Photoionization coefficients and photoelectron impact excitation efficiencies in the daytime ionosphere

Abstract

Photoelectron impact is an important or dominant excitation process for several dayglow emissions. Calculations show empirically that, to a sufficient approximation, both the photoionization coefficients of atmospheric gases and the photoelectron excitation efficiencies for high-lying states can be represented as simple functions of an effective total slant-column density of the neutral gases in the solar direction, a small correction for the local electron/neutral density ratio being necessary for the excitation efficiencies. The prediction, in any given model atmosphere, of photoionization rates and of the intensities of the Lyman Birge-Hopfield and second positive bands of molecular nitrogen and the 1356 A line of atomic oxygen, and of the photoelectron impact contribution to the excitation of the 1304 A resonance triplet of atomic oxygen, is thereby rendered trivial.