High-temperature rate constants for CH3OCOH + OH reactions: the effects of multiple structures and paths

Rate constants for hydrogen abstraction reactions of methyl formate by hydroxyl radical are computed with the one-well (1W) and multipath (MP) variational transition state theory with small-curvature tunneling at the temperature in the range of 800-1500 K. All possible conformations of reactants and transition states reached by internal rotations were optimized with M05-2X/maug-cc-pVTZ. Harmonic vibrational frequencies were performed to confirm the nature of the stationary points. Thirteen conformations of the transition states (including the mirror images) were found at this level of theory and separated into two conformational reaction channels (CRCs). Individual energy paths of each CRC were built and the thermal rate constants obtained with 1W and MP formalism. The 1W-CVT/SCT thermal rate constants underestimate the experimental results and indicate that the hydrogen abstraction reaction by the formyl group is predominant. When the multiple structures of reactants and transition states are taken into account, the values of the thermal rate constants shown excellent concordance with the experimental measurements. In addition, the MP-CVT/SCT product branching ratios are in good agreement with the experimental kinetic model.