Extended series in the ultra-violet absorption spectrum of thallium vapour

The 6 2 P 1/2 0 - n 2 S 1/2 , n 2 D 3/2 series of Tl I have been obtained in absorption, at good dispersion, and measurements made from n = 7 to 43 and n = 9 to 34 respectively. The series 6 2 P 3/2 0 - n 2 D 3/2,5/2 have been resolved for n = 10 to 12, and the 2 D 5/2 series extended to n = 24. An amendment to the Tl I ionization potential of 2 5 cm -1 is suggested. The level 6s6p 2 4 P 1/2 , which produces a perturbation in the n 2 S 1/2 series levels, has been resolved into a close doublet with an interval of 2.8 cm -1 presumably due to partially resolved hyperfine structure.