Measurements of the oscillator strengths for the 6p7s (1/2,1/2)1 → 6pnp (1/2,3/2)2 Rydberg transitions of lead

We report experimentally determined oscillator strength distribution in the bound region of lead corresponding to the 6p7s (1/2, 1/2)1 → 6pnp (1/2, 3/2)2 (20 ≤ n ≤ 52) Rydberg transitions. The absolute value of the photoionization cross section from the 6p7s (1/2, 1/2)1 excited state at the first ionization threshold 6p (2P1/2) has been determined as 27 ± 4 Mb using the saturation absorption technique. The threshold value of the photoionization cross section is used to calibrate the oscillator strengths of the above mentioned Rydberg transitions. Moreover, oscillator strengths in the bound region smoothly connect with the differential oscillator strength density at the first ionization threshold, and verify the fundamental condition of quantum defect theory.