The CF3+NO2 rate constant measured between 1.5 and 110 Torr and between 251 and 295 K by time resolved infrared emission

Abstract

The rate constant k1 for reaction of CF3 with NO2 was investigated over the pressure range 1.5–110 Torr Ar or N2 and at temperatures between 251 and 295 K. Time resolved emission from vibrationally excited CF2O and FNO products was used as a detection method for CF3 removal. The rate constant at room temperature shows no marked variation with pressure, with an average value of k1 = (1.75 ± 0.26) × 10−11 cm3 molecule−1 s−1, where the errors are 2σ, but a small reduction at the lowest pressure indicates the possible contribution from a third body recombination process. We conclude that this process is minor, and if it is treated as a separate reaction channel it results in a limiting high pressure branching ratio of 13 ± 7%, which drops to half that value at 10 Torr. As the limiting high and low pressure rate constants are within the 2σ error bars of k1, we recommend the average value as applying over the full pressure range. Combination with previous results shows that of the possible bimolecular channels, formation of CF2O + FNO dominates (ca. 95%). No temperature dependence is seen, within experimental error. Pitfalls in the extraction of rate constants from the analysis of time resolved product emission are discussed, and a method is described to assign rate constants unambiguously to reactive formation and collisional quenching. CF3 radicals were formed from the 248 nm photolysis of CF3I, and observations of emission from the radical show previously unobserved excitation in the asymmetric C–F stretching mode ν3.