OSCILLATOR STRENGTH DENSITY OF THE 4S2-4SNP, 3DNP, 1P1, 3P1 SERIES OF CALCIUM AS A 2-CHANNEL CASE IN QUANTUM DEFECT THEORY

It is shown that the main features of the autoionised singlet spectrum of Ca near the 42S ionisation limit, can be explained semi-empirically in terms of energy-dependent quantum defect theory with two strongly interacting channels. The description of the spectral dependence of the oscillator strength is simplified by the fact that one of the two close-coupling eigenstates has a vanishing transition amplitude. The analysis further shows that the existing experimental absolute values of the oscillator strengths and of the photon absorption cross section in the autoionised spectrum near the ionisation limit are inconsistent.