Cross Sections of Exchange Reactions

From the theoretical standpoint, the simplest reactions are those occurring via a long-lived complex. This is connected with the possibility to distinguish two independent steps of the process formation of a comple (or of the compound 

The probabilities of the decay of the complex can be calculated according to the theory of unimolecular reactions (see Section V.17) because the long-lived complex does not, in fact, differ from an active molecule. The decay probabilities for path i are defined by the microscopic rate constant ki(E) 

This expression is obtained by neglecting the total angular momentum conservation, it must however be allowed for when needed [275, 339, 345]. 

Examples of reactions proceeding via complexes and relevant calculation methods are given in [187, 275, 345]. 

Passing to direct reactions, the stripping reactions are more readily treated theoretically than rebound reactions. In particular, it has been found that in many stripping reactions of the type A + BC AB + C the transfer of atom B from molecule BC to AB does not involve recoil. Por such spectator-stripping reactions (C is the spectator), angular and energy distributions of products can be readily calculated, thus permitting a simple verification of the assumption on the reaction mechanism. 

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