Odd Rydberg spectrum of40Ar(I): high-resolution laser spectroscopy and multichannel quantum defect analysis of theJ= 2 and 3 levels

Using transverse resonant two-photon CW laser excitation of metastable 40 Ar(4s 3 P 2 ) atoms in a collimated beam via the Ar(4p 3 D 3 ) level, we have carried out a comprehensive high-resolution study of odd Ar( 2 P 3/2 n s, n d, J = 2,3) Rydberg states ( n = 13-90). The transition energies are determined with an uncertainty of 0.006 cm -1 and perturbations in the spectra associated with the Ar( 2 P 1/2 8d´9d´ J = 2,3) levels are clearly detected. Moreover, the low-lying Ar( n d´ J = 2,3) autoionization resonances ( n = 10-14) have been investigated and the respective widths (ranging from 5000 to 26 000 cm -1 ) determined. A very sharp resonance (reduced width 27 cm -1 ) has been detected and identified as a member of the n g´, J = 3 series. A multichannel quantum defect theory (MQDT) analysis of the measured bound Rydberg levels yields reliable eigenchannel quantum defect parameters which describe the odd J = 2 and 3 spectra of Ar in the bound as well as in the autoionization region. The MQDT-derived widths for the n d´ resonances are found to be in good agreement with the experimental results. The s-d coupling observed in the J = 2 spectrum is discussed in detail.