Kinetics and mechanism of the CN + NCO → NCN + CO reaction studied by experiment and theory

The rate coefficients for the CN + NCO → NCN + CO reaction have been measured by a laser-photolysis/ laser-induced fluorescence technique in the temperature range of 254-353 K and the He pressures of 123-566 Torr. The CN radical was produced from the photolysis of BrCN at 193 nm, and the NCO radical from the CN + O₂ reaction. The NCN radical was monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constants derived from kinetic modeling, with a negative temperature dependence but no pressure effect, can be expressed by k = (2.15 ± 0.70) × 10 ^-11 exp[(155 ± 92)/T]cm³ molecule^-1 s^-1, where the quoted errors are two standard deviations. The reaction mechanism and rate constant have also been theoretically predicted for the temperature range of 200-3000 K at He pressures ranging from 10^-4 Torr to 1000 atm based on dual channel Rice-Ramsperger-Kassel-Marcus (RRKM) calculations with the potential energy surface evaluated at the G2M and CCSD(T) levels. The rate constant calculated by variational RRKM theory agrees reasonably with experimental data.