Vibrational distribution of N₂(a¹Pig) in a DC glow discharge

The vibrational distribution of the singlet metastable state N 2 (a 1 Pi g ) was measured in a DC glow discharge by optical emission spectroscopy of the Lyman-Birge-Hopfield bands in the VUV range. The pressure ranged from 4 mTorr to 2 Torr and the current from 5 to 50 mA. The observed distribution is strongly non-Boltzmann. A population inversion similar to that in aurora was observed at low pressure and low current but not at higher pressures. The experimental results are compared with a kinetic model based on solutions to the electron Boltzmann equation and the rate balance equations for the N 2 (a 1 Pi g ) vibrational levels.