(385e) Thermochemistry and Kinetic Modeling for OH Addition to Propene and O2 Association to the Activated CH2(OH)C•HCH3 Adduct: OH Regeneration In Atmospheric Chemistry, Initial Modeling for Double Activation

Regeneration of OH radicals has recently been considered as an important process in atmospheric chemistry of unsaturated hydrocarbons. We study the reaction of OH with propene and the subsequent reactions of the energized and stabilized hydroxypropyl radical adducts with O2 using density functional theory and CBS-QB3 ab initio theoretical methods. Enthalpies of formation (df H°298) are determined using isodesmic reaction analysis at the CBS QB3 composite and density functional levels. Entropies (S°298) and heat capacities (C°p(T)) are determined using geometric parameters and vibrational frequencies obtained at the B3LYP/6-311G(2d,d,p) level of theory. Internal rotor contributions are included in S and Cp(T) values. Detailed potential energy surfaces for these reactions are presented, with rate parameters calculated for each reaction step from transition state theory. The chemically activated hydroxypropyl radical + O2 systems are modeled using quantum Rice-Ramsperger-Kassel (QRRK) theory, with master equation analysis for falloff. The reaction system is Chemkin modeled under conditions of atmospheric chemistry for varied NOx concentration using an elementary reaction mechanism with all reactions reversible. Hydroxyl radical addition forms an energized hydroxyl-propyl adduct with 29.2 kcal mol-1 from the new bond formation. The energized hydroxyl propyl radical is treated as 60 individual reactants (60 0.5 kcal mol-1 energy bins), each of which can be stabilized or react further via O2 activation. Each of the differently energized hydroxyl-propyl radicals can react with O2 (association) to form an activated peroxy-hydroxypropyl adduct with an additional 36.1 kcal mol-1 before stabilization. The chemical activation reactions of the distributed energized and the stabilized hydroxyl-propyl adducts with O2 can lead to OH regeneration via two paths: cyclic ether + OH and CH2O and CCHO +OH formation paths. Data is presented for different ΔE down step sizes and for presence of varied NO concentrations.