Infrared diode laser spectroscopic study of the active nitrogen. The electronic transition between the lowest singlet metastable states a 1Πg–a’ 1Σ−u, 0–0 band

The a 1Πg–a’ 1Σ−u, 0–0 band of the molecular nitrogen was observed in an electric discharge plasma of nitrogen using infrared diode laser spectroscopy at Doppler‐limited resolution. Precise values were obtained for the rotational constants and the energy separation between the two electronic states. The effect of Λ‐type doubling in the a 1Πg state was observed as small shifts of Q branch and P/R branch transitions to higher and lower frequencies, respectively, than those expected if Λ doubling were absent.