The - resonance line in neutral beryllium

The oscillator strength of the resonance transition - in neutral beryllium is evaluated using two independent codes: CIV3 and MCHF. Two separate approaches are executed using the code CIV3, which uses a common set of orbitals, the inclusion of valence, core - valence and core - core correlation being approached in different ways. In the MCHF scheme, the wavefunctions of the two states are optimized independently. The convergence of the MCHF results with respect to the addition of orbital functions is considered in some detail. This convergence, together with the results of the CIV3 calculations, lead us to recommend a value of 1.375 for the oscillator strength, with an estimated uncertainty of less than 0.5%. This agrees closely with other recent extensive calculations but is 2.5% higher than the value derived from beam-foil experiments.