The auroral 2150 Å feature: A contribution from lines of singly ionized atomic nitrogen

The observed auroral spectral feature at ∼ 2150 A may consist partially of spin forbidden transitions in singly ionized atomic nitrogen, N II. These transitions are analogous to the 1356 A feature of O I in that they represent transitions from the lowest lying quintet term to the ground state ³P. Prior consideration of these transitions may have been hampered both by the uncertainty of a precise wavelength value for the observed auroral spectral feature (due to its evidently complex nature) and by the relatively recent determination of the wavelengths of intercombination lines joining the quintet levels of N II to the more abundant triplet and singlet levels.