Triatomic complex

Fig. 9.21 A triatomic complex XYZ. Energy of diatomic molecule YZ with X is involved in A + a, where A is coulombic energy and a the exchange energy. The energy of other diatomic molecules may be represented accordingly. 

Of these, reaction (73) will not be discussed here, as its 39.5 kcal/mole activation energy renders it unobservable at temperatures below 500°K. However, it is possible that NO + Of1/)) is a much faster reaction, and the occasional occurrence of excited oxygen in discharge systems requires that this possibility be borne in mind. Of course it may turn out, as DeMore and Raper117-354 showed in the case of N2 and CO, that the reactions of Of1/)) are not important, because of the predissociation of the intermediate triatomic complex to give 0(3/>). The importance of this system makes the study of Of1/)) + NO worthwhile. 

A.Berengolts, E.I.Dashevskaya, E.E.Nikitin, and J.Troe, Dynamic polarization of diatomic fragments formed in decomposition of statistical triatomic complexes. I. Semiclassical study, Chem. Phys. 195,271 (1995)... 

Vibrational predissociation (VP) of a van der Waals triatomic complex A..BC is an example of a unimolecular reaction the rate of which is controlled by the intramolecular vibrational energy redistribution (TVR) [1]. Within a rigorous quantum mechanical approach, the VP dynamics is completely characterized by the complex-valued energies E = - /T / 2 that lie above the dissociation threshold of A..BC into an atom A and... 

It should be stressed that as v increases the equilibrium distance changes from 3.8 A for V = 0 to 4.9 A for V = 5. Thus if we describe the triatomic complex Hg--Ar2 as an atom (Hg) bound to a diatomic molecule (Ar2), the triatomic potential strongly depends on the vibrational state of the diatomic molecule. 

A comment on the result A decrease in entropy suggests a transition state that is more organized than the reactants. When you consider that this reaction is forming a single triatomic complex from two individual species, it makes sense that the entropy decreases. 

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