Ab initio chemical kinetics for the reactions of N 2 with singlet and triplet C 2O radicals

Abstract

The possible energy pathways for the reactions of N 2 with singlet and tripled C 2O 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 3C 2O + N 2. 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 cm 3 molecule −1 s −1 can be presented as k 1 ( 3CNN + CO) = 3.5 × 10 −11 exp(−36.8 kcal/mol/ RT), k 2 ( 1CNN + CO) ⩽ 2.9 × 10 −12 exp(−33.2 kcal/mol/ RT) and k 3 (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 C 2O with N 2 cannot compete with the CH + N 2 reaction for prompt-NO formation in hydrocarbon combustion.