Rydberg Series in Strontium Found in Absorption by Selectively Laser-Excited Atoms

Using a pulsed tunable dye laser pumped by a nitrogen laser, the 5 s 5 p 1 P 1 0 level in Sr I was selectively populated from the 5 s 2 1 S 0 ground state. A simultaneously pumped broad-band dye laser provided a background continuum for photographic registration of absorption spectra. Transitions from the 5 s 5 p 1 P 1 0 level to 5 sns 1 S 0 levels and 5 snd 1 D 2 levels were observed with principal quantum number up to n = 36 and n = 52, respectively. Substantial population in the lower lying energy levels 5 s 4 d 1 D 2 and 5 s 4 d 3 D 1,2,3 was obtained through radiative and collisional processes, making it possible to get simultaneous registrations of long absorption series out of these energy levels. Transitions from the 5 s 4 d 1 D 2 level to 5 snp 1 P 1 0 levels and 5 snf 1 F 0 3 levels were observed up to n = 29 for both series. From the 5 s 4 d 3 D 1,2,3 energy levels, transitions were obtained to the 5 snf 3 F 0 2,3,4 series up to n = 28. An ionization energy of 45 932.09 ± 0.15 cm -1 has been determined for series converging to the 5 s 2 S 1/2 level of Sr II.