Lifetime measurements of several S, P, and D states of thallium in a glow discharge by single-step and two-step laser-excited fluorescence.
The lifetimes of several states in a thallium see-through hollow cathode discharge, or galvatron, are obtained to characterize its potential as an atomic line filter. The lifetimes of the thallium 6(2)D(3/2), 6(2)D(5/2), and 7(2)S(1/2) states are measured by time-resolved single-step laser-excited fluorescence by use of a 276.787 nm laser pulse or a 535.046 nm laser pulse and measuring the resulting fluorescence waveform at the appropriate wavelength. Values of 6.4 +/- 0.1, 7.5 +/- 1.1, and 7.7 +/- 0.2 ns were obtained for the 6(2)D(3/2), 6(2)D(5/2), and 7(2)S(1/2) states, respectively, which agree with values obtained by previous authors, as well as calculated values. No current dependence was observed for each of these states. The lifetime of the long-lived thallium 6(2)P(3/2) degrees metastable state was measured by two-step laser-excited fluorescence at various applied currents. The metastable level was pumped by a 276.787 nm laser pulse, and a temporally delayed 535.046 nm laser pulse interrogated the population of the metastable state. Relating the fluorescence intensity to the population of the metastable state as a function of delay time yielded a decay curve for the 6(2)P(3/2) degrees metastable state. Values of 2.1 +/- 0.2, 2.8 +/- 0.1, 3.1 +/- 0.3, 3.8 +/- 0.4, and 4.8 +/- 0.6 micros were found for applied currents of 14.0, 12.0, 10.0, 8.0, and 6.0 mA, respectively. The resulting lifetimes for the 6(2)P(3/2) degrees metastable state clearly show a dependence on the applied current and are expected to be due to collisions with the wall of the cathode, as well as a contribution due to collisions with electrons.
Taylor
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Department of Chemistry, P.O. Box 117200, University of Florida, Gainesville, Florida 32611, USA.
Omenetto
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Smith
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Winefordner
J D
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