Pihlava Lassi, Niskanen Johannes, Kooser Kuno, Stråhlman Christian, Maclot Sylvain, Kivimäki Antti, Kukk Edwin
Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland.
Institute of Physics, University of Tartu, W. Ostwaldi 1, EE-50411 Tartu, Estonia.
Phys Chem Chem Phys. 2021 Sep 29;23(37):21249-21261. doi: 10.1039/d1cp03097c.
We studied the gas-phase photodissociation of a fully halogenated aromatic molecule, tetrabromothiophene, upon core-shell ionization by using synchrotron radiation and energy-resolved multiparticle coincidence spectroscopy. Photodynamics was initiated by the selective soft X-ray ionization of three elements - C, S, and Br - leading to the formation of dicationic states by Auger decay. From a detailed study of photodissociation upon Br 3d ionization, we formulate a general fragmentation scheme, where dissociation into neutral fragments and a pair of cations prevails, but dicationic species are also produced. We conclude that dicationic tetrabromothiophene typically undergoes deferred charge separation (with one of the ions being often Br) that may be followed by secondary dissociation steps, depending on the available internal energy of the parent dication. Observations suggest that the ejection of neutral bromine atoms as the first step of deferred charge separation is a prevailing feature in dicationic dissociation, although sometimes in this step the C-Br bonds appear to remain intact and the thiophene ring is broken instead. Ionization-site-specific effects are observed particularly in doubly charged fragments and as large differences in the yields of the intact parent dication. We interpret these effects, using first-principles calculations and molecular dynamics simulations of core-hole states, as likely caused by the geometry changes during the core-hole lifetime.
我们利用同步辐射和能量分辨多粒子符合光谱，研究了全卤代芳香分子四溴噻吩在核壳电离后的气相光解离。光动力学由碳、硫和溴三种元素的选择性软X射线电离引发，通过俄歇衰变导致双阳离子态的形成。通过对溴3d电离后的光解离进行详细研究，我们制定了一个通用的碎片化方案，其中分解为中性碎片和一对阳离子占主导，但也会产生双阳离子物种。我们得出结论，双阳离子四溴噻吩通常会经历延迟电荷分离（其中一个离子通常是溴），这可能会接着发生二次解离步骤，具体取决于母体双阳离子的可用内能。观察结果表明，作为延迟电荷分离的第一步，中性溴原子的逸出是双阳离子解离的一个主要特征，尽管有时在这一步中碳 - 溴键似乎保持完整，而是噻吩环断裂。特别是在双电荷碎片中观察到了电离位点特异性效应，并且完整母体双阳离子的产率存在很大差异。我们使用芯孔态的第一性原理计算和分子动力学模拟来解释这些效应，认为这可能是由芯孔寿命期间的几何变化引起的。
