Kinetic rate constants for the oxidation reactions of OH radicals with CH3SH (1), C2H5SH (2), n-C3H7SH (3) and iso-C3H7SH (4) under inert conditions (Ar) over the temperature range 252−430 K have been studied using the CBS-QB3 composite method. Kinetic rate constants under atmospheric pressure and in the fall-off regime have been estimated using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Comparison with experiment confirms that in the OH-addition pathways 1−4 leading to the related products, the first bimolecular reaction step has effective negative activation energies around −2.61 to 3.70 kcal mol−1. Effective rate coefficients have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a result of the negative activation energies, pressures larger than 104 bar would be required to restore to some extent the validity of this approximation for all the channels. By comparison with experimental data, all our calculations for both the OH-addition and H-abstraction reaction pathways indicate that from a kinetic viewpoint and in line with the computed reaction energy barriers, the most favourable process is the OH-addition pathway to n-C3H7SH to yield the [n-C3H7SH−OH]• species, whereas under thermodynamic control of the bimolecular reactions (R−SH+OH•), the most abundant product derived from the H-abstraction pathway will be the [n-C3H7 S•+H2O] species.

中文翻译：

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OH自由基与烷基取代的脂肪族硫醇之间的氧化反应机理和动力学：OH-加成途径

OH 自由基与 CH3SH (1)、C2H5SH (2)、n-C3H7SH (3) 和 iso-C3H7SH (4) 在惰性条件 (Ar) 下在 252-430 K 温度范围内的氧化反应动力学速率常数已被确定使用 CBS-QB3 复合方法进行研究。使用过渡态理论 (TST) 和统计赖斯-拉姆斯伯格-卡塞尔-马库斯 (RRKM) 理论估计了大气压下和衰减状态下的动力学速率常数。与实验的比较证实，在通向相关产物的 OH-加成途径 1-4 中，第一个双分子反应步骤具有大约 -2.61 至 3.70 kcal mol-1 的有效负活化能。根据两步模型反应机理的稳态分析计算了有效速率系数。由于负活化能，需要大于 104 bar 的压力才能在一定程度上恢复该近似值对所有通道的有效性。通过与实验数据的比较，我们对 OH-加成和 H-抽象反应途径的所有计算表明，从动力学的角度来看，与计算的反应能垒一致，最有利的过程是 OH-加成途径到 n- C3H7SH 产生 [n-C3H7SH-OH]• 物种，而在双分子反应 (R-SH+OH•) 的热力学控制下，从 H-抽象途径衍生的最丰富的产物将是 [n-C3H7 S •+H2O] 物种。