On the selectivity of population of the neon excited levels in the decaying $\mathrm{He}$–$\mathrm{Ne}$ plasma

The results of a spectroscopic study of the afterglow of a pulsed discharge in a $\mathrm{He}$–$\mathrm{Ne}$ mixture are presented, showing the unique selective population of the upper level of the $2p^{5}4p$ configuration ($3p_{1}$ in Paschen's notation) of a neon atom at a helium pressure of tens of Torr. The main measurements were conducted under conditions of competition between the excitation transfer from metastable He atoms $(2^{1}S_{0})$ and the dissociative recombination of $\mathrm{He}$–$\mathrm{Ne}^{+}$ ions with electrons as sources of excited atoms. Helium pressure $P_{\mathrm{He}}\approx0.08-20$ Torr, neon $P_{\mathrm{Ne}}\approx0.0005-0.003$ Torr, the electron density $[e]<10^{11}$ cm$^{-3}$. The results of the experiment indicate the existence of a mechanism that forms with an increase of helium pressure such a distribution of populations over $2p^{5}4p$ levels, in which more than $60\%$ of the radiation flux of $2p^{5}3s\leftarrow 2p^{5}4p$ transitions is concentrated in one spectral line of $352.0$ nm.