Thallium Oscillator Strengths and6dD322State hfs

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Abstract
The lifetime of the 7S122 state of thallium has been measured by the optical-double-resonance technique, with the result τ=7.4±0.3×10−9 sec, and by the level-crossing technique, with the result τ=7.6±0.2×10−9 sec. The intensity ratio of the 7S122−6P322 and 7S122−6P122 lines radiated by an optically pumped thallium beam was measured to establish the oscillator-strength ratio for these two transitions. The result is A5350A3776=1.16±0.05. The lifetime and hfs of the thallium 6D322 state were measured by the level-crossing technique. The results are τ=6.2±1×10−9 sec and |a|h=41±2×106 sec. (The Tl205 and Tl203 hfs were not resolved in the experiment.) A table of thallium oscillator strengths has been constructed from our results and from some of the oscillator-strength ratios reported in the literature. The values in the table are compared to those in the remainder of the literature in order to collect and comment on equivalent values from other experiments. The oscillator-strength values in the table are also compared to the predictions of Bates and Damgaard's and Vainshtein's approximation methods. It was found that when np*<2, the s−p transition probabilities calculated by extrapolating the tables of Bates and Damgaard are quite different from the values directly calculated using their theory. The directly calculated Bates-Damgaard values are in much better agreement with the experimental results (the average difference is 17% for 20 thallium transition). Vainshtein's calculated 7S122 to