THE 2S(2) S-1-2S2P P-1(O) RESONANCE LINE IN NEUTRAL BERYLLIUM

The oscillator strength of the resonance transition 2s(2 1)S(0)-2s2p ( 1p0)(1) in neutral beryllium is evaluated using two independent codes: CIV3 and MCHF. Two separate approaches are executed using the code CI V3, which uses a common set of orbitals, the inclusion of valence, cor e-valence and core-core correlation being approached in different ways . In the MCHF scheme, the wavefunctions of the two states are optimize d independently. The convergence of the MCHF results with respect to t he addition of orbital functions is considered in some detail. This co nvergence, together with the results of the CIV3 calculations, lead us to recommend a value of 1.375 for the oscillator strength, with an es timated uncertainty of less than 0.5%. This agrees closely with other recent extensive calculations but is 2.5% higher than the value derive d from beam-foil experiments.