Calculations of N₂ triplet states vibrational populations and band emissions in venusian dayglow

Abstract

A model for N₂ triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N₂ triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N₂, populations of different levels of N₂ triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N₂ triplet band emissions are calculated, the values for Vegard-Kaplan, (A³Σ_u⁺−X¹Σ_g⁺), First Positive (B³Π_g−(A³Σ_u⁺), Second Positive (C³Π_u−B³Π_g), and Wu-Benesch (W³Δ_u−B³Δ_g) bands of N₂, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1) kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0, 5), (0, 6), and (0, 7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK (0, 4), (0, 5), (0, 6) and (0, 7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N₂ triplet band emissions in the dayglow of Venus.