THE PERTURBED EVEN-PARITY J=1(E),2(E) AUTOIONIZING SPECTRA OF STRONTIUM BELOW THE 4D(5/2) THRESHOLD - OBSERVATION AND THEORETICAL-ANALYSIS

The even-parity J = 1e, 2e autoionizing spectra of neutral strontium are investigated below the 4d5/2 threshold in a two-step laser experiment via the 4d5p 1P1 level in a strontium atomic beam. The produced Sr+ ions are analysed by a time-of-flight microchannel plate detector. The J final level assignment is obtained by comparing the line intensity dependence from two recorded spectra with pi-pi and pi-sigma polarizations of the two lasers. More than 400 new resonance lines are measured with an accuracy of +/-0.2 cm-1 for the narrow ones using standard laser calibration procedures. They are assigned to fifteen autoionizing Rydberg series 4dns, 4dnd and 4dng and many perturbers belonging to the 5p6p configuration. Interpretation is made by a combination of the eigenchannel R-matrix and multichannel quantum defect methods (MQDT). Twelve and fourteen interacting channels are introduced for J = 1e and J = 2e respectively. Theoretical energy level positions and excitation profiles are compared with the experimental data and explain the behaviour of the strongly perturbed Rydberg series.