Alkyl radicals are important active intermediates in gas phase photochemistry and combustion reaction systems. With the exception of a limited number of the most elementary radicals, accurate thermodynamic properties of alkyl radicals are either not available or only rough estimations exist. An H atom Bond Increment approach is developed and a data base [sic] is derived, for accurately estimating thermodynamic properties (DH_f°₂₉₈, S°₂₉₈ and Cp(T)) for generic classes of hydrocarbon radical species.

Reactions of alkyl radicals with molecular oxygen are one of the major reaction paths for these radicals in atmospheric photochemistry, oxidation of hydrocarbon liquids and combustion process. Alkyl hydroperoxides are subsequently formed through the alkyl peroxy radicals reactions with varied chemical species present in the reaction system. Thermodynamic properties of the alkyl hydroperoxides and related radicals are therefore frequently required in gas phase modeling and kinetic studies on these systems. The thermodynamic properties of alkyl hydroperoxides, alkyl peroxy radicals and hydroperoxyl-1-ethyl radicals including the species with fluorine and chlorine substituents on the (a-carbon are evaluated using molecular orbital calculations

Chloroform is used as a model chlorocarbon system with high Cl/H ratio to investigate thermal decomposition processes of chlorocarbons in oxidative and pyrolytic reaction environments. A detailed reaction mechanism is developed to describe the important features of products and reagent loss and is shown to predict the experimental data well. Reaction pathways and rate constants are developed for CCl₃, CCl₂ and C₂CI₃ radical addition to O₂ and combination with O, OH HO₂ and ClO.

The reversible addition reaction of OH radical with benzene to form the hydroxyl-2,4-cyclohexadienyl (benzene-OH) adduct and the subsequent reactions of this benzene OH adduct with O₂ are important initial steps for the photooxidation [sic] of benzene and other aromatic species in the atmosphere. OH addition to the benzene ring, the subsequent reaction of O₂ with the hydroxyl-2,4-cyclohexadienyl to form hydroxyl-2-peroxy-4-cyclohexenyl (benzene-OH-O₂ adduct), are chemical activation reactions and are a function of both pressure and temperature. The kinetics of these two reaction systems at various pressure & temperatures using a quantum version of Rice-Ramsperger-Kassel theory (QRRK) and a modified strong collision approach are analyzed and calculated. The analogue reaction system of toluene photooxidation [sic] is also analyzed. Reaction mechanisms are developed for Initial steps of atmospheric oxidation of benzene and toluene, which include reverse reaction rates determined from thermodynamic parameters and microscopic reversibility. The model results show good agreement with the limited available experimental data.