Ion mobility mass spectrometry or electronic state chromatography, combined with gas-discharge ion sources, is an ideal tool to select ions of 3d transition elements in ground or excited electronic states that are not necessarily linked by dipole-allowed or one-electron transitions. Here, ion mobility mass spectrometry and cryogenic ion trapping with our ion trap endstation at BESSY II will be employed to prepare cold and electronic state-selected ions of 3d transition elements for x-ray spectroscopy. Ionization of transition elements in a gas discharge produces ground and excited state electronic configurations that are separated by the mobility analyser. A cryogenic ion trap will be used to accumulate and cool the ions, and serves as the interaction region with X-ray photons. For a given element, ground states, as well as long-lived excited states that differ in 3d electron configuration, will be of particular interest for high-resolution X-ray absorption and X-ray linear dichroism spectra in order to fundamentally test XMCD sum rules, and will give a library of experimental XAS and XMCD data that are important for computational developments in high-level theory for X-ray absorption spectroscopy. Changes in transition metal L-edge excitation energy with 3d electron configuration will also contribute to a fundamental understanding of the empiric concept of oxidation states. First steps towards state or isomer-selective X-ray spectroscopy of larger ions will be made. The work program will consist of an initial phase of laboratory work to prepare transitions metal ions in well-defined electronic states, followed by campaigns at the BESSY II synchrotron radiation facility for X-ray absorption and XMCD spectroscopy. (T. Lau, B. von Issendorff)

Research group of Prof. LAU