采用密度泛函理论方法M06-2X结合6-31+G(d,p)基组研究了CF3 CH2 CF2 CH3与Cl原子反应的反应机理.计算获得了CF3 CH2 CF2 CH3的两种可区分的稳定几何构象RC1和RC2以及与它们相对应的8条氢提取反应通道和2条取代反应通道.运用改进的正则变分过渡态理论(ICVT)并结合小曲率隧道效应校正(SCT),在M06-2X/6-31 +G(d,p)水平上计算了各氢提取通道的速率常数,并由Bohzmann配分函数得到总包反应的速率常数kT(cm3-molecule-1·s-1).计算结果表明,体系的总反应速率常数与已有实验值相吻合,进而给出了该反应在200～1000 K温度区间内反应速率常数κT的三参数表达式kT=1.88×10-22T3.76·exp(-1780.69/T),并讨论了两种构象RC1和RC2对总反应的贡献及各构象中氢提取发生在-CH3或-CH2-基团上的位置选择性.此外,由于缺少相关反应物及产物自由基标准生成焓△Hf,298K的数据,利用等化学键法估算了在上述物种的标准生成焓.%The mechanism of the CF3CH2CF2CH3+C1 reaction was investigated by the M06-2X method combining with the 6-31+G(d,p) basis set[ M06-2X/6-31+G(d,p) ]. There were two distinguishable stable con-formers (RC1 and RC2) for the reactant CF3CH2CF2CH3, and eight H-abstraction channels as well as two substitution channels were located associated with them. The rate constants for each of the H-abstraction channels were evaluated by the improved canonical variational transition state theory (ICVT) with the small-curvature tunneling(SCT) approximation at the M06-2X/6-31+G(d,p) level. The overall rate constant(kT) was obtained by considering the weight factor of each conformer from the Boltzmann distribution function, and the calculated values agree well with the available experimental values. Moreover, the contribution of the two con-formers to the whole reaction as well as the site selectivity for each of the conformers were discussed. A three-parameter rate constant-temperature expression for the total reaction within 200-1000 K was fitted to kT = 1. 88×l0-22T3.76exp( -1780. 69/T). In addition, because of the lack of available experimental data for the reactant as well as the corresponding product radicals involved in the reactions, their enthalpies of the formation (△Hf,298K) were predicted via isodesmic reaction at the M06-2X/6-31+G(d,p) level.
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