Abstract

The ${\text{N}}_2^{+}$ C-X electronic system, extending in emission from about 137 - 207 nm, has a number of unusual features which have been the focus of spectroscopic studies for many years. When produced in an electric discharge, the intensities of individual vibrational bands are extremely sensitive to excitation conditions. In discharges through helium with a trace amount of nitrogen, bands with v' ≥ 3 are readily excited whereas bands with v' < 3 are absent. Discharges through pure nitrogen, or trace amounts of nitrogen in neon or argon produce emission only in bands with v' < 3. In addition, there are irregularities in the vibrational structure of the ${\text{C}}^{\text{2}}{\text{Σ}}^{\text{+}}{}_{\text{u}}$ state as well as weak rotational perturbations. Predissociation in vibrational levels with v' ≥ 3 is thought to be centrally involved in the character of the emission spectrum, although the mechanism has never been fully explained.

© 1995 Optical Society of America