Ionospheric ion‐molecule reaction rates

Abstract

The current status of laboratory measurements of ion‐molecule reactions of ionospheric relevance is reviewed. Rate constants for the atmospheric loss reactions of He + , O + , and N 2 + appear to be established to within about a factor of 2 at 300°K. The laboratory rate constants for O + and N 2 + ion loss are compatible with quiet midlatitude E ‐ and F ‐region requirements. The He + loss reactions appear to be higher than is compatible with some He + concentrations observed; however, the laboratory rate constants have been measured by so many investigators that they are unlikely to be seriously in error. In the D region, on the other hand, many of the important reactions are as yet unmeasured. Measurements of the relevant negative ion reactions with neutrals have only recently been started. No in situ atmospheric negative ion composition studies have as yet been carried out to guide the laboratory investigations. Many positive ion reactions of importance in the D region (as well as in sporadic E layers) remain to be measured. Finally, very little information concerning reactions of excited state ions with neutrals has been obtained. This will be important for certain disturbed ionospheric conditions and possibly for a precise analysis of normal ionospheric conditions, when this is merited.