Osculating complexes

In real experiments, a combination of both mechanisms can be observed. That happens when multiple microscopic reaction mechanisms occur. Also, in certain cases where a bound intermediate does exist, its lifetime can be relatively short and insufficient to lose the memory of the initial directions of the reagents ( osculating complex ) [57]. 

This transition-state theory has been applied to exchange reactions of Li atoms with alkali halides (Kwei et al, 1971 Lees and Kwei, 1973) where examples of short-lived, or osculating, complexes may be found, and to beam studies of unimolecular decay (Lee et al, 1972), in particular on the extent of internal equilibration. 

Fig. 17. Solid-angle differential cross section for the reaction 0( D) + H OH + H proceeding via the insertion-decomposition pathway. The best fit from the osculating complex model (OCM) is the solid curve which is shown superimposed on the histogrammic representation of the trajectory data. The collision energy is 2 kcal/mol. Arrows indicate the range of scattering angles obtained in the trajectory calculations.

Summary of the application of the osculating complex model (OCM) to reactions of 0( D) with isotopic hydrogen molecules proceeding via the insertion-decomposition pathway. 

The direction in which the light atom leaves is uncorrelated with the initial direction of the carbon atom. Neither reaction channel, therefore, may be appropriately treated by the osculating complex model. 

One system is 0( D) with the (v=0,j=l) state of H2, HD, or D2 at a collision energy of 2 kcal/mol. Most reactions proceed via an intermediate complex. An analysis of the differential cross sections by the osculating complex model indicates that the average lifetime of the complex is less than or on the order of a rotational period. 

There is a time regime between the obviously bimolecular and obviously unimolecular pathways which encompasses a short-lived complex that exists for only a fraction of a rotation period. Such species have come to be known as osculating-complexes and are characterized by a somewhat asymmetric c.m. angular distribution that exhibits either a maximum or a minimum in both the forward and backward hemispheres. At low collision energies certain reactions occur via osculating complex mechanism but become... 

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