Intermediate, lifetime TRANSIENT CHEMICAL SPECIES

Referring to a reaction intermediate or free radical that has a lifetime longer than that of a transient species, typically on the time-scale of at least several minutes in dilute solution in inert solvents. Persistence is therefore a kinetic property related to reactivity. The stability of an intermediate or free radical is a thermodynamic property, often expressed in terms of the appropriate bond strengths. See Transient Chemical Species D. Griller and K. U. Ingold (1976) Acc. Chem. Res. 9, 13. 

A. General Remarks on Unimolecular Decompositions of Chemically Activated Radicals. A major portion of the molecular beam studies of fluorine atom chemistry (12-19,37) has been concerned with a class of reactions characterized by the formation of a transient species from bimolecular association of the reactants and whose lifetime is long compared to its rotational or vibrational periods. The formation of such a long lived complex implies that the reactants experience a net attraction and consequently the potential energy surface for the reaction possesses a deep well of course, the total energy of the system is greater than that required to dissociate the intermediate, either to reactants or products, so that in the absence of a third body or relatively improbable photon emission (radiative lifetime > 10 sec), the intermediate must decay prior to detection. Under certain favorable conditions where a large... 

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