Intramolecular CH3-migration-controlled cation reactions in the VUV photochemistry of 2-methyl-3-buten-2-ol investigated by synchrotron photoionization mass spectrometry and theoretical calculations
Intramolecular CH3-migration-controlled cation reactions in the VUV photochemistry of 2-methyl-3-buten-2-ol investigated by synchrotron photoionization mass spectrometry and theoretical calculations
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DOI：
10.1039/d1cp00490e
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发表时间：
2021-04-08
影响因子：
3.3
通讯作者：
Wang, Zhandong
中科院分区：
文献类型：
--
作者：
Li, Yanbo;Chen, Weiye;Wang, Zhandong
2-甲基-3-丁烯-2-醇（MBO 232）是一种生物源挥发性有机化合物（BVOC），在大气中的排放量很大。BVOCs的真空紫外光化学研究在大气化学中具有重要意义。对几种BVOCs进行了研究，但尚未扩展到MBO 232。在本报告中，MBO 232的光电离和解离过程中的能量范围为8.0-15.0 eV的可调谐真空紫外同步辐射耦合飞行时间质谱仪进行了研究。通过测量光电离光谱，MBO 232的绝热电离能（AIE）和八个识别的碎片离子（即，C4H7O+、C3H7O+、C5H9+、C3H6O+、CH3CO+、CH3O+、C4H5+和C3H5+）。高水平的量子化学计算表明，有3个直接通道和5个间接通道，通过过渡态和中间体负责这些碎片。在反应通道中，CH 3的直接消除是最主要的通道，并产生共振稳定的自由基阳离子。最有趣的是，我们的研究结果表明，CH 3选择性地迁移到阳离子，这导致了不同的间接通道。在无金属有机分子的解离光电离中，甲烷的迁移是一个罕见的过程。通过分子轨道计算和电子局域化函数分析解释了这一过程，并通过CH 3漫游机制探索了非常规解离通道。我们进一步使用RRKM理论对感兴趣的通道进行动力学分析。的活化势垒，和速率常数进行了分析的分支馏分的产品。这些结果为大气中BVOCs的真空紫外光化学研究提供了重要的启示。
2-Methyl-3-buten-2-ol (MBO232) is a biogenic volatile organic compound (BVOC), and has a large percentage of emission into the atmosphere. The vacuum ultraviolet (VUV) photochemistry of BVOCs is of great importance for atmospheric chemistry. Studies have been carried out on several BVOCs but have not extended to MBO232. In the present report, the photoionization and dissociation processes of MBO232 in the energy range of 8.0-15.0 eV have been studied by tunable VUV synchrotron radiation coupled with a time-of-flight mass spectrometer. By measuring the photoionization spectra, the adiabatic ionization energy (AIE) of MBO232 and the appearance energies (AEs) of the eight identified fragment ions (i.e., C4H7O+, C3H7O+, C5H9+, C3H6O+, CH3CO+, CH3O+, C4H5+, and C3H5+) were determined. High-level quantum chemistry calculations suggest that there are 3 direct channels and 5 indirect channels via transition states and intermediates accountable for these fragments. Among the reaction channels, the direct elimination of CH3 is the most dominant channel and produces the resonance-stabilized radical cation. Most interestingly, our results show that the CH3 selectively migrates towards the cation, which leads to the different indirect channels. The CH3 migration is a rare process in the dissociative photoionization of metal-free organic molecules. We explain the process by molecular orbital calculations and electron localization function analysis and explore the non-conventional dissociation channels via the CH3 roaming mechanism. We further perform kinetics analysis using RRKM theory for the channels of interest. The activation barrier, and rate constants are analyzed for the branching fractions of the products. These results provide important implications for the VUV photochemistry of BVOCs in the atmosphere.