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

Using a pulsed tunable dye laser pumped by a nitrogen laser, the 5s5p¹P₁⁰ level in Sr I was selectively populated from the 5s^{2 1}S₀ ground state. A simultaneously pumped broad-band dye laser provided a background continuum for photographic registration of absorption spectra. Transitions from the 5s5p¹P₁⁰ level to 5sns¹S₀ levels and 5snd¹D₂ levels were observed with principal quantum number up to n = 36 and n = 52, respectively. Substantial population in the lower lying energy levels 5s4d¹D₂ and 5s4d³D_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 5s4d¹D₂ level to 5snp¹P₁⁰ levels and 5snf¹F⁰₃ levels were observed up to n = 29 for both series. From the 5s4d³D_1,2,3 energy levels, transitions were obtained to the 5snf³F⁰_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 5s²S_1/2 level of Sr II.