Reaction Mechanisms in Heterogeneous Systems

Outer sphere mechanism (contact of coordination spheres) 

Inner sphere mechanism (overlap of coordination spheres) 

F%urel8.4. Transition states in electron-exchange reactions. 

Information about details of various chemical reactions can be obtained by application of radiotracers. The photographic process may be mentioned as an example if a thick cylindrical pellet of Agl is labelled on one side by isotope exchange with I, arranged in such a way that light has no access to the labelled side, and irradiated on the opposite side by visible light, l-labelled iodine is immediately liberated. It may be carried away by a stream of an inert gas and measured continuously in a gas counter. The immediate liberation of h is due to fast transport of defect electrons in Agl, in agreement with the proposed mechanism of the photographic process. 

In heterogeneous systems, radiotracer methods also have a wide range of applications with respect to elucidation of reaction mechanisms as well as to the determination of kinetic data. 

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