The absorption of light by calcium vapour (2100 to 1080 Å)

Continuous absorption and line absorption of radiation in calcium vapour has been measured from the 4s4s1S0 → 4snp1P1 series limit at 2028 to 1080 Å. Two perturbed series of auto-ionization lines (4s4s1S0 → 3dnp1P1 and → 3dnp3P1) are recorded and analyzed. A second series limit is observed at 1589 Å. This is probably two unresolved limits corresponding to the two series of auto-ionization lines. No absorption lines are observed on the short wavelength side of 1589 Å. The f-values of the lines vary from 2.4 x 10-2 to 6 x 10-5 and the half-lives (calculated from measurements of the half-widths of the lines) vary from 30 to 260 x 10-15 s. The f-value for the 4s4s1S0 → 4snp1P1 continuum is estimated to be 0.012 (including an allowance for a portion below 1589 Å) and the f-value for the continua from wavelength 1589 to 1080 Å corresponding to the two series of auto-ionization lines is estimated to be 0.003. The measured value of the absorption near 2028 Å is about one-fiftieth of the theoretical value which has been used in astrophysical calculations.