Two-photon spectroscopy of neutral barium: Observations of the highly excited even levels and theoretical analysis of theJ=0spectrum

Abstract

Extensive new data on the even parity $J=0\mathrm{}$ and $J=2\mathrm{}$ levels of neutral barium have been obtained using two-photon absorption spectroscopy with a nitrogen-pumped dye laser and space-charge detection. Members of the Rydberg series $6sns{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ ($16<~n<~61$), $6snd{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ ($15<~n<~81$), and $6snd{}_{}{}^3{}_{}{}^{}D_2^{}{}_{}{}^{}$ ($15<~n<~30$) and perturbing levels of these series belonging to the $5d7d$ configuration have been observed; the corresponding wave numbers have been determined. A detailed description of the experimental method is given, followed by the presentation of the new data and the theoretical analysis of the $J=0\mathrm{}$ spectrum. All $J=0\mathrm{}$ levels in the energy range between 34370 ${\mathrm{cm}}^{-1\mathrm{}}$ and the first limit were interpreted by means of the multichannel quantumdefect theory. In this energy range, the $6sns{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ series is perturbed by two levels at 38924 and 41441 ${\mathrm{cm}}^{-1\mathrm{}}$; these levels are assigned to $5d6d{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and $5d7d{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, respectively.