Interacting asymmetric double Rydberg series: the Ba 8snl(l= 5) + 5fjn′l′ case

The 8s nl double Rydberg states of barium with l = 5 and n = 12–15 are populated by employing an isolated core excitation (ICE) scheme in conjunction with the Stark switching technique. The recorded spectra show strong configuration interaction with three adjacent 5f j n ' l ' series. One of the latter series is converging to the 5f 5/2 ionization limit and the other two to the higher lying 5f 7/2 one. A multichannel quantum defect theory (MQDT) analysis reveals the presence of low-lying members of double Rydberg series converging to higher ionization thresholds and determining the configuration mixing. At least two perturbers, affecting energy level positions, are identified while a comparison between experimental and fitted excitation profiles points towards the presence of a third one. Finally, theoretical calculations of the 8s nl ( l = 5) series members quantum defects demonstrate the onset of mutual penetration between the two excited electrons. Nevertheless, the most important quantum defect contributions stem from exchange and polarization effects and thus long-range interactions alone are insufficient for a proper description of the double Rydberg states involved.