Ab Initio Kinetic Study of H-, CH₃-, NH₂-, HO₂-, OH-, and NO₂-Mediated H-Abstraction in 3-Pentanone Oxidation

The H-abstraction reactions by small molecule radicals constitute a critical step in the low-temperature chain propagation during 3-pentanone oxidation. This work presents a kinetic investigation of H-, CH₃-, NH₂-, HO₂-, OH-, and NO₂-mediated H-abstraction from 3-pentanone, employing CCSD(T)/CBS calculations integrated with RRKM and TST. Sixteen reaction channels are explored to elucidate the reaction mechanisms. All reaction pathways exhibit energy barriers within the range of 1.1-37.2 kcal/mol. The H-, CH₃-, NH₂-, and OH-mediated H-abstractions are exothermic, whereas those by HO₂ and NO₂ are endothermic. For H, CH₃, NH₂, HO₂, and NO₂ radicals, the barrier heights increase from the 1-site to the 2-site, while the opposite trend is observed for OH. The prevailing reaction site of 3-pentanone migrates from one site to another with increasing temperature. The OH process displays the lowest barriers, leading to the highest rate constants, while the NO₂-mediated pathways are kinetically unfavorable. Furthermore, the integration of calculated data into the 3-pentanone oxidation model improves predictive accuracy in matching ignition delay times measured in experiments. The sensitivity analysis identifies dominant consumption pathways and key reactions in 3-pentanone oxidation.