Laser spectroscopy of ground-state scandium ions in a high-pressure metal halide discharge I. Saturated laser-induced fluorescence

Abstract

Ground-state scandium ions in a vertically burning 60-Hz high-pressure metal halide discharge were detected by saturated laser-induced fluorescence (LIF). 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 laser-induced fluorescence, observed at 440.0 nm (z3F03 → a3F3), was optically thin. The Sc+ LIF profiles along a diameter were asymmetric about the center, with a local minimum near the axis, and maxima at about ±2 mm (radius=6.5 mm). The profiles varied with axial position and lamp power. The LIF Sc+ signals are modulated during the ac phase angle. At the discharge axis the maximum signals occur just after the current zero crossings (near the voltage reignition spikes) and the minima just after the current maxima. LIF was also observed from other nearby excited electronic states of Sc+, populated by collisions. From the positional dependence of the ratio of the fluorescence at 437.5 (z3F04(z3F04→ a3F4) to 440.0 nm we suggest that neutral scandium atoms are responsible for the collisional energy transfer.