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1、物理化学学报(WuliHuaxueXuebao)AprilActaPhys.鄄Chim.Sin.,2008,24(4):587-594587[Article]www.whxb.pku.edu.cn·OH自由基与CH3CN反应机理及动力学1,21,鄢11田燕何天敬陈东明刘凡镇(1中国科学技术大学化学物理系,合肥230026;2安徽农业大学理学院,合肥230036)摘要:在CBS鄄QB3水平上研究了CH3CN和·OH反应的势能面,其中包括两个中间体和9个反应过渡态.分别给出了各主要物质的稳定构型、相对能量及各
2、反应路径的能垒.根据计算的CBS鄄QB3势能面,探讨了CH3CN+·OH反应机理.计算结果表明,生成产物P1(·CH2CN+H2O)的反应路径在整个反应体系中占主要地位.运用过渡态理论对产物通道P1(·CHCN+HO)的速率常数k(cm3·molecule-1·s-1)进行了计算.预测了k(cm3·2211molecule-1·s-1)在250-3000K温度范围内的速率常数表达式为k(250-3000K)=2.06伊10-20T3.045exp(-780.00/T).通1过与已有的实验值进行对比得出,在
3、实验所测定的250-320K范围内,计算得到的k1的数值与已有的实验值比较吻合.由初始反应物生成产物P1(·CHCN+HO)只需要克服一个14.2kJ·mol-1的能垒.而产物·CHCN+HO2222生成后要重新回到初始反应物CHCN+·OH,则需要克服一个高达111.2kJ·mol-1的能垒,这就表明一旦产物P13生成后就很难再回到初始反应物.关键词:·OH自由基;CH3CN;反应机理;CBS鄄QB3中图分类号:O641;O643ReactionMechanismandKineticsfortheRea
4、ctionof·OH+CH3CN1,21,鄢11TIANYanHETian鄄JingCHENDong鄄MingLIUFan鄄Chen(1DepartmentofChemicalPhysics,UniversityofScienceandTechnologyofChina,Hefei230026,P.R.China;2SchoolofScience,AnhuiAgriculturalUniversity,Hefei230036,P.R.China)Abstract:Thecomplexpotentialen
5、ergysurfaceforthereactionof·OHradicalwithCH3CN,including2intermediatecomplexes,9transitionstates,wastheoreticallyprobedattheCBS鄄QB3level.Thegeometriesandrelativeenergiesforvariousstationarypointsweredetermined.BasedonthecalculatedCBS鄄QB3potentialenergysur
6、face,thepossiblereactionmechanismof·OH+CH3CNwasproposed.ThecalculatedresultsdemonstratedthattheformationofP1(·CHCN+HO)wasthedominantreactionchannel.Therateconstant(k,cm3·molecule-1·s-1)ofP1was221calculatedbyTStheory.Overthetemperaturerange250-3000K,wepred
7、ictedthattheexpressionofk1wask1(250-3000K)=2.06伊10-20T3.045exp(-780.00/T).Bycomparingwiththeobtainedexperimentalvaluesitwasshownthatthevaluesofk1wereingoodagreementwiththeexperimentalresultsoverthetemperaturerange250-320K.Thecalculatedresultsindicatedthef
8、ormationofP1(CHCN+·OH)onlyneededabarrierof14.2kJ·mol-1.Whiletheproducts3·CHCN+HOretrogradedtothereactantsCHCN+·OH,anenergybarrierof111.2kJ·mol-1wasrequired.These223resultssuggestedthatthebackwarddirectionforthepathw