A study of the nighttime ionosphere and its reaction rates

Analysis of the nighttime ionosphere suggests that the reactions O+ + N2 → (rate γ1) → NO+ + N and O+ + O2 → (rate γ2) → O2+ + O are 3 × 10−13 cm3 sec−1 and 3 × 10−12 cm3 sec−1, respectively, within a factor of about 3. An additional requirement is that γ1/γ2 = 0.1 within a factor of about 2. No important temperature dependence is evident for either process at thermopause temperatures. The dissociative recombination rates α(O2+) for O2+ + e →O + O and α(NO+) for NO+ + e → N + O are shown to have a ratio of about unity within a factor of 2. It is suggested that the temperature dependence for both rates lies within Te−1.0±0.5 for T ≳ 200°K. Upper limits for the reaction O2+ + N2 → NO+ + NO are determined to be 10−15 cm3 sec−1 near 400°K and 10−14 cm3 sec−1 at 1000°K. It is demonstrated that the acceptance of approximately 10−7 cm3 sec−1 for α(o2+) and α(NO+) at 300°K, which is roughly in accord with both laboratory measurements and the daytime solar E-region flux, requires the existence of a nighttime E-region source of ionization. The possible contributions of meteors, scattered H Lyman α, and H Lyman β as sources at night are briefly discussed.