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

Abstract

Using transverse resonant two-photon CW laser excitation of metastable 40Ar(4s 3P2) atoms in a collimated beam via the Ar(4p 3D3) level, we have carried out a comprehensive high-resolution study of odd Ar(2P3/2 ns,nd,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(2P1/2 8d´9d´J = 2,3) levels are clearly detected. Moreover, the low-lying Ar(nd´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 ng´,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 nd´ 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.