Energies and oscillator strengths for lithiumlike ions

The Hylleraas-type variational method is used to calculate the energies of the lithium ${1s}^{2}2s{}^{2}S$ and ${1s}^{2}2p{}^{2}P$ isoelectronic sequences up to $Z=20$. The oscillator strengths for the ${1s}^{2}2s{}^{2}\stackrel{\ensuremath{\rightarrow}}{S}{1s}^{2}2p{}^{2}P$ 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 ${1s}^{2}2p{}^{2}P$ state of lithium is in good agreement with recent high-precision measurements.