O₂ (<i>c</i>¹Σ_<i>u</i>⁻ → <i>X</i>³Σ_<i>g</i>⁻) emission in the terrestrial nightglow

Abstract

Synthetic spectra have been calculated incorporating three O 2 emission systems, A ³Σ u + → X ³Σ g − , A′ ³Δ u → a ¹Δ g , and c ¹Σ u − → X ³Σ g − , and matched to the 3100‐ to 4500‐Å nightglow spectrum of Broadfoot and Kendall (1968). The synthesis necessitated the inclusion of the c ¹Σ u − → X ³Σ g − system, which has never been previously identified in the airglow, although it is a dominant system in the Venusian nightglow. The emissions from the extremely metastable A′ ³Δ u and c ¹Σ u − states account for half the radiation in the 3100‐ to 4500‐Å region, from which it may be deduced that the mesospheric concentrations of O 2 ( A′ ³Δ u ) and O 2 ( c ¹Σ u − ) are much higher than that of O 2 ( A ³Σ u + ). The vibrational distributions are quite unrelaxed for all three states.