Laser spectroscopy of the thallium atom based on transitions 6p1/2 → 6D3/2 → nF5/2 (n = 13–24)

The energies and quantum defects of Rydberg states nF5/2 (n = 13–24) of the thallium atom have been studied experimentally. The Rydberg states were excited from the ground state 62P1/2 by the two-stage scheme through the intermediate state 62D3/2. By using a collimated atomic beam and monochromatic radiation of two narrow-band tunable lasers, we have succeeded in resolving the hyperfine and isotopic structures of the ground state of the thallium atom and in determining the energy positions of the states nF5/2 accurate to 0.03 cm−1, which exceeds the accuracy achieved in the previous works by more than an order of magnitude. The quantum defect of nF5/2 states is independent of n within the measurement accuracy and is equal to Δ = 1.0344 ± 0.0008. The ionization potential Ip = 49266.55 ± 0.03 cm−1 has been found for the 205Tl isotope from the level 62P1/2 (F = 0). The energy of the 62D3/2 level measured experimentally relative to the state F = 0 of the 205 isotope amounted to 36118.56 ± 0.02 cm−1.