A theoretical analysis of propargyl oxidation by the hydroperoxyl radical

The kinetics of the C 3 H 3 + HO 2 reaction system were investigated theoretically using high-level quantum chemical methods combined with statistical rate theory. The potential energy surface (PES) was explored to identify intermediates and transition states using reactive molecular dynamics with ChemTraYzer-TAD. The resulting thermochemical data and energy barriers for products P0 to P13 were used in RRKM/master equation calculations to determine the temperature-and pressure-dependent rate constants suitable for incorporation into chemical kinetic models. Implications for chemical kinetic model predictions and future model development were assessed by representative jet-stirred reactor simulations of stoichiometric propyne/air mixtures at 10 atm and 800-1200 K. These simulations show that the widely employed allyl + HO 2 analogy overestimates propargyl consumption. In the jet-stirred reactor case considered here, replacing the analogy-based treatment with the theory-based update reduces the contribution of C 3 H 3 + HO 2 reactions to the overall consumption of C 3 H 3 from up to 26 % to no more than 15 %. The corresponding changes in benzene predictions are visible, but remain within the experimental uncertainty. Based on these findings, a compact reduced three-reaction submodel is proposed for future chemical kinetic model development. Novelty and significance statement We present the first comprehensive ab initio and master equation-based kinetic investigation of the C 3 H 3 + HO 2 reaction system. Barrierless and new low-barrier channels were identified using potential energy surface exploration with ChemTraYzer-TAD, and the resulting temperature-and pressuredependent rate coefficients provide a substantially more reliable description of this chemistry than the allyl + HO 2 analogy commonly used in chemical kinetic models. Jet-stirred reactor simulations show that replacing the analogy-based treatment reduces predicted C 3 H 3 consumption via reactions with HO 2 and leads to visible changes in benzene predictions that remain within the experimental uncertainty. Brute force sensitivity analysis further shows that only the OH-forming channel, C 3 H 3 + HO 2 = P-C 3 H 3 O + OH, noticeably affects the predicted C 3 H 3 and benzene mole fractions. Based on these findings, a compact reduced three-reaction submodel is proposed for future chemical kinetic model development. Because C 3 H 3 is a key C0-C4 core species, the refined kinetics are relevant beyond aromatic chemistry.