## Abstract

The emission of the Lyman-Birge-Hopfield bands of N$_{2}$(a$^{1}\Pi _{\text{g}}$)-X$^{1}\Sigma _{g}^{+}),v^{\prime}\leq 6$ in active nitrogen is shown to originate from the recombination of ground state nitrogen atoms. Two parallel processes occur: (a) A two-body inverse predissociation populates rotational levels J > 13 of N$_{2}$(a$^{1}\Pi _{\text{g}}$), $v^{\prime}$ = 6, from which there is rapid rotational and vibrational relaxation; this gives an emission intensity proportional to $\text{[N]}^{2}$. (b) The reaction N($^{4}$S) + N$_{2}$(B$^{3}\Pi _{\text{g}}$) = N$_{2}$(a$^{1}\Pi _{\text{g}}$) +N($^{4}$S) (5) populates mainly lower levels of the a$^{1}\Pi _{\text{g}}$ state giving emission proportional to $\text{[N]}^{3}$ which is enhanced by argon carriers. Some measurements on N$_{2}$(a$^{\prime}\ ^{1}\Sigma _{u}^{-}$), $v^{\prime}$ = 0 are also reported.