Photoelectron excitation of atomic‐oxygen resonance radiation in the terrestrial airglow

Recent laboratory measurements of the absolute cross sections for the excitation of the O I ( 3 S ) resonance state by electron impact on O and O 2 when combined with in situ measurements of the photoelectron energy distribution from 120 to 300 km show that photoelectron impact is the principal excitation mechanism for λ1304‐A resonance radiation in the dayglow; dissociative excitation of O 2 is found to play a minor role. The laboratory measurements indicate that the 3 S state is strongly populated by cascade processes and imply that the O I(3 p 3 P → 3 s 3 S; λ8446 A) transition should be a prominent dayglow emission feature. These experiments also show that the excitation of atomic oxygen by low‐energy electron impact cannot account for the λ1304‐ or 1356‐A emission observed in the tropical ultraviolet airglow.