Reaction of hydroxyl radical with acetone. 2. Products and reaction mechanism

The products of the reaction of OH with acetone (OH + CH3C(O)CH3 --> 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) x 10(-11) and (3.45 +/- 0.24) x 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 CH3C(O)CH2 and H2O. The atmospheric implications of our findings are discussed.