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

The even parity J = 3 autoionizing spectra of calcium were investigate d below the 3d threshold by a two-step laser excitation from the 3d 4s metastables through the 3 d 4 p 3P2, 1F3 intermediate states. The 3 d 4 s were populated by electronic collisions in a d.c. glow discharge through a Ca heat-pipe. More than a hundred resonance transitions have been measured with an accuracy of approximately 0.2 cm-1 for the narr ow ones using standard laser calibration techniques. Their upper level s are assigned to all expected nine autoionizing 3 d n s, 3 d n d and 3 d n g Rydberg series and the 4 p 5 p 3D3 perturber. The theoretical interpretation is achieved by a combination of the eigenchannel R-matr ix and multichannel quantum defect (MQDT) methods. Ten closed and two open J = 3 interacting channesl are used. Theoretical energy level pos itions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixi ng between the 3d3/2 nd5/2 and 3d5/2 nd3/2 series is found, while the 3d3/2 nd3/2 and 3d5/2 nd5/2 series are almost pure jj-coupled. The cal culations were particularly successful in reproducing the spectrum in the region of the 4 p 5 p 3D3 perturber, where strong chancel mixing a ppears leading to interference effects in the excitation cross section s.