A QCISD(T)/6-311＋＋G(d,p)//B3LYP/6-311＋G(d,p) method was employed to reveal the reaction mechanism and to predict the micro-dynamics character of the unimolecular decomposition of H2FCS. The rate constants of the reactions were evaluated by means of the classical transition state theory and the canonical variational transition state theory in which the small-curvature tunneling correction was included. The results indicate that H2FCS can decompose through several production channels to form ten small molecules. The elimination of HF or H atom is the dominant channel of the title reaction and the formation of the product HCS＋HF will undergo two different channels. The fitted Arrhenius expressions of the calculated CVT/SCT rate constants are ＝3.6×10－41T12.8exp(11597.7/T) cm3•molecule－1•s－1, ＝3.6×10－15T5.52exp(19769.4/T) cm3•molecule－1•s－1, and ＝1.5×10－3T2.03exp(21821.6/T) cm3•molecule－1•s－1 in the temperature range of 200～3000 K for the three elimination channels, respectively. In addition, the tunneling effect was considerable at the lower temperature, while the variational effect was almost negligible in the entire process.

Key words: H2FCS, density functional theory (DFT), reaction mechanism, rate constant