the 5f shell from the lowest orbital energy from = 5f() into higher orbital energy = 5f(). We show that the second peak in the Pu M edge and the high-energy shoulder of the Pu M edge HR-XANES spectra probe the 5f() a orbital; thus, these spectral features are expected to change upon bond variations. We describe theoretical and spectroscopy tools, which can be applied for all actinide elements in materials with cubic structure.
钚被用作新一代核燃料以及火星探测器放射性同位素电池的主要成分，但它也是一种环境污染物。钚显然具有高度的技术和环境重要性，但其电子结构极其复杂，尚未得到充分理解。钚5f价轨道的共价性水平及其在化学键合中的作用仍是一个谜，因此处于锕系元素科学研究的前沿。我们对Pu离子和PuO化合物的电子结构进行了全相对论量子化学计算。使用四种不同的理论工具表明，5f轨道的共价特征非常小，尽管在PuO中轨道能量最高的5f(α)轨道具有最大程度的共价性。结果表明，Pu M边高能分辨X射线吸收近边结构（Pu M HR-XANES）光谱不能根据单个3d和5f轨道之间应用的偶极选择规则来解释，而选择规则必须应用于初始态和激发态的总波函数之间。这是因为这些态不能用单行列式来表示。结果表明，它们涉及5f电子在不同5f轨道上的重大重新分布。这些重新分布可被视为5f壳层中从最低轨道能量（α = 5f(α)）到较高轨道能量（α = 5f(β)）的类似振激激发。我们表明，Pu M边的第二个峰和Pu M边HR-XANES光谱的高能肩探测5f(α)轨道；因此，预计这些光谱特征会随键的变化而改变。我们描述了可应用于具有立方结构材料中所有锕系元素的理论和光谱学工具。
