Vacuum ultraviolet absorption cross-section measurements in lead vapour

The absorption cross-section curve for lead vapour has been determined from 1671 to 1470 Å. Three autoionization features corresponding to the transitions 6s2 6p2 3P0 → 6s26p 6d3P10, 1P1Ɵ and 6s26P8s1P10 were investigated and their line profile parameters determined. The value of the cross-section at the series limit (1671 Å) was found to be 10 ±1 Mb and falls to zero within each of the autoionizing features. The unperturbed photoionization continuum, in the absence of autoionization, was inferred from the experimental curve and the autoionization parameters. It was found to decrease steadily from about 15 Mb at the ionization parameters. It was found to decrease steadily from about 15 Mb at the ionization threshold to a value of less than 5 x 10-2 Mb at 1470 Å. It is suggested that this low value of the photoionization continuum can account for the missing 6p9sautoionization feature which should otherwise appear at 1470 Å.