Reaction of Hydroxyl Radical with Acetone. 2. Products and Reaction Mechanism

The products of the reaction of OH with acetone (OH + CH 3 C(O)CH 3 → products) were investigated using a discharge flow tube coupled to a chemical ionization mass spectrometer. It was shown that the yield of acetic acid from the reaction was less than 1% between 237 and 353 K. The yield of acetonyl radical was measured to be (96 ± 11)%, independent of temperature, between 242 and 350 K. The rate coefficients for the reaction were measured with this system to be the same as those reported in part 1 ( J. Phys. Chem. A 2003, 107, 5014). The rate coefficients for the removal of OH ( v = 1) by acetone and acetone- d 6 were shown to be (2.67 ± 0.15) × 10 -11 and (3.45 ± 0.24) × 10 -11 cm 3 molecule -1 s -1, respectively, at 295 K. It was shown that the enthalpy of reaction for the formation of an OH−acetone adduct is more than −8 kcal mol -1 (i.e., the adduct is bound by at most 8 kcal mol -1 ) at 203 K. On the basis of these observations and those from part 1, we deduce that the reaction of OH with acetone occurs through a hydrogen-bonded complex that gives almost exclusively CH 3 C(O)CH 2 and H 2 O. The atmospheric implications of our findings are discussed.