Recent laboratory measurements of the absolute cross sections f o r the excitation of the OI(3S) resonance s t a t e by electron impact on 0 and O2 when combined w i t h c -i n situ measurements o f the photoelectron energy distribution from 120 t o 300 km show t h a t photoelectron impact is the principal excitation mechanism f o r A1304 A resonance radiation i n the 0 dayglow; dissociative excitation of O2 is found t o play a minor role. The laboratory measurements indicate t h a t the 3S s t

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... a t e is strongly population by cascade processes and imply t h a t the 01(3p3P -t 3s3S; A8446 A) 0 transition should be a prominent dayglow emission feature. These experiments also show t h a t the excitation of atomic oxygen by low-energy electron impact cannot account f o r the A1304 A o r 1356 A emission observed i n the tropical u l traviol e t a i rgl ow. 0 0