Dissociative recombination of Ne$_{2}^{+}$ molecular ions with electrons: Population of Ne$(2p^{5}4p)$ atoms in a decaying plasma

Decaying neon plasma has been investigated by kinetic spectroscopy. The experimental conditions were neon pressure of 0.2–152 Torr and electron density in the initial stage of decay $[e]\le 5\times$ 10$^{10}$ cm$^{-3}$. The plasma was created by a pulsed barrier discharge with electrodes on the outer surface of a cylindrical glass tube. The discharge frequency was 40–160 Hz. It has been shown based on a comparative analysis of the dependences of the intensities of spectral lines on the time and electron temperature in the afterglow that the $2p^{5}4p$ levels are clearly divided into two groups in terms of population mechanisms. The lower levels (from $3p_{10}$ to $3p_{3}$ (Paschen notations)) are related to dissociative recombination of Ne$_2^+$ molecular ions with electrons, and the lines emitted by them behaved identically to the lines of the transitions $2p^{5}3s\leftarrow 2p^{5}3p$ and $2p^{5}3p\leftarrow 2p^{5}3d$ up to pressures of 0.6 Torr. The kinetics of the upper levels ($3p_{5}$, $3p_{2}$, $3p_{4}$, and $3p_{1}$) had a more complicated character, and, at low pressures, the populations of all $2p^{5}4p$ levels were related to a collisional-radiative recombination of Ne$^+$ ions. Significant differences in the dependences of the relative populations of $3d$- and $4p$ levels on neon pressure are discussed.