4pnp J=0e-2e autoionizing series of calcium: experimental and theoretical analysis

The even parity 4pnp J=0, 1, 2 doubly excited autoionizing states of neutral calcium in an atomic beam are investigated by a two-step isolated core excitation (ICE) method using two different combinations of polarization of the laser beams. The different excited energy levels are assigned to nine autoionizing Rydberg series 4p_{1/2, 3/2}np J=0, 1, 2 for ≤ n ≤ 22. The theoretical interpretation is achieved by a combination of the eigenchannel R-matrix theory and the multichannel quantum defect (MQDT) method. Two, five and six closed interacting channels are introduced for the J=0, J=1 and J=2 series respectively. Theoretical energy level positions, autoionization widths and excitation profiles are compared with the experimental data, confirming the identification of the observed structures and providing evidence of extended mixing between the 4p_1/2np and 4p_3/2np series.