Population of N₂(A³Σu⁺) metastable states in a pure nitrogen glow discharge

The concentration of the nitrogen metastable molecule N 2 (A 3 Sigma u + ) is determined in a pure nitrogen glow discharge as a function of the pressure (from 0.1 to 2 Torr) and of the discharge current (up to 30 mA cm -2 ) using the optical absorption of the first positive system bands. The absorption maximum is of the order of 2% corresponding to a N 2 (A 3 Sigma u + , nu =0) concentration of about 1.4*10 12 cm -3 . Measurements of the concentration of nitrogen atoms, the electronic field are also reported. A kinetic model indicates that the N 2 (A) molecules are created by electronic excitation from ground-state molecules and lost mainly by diffusion to the walls and collisions with N( 4 S) atoms.