Search for intercombination lines in few-electron spectra of rare-earth sequence ions of Os through Au

Abstract

The eventual reordering along the isoelectronic sequences of the atomic shells of ions with 61 to 64 electrons (Pm I- to Gd I-like) into systems with one to four electrons outside the closed 4f14 electronic shell has been predicted by theory. However, this prediction provides a formidable challenge for an experimental proof, since very line-rich spectra are associated with ions with so many electrons. The possibilities and problems of a beam-foil spectroscopic approach which combines wavelength and lifetime measurements are discussed, and the results of a search for the intercombination lines expected in such few-electron spectra are presented for ions of Os, Pt and Au. Tentative identifications are given for intercombination lines in the Sm I- and Eu I-like spectra.