Kinetics Study of the OH + Alkene → H2O + Alkenyl Reaction Class

Performance of First-Principles-Based Reaction Class Transition State Theory

Performance of the Reaction Class Transition State Theory (RC-TST) for prediction of rates constants of elementary reactions is examined using data from its previous applications to a number of different reaction classes. The RC-TST theory is taking advantage of the common structure denominator of all reactions in a given family combined with structure activity relationships to provide a rigorous theoretical framework to obtain rate expression of any reaction within a reaction class in a simple and cost-effective manner. This opens the possibility for integrating this methodology with an automated mechanism generator for "on-the-fly" generation of accurate kinetic models of complex reacting systems.

Gas-phase kinetics of the hydroxyl radical reaction with allene: absolute rate measurements at low temperature, product determinations, and calculations

The gas phase reaction of the hydroxyl radical with allene has been studied theoretically and experimentally in a continuous supersonic flow reactor over the range 50 ≤ T/K ≤ 224. This reaction has been found to exhibit a negative temperature dependence over the entire temperature range investigated, varying between (0.75 and 5.0) × 10(-11) cm(3) molecule(-1) s(-1). Product formation from the reaction of OH and OD radicals with allene (C(3)H(4)) has been investigated in a fast flow reactor through time-of-flight mass spectrometry, at pressures between 0.8 and 2.4 Torr. The branching ratios for adduct formation (C(3)H(4)OH) in this pressure range are found to be equal to 34 ± 16% and 48 ± 16% for the OH and OD + allene reactions, respectively, the only other channel being the formation of CH(3) or CH(2)D + H(2)CCO (ketene). Moreover, the rate constant for the OD + C(3)H(4) reaction is also found to be 1.4 times faster than the rate constant for the OH + C(3)H(4) reaction at 1.5 Torr and at 298 K. The experimental results and implications for atmospheric chemistry have been rationalized by quantum chemical and RRKM calculations.