1. Department of Experimental Physics, Institute of Physics, University of Pécs, Ifjúság u. 6., H-7624 Pécs, Hungary, Department of Biophysics, University of Pécs, Szigeti út 12., H-7625 Pécs, Hungary, and Department of Chemistry, University of Jyväskylä, P.O. Box 35, FIN-40351 Jyväskylä, Finland