Thermochemical and Kinetic Analysis of the H, OH, HO_2, O, and O_2 Association Reactions with Cyclopentadienyl Radical

摘要

Reaction pathways and kinetics for cyclopentadienyl radical association with H, OH, HO_2, O, and O_2 are presented in the temperature range 900-1300 K and atmospheric pressure. Thermochemical data for reactants, intermediate, and product species are evaluated from literature data and from group additivity with hydrogen bond increments. High-pressure limit rate constants for the radical combination reactions and decomposition of the energized adducts are estimated. Pressure-dependent rate constants for each channel in the reaction systems are calculated using bimolecular quantum Rice Ramsperger Kassel, QRRK, for k(E) with a modified strong collision approach for falloff. A submechanism of important cyclopentadienyl radical reactions is assembled and tested in an elementary reaction model for combustion of benzene, where the cyclopentadienyl radical is a key intermediate in the stepwise (C6 → C5 → C4) decomposition. Modeling results are compared with limited literature data on species profiles for appropriate reaction systems, where benzene, cyclopentadiene, and carbon monoxide are the initial fuel, observed intermediate, and major combustion product, respectively. H atom association with cyclopentadienyl radical (CY13PD5·) leads to stabilized cyclopentadiene (CY13PD) as the primary product, with linear pentadienal diradical as a minor product. The hydroxyl association with cyclopentadienyl radical forms an energized adduct, which primarily rearranges to cyclopentadienol isomers, which are stabilized. O~((3p)) association with cyclopentadienyl radical leads to two main product sets: cyclopenadienone plus H atom or 1,3-butadienyl radical plus carbon monoxide. Hydroperoxy radical combination with cyclopentadienyl radical forms an energized hydroperoxy-cyclopentadiene, which can dissociate to lower energy products cyclopentenoxy radical plus OH, to cyclopentadienone + H_2O, or back to the initial reactants. Oxygen molecule addition to cyclopentadienyl radical forms an energized cyclopentadiene peroxy radical with a very shallow well (ca. 13 kcal/mol), which predominantly dissociates back to reactants. A small, but important, fraction of the energized peroxy adduct undergoes reactions that lead to ring-opening with formation of resonance-stabilized 2-pentenedialdehyde radical or vinyl ketene and formyl radical. These reactions provide paths for cyclopentadienyl radical conversion to linear. unsaturated, oxyhydrocarbons.