Excitation in radio-frequency discharges

Abstract

The possibility of using a radio-frequency, flame-like discharge as an excitation source for spectroscopy, discussed in an earlier publication, has been investigated. Both a triode driven oscillator of 250 W output at 30 Mc, and a magnetron powered unit of 2 kW output at 2450 Mc were employed. The RF-excited spectra, between 2000 and 10,000 Å, of air, N 2, O 2, He and H 2 have been examined. Helium and H 2, producing simple spectra, provide advantageous discharge sustaining atmospheres for excitation of line and band spectra of many chemical species. The neutral-gas temperature of the discharge in He and H 2 of approximately 3000°K limits the ability of the discharge in melting, volatilizing and dissociating samples, and imposes pronounced preferential excitation effects. However, a much higher electron temperature permits excitation of vapor species requiring high excitation energies. Techniques are described for the introduction of solid and liquid samples into the discharge. Spectra of some seventy-five elements were excited and their emissions are discussed. The application of RF excitation to quantitative analysis is illustrated by the analysis of tin-lead solders, within the range of 30–55% tin, for major constituents. The RF discharge at atmospheric pressure in He or H 2 appears to be a valuable technique, widely applicable for spectroscopic investigations.