Department of Physical Chemistry, Wroclaw Medical University, pl. Nankiera 1, 50-140 Wroclaw, Poland.
J Mol Model. 2013 Apr;19(4):1489-505. doi: 10.1007/s00894-012-1709-4. Epub 2012 Dec 14.
Ab initio calculations at the G2 level were used in a theoretical description of the kinetics and mechanism of the hydrogen abstraction reactions from fluoro-, chloro- and bromomethane by chlorine atoms. The profiles of the potential energy surfaces show that mechanism of the reactions under investigation is complex and consists of two - in the case of CH3F+Cl - and of three elementary steps for CH3Cl+Cl and CH3Br+Cl. The heights of the energy barrier related to the H-abstraction are of 8-10 kJ mol(-1), the lowest value corresponds to CH3Cl+Cl and the highest one to CH3F+Cl. The rate constants were calculated using the theoretical method based on the RRKM theory and the simplified version of the statistical adiabatic channel model. The kinetic equations derived in this study[Formula: see text]and[Formula: see text]allow a description of the kinetics of the reactions under investigation in the temperature range of 200-3000 K. The kinetics of reactions of the entirely deuterated reactants were also included in the kinetic analysis. Results of ab initio calculations show that D-abstraction process is related with the energy barrier of 5 kJ mol(-1) higher than the H-abstraction from the corresponding non-deuterated reactant molecule. The derived analytical equations for the reactions, CD3X+Cl, CH2X+HCl and CD2X+DCl (X = F, Cl and Br) are a substantial supplement of the kinetic data necessary for the description and modeling of the processes of importance in the atmospheric chemistry.
采用 G2 水平的从头算方法对氟代、氯代和溴代甲烷与氯原子的氢提取反应的动力学和反应机理进行了理论描述。势能面的轮廓表明，所研究反应的机理是复杂的，由两个步骤组成 - 对于 CH3F+Cl - 和三个基本步骤组成 - 对于 CH3Cl+Cl 和 CH3Br+Cl。与 H 提取相关的能量势垒高度为 8-10 kJ mol(-1)，最低值对应于 CH3Cl+Cl，最高值对应于 CH3F+Cl。使用基于 RRKM 理论和简化统计绝热通道模型的理论方法计算了速率常数。本研究中推导出的动力学方程[公式：见文本]和[公式：见文本]允许在 200-3000 K 的温度范围内描述所研究反应的动力学。还将完全氘代反应物的反应动力学纳入了动力学分析。从头算计算的结果表明，D 提取过程与从相应的非氘代反应物分子中提取 H 的能量势垒相关，高出 5 kJ mol(-1)。对于反应 CD3X+Cl、CH2X+HCl 和 CD2X+DCl（X = F、Cl 和 Br）推导的解析方程是对大气化学中重要过程进行描述和建模所需的动力学数据的重要补充。
