X-ray absorption spectroscopy of mass-selected transition metal clusters using a cyclotron ion trap: An experimental setup for measuring XMCD spectra of free clusters

► An FT-ICR mass spectrometer has been combined with a soft-X-ray undulator beamline at the BESSY storage ring for determining spin and orbital magnetic moments of free mass-selected clusters. ► First L-edge absorption spectra of Nb 13 +, V 13 + and Co 22 + are shown. ► Using circularly polarized X-ray's a dichroic signal is evident for Co 22 + at a cluster temperature of 100 K. A Fourier-Transform-Ion-Cyclotron-Resonance mass spectrometer has been installed at the BESSY II storage ring. This unique setup enables to record soft X-ray absorption and magnetic circular dichroism spectra (XMCD) of mass-selected clusters in the photon energy range 200–1200 eV. The photoabsorption signal is obtained by recording the fragmentation pattern as produced after X-ray absorption and subsequent Auger decay of the core-excited parent cluster ion. The experimental setup and first X-ray absorption spectra on V 13 + and Nb 13 + are discussed. The feasibility of recording X-ray induced XMCD spectra is demonstrated for Co 22 +. Improvements that allow for quantitative determination of spin and orbital momenta in the future are briefly outlined.