Laser spectroscopy of ground-state scandium ions in a high-pressure metal halide discharge II. Optogalvanic spectroscopy

Abstract

Pulsed laser irradiation of ground-state scandium ions in a vertically burning 60-Hz high-pressure metal halide discharge decreased the voltage required to sustain the discharge. The scandium ions were excited with a pulsed dye laser at 363.1 nm from the a3D2 spin-orbit component of the ground state (68 cm−1 above the ground state) to the z3F03 state. The optogalvanic Sc+ signals were compared with the optogalvanic signals from excitation of an excited state of neutral Hg at 365.0 nm (6 3P2 → 6 3D3). The Sc+ and Hg optogalvanic signals had the same polarity and very similar temporal response. The optogalvanic signals from Sc+ and Hg had a similar nonlinear dependence on laser energy. The comparison between Sc+ and Hg suggests that a common mechanism produces the optogalvanic signal for ions and neutrals in this high-pressure discharge. The radial and axial dependencies of the Sc+ optogalvanic signals were compared with saturated laser-induced fluorescence (LIF) measurements. The radial optogalvanic profiles were compressed relative to the LIF profiles, but the axial optogalvanic profiles showed good agreement with the LIF values. From 355 to 370 nm there was good correspondence between the optogalvanic and emission spectra. The transitions in this wavelength range are from Sc+ and Hg. The optogalvanic signals for Sc+ were coupled with LIF data for Sc+ and Sc to calculate the shape of the electron density profile and as an independent check of the temperature dependence of the Saha equation.