Temperatureand Pressure Dependent Rate Coefficientsfor the Reaction of C2H4+ HO2onthe C2H4O2H Potential Energy Surface.

Thepotential energy surface (PES) for reaction C2H4+ HO2was examined by using the quantum chemicalmethods. All rates were determined computationally using the CBS-QB3composite method combined with conventional transition state theory(TST),variational transition-state theory (VTST) and Rice–Ramsberger–Kassel–Marcus/master-equation(RRKM/ME) theory. The geometries optimization and the vibrationalfrequency analysis of reactants, transition states, and products wereperformed at the B3LYP/CBSB7 level. The composite CBS-QB3 method wasapplied for energy calculations. The major product channel of reactionC2H4+ HO2is the formation C2H4O2H via an OH···π complex with 3.7 kcal/mol binding energy which exhibits negative-temperaturedependence. We further investigated the reactions related to thiscomplex, which were ignored in previous studies. Thermochemical propertiesof the species involved in the reactions were determined using theCBS-QB3 method, and enthalpies of formation of species were comparedwith literature values. The calculated rate constants are in goodagreement with those available from literature and given in modifiedArrhenius equation form, which are serviceable in combustion modelingof hydrocarbons. Finally, in order to illustrate the effect for low-temperatureignition of our new rate constants, we have implemented them intothe existing mechanisms, which can predict ethylene ignition in ashock tube with better performance. [ABSTRACT FROM AUTHOR]