Eigenvalues of the2p3pP3and2p3dD1,3Bound States of the Helium Isoelectronic Sequence

The $\frac{1}{Z}$ expansion method is used to calculate the eigenvalues of the $2p3p{}_{}{}^3{}_{}{}^{}P$ and $2p3d{}_{}{}^{1,3}{}_{}{}^{}D$ states of the helium isoelectronic sequence. The results are compared to variational calculations for neutral helium. Wavelengths are predicted for a number of transitions originating in doubly excited states of the heliumlike ions up to Fe xxv. The results for neutral helium are compared to recent beam-foil experiments and alternative line identifications are made. The predicted wavelength for the $2p3d{}_{}{}^3{}_{}{}^{}D-2\mathrm{}{p}^2{}_{}{}^3{}_{}{}^{}P$ transition is 3014 Å, in close agreement with the line observed by Berry et al. at 3012 ± 2 Å.