Probing configuration interaction of the Ba5d7dD21state using radio-frequency spectroscopy and lifetime measurements

To probe the configuration mixing between the Ba $6snd{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}D_2^{}{}_{}{}^{}$ Rydberg series and the $5d7d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ perturber we have observed the radio-frequency transitions between the $5d7d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ state and the $6s28s{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$, $6s24f{}_{}{}^3{}_{}{}^{}F_2^{}{}_{}{}^{}$, and $6s24f{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ states using a delayed-field-ionization approach. The transitions are observed in the presence of small (∼1 V/cm) electric fields, and from the Stark shifts of the transitions we are able to estimate the ${}_{}{}^1{}_{}{}^{}D$ and ${}_{}{}^3{}_{}{}^{}D$ Rydberg fractions of the $5d7d$ state. Our measured zero-field term separations tie together previous optical measurements of the various Rydberg series involved. In addition, we have measured the lifetimes of the $6snd$ states in the vicinity of the $5d7d$ perturber to estimate the fraction of $5d7d$ character in each of the Rydberg states. The values we find for the configuration mixing are in reasonable agreement with those determined by a multichannel-quantum-defect-theory analysis of the optical spectrum of the even-parity $J=2\mathrm{}$ states of Ba.