OGO-4 observations of the ultraviolet auroral spectrum

Auroral ultraviolet spectra in the range from 1200 to 3200 A have been obtained by the spectrometer on board the OGO-4 satellite. Emissions of N2, H, O, and N are readily identified. Atomic and molecular intensities are deduced from the comparison with a synthetic spectrum and compare reasonably well with some previous measurements and calculations. A feature at 2150 A is assigned to the (1-0) NO gamma band. Taking into consideration the various excitation mechanisms of NO(A2 Sigma), it is proposed that energy transfer from N2 metastable molecules to oxygen accounts for the excitation of the NO gamma bands. In particular, it is suggested that the resonant reaction between O2 and highly metastable N2 molecules may be a major source of NO(A2 Sigma).