Wasowicz Tomasz J, Dąbkowska Iwona, Kivimäki Antti, Richter Robert
Division of Complex Systems Spectroscopy, Institute of Physics and Computer Science, Gdansk University of Technology, ul. G. Narutowicza 11/12, 80-233 Gdansk, Poland.
Department of Analytical Chemistry, Faculty of Chemistry, University of Gdansk, ul. Wita Stwosza 63, 80-308 Gdansk, Poland.
Phys Chem Chem Phys. 2023 Nov 29;25(46):31655-31666. doi: 10.1039/d3cp03760f.
The dissociative double photoionization of isoxazole molecules has been investigated experimentally and theoretically. The experiment has been carried out in the 27.5-36 eV photon energy range using vacuum ultraviolet (VUV) synchrotron radiation excitation combined with ion time-of-flight (TOF) spectrometry and photoelectron-photoion-photoion coincidence (PEPIPICO) technique. Five well-resolved two-body dissociation channels have been identified in the isoxazole's coincidence maps, and their appearance energies have been determined. The coincidence yield curves of these dissociation channels have been obtained in the photon energy ranges from their appearance energies up to 36 eV. The double photoionization of isoxazole produces a CHNO transient dication, which decomposes into fragments differing from previously reported photofragmentation products of isoxazole. We have found no evidence of pathways leading to the CHNO, HCN, CHO, CHN, or CH fragments or their neutral counterparts that have been observed in previous neutral photodissociation and single photoionization studies. Instead, the dissociation of isoxazole after the ejection of two electrons is bond-selective and is governed by two reactions, HCO + HCCN and HCO + HCCN, whose appearance energies are 28.6 (±0.3) and 29.4 (±0.3) eV, respectively. A third dissociation channel turns out to be a variant of the most intense channel (HCO + HCCN), where one of the fragment ions contains a heavy isotope. Two minor dissociation channels occurring at higher energies, CO + CHCN and CN + HCCO, are also identified. The density functional and quantum chemical calculations have been performed to elucidate the dissociative charge-separating mechanisms and determine the energies of the observed photoproducts. The present work unravels hitherto unexplored photodissociation mechanisms of isoxazole and thus provides deeper insight into the photophysics of five-membered heterocyclic molecules containing two heteroatoms.
已通过实验和理论研究了异恶唑分子的离解双光离化。实验在27.5 - 36 eV光子能量范围内进行，采用真空紫外（VUV）同步辐射激发，并结合离子飞行时间（TOF）光谱和光电子 - 光离子 - 光离子符合（PEPIPICO）技术。在异恶唑的符合图谱中识别出了五个分辨率良好的双体离解通道，并确定了它们的出现能。这些离解通道的符合产率曲线已在从其出现能到36 eV的光子能量范围内获得。异恶唑的双光离化产生一个CHNO瞬态双阳离子，其分解成的碎片与先前报道的异恶唑光解离产物不同。我们没有发现导致CHNO、HCN、CHO、CHN或CH碎片或其在先前中性光解离和单光离化研究中观察到的中性对应物的途径的证据。相反，异恶唑在两个电子射出后的解离具有键选择性，由两个反应控制，即HCO + HCCN和HCO + HCCN，其出现能分别为28.6（±0.3）和29.4（±0.3）eV。第三个离解通道原来是最强通道（HCO + HCCN）的一个变体，其中一个碎片离子含有重同位素。还识别出了在较高能量下出现的两个次要离解通道，即CO + CHCN和CN + HCCO。已进行密度泛函和量子化学计算以阐明离解电荷分离机制并确定观察到的光产物的能量。本工作揭示了异恶唑迄今未被探索的光解离机制，从而为含两个杂原子的五元杂环分子的光物理提供了更深入的见解。
