A laboratory study of the dissociative excitation of the N+(5S) state

The prominent auroral emission feature near λ2145 Å has been tentatively identified as the N+ (5S) doublet lines [λ2139.68 Å and λ2143.55 Å]. Dissociative excitation of N2 by electron impact with a predicted cross section value ≥2 × 10−18 cm² has been proposed as the source of this metastable species. We have observed the N+ (5S) emission lines for the first time in a laboratory electron‐impact experiment and found that the cross section has a value of ∼ 3 × 10−21 cm² at 100 eV. This result eliminates dissociative excitation as a significant N+ (5S) source in auroras. Observation of the spatial distribution of the doublet radiation around the electron beam has provided some insights into the radiative lifetime of the 5S state, and we show that τr ∼ 5 µsec if the fragment ions are produced with a kinetic energy of ∼ 3 eV but ∼ 100 µsec if the N+ ions are formed with thermal energies.