Oxidation of norbornadiene:Theoretical investigation on H-atom abstraction and related radical decomposition reactions

The chemical kinetics of hydrogen atom(H-atom)abstraction reactions from norbornadiene(NBD)by five radicals(H,O(^(3)P),OH,CH_(3),and HO_(2)),and the unimolecular reactions of three NBD derived radicals,were studied through high-level ab-initio calculations.The geometries optimization and vibrational frequencies calculation for all the reactants,transition states,and products were obtained at the M06-2X/6-311ttG(d,p)level of theory.The zeropoint energy(ZPE)corrected potential energy surfaces(PESs)were determined at the QCISD(T)/cc-pVDZ,TZ level of theory with basis set corrections from MP2/cc-pVDZ,TZ,QZ methods for single point energy calculations.Conventional transition state theory(TST)was used for the rate constants calculations of H-atom abstraction reactions by five radicals(H,O(^(3)P),OH,CH_(3),and HO_(2))at temperatures from 298.15 to 2000 K,while the a-site H-atom abstraction reaction rate constant of NBD by OH radical has been obtained through variational transition state theory(VTST).The results show that the H-atom abstraction reactions from the α-carbon atom of NBD are the most critical channels at low temperatures.Total rate constants for H-atom abstraction reactions by OH radical are also the fastest among all of the reaction channels investigated at the temperature range from 298.15 to 2000 K.Rice-Ramsperger-Kassel-Marcus/Master Equation(RRKM/ME)has been used to calculate the pressure-and temperature-dependent rate constants for the unimolecular reactions of three related C7H7 product radicals which generated from H-atom abstraction reaction within temperature ranges of 300-2000 K and pressures of 0.01-100 atm.A combination of composite methods has been used to calculate the temperature-dependent thermochemical properties of NBD and related radicals.All the calculated kinetics and thermochemistry data can be utilized in the model development for NBD oxidation.