Recombination of O₂⁺in the ionosphere

Although laboratory measurements of the recombination rate of O2+ with electrons by several different groups are in excellent agreement, this does not necessarily mean that the results may be applied without question to the earth's upper atmosphere. It is not known whether the recombination rate is dependent on the vibrational state of the O2+ ion, nor is it known to what degree the ionospheric O2+ population is vibrationally excited. The direct determination of the recombination rate in the ionosphere is difficult because of the need for a direct measurement of the O2 density. We have used the open source mass spectrometer on the Atmosphere Explorer-C satellite in a special mode of operation, which has recently been reported in the literature, to obtain a limited sample of in situ measurements of the O2 density. Using simultaneous measurements of ion and neutral densities and temperatures, we have determined the recombination rate of O2+ over a range of electron temperatures between 1200° and 2000°K. We find that O2+ recombines at the same rate in the ionosphere in the altitude range 190–240 km as it does in the laboratory. The recombination rate coefficient is given by α = 1.6 × 10−7(Te/300)−0.55.