Vibrational populations of the excited states of N2 under auroral conditions

Abstract

The equations of statistical equilibrium for the population and depopulation of the electronic states of N2 have been solved for steady state normal auroral conditions. All vibrational levels for the seven lowest triplet electronic states (A, B, W, B′, C, E, D) and the three lowest excited singlet electronic states (a, a′, w) of N2 were included in the calculations. Recently measured auroral secondary electron spectra were employed to calculate the rates for electron impact excitation. The transition probabilities, electron impact excitation cross sections, and vibrationally dependent quenching rates used were a combination of the best available experimental and theoretical data. The results of these calculations are the absolute vibrational populations of all the electronic states. Intrasystem cascading and vibrationally dependent quenching were found to be important in determining the vibrational populations in the lower singlet and triplet excited electronic states. The predicted vibrational populations for the A and B triplet states agree well with the available experimental data. These calculations predict that a fairly large density of N2 in excited metastable states is produced under auroral conditions.