The absorption of light by thallium vapour on the short wave-length side of the series limit

Abstract

Measurements of the absorption of light in thallium vapour from the series limit at 2030 to 1450Å are described. The absorption cross-section at the series limit is 4∙5 ± 0∙8 × 10 -18 cm 2 and the f -number for the continuum over the range of the experiment is 0∙025 ± 0∙005. Auto-ionization lines are observed at 2007, 1610 and 1490Å in agreement with those reported by Beutler & Demeter (1934 b ). The moderately sharp line at 2007Å ( 2 P 0 ½ → 4 P 3/2 ) has an f -number of 0∙005 ± 0∙001 and a lifetime of 18 ± 5 × 10 -15 s, while the broad line at 1610Å ( 2 P 0 ½ → 2 D 3/2 ) has an f -number of 0∙52 ± 0∙09 and a lifetime of 2∙2 ± 0∙1 × 10 -15 s. The 1490Å line ( 2 P 0 ½ → 2 P ½ ) is sharp and the f -number is estimated to be of the same order as that of the line 2007Å. These results are discussed in relation to the auto-ionization selection rules and previous experimental and theoretical work is reviewed.