Quantum defect and fine structure of terms of Rydberg Na I atoms in S-, P- and D states

High-precision measurements were made of the frequencies of the nS → nP and nD → (n + 1)P transitions in the Na I atom. This was done in the range of the principal quantum numbers n = 23–33 at frequencies 53–350 GHz. The quantum defects for the P_1/2,3/2 and D_3/2,5/2 terms, as well as the LS splitting, were determined more accurately. A combined analysis of the frequencies of the transitions in Na I in the optical, infrared, and microwave ranges yielded sets of constants for the quantum defect, describing the energy of the atom forI = 0, 1, 2 and n > 3.