Accurate spectroscopy of single‐electron and single‐vacancy ions

This report focuses on one‐electron and one‐vacancy spectroscopy in the X‐ray region where data are of adequate or nearly adequate quality to be of possible interest to this workshop, i.e., data where relativistic and QED effects are not merely noticeable but where measurements of significance may be found or at least hoped for. Several experimental difficulties are discussed including production of clean and interpretable spectra; securing appropriate wavelength normalization; and problems of spectator electrons and spectator vacancies. Available experimental results are summarized and an attempt made to combine information from single‐electron and single vacancy spectra. Brief discussion of some directions in which future progress may be anticipated is also included.