Importance of intersystem crossing in the C(³P) + SiH₄ reaction

The contribution of intersystem crossing (ISC) in the C(³P) + SiH₄ 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(³P) + SiH₄ 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^-1) 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(³P) + SiH₄ 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(³P) + SiH₄ reaction with no entrance barrier to the reaction in the triplet state. The triplet insertion complex initially formed (³H₃SiCH) 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 H₂ 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.