Measurement ofnd→(n+1)pintervals in sodium Rydberg states

We report the measurement of $\mathrm{nd}\to \mathrm{}(n+1\mathrm{})p$ intervals in sodium Rydberg states with $n=30-32\mathrm{}$. The measurements were made using a microwave-resonance technique which utilizes selective field ionization. Fine-structure intervals of the $p$ state are reported and shown to continue the ${\left(n^{*}\right)}^{-3\mathrm{}}$ scaling law, where $n^{*}=n-\delta$ is the effective quantum number and $\delta$ is the quantum defect. Quantum defects for the $p$ states are derived and compared to spectroscopic measurements.