3DNL J=0(E)-2(E) AUTOIONIZING LEVELS OF CALCIUM - OBSERVATION BY LASER OPTOGALVANIC SPECTROSCOPY AND THEORETICAL-ANALYSIS

The even parity J = 0-2 autoionizing spectra of calcium are investigat ed below the 3d threshold by a two-step laser excitation from the 3d4s metastables through the 3d4p P-3(0,1,2) intermediate states. The 3d4s are populated by electronic collisions in a DC glow discharge through a Ca heat-pipe. Around 300 resonance transitions are measured with an accuracy of approximately 0.2 cm-1 for the narrow ones using standard laser calibration techniques. Their upper levels are assigned to 17 a utoionizing 3dns, 3dnd and 3dng Rydberg series and several perturbers belonging to the 4p2 and 4p5p configurations. The theoretical interpre tation is achieved by a combination of the eigenchannel R-matrix and m ultichannel quantum defect (MQDT) methods. Five, twelve and fourteen i nteracting channels are introduced for J = 0, J = 1 and J = 2 series r espectively. Theoretical energy level positions and excitation profile s are compared with the experimental data, confirming the identificati on of the observed structures and pointing out the behaviour of the di fferent perturbed Rydberg series.