Evidence for charge exchange between N+ and N2(A 3Σ+u) in a low-temperature nitrogen plasma

The emission from the first negative system, N2+(B 2Σ+u)→N2+(X 2Σ+g)+hν, is studied in the flowing nitrogen afterglow of a DC arc plasma. Investigation of the spectrum shows overpopulation of the vibrational levels 6 and 7 of the excited molecular ion, N2+(B 2Σ+u). Selective excitation of these levels is explained by a charge exchange reaction between atomic ions in the ground state and metastable molecules in the N2(A 3Σ+u) state. The emitted intensity of the first negative system is shown to be linear with electron density ne for ne>2×1016 m−3, a higher-order dependence exists below this value. This is consistent with population of N2+(B 2Σ+u) by atomic ions, N+.