A model of a thermal explosion of an exothermic mixture of complex molecules is described. Active intermediates are formed in the course of the explosion. An analysis of various kinetic regimes is offered and the dependence of explosion kinetics on gas composition and initial pressure is investigated. It is shown that there are regions of mixture composition and initial concentrations in which the nonequilibrium atom concentration is large and approaches the initial concentration of the unstable molecules. Population inversion occurs for the electronic-vibrational levels of the product molecules from recombination reactions. The criterion for inversion proves to he essentially dependent on the phototransition frequency to. For small to, the inversion criterion on the "initial composition--pressure" plane is fulfilled in the restricted regions corresponding to small dilutions. With an increase ofto these regions turn into shortening "'islands." For some value to = to I the islands shrink into a point, so that inversion becomes impossible.
This model is applied to CO--O 3 gas mixtures. Inversion is shown to arise in the mixture for phototransitions ofO 2 and CO 2 molecules throughout the visible range. Exact calculations for the explosion kinetics show that it is necessary to use high pressure gases to obtain an appreciable light gain.