The fate of the hydroxyalkoxy radical in the OH‐initiated oxidation of isoprene

Abstract

Rate constants for several intermediate steps in the OH-initiated oxidation of isoprene were determined using laser-photolysis/laser-induced fluorescence of OH radicals at total pressures between 3 and 4 Torr at 295 K. The rate constant for decomposition of the hydroxyalkoxy radical was determined to be (3.0 ± 0.5) × 10 4 s −1 in this pressure range, which is in fair agreement with previous work. The presence of a prompt alkoxy decomposition pathway was also investigated and found to contribute less than 10% to the total hydroxyalkoxy radical decomposition. The rate constant for the reaction of the hydroxyperoxy radical with NO was determined to be (2.5 ± 0.5) × 10 −11 cm 3 molecule −1 s −1 , which is moderately higher than previously reported.

Overall rate constant measurements of the reactions of alkene-derived hydroxyalkylperoxy radicals with nitric oxide

“…As noted in the Introduction, there have been previous studies of the alkene-derived hydroxyalkylperoxy þ NO rate constant for ethene, 18 2-methyl propene 7 and isoprene. 12,15,17 In Table 2 and in Fig. 5, the values determined in the present study are compared with these previous results.…”

OH/OD Initiated Oxidation of Isoprene in the Presence of O2 and NO

“…A similar value was recently reported by Hynes and coworkers. 19 The reported value of (2.5 ( 0.5) × 10 -11 molecule -1 cm 3 s -1 by Reitz et al, 25 also based on OH cycling measurements, lies out of the error limit of those values.…”

“…The value is consistent with the rate constant previously reported. 25,26,[33][34][35] We find that the present experiments are not sensitive to the nitrate yield given the experimental conditions and we have adopted a value of 5% that is close to the value proposed by Chen et al 32 The rate constant for the reaction of hydroxy peroxy radical with NO is substantially higher that the value of 3.8 × 10 -12 Table 3) assuming [C5H8] ) 7.5 × 10 13 molecules cm -3 and [O2] ) 3.45 × 10 16 molecules cm -3 .…”

The OH-Initiated Oxidation of 1,3-Butadiene in the Presence of O2 and NO: A Photolytic Route To Study Isomeric Selective Reactivity

“…Recent kinetic studies have relied on OH regeneration to infer information about the isomeric branching. [10][11][12][13][14] Analysis of the results suggests qualitative agreement with theoretical predictions but the complexity of the reaction systems has precluded a quantitative comparison. To date all of the kinetic data reflect "lumped", nonisomeric selective, rate constants.…”