The carbon monoxide fourth positive bands in the Venus dayglow 1. Synthetic spectra

Abstract

Spectral observations of the Venus dayglow from 1200–1800 Å were made with the Pioneer Venus ultraviolet spectrometer (13‐Å resolution), a sounding rocket telescope and spectrometer (4‐Å resolution, and the International Ultraviolet Explorer (0.4‐Å resolution). Emissions due to H I, C I, O I, and the CO fourth positive system are identified. Emission rate factors for the fourth positive system are calculated using a high‐resolution solar flux. The importance of solar emission line excitation to this flourescence spectrum is shown. In particular, several bands of the υ′=14 progression are identified and their excitation mechanism is shown to be fluorescent scattering of solar Lyman α radiation. The CO (14, 5) band at 1392 Å is a prominent unblended spectral feature in the Venus dayglow. The (14, 3) and (14, 4) bands at 1317 and 1354 Å are blended with the O I 1304‐ and 1356‐Å features in lower‐resolution spectra. This identification resolves the problem of the interpretation of the ratio of the O I 1304/1356 Å emissions from Venus. It also provides an additional remote sensing technique to determine the density distribution of CO in the upper atmosphere of Venus.