Measurements of Oscillator Strengths for the Transitions from the Metastable 3P Levels of Alkaline-Earth Atoms. II. Magnesium

Oscillator strengths (f values) for the transitions 3s3p 3P-3sns 3S (n=4 and 5), -3snd3D (n=4 and 6 to 9) and -3p2 3P in Mg I have been determined by using the hook method. The metastable 3s3p 3P levels have been populated by a DC discharge of the Mg-He mixture. The absolute scale is based on the absolute f values for 3s3p 3P-3s3d3D (~0.62). The determined f values are in good agreement with recent theoretical predictions. An estimate of the photoionization cross section from the 3P levels by extrapolating the f values results in 20.2 Mb at the threshold.