Rate constants of CH3O2 + NO2 CH3O2NO2 and C2H5O2 + NO2 C2H5O2NO2 reactions under atmospheric conditions

Abstract

AbstractPeroxy (RO2) radicals derived from short‐chain alkanes were detected by an improved technique involving combined fluorescence assay by gas expansion and laser‐induced fluorescence (FAGE‐LIF) and chemical conversion under atmospheric conditions (298 K and 1 bar). The suitability of the system for measuring RO2 kinetics was tested using the CH3O2 + NO2 + M CH3O2NO2 + M reaction. CH3O2 radicals were generated by the OH + CH4 → CH3 + H2O reaction and subsequent O2 addition. The CH3O2 radicals were monitored using the LIF intensity of the OH radicals, which were converted from CH3O2 radicals by chemical reaction with NO and O2. The decay rates of CH3O2 radicals were measured at various NO2 concentrations, and the bimolecular rate constant was determined to be k = (3.9 ± 0.3) × 10−12 cm3 molecule−1 s−1. The result is consistent with the literature value, thus demonstrating the validity of the improved system. We also constructed a fitting equation for the simultaneous determination of the forward and reverse reaction rates because the thermal decomposition of CH3O2NO2 was not negligible. From the global fitting analysis using the fitted equation, the decomposition rate of CH3O2NO2 was determined to be k = 2.0 ± 0.6 s−1. Furthermore, we investigated the C2H5O2 + NO2 + M C2H5O2NO2 + M reaction. The forward reaction rate was approximately 1.7 times faster than that of the CH3O2 + NO2 + M reaction: = (6.5 ± 0.4) × 10−12 cm3 molecule−1 s−1, and the reverse reaction rate was 3.6 ± 0.7 s−1. These results agree with the previous estimates.