A theoretical kinetics study of the reactions of methylbutanoate with hydrogen and hydroxyl radicals

The chemical kinetics for the reactions of methylbutanoate (MB) with hydrogen and hydroxyl radicals were studied theoretically with the ab initio transition state theory. In addition to the hydrogen abstraction reactions of MB by the radicals, the potential energy surfaces of MB + H and MB + OH were further investigated to search for additional significant hydrogen addition channels, which are followed by β-scission reactions to produce non-hydrogen and non-water products, respectively. Stationary points on the potential energy surfaces were calculated at the QCISD(T)/CBS//B3LYP/6-311++G(d,p) level. Phenomenological rate coefficients for temperature- and pressure-dependent reactions were calculated over broad ranges of temperature (200-2500 K) and pressure (1.3 × 10−3-102 atm) by solving the time-dependent multiple-well master equation. The theoretical rate coefficients were compared with the available experimental and theoretical data and observed discrepancies were analyzed. The predicted rate coefficients are represented in the forms that may readily be used in combustion modeling of MB.