双芯空穴价-芯X射线发射光谱：含时密度泛函理论的理论探索
Double Core Hole Valence-to-Core X-ray Emission Spectroscopy: A Theoretical Exploration Using Time-Dependent Density Functional Theory
摘要：
借助新研制的X射线自由电子激光（XFEL）光源，在分子中相同或不同原子位置同时产生双芯空穴已成为可能。双芯空穴（DCH）X射线发射是一种新型的X射线非线性光谱，可以用XFEL进行研究。本文采用含时密度泛函理论，计算探讨了一系列过渡金属配合物中金属/金属和金属/配体双核空穴态的金属K边价核（VtC）X射线发射光谱（XES）。将模拟的DCH VtC-XES信号与传统的单芯孔（SCH）XES信号进行比较。DCH发射线相对于相应的SCH-XES特征的能量位移和强度变化是第二芯孔与DCH周围的占据轨道之间的耦合的指纹，其包含复合物的重要化学键合信息。还简要讨论了芯孔局域化对DCH VtC-XES的影响。我们从理论上证明，DCH XES提供了微妙的信息，在过渡金属络合物中的金属中心周围的局部电子结构超出传统的线性XES。我们预测的SCH-XES和DCH-XES功能之间的计算变化应该与现代XFEL源检测。
英文摘要：
With the help of newly developed X-ray free-electron laser (XFEL) sources, creating double core holes simultaneously at the same or different atomic sites in a molecule has now become possible. Double core hole (DCH) X-ray emission is a new form of X-ray nonlinear spectroscopy that can be studied with a XFEL. Here we computationally explore the metal K-edge valence-to-core (VtC) X-ray emission spectroscopy (XES) of metal/metal and metal/ligand double core hole states in a series of transition metal complexes with time-dependent density functional theory. The simulated DCH VtC-XES signals are compared with conventional single core hole (SCH) XES signals. The energy shifts and intensity changes of the DCH emission lines with respect to the corresponding SCH-XES features are fingerprints of the coupling between the second core hole and the occupied orbitals around the DCHs that contain important chemical bonding information of the complex. The core hole localization effect on DCH VtC-XES is also briefly discussed. We theoretically demonstrate that DCH XES provides subtle information on the local electronic structure around metal centers in transition metal complexes beyond conventional linear XES. Our predicted changes from calculations between SCH-XES and DCH-XES features should be detectable with modern XFEL sources.
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