Using the DFT-B3LYP based on 6-311++G** basis set, the geometries of the reactants, the intermediates and the transition states were fully optimized at the B3LYP/6-311++G** level. The intermediates and the transition states were examined by using the frequency calculations and the intrinsic reaction coordinate (IRC). Furthermore, single-point energy calculations were refined at the QCISD level of theory with the same basis set (6-311++G**). As a result, the singlet reaction of silylene with isothiocyanic acid contain S-atom abstraction channel, N—H inserted channel, and NH abstraction channel, respectively. The pathway written as SiH2＋HNCS→IM1→TS2→IM3→TS3→IM4→SiH2S＋HNC(P1) was the main pathway, whose the activation energy was the lowest and the primary products were SiH2S and HNC, respectively. While the channel of NH abstraction, which was a minor channel comparing those of direct S-atom abstraction and N—H insertion, was the competitive reaction channel and can process under the room temperature.

Key words: silylene, isothiocyanic acid, reaction mechanism, activation energy, transition state