A study of oxygen 6300 A airglow production through chemical modification of the nighttime ionosphere

The Release Experiments to Derive Airglow Inducing Reactions (RED AIR) conducted on April 3, 1989, and December 6, 1991, offer a unique set of observations for studying the specific processes associated with the production of the O(P-3-D-1) emission at 6300 Angstrom. In these experiments, sounding rockets were used to place equal quantities of CO2 above and below h(max) of the nocturnal F region. CO2 leads to 6300 Angstrom emission by a three-step process: (1) CO2 + O+ --> O-2(+) + CO, (2) O-2(+) + e(-) --> O* + O, (3) O* --> O + h nu(6300). Direct measurements of plasma parameters and indirect measurements of the neutral atmosphere densities were used in conjunction with the Fluid Element Simulation (FES) computer code to model the temporal and spatial evolution of the observed 6300 Angstrom airglow enhancement and accompanying plasma depletion. Using the currently accepted set of reaction rates relevant to F region chemistry, the quantum yield of O(D-1) from reaction (2) was found to have a mild altitude dependence, decreasing by 16% from 275 to 350 km. Since the initial vibrational distribution of the nascent O-2(+) was the same for the two releases, this result implies an altitude dependence in the quenching of O-2(+) vibrational states. Building on previous evidence that O-2(+) is vibrationally excited in the nighttime thermosphere, we further conclude that this vibrational distribution is altitude dependent. In terms of 6300 Angstrom airglow production, the effect is manifested in an altitude dependence of f(D-1). Additionally, quenching by O(P-3) was found to contribute very little to the depopulation of the nascent O(D-1), with Q(O) = o giving the best fit to the RED AIR observations.