Interferometric Study of Dissociative Recombination Radiation in Neon and Argon Afterglows

A photoelectric recording, pressure-tuned Fabry-Perot interferometer of high resolution is used to determine the spectral line profiles of 22 neon and 5 argon (2pₙ→1sₘ) lines emitted from a microwave discharge and during the ensuing afterglow. All afterglow line profiles are broader than the corresponding discharge lines, and in most cases the afterglow line shapes are consistent with a dissociative origin of the excited atoms, indicating that the 2pₙ excited states of neon and argon are produced by dissociative recombination of electrons with Ne₂⁺ and Ar₂⁺ ions, respectively. Detailed examination of the line profiles in neon indicates a "multishouldered" structure corresponding to several different dissociation kinetic energies, suggesting that different initial states of the Ne₂⁺ ion are involved in the dissociative recombination process. From the deduced molecular ion energy levels it appears that, in addition to the Ne₂⁺ ion state with a dissociation energy $D=1.35$ eV reported by Connor and Biondi, there may be a more weakly bound state with D~0.5 eV which contributes to the recombination.