H_2FCS单分子分解反应的直接动力学研究

Direct Dynamics Study on the Unimolecular Decomposition Reactions of H_2FCS

采用量子化学QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)方法研究了H2FCS单分子分解反应的微观动力学性质,构建了反应势能剖面.利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT),分别计算了在200～3000K温度范围内的速率常数kTST,kCVT和kCVT/SCT.计算结果表明,H2FCS可经过不同的反应通道生成10种小分子产物,脱H反应和HF消去反应为标题反应的主反应通道,其中HF消去反应产物HCS可由两条反应通道生成.在200～3000K温度区间内得到三条反应通道的表观反应速率常数三参数表达式分别为kPath(1)CVT/SCT=3.6×10-41T12.8exp(11597.7/T)cm3·molecule-1·s-1,kPCaVthT(3/S)CT=3.6×10-15T5.52exp(19769.4/T)cm3?molecule-1·s-1和Path(4)CVT/SCT=1.5×10-3T2.03exp(21821.6/T)cm3·molecule-1·s-1.速率常数计算结果显示,量子力学隧道效应在低温区间对反应速率常数的影响显著,而变分效应在计算温度范围内可以忽略.

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 m,o different charmels. The fitted Arrhenius expressions of the calculated CVT/SCT rate constants are Kath（1）^CVT/SCT = 3.6 ×10^-41T^12.8 exp（11597.7/T） cm^3·molecule^-1·s^- 1, KPath（3）^CVT/SCT =3.6× 10^-15T^5.52exp（19769.4/T） cm^3·molecule^-1·s^-1, and KPath（4）^CVT/SCT = 1.5 × 10^-3T^2.03exp（21821.6/T） cm^3·omolecule^-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.