Hyperfine Structure and Isotope Shift in the 7 ^2S_1/2–6 ^2P_1/2 Transition of Natural Thallium by Atomic Beam Absorption*

The isotope shift in the 72S12−62P12 transition (3776 Å) and the hyperfine-structure separations of Tl203 and Tl205 in the 72S12 state have been determined spectroscopically by atomic beam absorption with the use of a Fabry–Pérot interferometer crossed with a 10-in. diffraction grating. Our results are: 0.0554 ± 0.0012 cm−1 for the isotope shift in the 3776 Å line; −0.0405 ± 0.0013 cm−1 in the 62P12 level; and Δν(72S12)=0.4078±0.0014cm−1 and 0.4109 ± 0.0012 cm−1 for the hyperfine-structure separation in Tl203 and Tl205, respectively.