Free-Radical Stabilization in Condensed Phases

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Abstract
The formation of stabilized free‐radical mixtures by the low‐temperature condensation of gases containing such species is considered. A primary concern is the amount of free radicals resulting from such a process. The over‐all process of formation of condensed phase stabilized free‐radical mixtures involves the original means of their production as gases, the recombination of free radicals as the gaseous mixtures are transported to the seat of condensation, and the recombination which occurs in the immediate vicinity of and within the condensed phase which is formed. For the present purpose only the latter aspect is considered in any detail, the effects of production and prior recombination being summarized in a stated composition for the condensing gas. For simplicity, only mixtures consisting of a single species of atomic free radicals, diatomic molecules which may be formed from their recombination, and inert atomic species are treated. The basis for stabilization is taken to be isolation. Thus, those condensed phase mixtures are regarded as stable which do not permit free radicals to come in contact with one another. It is assumed, therefore, that condensation occurs at a temperature sufficiently low to render the effect of diffusion negligible. Such recombination which does occur is presumed to do so as a result of the juxtaposition of the atomic free radicals. Several models of the stabilization process are considered from a statistical viewpoint. In each instance no explicit reference is made to the kinetics of the recombination process. The effects of coordination number, surface condensation versus bulk condensation, condensation coefficient and clustering are treated. In each of the models the dependence of the condensed phase composition upon the gas phase composition and the statistical properties of the constituents is determined.

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