Vibrational development of the N2+ Meinal band system in the aurora

The relative column abundances of N2+(A2Πu, ν') ions with ν' = 0-2 have been examined for a wide range of auroral conditions. Statistically significant change sin the distribution were found to be strongly correlated with auroral height indicators such as the red-to-blue (R/B) ratio, the intensity ratio I([NI]3F)/I[N2+M(0,0)], and the effective rotational temperature of selected molecular electronic bands (N21P, N2+M). The lower-altitude [(R/B) ≤ 0.1] distributions closely approached that observed in the laboratory using a low-pressure N2(X1Σg+, ν = 0) target and a 125-eV electron beam. In sharp contrast, the higher-altitude [(R/B) ≥ 1] distributions were characterized by a substantial excess (up to ∼60%) of N2+(A2Πu, ν' = 1) ions. A plausible explanation of these observations is afforded by the long-standing suggestion that the accidental resonance charge transfer between O+(2D) and N2(X1Σg+, ν = 0) may provide a selective auroral source of N2+(A2Πu, ν' = 1)