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

Abstract

The possible energy pathways for the reactions of N(2) with singlet and tripled C(2)O 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 (3)CNN + CO, NCO + CN and (3)NCN + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants (3)C(2)O + N(2). Formation of (1)CNN + CO and (1)NCN + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are (1,3)CNN + CO and cyc-(1)NCN + CO, their rate constants in cm(3) molecule (1) s (1) can be presented as k(1) ((3)CNN + CO) = 3.5 x 10(-11) exp(-36.8 kcal/mol/RT), k(2) ((1)CNN + CO) <= 2.9 x 10(-12) exp(-33.2 kcal/mol/RT) and k(3) (cyc-(1)NCN + 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 (3)NCN + 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, (3)CNN + CO and (3)NCN + 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(2)O 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.