Rate constant estimation for C₁ to C₄ alkyl and alkoxyl radical decomposition

Rate coefficients for alkyl and alkoxy radical decomposition are important in combustion, biological, and atmospheric processes. In this paper, rate constant expressions for C₁-C₄ alkyl and alkoxy radicals decomposition via β-scission are recommended based on the reverse, exothermic reaction, the addition of a hydrogen atom or an alkyl radical to an olefin or carbonyl species with the decomposition reaction calculated using microscopic reversibility. The rate expressions have been estimated based on a wide-range study of available experimental data. Rate coefficients for hydrogen atom and alkyl radical addition to an olefin show a strong temperature curvature. In addition, it is found that there is a correlation between the activation energy for addition and (i) the type of atom undergoing addition and (ii) whether this radical adds to the internal or terminal carbon atom of the olefin. Rate coefficients for alkoxy radical decomposition show a strong correlation to the ionization potential of the alkyl radical leaving group and on the enthalpy of reaction. It is shown that the activation energy for alkyl radical addition to a carbonyl species can be estimated as a function of the alkyl radical ion ization potential and enthalpy of reaction.