Atom and Radical Recombination Reactions

Radical reactions are rarely reviewed as a separate field. They are either included in general surveys of reaction kinetics, or they are considered in dis­ cussions of the reverse dissociation processes. It is therefore attractive to present the subject from the less common recombination point of view instead of the normal unimolecular reaction side. The intimate relationship between the and the reverse dissociation processes, nevertheless, remains a most important fact. The present review considers the of atoms and the combination or association of atoms or poly atomic species with molecules in the gas phase. Many experimental examples have already been included either in earlier reviews in this series (1-4) or in other earlier reviews and compilations (e.g. 5-18). Various aspects of the theoretical analysis have been described for the cases of atom (19) and combination of poly atomic species in reviews of modern unimolecular rate theory ( 16, 17, 20). Since these references include fairly exhaustive collections of experimental data, only a few are cited in the following pages. Instead we intend to present characteristic experiments for the reactions under a wide variety of conditions and to compare these with theoretical models. Only for a qualitative orientation do we first consider the simple energy transfer mechanism with association, dissociation, and collisional energy transfer steps. Two species, A and B, associate and form highly excited unstable molecules AB* that then either redissociate or are collisionally stabilized in collisions with arbitrary particles M: