The Vibrational Distribution of N₂⁺ in the Terrestrial Ionosphere

The densities and vibrational distributions of N ₂ ⁺ in the X ²Σ _g ⁺ , A ²Π _u , and B ²Σ _u ⁺ states in the daytime terrestrial ionosphere are computed for both low and high solar activity. Altitude profiles of the relative populations of the vibrational levels of N ₂ ⁺ X ²Σ _g ⁺ are presented. The fraction of vibrationally excited N ₂ ⁺ varies from 5% at 100 km to 50% at 450 km. Several models are examined in which loss of N ₂ ⁺ ( v ) is enhanced for v > 0 and in which various assumptions are made about the vibrational distributions produced in charge transfer reactions. The N ₂ ⁺ densities are significantly reduced if N ₂ ⁺ ( v ) reacts with O at rates which are near gas-kinetic. Vibrational distributions of the A ²Π _u and B ²Σ _u ⁺ states are also presented, as well as volume emission rates and integrated overhead intensities of the major bands of the Meinel and first negative systems.