On the Combination Reactions of Hydrogen Atoms with Resonance-Stabilized Hydrocarbon Radicals

Procedures for accurately predicting the kinetics of H atom associations with resonance stabilized hydrocarbon radicals are described and applied to a series of reactions. The approach is based on direct CASPT2/cc-pvdz evaluations of the orientation dependent interaction energies within variable reaction coordinate transition state theory. One-dimensional corrections to the interaction energies are estimated from a CASPT2/aug-cc-pvdz minimum energy path (MEP) on the specific reaction of interest and a CASPT2/aug-cc-pvtz MEP for the H + CH3 reaction. A dynamical correction factor of 0.9 is also applied. For the H + propargyl, allyl, cyclopentadienyl, and benzyl reactions, where the experimental values appear to be quite well determined, theory and experiment agree to within their error bars. Predictions are also made for the combinations with triplet propargylene, CH2CCCH, CH3CCCH2, CH2CHCCH2, CH3CHCCH, cyclic-C4H5, CH2CCCCH, and CHCCHCCH.