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

The spin-forbidden CH + N₂ = HCN + N reaction, which had been extensively employed for kinetic modeling of "prompt" NO formation in the past 3 decades, was recently theoretically predicted to be inconsistent with high temperature kinetic data. In an extensive search for the new reaction path over the ground electronic doublet potential energy surface, the key conceded transition state which links a cyclic-C(H)NN^- intermediate with the most stable HCN₂ isomer, HNCN, was uncovered. At high temperatures, the HNCN radical fragments to yield H and NCN, whose oxidation by O_x and HO_x under combustion conditions produces NO and its precursor, CN and NCO. The result of the RRKM calculation for NCN production agreed closely with the kinetically modeled rate constants for CH decays and N-production measured in shock-tube studies. Original is an abstract.