An investigation of the physicochemical processes governing electron density in the earth's mesosphere. Ionization results from the weak background cosmic radiation, daytime solar X rays, and special events, and is ordinarily detected by its effect on radio waves. The macroscopic reaction coefficients are defined in terms of microscopic chemical reactions among positive ions, negative ions, and free electrons, with emphasis on the minor constituents of the atmosphere. Different models of negative ion kinetics are examined in an attempt to discover the mechanism presumed to exist for inhibiting the associative detachment of negative oxygen ions by atomic oxygen. A terminating ion seems to be the answer; nitric oxide is a possibility. Methodology developed for treating the complex multi-negative-ion model allows for systematic calculation of the properties of the lower ionosphere, but it may be difficult to apply the model to the polar cap absorption phenomena that occur at high latitudes. 44 pp. Refs.