Investigation of the M-shell unresolved transition array of aluminium-like iron using monochromatic soft x-ray synchrotron radiation

In various astrophysical observations, the n = 2 → 3 transitions of highly charged iron appear in the soft x-ray region as an unresolved transition array (UTA). The structure of the UTA is directly related to the ionization balance of the plasma and is therefore of high astrophysical interest. The models used to analyse the astrophysical spectra are highly sensitive to the input atomic data, which is mainly based on theoretical calculations. Therefore high precision laboratory measurements are needed for benchmarking theory. Within this thesis, a systematic measurement over the whole UTA energy range has been conducted to determine the transition energies and rates for the thirteen-fold ionized iron (Fe13+), an important constituent of the UTA. The ions of interest were produced by an electron beam ion trap and resonantly excited by the synchrotron radiation of PETRA III. By utilizing an ion-extraction beamline, the radiative as well as the autoionization decay channels have been observed in parallel. 31 hitherto unexplored transitions of the UTA have been resolved with a relative accuracy on the level of 40 parts-per million, serveral orders of magnitude higher than the accuracy obtained in the astrophysical observations. An additional high resolution measurement lead to the extraction of the natural linewidth, which has been used to determine the absolute radiative and autoionization rates of two prominent lines of the UTA. A comparison with state-of-the-art theory revealed a significant 80(7)meV offset in transition energies as well as a three to four-fold smaller natural linewidth, leading to the question how reliable the astrophysical models are