Tunneling Model for Hydrogen Abstraction Reactions in Low-Temperature Solids. Applications to Reactions in Alcohol Glasses and Acetonitrile Crysals

Article abstract of DOI:10.1021/ja00527a033

A simple and internally consistent quantitative model for hydrogen-abstraction reactions in low-temperature solids, which implicitly incorporates zero point energy effects which allow for finite reaction rates at T=0 K, is derived and applied to new measurements of H-abstraction rate constants by methyl radicals in methanol and ethanol glasses at T=13-99 K and in acetonitrile and methyl isocyanide crystals at 69-128 K.Nonlinear least-squares fits of the model to the experimental data yield effective one-dimensional barriers to reaction whose heights are virtually independent of the analytic form used for the potential energy barrier, and are somewhat larger than the activation energies measured for the corresponding reactions in the gas phase.This model predicts that values of the isotopic rate constant ratio k_H/K_D will be larger than 10¹² at T=0 K.