Challenges in the analysis of neutral and singly-ionized iron-group spectra.

For over 30 years the use of high-resolution Fourier transform and grating spectroscopy has revitilized the analysis of neutral and singly-ionized iron-group elements, with new measurements for many elements replacing previous observations that were 40 years old or more. In many cases, the accuracy of the wavelengths has been improved by an order of magnitude or more, with increases in the number of known spectral lines of factors of 2 or more. However, despite these new measurements, the publication of new linelists and analyses for these spectra has been slow. Challenges in the analysis include the large number of spectral lines and energy levels in many of these spectra, the prescence of hyperfine or isotope structure, inaccurate atomic structure calculations, line blends, and mis-identifications. I shall present examples of some of these challenges that we have seen in a re-analysis of the spectrum of Mn II that is being done by NIST and Imperial College London.