Oscillator strengths of transitions in the beryllium sequence

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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 3Pe; 1P0 to 1De; 1P0 to 1Se. 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 1s22p2 1S state of neutral beryllium appears to be about 0.01 a.u. above the Be+ 2s threshold. The calculations of Burke (1972) for the 1s22s2 1S to 1s22s2p1P0 transition are extended, and compared with the accurate calculations of Sims and Whitten (1973). Agreement to within 2% is achieved.
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