Reinvestigation of the Branching Ratio of the CN + O₂ Reaction

Abstract

The reaction of the CN radical with O(2) was studied using infrared diode laser absorption spectroscopy. Detection of NO and secondary N(2)O products was used to directly measure the product branching ratio. After consideration of possible secondary chemistry and comparison to kinetic modeling simulations, the branching ratio of the CN + O(2) reaction into the NO + CO channel was determined to be phi (NO + CO) = 0.20 +/- 0.02, with little or no temperature dependence over the range 296-475 K.

Modeling nitrogen chemistry in combustion

“…However, the branching fraction to the two product channels NCO + O (R37) and NO + CO (R38) has been in discussion. Measurements of the branching fraction [150,155,156] are in good agreement at room temperature.…”

“…Recently, Feng and Hershberger [150] veried that the NO + CO channel (R38) constituted 20% with little or no temperature dependence over the range 296-475 K, in contrast to earlier results from the same group [156], and we have adopted their recommendation.…”

Astrochemistry: Synthesis and Modelling

“…Under dense cloud conditions and with a gas-grain model (and an elemental C/O ratio of 1.2), the CN molecule is abundant and reacts with O 2 to form either O + OCN or CO + NO. The total rate coefficient of this reaction has been measured by Sims et al [96] between 13 and 295 K, and the product branching ratios by Feng & Hershberger [97] so that the temperature dependent rate coefficients are: The rates of these reactions also depend on the abundance of CN, a molecule significantly destroyed by the neutral-neutral reaction with atomic nitrogen. The rate coefficient of the reaction N + CN has recently been revised.…”

Kinetics and Mechanism of the NCCO + NO Reaction

“…26 Note that the CN + NO reaction is quite slow at low pressures, with a rate constant of ∼1.6 × 10 -13 cm 3 molecule -1 s -1 at 298 K, 2 Torr, 27 and is therefore not important in this experiment. Based on the analysis above, we can assume that:…”