Variational Bethe-Goldstone calculations of atomic oscillator strengths. Be sequence

Atomic oscillator strengths have been computed by applying a Bethe-Goldstone hierarchy of variational calculations consistently to both initial and final states of a given transition. For the 1s²¹S→1s2p¹Pᵒ transitions in the He isoelectronic sequence, computed fₗ (length) and fᵥ (velocity) values and the corresponding transition energies are in good agreement with the accurate f values of Pekeris et al. and with observed transition energies. For the Be isoelectronic sequence, fₗ and fᵥ for 1s²2s²¹S→1s²2s2p¹Pᵒ are in close agreement with each other if all double virtual excitations from $1s2s2p$ (with respect to 1s²2s2p as reference configuration) are included in the variational calculations. The agreement between computed and observed transition energies is very good. Similar results have been obtained for other valence shell excitations of Be i: 2s2p³Pᵒ→2p²³P, 2s2p¹Pᵒ→2p²¹D, 2s2p¹Pᵒ→2p²¹S. The 2p²¹S state apparently lies slightly above the Be ii $2s$ threshold. The 2p²¹D state interacts strongly with the 2s3d¹D Rydberg state. The oscillator strength is nearly zero for the ¹Pᵒ→¹D transition.