1. Institute of Solid State Physics, University of Latvia; Kengaraga Street 8 LV-1063 Riga Latvia
2. Department Chemie, Naturwissenschaftliche Fakultät, Universität Paderborn; Warburger Straße 100 D-33098 Paderborn Germany
3. DESY Photon Science; Notkestraße 85 D-22607 Hamburg Germany