Narrow 6${\mathit{p}}_{1/2,3/2}$np J=1 autoionizing Rydberg series in barium and their interaction with 6${\mathit{p}}_{3/2}$nf states

The 6${\mathit{p}}_{1/2,3/2}$np and 6${\mathit{p}}_{3/2}$nf (J=1) series in barium were excited in a two-step pulsed laser experiment starting on the 6s5d ${}_{}{}^3{}_{}{}^{}$ ${\mathit{D}}_1$ metastable state via the 5d6p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ as intermediate level. Use was made of the 6${\mathit{s}}_{1/2}$6${\mathit{p}}_{1/2}$ character mixed into the 5d6p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ level to excite the 6pnp series, which appear to have extremely low autoionizing rates compared to other 6pnl series. The observed spectra were analyzed using a seven-channel multichannel quantum-defect theory analysis. Evidence of configuration interaction between the 6${\mathit{p}}_{1/2}$np and 6${\mathit{p}}_{3/2}$nf series was found.