We present an experimental study of the Ba 8<i>snl</i> double-Rydbergstates, using two-photon core-electron excitation from selectively preparedhigh-l 6<i>snl</i> Rydberg states (n=12–15 and l=6–7). The 8<i>snl</i> resonances recorded in the vicinity of the 6s→8s two-photon ionic transition exhibit mixing with the neighboring 5f<sub>7/2, 5/2</sub>n<sup>′</sup>l<sup>′</sup> double-Rydbergseries. The increasing strength of this configuration mixing as l decreases is due to the multipole terms of the e–e Coulomb interaction expansion in the final excited state that resultsfrom polarization of the inner 8s core electron by thepresence of the outer <i>nl</i> electron. The interpretationof the complex 8<i>snl</i>=6+5fn<sup>′</sup>l<sup>′</sup> structures is carried out through the parametricalmultichannel quantum defect theory and a Lu–Fano plot analysis.
© 1997 Optical Society of America
Pierre Camus and Samuel Cohen, "Neutral Ba 8snl (l = 6, 7)+5fn‘l’ double Rydberg spectroscopy," J. Opt. Soc. Am. B 14, 2430-2442 (1997)