Precise quantum defects of nS, nP and nD levels in CsI

Very accurate measurements of the n2Ssub(1/2) (n=9-30), n2Psub(1/2,3/2) (n=9-50) and n2Dsub(3/2,5/2) (n=5, 8-32) energy levels in CsI have been performed in the wavelength-range 6.379 A<lambda<7,432 A with a high-precision vacuum-wavemeter using either Doppler-free two-photon spectroscopy or Doppler-limited one-photon spectroscopy with a frequency-doubling crystal. Thermionic detectors were used throughout the experiments. By fitting the experimental energy values to extended Rydberg-Ritz formulas, accurate quantum defect data and series limits are given. The ionization energy Esub(i)=31,406.4710(7) cm-1 was adopted to be the best fit value, differing significantly from most recent evaluations of other authors, but agreeing well with former, less accurate measurements performed in our laboratory. (orig.)