Tunneling in the reaction of acetone with OH
Based on recent detailed quantum mechanical computations of the mechanism of the title reaction (Phys. Chem. Chem. Phys., 2003, 5, 333) and (J. Chem. Phys., 2003, 119, 10 600), this paper presents kinetics analysis of the overall rate constant and its temperature dependence, for which ample experimental data are available for comparison. The analysis confirms that the principal channel is the formation of acetonyl radical + H2O, while the channel leading to acetic acid is of negligible importance. It is shown that the unusual temperature dependence of the overall rate constant, as observed experimentally, is well accounted for by standard RRKM treatment that includes tunneling. This treatment is applied at the microcanonical level, with chemically activated distribution of entrance species, i.e. using a stationary rather than a thermal distribution that incorporates collisional energy transfer and competition between the redissociation and exit channel. A similar procedure is applied to the isotopic reaction acetone-d6 + OH with equally satisfying results, so that the experimental temperature dependence of the KIE (kinetic isotope effect) is perfectly reproduced. This very good agreement between calculation and experiment is obtained without any fitting to experimental values and without any adjustment of the parameters of calculation.