The absorption spectrum of Tl in the vacuum ultraviolet: single and double excitations of 5d, 6s and 6p electrons

The authors report new high resolution observations of the 5d inner shell and of the doubly excited spectrum of Tl I. Long series to four conspicuous limits of the 5d-excited parent ion have been studied, and three doubly excited series have also been observed. A detailed analysis is presented including, in particular, a discussion of the number of expected series and limits based on an independent-particle model for single excitations from the inner shell augmented by the spectator-electrons approximation. Perturbations are unfolded using multichannel quantum defect theory, and are found to be generally rather weak. As regards double excitations, only some of the terms are observed, and different mixing schemes are discussed in relation to photo-double-ionization data for Tl I and Pb I.