Ion chemistry governing mesospheric electron concentrations

A theory and methodology for investigating the ion chemistry governing mesospheric electron concentrations is presented. In this theory, macroscopic reaction coefficients are defined in terms of the microscopic chemical reactions that take place between positive ions, electrons, and negative ions. The role of minor constituents of the atmosphere, O, O3, CO2, NO, and NO2, is discussed using reaction rates measured in the laboratory. One reaction, the associative detachment of O2− by atomic oxygen, is so fast that mechanisms for inhibiting or suppressing this reaction are required. The need for such mechanisms is dictated by field data on riometer absorption induced by the nuclear explosions of the 1962 Christmas Island air drops. The importance of terminating negative ions, i.e., negative ions that withstand the attack of atomic oxygen, is emphasized. Also emphasized is the influence of the ion-ion mutual neutralization coefficient of terminating negative ions. Four illustrative models of the ion chemistry are presented ranging from the simplest O2− model, which is certainly unrealistic, to a more complex model involving six species of negative ions. This model, which is suggested by recent measurements of reaction rates in the laboratory, does not include the effect of water vapor in the reaction scheme since little laboratory data exist on the reaction of negative ions with water.