Ab initio chemical kinetics for the reactions of N-2 with singlet and triplet C2O radicals

Abstract

The possible energy pathways for the reactions of N-2 with singlet and tripled C2O have been investigated at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level of theory. Our results show that the rate-controlling transition states for the formation of (CNN)-C-3 + CO, NCO + CN and (NCN)-N-3 + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants (C2O)-C-3 + N-2. Formation of (CNN)-C-1 + CO and (NCN)-N-1 + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are (CNN)-C-1,3 + CO and cyc-(NCN)-N-1 + CO, their rate constants in cm(3) molecule (1) s (1) can be presented as k(1) ((CNN)-C-3 + CO) = 3.5 x 10(-11) exp(-36.8 kcal/mol/RT), k(2) ((CNN)-C-1 + CO) <= 2.9 x 10(-12) exp(-33.2 kcal/mol/RT) and k(3) (cyc-(NCN)-N-1 + CO) = 6.86 x 10(-20)exp(-27.7 kcal/mol/RT), which are signi. cantly lower than those assumed in the literature. The rate constants for the formation of (NCN)-N-3 + CO and NCO + CN are too small to be important due to their high exit barriers. The predicted heats of reaction for formation of products NCO + CN, (CNN)-C-3 + CO and (NCN)-N-3 + CO are 45.9, 18.1 and -10.7 kcal/mol, which agree excellently with the experimental values, 45.8, 17.7 and -10.7 kcal/mol. Our results imply that the reaction of C2O with N2 cannot compete with the CH + N-2 reaction for prompt-NO formation in hydrocarbon combustion. (C) 2010 Elsevier B. V. All rights reserved.