Resonance measurements ofd−fsplittings in highly excited states of sodium

Microwave transitions from the $d$ to the $f$ orbital levels have been observed in sodium with principal quantum number $n$ from 11 to 17 by detecting optical radiation from the $f$ levels, yielding precise values for the difference in the $d$ and $f$ quantum defects as well as the $d$ and $f$ fine-structure splittings. We found the $f$ doublets to be normal, reversed from the $d$ doublets, which are known to be inverted.