Eigenchannel R-matrix study of the J=0 and J=2 even parity spectra of calcium below the Ca⁺3d3/2threshold

The J=0 and J=2 even parity spectra of calcium are studied through a combination of the eigenchannel R-matrix and multichannel quantum defect (MQDT) methods. The bound and autoionizing spectra below the 3d 3/2 threshold are investigated. The calculation reproduces well the perturbations of the 4sns 1 S 0 , 4snd 1.3 D 2 series by low-lying doubly excited states observed experimentally and provides new insight on the identification of the perturbers. Theoretical predictions of the positions of the 3dnl and low-lying 4pnp J=0 e and J=2 e resonances are given. Results of photoionization spectra from low-lying states are presented. Particular attention is paid to analyse the effects of the strong interaction between the 3dnd and 4pnp singlet channels which dominates the bound and autoionizing spectra above the first limit. Comparisons are made with the results of previous experimental and theoretical studies.