Evidence for [2p(s)4f] multielectron resonances in x-ray-absorption spectra of sixth-period elements

Clear evidence for multielectron excitation channels involving 2p or 2s and 4f electrons has been discovered in x-ray-absorption L-edge spectra of several sixth-period elements. Measurements on liquid Pb and Bi, as well as in PbO, Pb(CH₃{CO}₂)₂, and Bi₂{O}₃$ compounds are reported and compared with previous data on vapor Hg. Onset energies of the double-electron excitation channels are found to be in agreement with previously published self-consistent calculations. A weaker feature, which has been observed in several spectra, is assigned to a triple-electron excitation involving two strongly correlated 4f electrons. The importance of these findings for the extended x-ray-absorption fine structure structural analysis of sixth-period elements is discussed.