CF_3CH_2CF_2CH_3(HFC-365mfc)与Cl原子反应的微观机理及动力学性质  

Mechanism and Kinetics for Reaction of CF_3CH_2CF_2CH_3(HFC-365mfc) with Cl Atom

作　　者：金铜音[1] 王钦[1] 刘靖尧[1] 

机构地区：[1]吉林大学理论化学研究所理论化学计算国家重点实验室,长春130021

出　　处：《高等学校化学学报》2013年第3期641-649,共9页Chemical Journal of Chinese Universities

基　　金：国家自然科学基金(批准号:20973077;20303007);教育部新世纪优秀人才支持计划资助

摘　　要：采用密度泛函理论方法 M06-2X结合6-31+G(d,p)基组研究了CF3CH2CF2CH3与Cl原子反应的反应机理.计算获得了CF3CH2CF2CH3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Boltzmann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kT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ΔHf,298 K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＋Cl 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 conformers（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 conformers 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=1.88×10-22T3.76exp（-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（ΔHf,298 K） were predicted via isodesmic reaction at the M06-2X/6-31＋G（d,p） level.

关 键 词：密度泛函理论 直接动力学 速率常数 改进的正则变分过渡态理论 CF3CH2CF2CH3 

分 类 号：O641[理学—物理化学] O643[理学—化学]