Near-Infrared Diode Laser Spectroscopy of the (2, 0) Band of the A²Π_u-X²Σ⁺_g System of the N⁺₂ Ion

The (2.0) vibrational band of the A²Π_u-X²Σ⁺_g system of the N⁺₂ ion has been observed by near-infrared diode laser absorption spectroscopy. A signal-to-noise ratio greater than 50 at a time constant of 100 msec was obtained using the hollow cathode discharge modulation technique. In total, 108 lines were identified as belonging to the (2,0) band of the N⁺₂A-X system. The observed wavenumbers were least-squares fitted, yielding precise spectroscopic constants, the band origin T₂₀ and the spin-orbit coupling constant A₂ being 12 732.83583(31) and -74.63529(54) cm^-1, respectively, where the uncertainties given in the parentheses correspond to one standard deviation. The Dunham coefficients revised by combination of the present result and previous results of high-resolution studies are also presented.