ON THE MECHANISM AND BRANCHING RATIO OF THE CN-]CO+NO REACTION CHANNEL USING TRANSIENT IR EMISSION-SPECTROSCOPY(O2)

The contribution of the title reaction to the total reaction of CN + O 2 has been determined, using time-resolved IR emission spectroscopy of the product CO(v''). This product channel is found to contribute up t o 29% with 2% experimental variance to the total reaction. A contribut ion of this magnitude to the total reaction of CN + O2 by this product channel proceeding via a four-center transition state is energeticall y improbable. Ab initio calculations have been performed on two- and f our-center transition states which are presumably formed in the reacti on between CN radicals and molecular oxygen. The results of these calc ulations confirm the existence of a very high barrier to the formation of a four-center transition state. Consequently, a new mechanism for the formation of CO in reaction 1 is proposed. This new mechanism cons ists of two sequential steps rather than two parallel steps to explain the formation of the products NCO, O, and CO in the reaction CN + O2.