Reported here is a model of ionndash;molecule reactions that includes a variety of constituent steps which might be appropriate in an environment at atmospheric pressures. A fairly general structure has been assumed for the type of reaction complex that might be assembled from the reacting partners and both coherent and incoherent processes of excitation of the complex have been included in the model. The transition to the product state was modeled as a simple predissociation. From these considerations a comprehensive reaction rate matrix was constructed that described the transition rates between each pair of levels of the complex for a particular set of experimental parameters. The smallest eigenvalue of such a rate matrix was found to generally correspond to an eigenvector of populations that reasonably described the decay of the original reacting species. Since the reaction of He+2with N2at atmospheric pressures was the best characterized of the systems appearing in the literature, it was chosen as a vehicle for the first application of this model. The results were found to be in complete agreement with experiment for reasonable values of model parameters.
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