Fine-structure intervals offstates in highly excited Na

The fine-structure intervals of the Na $11f$, $13f$, and $14f$ states have been measured by a microwave-resonance method yielding values of 10.52(21), 6.34(12), and 5.02(8) MHz, respectively. These values are ∼5% lower than the theoretical values for the corresponding hydrogenic states. We have also investigated the use of Ramsey's method of separated oscillatory fields as a means of obtaining narrower resonances.