Calculations of (nl)2 and (3lnl′) autoionizing states in two-electron systems

Abstract

In this paper, we calculate energies for ns2 1S, np2 1D, nd2 1G, nf2 1I, 3snp 1,3P°, 3s3d 1,3D and 3p3d 1,3F° doubly excited states (DES) of the helium isoelectronic sequence using the screening constant by unit nuclear charge (SCUNC) method in the framework of a semi-empirical procedure. Calculations are performed for total energies of low-lying DES (n⩽ 5) in He-like ions with 2⩽Z⩽ 10. The possibility of using the SCUNC method in the investigation of high-lying DES in two-electron systems is demonstrated in the present paper in the case of ns2 1S levels, where accurate energy positions are tabulated up to n=20 and compared to the spin-dependent localized Hartree–Fock density functional (SLHF) with exchange-correlation (XC) potential calculations (Zhou and Chu 2005 Phys. Rev. A 71 022513) and to the works-function (WF)-based exchange (WF XC) potential approach values (Roy and Chu 2005 Phys. Rev. A 71 022513). In addition, the present method is used in the calculation of energy resonances for ns2 1S, np2 1D and nd2 1G excited states (n⩽ 5) in high-Z-helium-like ions (11⩽Z⩽ 19), and a comparison with the double sums over the complete hydrogen spectrum calculations (Ivanov and Safronova 1993 Opt. Spektrosk. 75 506) is made. All the results obtained in the present work agree with the available literature values.