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A half-life with Fe ii: tight bonds and loose ends

A brief review of the development of term analysis of Fe ii is given in this paper. Since the time my work on Fe ii started in 1972, about 700 new energy levels have been established and the total number of levels known today is just a little more than 1000. Almost all new levels have transitions that are present in various kinds of astrophysical spectra: forbidden and fluorescent emission lines in nebular regions of symbiotic stars and luminous blue variables, chromospheres around cool stars, nebulae, etc and photospheric absorption lines in cool to hot stars. In this paper, I have given some examples of individual strange transitions appearing in stellar spectra. I have also presented new identifications of levels solely based on stellar spectra recorded at the VLT/UVES. The excitation potential of the lower level is about 13 eV. During the last 8 years, I have collaborated with V Letokhov on laser transitions appearing in nebular blobs close to the central star(s) in Eta Carinae. A network of institutes have so far been involved in the FERRUM project, directed from Lund, with the aim of producing accurate oscillator strengths. In spite of the progress of the term structure of Fe ii, there are still numerous missing identifications of lines that are present both in laboratory and stellar spectra.