Experimental and theoretical analysis of the 5pnpJ=0e, 1e, 2e autoionizing spectrum of Sr

The even parity 5pnpJ=0,1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s21S0-λ1→5sn'p1P1(n'=12-16)-λ2→[5p3/2np]J. The final ICE transition probes the [5p3/2np]J resonances. However, the [5p1/2np]J series below the 5p1/2 threshold were excited also due to their mixing with the [5p3/2np]J perturbers. An extended energy region was covered below and above the 5p1/2 ionization limit by saturating the central ICE lobe and recording as many as possible ''red'' and ''blue'' secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4d5p1P1 valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory. (orig.)