A new path to "prompt" NO: CH + N₂ = H + NCN studied by ab initio MO and statistical theory calculations

In the past two decades, the CH(²Π) + N₂ → HCN + N(⁴S) reaction has been routinely employed for kinetic modeling of NO_x formation in hydrocarbon combustion. The reaction has been studied by many investigators 1-17 since Fenimore 18 suggested it to be a potential "prompt" NO precursor process in 1971. The result of a recent comprehensive study by Morokuma and co-workers, 19,20 however, indicated that the theoretically predicted rate constant for the formation of the spin-forbidden HCN + N products is about two orders of magnitude lower than experimentally measured values. 1,2,7,8 The result of our high-level molecular orbital study aided by a statistical-theory calculation reveals that the spin-allowed H + NCN products occurring by the ground electronic doublet surface is the dominant CH + N₂ process under combustion conditions.