The afterglow and energy transfer mechanisms of active nitrogen

The complex spectrum of active nitrogen is reviewed from the vacuum ultraviolet to the infrared. Its variations with change of pressure, temperature and additive are described. Many of the mechanisms which have been individually proposed to account for various spectral features of the afterglow are also reviewed. Some of these mechanisms, suitably modified, together with some new suggestions, are shown to provide a comprehensive and self-consistent model that accounts for all of the complex spectroscopic phenomena of active nitrogen. Collision-induced radiationless transitions are shown to be very significant in the afterglow, particularly when relevant selection rules are taken into account. The B 3 Π g (ν = 12), B prime 3 Σ u − (ν = 8), a 1 Π g (ν = 5) and a prime 1 Σ u − (ν = 7) levels are populated by collision-induced radiationless transitions from the shallow 5 Σ g + state. The population distributions among the B 3 Π g (ν = 12−9), B prime 3 Σ u − (ν = 8−4), a 1 Π g (ν = 5−0) and a prime 1 Σ u − (ν = 7−0) levels are then each determined by the competing decay processes of spontaneous radiation, and collision-induced vibrational relaxation and electronic quenching. The B 3 Π g (ν = 6) level is populated by collision-induced radiationless transition from the A 3 Σ u + (ν = 16) level. The B 3 Π g (ν = 4−0) levels are populated by transitions from B prime 3 Σ u − (ν = 8−4) and 3 Δ u (ν = 7−0). In the cooled afterglow the C 3 Π u (ν = 4) level is populated by an inverse predissociation of N( 4 S) and N( 2 D) atoms; the C 3 Π u (ν = 0) level is populated by collision-induced radiationless transitions from 5 Π u (ν = 0). The 5 Π u (ν = 0) level lies a little below, not above, the C 3 Π u (ν = 1) level. The 5 Σ g + (ν = 0) level lies 950 ± 50 cm −1 below the N( 4 S) + N( 4 S) dissociation limit.