Dissociative Recombination in the Afterglow of Low-pressure Barrier Discharge. Population of Ne(2p-=SUP=-5-=/SUP=-3d) Atoms

Abstract

The decaying neon plasma produced by the dielectric barrier discharge (DBD) in a cylindrical tube at a pressure of 0.1-40 Torr has been spectroscopically investigated to analyze the dissociative recombination (DR) of molecular ions with electrons as a mechanism for the formation of excited atoms. It is shown that, at the electron density in the afterglow less than 5·1010 cm-3 the DR is the dominant source of population of 3d levels at pressures PNe≥ 0.6 Torr. At lower pressures, the optical properties of the decaying plasma are formed to a greater extent by the collisional-radiative recombination of Ne+ ions. A significant variation of the relative intensities of the 3d->3p transition lines in the afterglow with a change in gas pressure was found, reflecting the effect of inelastic collisions on the formation of the spectrum of decaying plasma in the near infrared region. From measurements carried out at a pressure of 0.6 Torr, the relative values of the partial DR coefficients for the 3dj levels of the neon atom were found. Comparison of these data with measurements in the near ultraviolet region, containing the lines of 4p->3s transitions, indicates the need to take into account the cascade 4p->3d transitions to correctly solve the problem of the final products of dissociative recombination. Keywords: dielectric-barrier discharge, low-pressure plasma, optical emission spectroscopy, dissociative recombination, molecular ions, collisional-radiative recombination, cascade transitions.