Ab initio chemical kinetics for the reactions of N2 with singlet and triplet C2O radicals

The possible energy pathways for the reactions of N2 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 3CNN + CO, NCO + CN and 3NCN + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants 3C2O + N2. Formation of 1CNN + CO and 1NCN + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are 1,3CNN + CO and cyc-1NCN + CO, their rate constants in cm3 molecule−1 s−1 can be presented as k1 (3CNN + CO) = 3.5 × 10−11 exp(−36.8 kcal/mol/RT), k2 (1CNN + CO) ⩽ 2.9 × 10−12 exp(−33.2 kcal/mol/RT) and k3 (cyc-1NCN + CO) = 6.86 × 10−20exp(−27.7 kcal/mol/RT), which are significantly lower than those assumed in the literature. The rate constants for the formation of 3NCN + 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, 3CNN + CO and 3NCN + 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 + N2 reaction for prompt-NO formation in hydrocarbon combustion.