Theoretical kinetics analysis for ȮH radical addition to 1,3-butadiene and application to model prediction

The kinetics of the 1,3-butadiene + ȮH reactions and its impact on combustion kinetic model predictions have been investigated in this work. Geometries and vibrational frequencies for all stationary points were determined at the BH&HLYP/6–311++G(d,p) level of theory, accounting explicitly for the degeneration of torsional motions into hindered rotors. Electronic energies for all stationary points on the related potential energy surface were calculated at the ROCCSD(T)/CBS and G4 levels of theory. Hydroxyl radical addition to the 1,3-butadiene terminal carbon forming allylic hydroxyl radical is the dominant addition entrance channel, while CH₂double bondCHCHO+ĊH₃ and allyl radical + formaldehyde are the main bimolecular products. A three-membered ring intermediate (IT7) is found to be important in merging pathways originated from terminal and central addition reactions. Pressure and temperature dependent rate constants for ȮH radical addition to 1,3-butadiene are determined integrating the Master Equation on the investigated potential energy surface. Variational transition state theory was used to determine rate constants for the terminal and central addition entrance channels, finding a good agreement with previous experimental measurements. Hydrogen atom abstraction reactions by ȮH radicals from 1,3-butadiene have also been investigated in this work. Rate constants of the important reactions and thermochemistry data for key species calculated in this work were incorporated into AramcoMech3.0 to investigate their influence on the prediction of the reactivity active during 1,3-butadiene oxidation.