Photochemistry of Ions at D-region Altitudes of the Ionosphere: A Review

Abstract

The current state of knowledge of the D-region ion photochemistry is reviewed. Equations determining production rates of electrons and positive ions by photoionization of atmospheric neutral species are presented and briefly discussed. Considerable attention is given to the progress in the chemistry of O+(4S), O+(2D), O+(2P), N+, N2+, O2+, NO+, N4+, O4+, NO+(N2), NO+(CO2), NO+(CO2)2, NO+(H2O)n for n = 1–3, NO+(H2O)(N2), NO+(H2O)2(N2), NO+(H2O)(CO2), NO+(H2O)2(CO2), O2+(H2O), H3O+(OH), H+(H2O)n for n = 1–8, O−, O2−, O3−, O4−, OH−, CO3−, CO4−, NO2−, NO3−, ONOO−, Cl−, Cl−(H2O), Cl−(CO2), HCO3−, CO3−(H2O), CO3−(H2O)2, NO3−(H2O), NO3−(H2O)2, OH−(H2O), and OH−(H2O)2 ions. The analysis of the D-region rocket ion mass spectrometer measurements shows that, among these ions, O2+, NO+, NO+(H2O), and H+(H2O)n for n = 1–7 can make the main contribution to the total positive ion number density, and O−, O2−, Cl−, OH−(H2O), CO3−, HCO3−, NO3−, ONOO−, CO4−, NO3−(H2O), NO3−(H2O)2, and 35Cl−(CO2) ions can be responsible for the main contribution to the total negative ion number density. Photodetachment of electrons from O−, Cl−, O2−, O3−, OH−, NO2−, and NO3−, dissociative electron photodetachment of O4− and OH−(H2O), and photodissociation of O3−, O4−, CO3−, CO4−, ONOO−, HCO3−, CO3−(H2O), NO3−(H2O), O2+(H2O), O4+, N4+, NO+(H2O), NO+(H2O)2, H+(H2O)n for n = 2–4, NO+(N2), and NO+(CO2) are studied, and the photodetachment and photodissociation rate coefficients are calculated using the current state of knowledge on the cross sections of these processes and fluxes of solar radiation.