The acetic acid forming channel in the acetone + OH reaction: A combined experimental and theoretical investigation

Abstract

In a flow reactor–molecular beam sampling mass spectrometry investigation of the elementary reaction of acetone with OH at 290 K, no significant production of acetic acid could be measured; absolute calibrations result in a branching fraction of the OH-addition/CH₃-elimination channel of at most ≈ 5%. In a theoretical study of the acetone + OH reaction, the potential energy profiles of the OH-addition/CH₃-elimination channel, the direct H-abstraction channel, and the indirect H-abstraction path via a hydrogen-bonded OH–acetone complex, were characterized at the B3LYP-DFT/6-31G(d,p) and B3LYP-DFT/6-311++G(d,p) levels of theory, with single-point CCSD(T)/6-311++G(2d,2p) energy calculations. At all levels, the barrier for OH-addition is found to be 6 ± 0.5 kcal mol⁻¹, and at least 2.5 kcal mol⁻¹ higher than that for the H-abstraction channels. Transition state theory and RRKM - master equation calculations indicate that the OH-addition channel is negligible at all relevant atmospheric temperatures. These results are in disagreement with recent reports that the OH-addition/CH₃-elimination channel contributes about 50% at room temperature.