Intensities of the martian N₂ electron-impact excited dayglow emissions

The first N₂ emissions in the Martian dayglow were detected by the SPICAM UV spectrograph on board the Mars Express spacecraft. Intensities of the (0,5) and (0,6) Vegard-Kaplan bands were found to be about one third of those predicted more than 35 years ago. The Vegard-Kaplan band system arises from the transition from the lowest N₂ triplet state (A ³Σ_u⁺;v′) to the electronic ground state (X¹Σ_g⁺;v″). It is excited in the Martian dayglow by direct electron-impact excitation of the ground N ₂(X) state to the A state and by excitation to higher triplet states that populate the A state by cascading. Using revised data, we compute here updated intensities of several of the bands in the N₂ triplet systems and those involving the a¹Π_g state, the upper state of the Lyman-Birge-Hopfield bands. We find that the predicted limb intensities for the (0,5) and (0,6) Vegard-Kaplan bands are consistent with the measured values.