New experiments and validated master-equation modeling for OH production in propyl + O2 reactions

The propyl + O2 reactions are important prototype reactions for general alkyl + O2 systems, possessing the most important reactive channels of larger species while remaining small enough for accurate quantum chemistry calculations and theoretical kinetics. Previous experiments [8] that characterized the production of OH in the propyl + O2 reactions could be only qualitatively modeled by rigorous master-equation calculations, leaving a deficient validation of, for instance, the critical RO2 ↔ QOOH isomerization pathways. This article revisits the combined experimental and modeling study of DeSain et al., using an improved experimental method to obtain time-resolved OH concentrations for pulsed-photolytic Cl-initiated oxidation of propane. The results are modeled with master-equation-based rate coefficients incorporated into a kinetic mechanism. Quantitative agreement can be obtained, providing experimental validation for the OH-producing pathways that are crucial for autoignition. The importance of the rigorous treatment of the kinetics for these highly pressure and temperature dependent reactions is emphasized, as well as the significance of the formally direct pathways such as chemical activation.