The Red Line of Atomic Oxygen in the Day Airglow

A. Dalgarno Queens University, Belfast, Northern Ireland

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James C. G. Walker Goddard Institute for Space Studies, NASA, New York, N. Y.

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Abstract

It is argued from the observations of the red line that the rate coefficient for deactivation of the excited oxygen atoms in collisions with molecular oxygen cannot be much less than 10−10 cm3 sec−1 and that the solar flux in the region of 1450 Å cannot be as large as the reported measured values. It is further argued that photodissociation of molecular oxygen and recombination of molecular ions are inadequate to explain the observations and that an additional mechanism is operative at high altitudes. The mechanisms of fluorescent excitation and of non-thermal excitation by photoelectrons are briefly examined and it is concluded that although the latter may be a significant source of excited atoms, neither mechanism explains the observed variability. It is suggested that the variability in red line intensities is associated with the presence of hot thermal electrons and sample calculations are presented of the altitude profiles that may result from this source.

Abstract

It is argued from the observations of the red line that the rate coefficient for deactivation of the excited oxygen atoms in collisions with molecular oxygen cannot be much less than 10−10 cm3 sec−1 and that the solar flux in the region of 1450 Å cannot be as large as the reported measured values. It is further argued that photodissociation of molecular oxygen and recombination of molecular ions are inadequate to explain the observations and that an additional mechanism is operative at high altitudes. The mechanisms of fluorescent excitation and of non-thermal excitation by photoelectrons are briefly examined and it is concluded that although the latter may be a significant source of excited atoms, neither mechanism explains the observed variability. It is suggested that the variability in red line intensities is associated with the presence of hot thermal electrons and sample calculations are presented of the altitude profiles that may result from this source.

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