304 Å photoelectron spectra of atomic Hg, Tl, and Pb 5d levels; interaction of open shells

Photoelectron spectra of atomic Hg, Tl, and Pb 5d levels are reported using He ii 304 Å radiation. The spectrum of Hg is simple and shows only a spin–orbit doublet. The spectra of Tl and Pb are complex, both consisting of eight lines. Using the energies from the optical data and the existing intermediate–coupling–configuration–intercation calculations, the Tl spectrum could be assigned. The calculated intensity distribution correlates with the observed one in Tl very closely. In the Pb spectrum only the two strongest lines could be identified and tentatively assigned to the 5d9(2D5/2)6s26p21/2 and 5d9(2D3/2)6s26p21/2 states of Pb+. Both in Tl and Pb, ionization from the 5d5/2 and 5d3/2 subshells can be understood in terms of a special kind of two-electron configuration-interaction mechanism. The 5d9(2D3/2) 6s26pn1/2 (n=1 for Tl and 2 for Pb) hole resulting from the ionization of an 5d3/2 electron, interacts strongly with the 5d9(2D5/2)6s26pn−11/26p13/2 states in which one electron from the (closed) 5d5/2 subshell drops to the 5d3/2 hole and another electron from the 6p1/2 subshell moves up to 6p3/2 subshell. This one-electron-down one-electron-up mechanism (a virtual Auger process) is favored for the 5d3/2 and not for the 5d5/2 subshell for energetic reasons and is responsible for the occurrence of multiline structure for one and not the other.