Near ultraviolet emission of nonequilibrium inert gas plasmas. II. Theory

Theoretical models for the appearance of the third UV continuum in the emission spectrum from nonequilibrium inert gas plasmas are reviewed. A model is proposed which attributes the continuum to transitions from low-lying excited states of the molecular ion that correlate with $R^*(^3P) + R^+(^2P)$ in the low-lying dissociating states of $R_2^+$. The emission efficiency in a beam plasma is $\sim2\%$ in accordance with experiment. In a discharge plasma this quantity may be an order of magnitude higher. The features of the continuum in $\rm He, \rm Ne$, and $\rm Ar$, as well as other experimental data, are explained in terms of the model.