反应类等键反应方法及类反应热动力学参数计算

Reaction Class Isodesmic Reaction Method and Calculation of Thermokinetic Parameters for Reactions in a Class

提出了反应类等键反应方法,将通常用于热力学性质计算的等键反应方法推广用于类反应中反应势垒和反应焓变的计算.对碳氢燃料低温燃烧反应机理中的一类重要反应类——β烷基自由基过氧化氢裂解生成烯烃和HO2自由基的反应势垒和反应焓变进行了计算.通过对该类16个反应中的5个代表性反应分别在不同计算水平HF,DFT,MP2和CCSD(T)的计算比较发现,采用反应类等键反应方法可在较低从头算级别计算得到类反应较高精度的反应势垒,提高了计算效率.采用反应类等键反应方法在B3LYP/6-311G(d,p)水平对该类16个反应进行了反应势垒和反应焓变的计算,并建立了反应势垒和反应能的线性自由能关系:ΔV≠=71.02+0.41ΔE.

Reaction class isodesmic reaction method was proposed,which extends the isodesmic reaction method usually used for the calculation of the thermodynamic properties to calculate the reaction barriers and reaction enthalpies for reactions in a class.The pyrolysis of β alkyl hydrogen peroxide generating olefin and HO2 radical was studied.It is an important class of reactions in the combustion of the hydrocarbon in low-temperature phase.Calculations for 5 representative reactions in this reaction class using reaction class isodesmic reaction method and direct calculation method respectively,at HF,DFT,MP2,CCSD（T） level reveal that low-level ab initio method such as B3LYP method using reaction class isodesmic reaction method can reproduce reaction barriers by high-level ab initio method such as CCSD（T）.In this study,reaction barriers and the reaction enthalpies for 16 reactions of this class at B3LYP/6-311G（d,p） level were calculated using reaction class isodesmic reaction method and a linear free energy relationship between the reaction barrier and the reaction energy was obtained： ΔV≠=71.02＋0.41ΔE.