Reaction and complex formation between OH radical and acetone

Abstract

Kinetics and mechanism of the reaction of OH with CH₃C(O)CH₃ have been studied by discharge-flow experiments and CCSD(T) quantum chemical computations. In the experiments, the rate coefficient for the overall reaction, OH + CH₃C(O)CH₃ → products (1), and the branching ratio for the specific reaction channel OH + CH₃C(O)CH₃ → CH₂C(O)CH₃ + H₂O (1a) have been determined to be k₁ = (1.04 ± 0.03) × 10¹¹ cm³ mol⁻¹ s⁻¹ and Γ_1a = k_1a/k₁ = 0.50 ± 0.04, respectively (T = 298 K). Two different reaction pathways have been characterized by ab initio calculations. Both H atom abstraction and OH addition to the CO group have been found to occur through hydrogen bonded OH···CH₃C(O)CH₃ complexes. Most of our results support recent findings (M. Wollenhaupt, S. A. Carl, A. Horowitz and J. N. Crowley, J. Phys. Chem. A, 2000, 104, 2695; M. Wollenhaupt and J. N. Crowley, J. Phys. Chem. A, 2000, 104, 6429) but contradictions remain concerning the mechanism of this atmospherically important reaction.