Energies and oscillator strengths for lithiumlike ions

The Hylleraas-type variational method is used to calculate the energies of the lithium 1s²2s²S and 1s²2p²P isoelectronic sequences up to $Z=20$. The oscillator strengths for the 1s²2s²→S1s²2p²P transitions are evaluated for Z up to 20, including finite nuclear mass effects, and the corresponding lifetimes are determined. The $1/Z$ expansion method is used to extend the variational results to larger values of Z. Relativistic corrections to the dipole transition moment squared are estimated by comparison with the relativistic many-body perturbation theory results of Johnson et al. [At. Data Nucl. Data Tables 64, 279 (1996)]. The final lifetime for the 1s²2p²P state of lithium is in good agreement with recent high-precision measurements.