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

Abstract

The kinetics of the isoprene−OH/OD reaction in the presence of O2 and NO have been studied using laser photolysis/laser-induced fluorescence. We report pressure and temperature-dependent rate constants for the addition of OH/OD to isoprene are in good agreement with previous studies. On the basis of simulations to OH cycling curves, we find a value of (9.0 ± 3.0) × 10-12 molecule-1 cm3 s-1 for the overall reaction rate constant of hydroxy peroxy radical with NO at 298 K. We report a rate constant for O2 addition to the hydroxy alkyl radical of (2.3 ± 2.0) × 10-12 molecule-1 cm3 s-1 at 298 K. We find little generation of OH from the OD initiated oxidation of isoprene, and no significant differences in OH and OD cycling, suggesting that H-shift isomerization is the major pathway for δ-hydroxy alkoxy radicals, in agreement with theoretical predictions.