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

Abstract

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.