Evidence for [2p(s)4f] multi-electron 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(CH3CO2)2, and Bi2O3 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.