Analysis of ion densities in the vicinity of space vehicles: Ion‐neutral chemical kinetics

Recent laboratory studies of ion‐molecule reactions relevant to the analysis of ion densities in the vicinity of space vehicles in low‐Earth orbit are discussed. The studies include new cross‐section measurements of the important O++ H2O charge transfer collisions and the H3O+ ‐producing H2O++ H2O collisions, as well as product kinetic energy analysis of the reaction products. The charge transfer reaction rate is found to be less collision energy dependent than previously assumed, whereas the H3O+ ‐producting reaction rate is highest at thermal energies and decreases rapidly with increasing collision energy. Implications of the new results on previous interpretations and recent space observations are discussed.