On the possible catalytic role of a single water molecule in the acetone plus OH gas phase reaction: a theoretical pseudo-second-order kinetics study

In this work, we have revisited the mechanism of the acetone + OH radical reaction assisted by a single water molecule simulating atmospheric conditions. Density functional methods are employed in conjunction with CCSD(T) and large basis sets to explore the potential energy surface of this radical-molecule reaction. Computational kinetics calculations in a pseudo-second order mechanism have been performed, taking into account average atmospheric water concentrations and temperatures. We have used this method recently to study the single-water molecule-assisted H-abstraction in acetaldehyde (Iuga et al. in J Phys Chem Lett 1:3112, 2010) and in glyoxal (Iuga et al. in Chem Phys Lett 501:11, 2010) by OH radicals, and we showed that the initial water complexation step is essential in the rate constant calculation. In both cases, the amount of complex formed is only about 0.01% of the total organic molecule concentration, and as a consequence, water does not accelerate the reaction. In the acetone reaction with OH radicals under atmospheric conditions, we also find that the water-acetone complex concentration is much too small to be relevant, and thus, the rate constant of the water-assisted mechanism is orders of magnitude smaller than the water-free corresponding value.