Impact of the Water Molecule on the Gas-Phase Reaction between Acetone and Cl Atoms

The role of the water molecule in the atmospheric reaction between CH₃COCH₃ and Cl atoms was investigated at the theoretical level of CCSD­(T)/aug-cc-pVTZ//BHandHLYP/aug-cc-pVDZ. The reaction between acetone and Cl atoms proceeds through three paths: an H-abstraction reaction, a −CH₃ abstraction reaction, and an addition/elimination reaction by Cl, leading to the formation of CH₃COCH₂ + HCl (+H₂O), CH₃CO + CH₃Cl (+H₂O), and CH₃COCl + CH₃ (+H₂O), respectively. The formation pathway of CH₃COCH₂ + HCl in the three paths occupies a dominant position, with a rate constant of 1.08 × 10^–12 cm³ molecule^–1 s^–1. However, water-assisted CH₃COCH₃ + Cl reactions become more complex, proceeding through 10 different paths. At 298 K, the effective rate constant for CH₃COCH₂ + HCl + H₂O formation is 8.46 × 10^–15 cm³ molecule^–1 s^–1, and the effective rate constant decreases by 3–4 orders of magnitudes in the temperature range of 216.69–298.15 K. Therefore, it is concluded that water exerts a hindering effect on the CH₃COCH₃ + Cl + H₂O reaction under atmospheric conditions, but it is not enough to change the dominant position of the CH₃COCH₃ + Cl reaction under anhydrous conditions.