Mandal Mrinmoy, Mahata Prabhash, Maiti Biswajit
Department of Chemistry, Institute of science, Banaras Hindu University, Varanasi-221005, India.
Phys Chem Chem Phys. 2020 Apr 28;22(16):8418-8426. doi: 10.1039/c9cp06680b. Epub 2020 Apr 9.
The contribution of intersystem crossing (ISC) in the C(P) + SiH reaction that leads to products formation in the singlet electronic state is investigated using a direct dynamics trajectory surface hopping (TSH) method with Tully's fewest switches algorithm. Interestingly, in contrast to the O(P) + SiH reaction with no ISC effect, for the title reaction we observed ∼7% product formation through ISC despite weak spin-orbit coupling interactions (less than 25 cm) between the ground singlet and triplet states. This is presumably because of the topological differences in the potential energy surfaces of the two reactions at the entrance channel. The O(P) + SiH reaction follows either an addition reaction (with shallow attractive potential and a late singlet-triplet crossing) or a direct abstraction pathway with singlet-triplet crossing at near or after the top of the barrier making ISC ineffective. On the other hand, an insertion mechanism is exclusively followed by the C(P) + SiH reaction with no entrance barrier to the reaction in the triplet state. The triplet insertion complex initially formed (HSiCH) can go to the singlet state through ISC due to the fact that the triplet-singlet crossing is accessed several times during the course of the reaction. Our computed overall product angular distributions for H and H elimination channels are found to be broad and flat or nearly isotropic in nature indicating the formation of stable intermediate complexes, which corroborates the most recent crossed molecular-beam study.
采用带有塔利最少开关算法的直接动力学轨迹表面跳跃（TSH）方法，研究了系间窜越（ISC）在C(P) + SiH反应中对单重态电子态产物形成的贡献。有趣的是，与不存在ISC效应的O(P) + SiH反应不同，对于本研究的反应，尽管基态单重态和三重态之间的自旋轨道耦合相互作用较弱（小于25 cm），但我们观察到约7%的产物通过ISC形成。这可能是由于两个反应在入口通道处势能面的拓扑差异所致。O(P) + SiH反应要么遵循加成反应（具有浅吸引势和较晚的单重态 - 三重态交叉），要么遵循直接提取途径，在势垒顶部附近或之后发生单重态 - 三重态交叉，使得ISC无效。另一方面，C(P) + SiH反应专门遵循插入机制，三重态下反应没有入口势垒。最初形成的三重态插入复合物（HSiCH）可以通过ISC进入单重态，因为在反应过程中三重态 - 单重态交叉会多次发生。我们计算得到的H和H消除通道的总产物角分布在本质上是宽而平的或几乎各向同性的，表明形成了稳定的中间体复合物，这与最近的交叉分子束研究结果相符。
