S,P, andDstates of two-electron ions viaZ-dependent perturbation theory

A perturbation study of singly excited $S$, $P$, and $D$ states of two-electron atoms has been made. Perturbation expansion coefficients for the nonrelativistic energies are computed and estimates of the relativistic corrections to low orders in $Z$ are also obtained. A simple one-electron Lamb-shift correction is then combined with these results to yield theoretical transition energies in excellent agreement with experimental data for HeI through FeXXV.