Effect of small quantities of oxygen in a neon glow discharge

Abstract

Many studies have already been carried out on the effect of small quantities of molecular gases (oxygen, hydrogen and nitrogen) in argon analytical glow discharges (GD). We report here the first comprehensive study using small amounts of oxygen in a neon GD plasma with copper sample. Whilst neon is too costly for routine use in analytical GD spectrometry, such studies help the interpretation of the excitation and ionization processes taking place in the discharge. In all GD, Penning ionization (PI) of analyte atoms, asymmetric charge transfer (ACT) and Penning excitation (PE) of analyte ions have significant roles in populating excited ionized levels, so the higher energy of the neon metastable states and the higher ionization energy compared to argon have a major effect on the appearance of the copper spectrum. Examples of all these effects for copper ionic lines in neon–oxygen mixtures will be presented. For copper atomic lines, it is observed that the changes (such as enhancement due to change in self-absorption and three body collisional recombination or reduction where neutralization of copper ions is suppressed) in emission yield ratios are more significant when higher oxygen concentrations are used. A clear trend of cascading for neon ionic lines with excitation energies about ∼56 eV and ∼53 eV could be observed in neon–oxygen mixtures. Excitation of the higher atomic energy levels of copper and neon by neutralization of their ionic ground states is also discussed in this work.