Rate constants for the reactions of CH3O and C2H5O with NO2 over a range of temperature and total pressure

Abstract

The kinetics of the reactions of CH₃O and C₂H₅O radicals with NO₂ have been studied using pulsed laser photolysis to create the radicals from the corresponding alkyl nitrite and by time-resolved, laser-induced fluorescence to observe the decay of the radical concentration. At 295 K, rate constants for CH₃O + NO₂ have been measured in the presence of Ar (6–100 Torr), He (30–100 Torr) and CF₄(30–125 Torr). The association reaction to CH₃ONO₂ appears to predominate, and rate constants in the limit of low and high pressure are deduced: (k°/10^–29 cm⁶ molecule^–2 s^–1)= 2.8 ± 0.6 (M = Ar); 1.6 ± 0.6 (M = He); 3.4 ± 1.0 (M = CF₄), and (k^∞/10^–11 cm³ molecule^–1 s^–1)= 2.0 ± 0.4, where the quoted errors correspond to two standard deviations. A limited number of measurements is also reported for this reaction at 390 K. The rate of the reaction of C₂H₅O with NO₂ at 295 K is found to be the same in the presence of 15 and 100 Torr of Ar, and the measurements yield a rate constant: (k^∞10^–11 cm³ molecule^–1 s^–1)= 2.8 ± 0.3.