Ethylene Intersystem Crossing Caught in the Act by Photofragment Sulfur Atoms
Ethylene Intersystem Crossing Caught in the Act by Photofragment Sulfur Atoms
复制标题
光碎片硫原子捕获乙烯系间穿越行为
DOI：
10.1021/acs.jpca.9b11445
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Suits, Arthur G.
中科院分区：
文献类型：
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作者：
Weeraratna, Chaya;Amarasinghe, Chandika;Joalland, Baptiste;Suits, Arthur G.
乙烯，C2 H4，最简单的π键分子，具有巨大的基础和商业重要性。它的最低三重态，其中CH 2部分占据垂直平面，是众所周知的理论，但一直没有明确的实验观察到这种物种。在这里，硫原子在硫化乙烯（c-C2 H4 S）在217 nm的光解速度图成像被用来揭示副产物乙烯的内部状态分布。虽然S（1D）和S（3 P）的平移能分布显示出三个不同的区域，分别在c-C2 H4 S的单重态和三重态激发态中找到它们的起源，但S（3 P）分布由第四个低反冲区域主导。在该区域中，在9 ± 1 kcal/mol的反冲下，分布是完全各向同性的，对应于三重态乙烯通道的打开。多参考计算表明，这种光解离途径是介导的热，瞬态biradical CH 2CH 2S，强烈有利于CH 2-阻碍旋转predissociated复杂。这种光化学开环机制被调用到占在这个低反冲区域，这是由于三重态乙烯放松到扭转鞍点的基态单重态表面上观察到的振动特征。本研究首次从实验上证实了乙烯的绝热单重态-三重态分裂为66 ± 1 kcal/mol，扭转势垒高度为64 ± 1 kcal/mol。
Ethylene, C2H4, the simplest π-bonded molecule, is of enormous fundamental and commercial importance. Its lowest triplet state, in which the CH2moieties occupy perpendicular planes, is well known from theory, but there has been no definitive experimental observation of this species. Here, velocity map imaging of the sulfur atoms in ethylene sulfide (c-C2H4S) photodissociation at 217 nm is used to reveal the internal state distribution of co-product ethylene. While both S (1D) and S (3P) translational energy distributions display three distinct regions that find their origins in singlet and triplet excited states of c-C2H4S, respectively, the S (3P) distribution is dominated by a fourth, low-recoil region. In this region, the distribution is fully isotropic at a recoil of 9 ± 1 kcal/mol, corresponding to the opening of the triplet ethylene channel. Multireference calculations suggest that this photodissociation pathway is mediated by a hot, transient biradical CH2CH2S that strongly favors CH2-hindered rotations in the predissociated complex. This photochemical ring-opening mechanism is invoked to account for the vibrational features observed in this low-recoil region, which are attributed to triplet ethylene relaxing to the torsional saddle point on the ground-state singlet surface. This study thereby gives for the first time the experimental confirmation of an adiabatic singlet–triplet splitting of 66 ± 1 kcal/mol and a torsional barrier height of 64 ± 1 kcal/mol in ethylene.