Oscillator strengths of transitions in the beryllium sequence

Abstract

Configuration interaction wavefunctions have been used to evaluate absorption oscillator strengths, using both the length and velocity forms, for transitions between the 1s²2s2p and 1s²2p² states: ³P⁰ to ³P^e; ¹P⁰ to ¹D^e; ¹P⁰ to ¹S^e. It is found that the length values stabilize fairly quickly while the corresponding velocity values are more sensitive. Both L-shell and K-L inter-shell correlations are considered. The latter make small changes to length values, but alter velocity values by up to 10%. All-external configurations are important for neutral beryllium and to some extent for B II also. The 1s²2p^{2 1}S state of neutral beryllium appears to be about 0.01 a.u. above the Be⁺ 2s threshold. The calculations of Burke (1972) for the 1s²2s^{2 1}S to 1s²2s2p¹P⁰ transition are extended, and compared with the accurate calculations of Sims and Whitten (1973). Agreement to within 2% is achieved.