1. a Humboldt-University Berlin, Dept. of Chem. , Erieseering 42, 10319 , Berlin , FRG
2. c University of Potsdam, Dept. of Physics , Am Neuen Palais, 14469 , Potsdam
3. b University Hannover, Dept. of Chem. , Am Kleinen Felde, 30167 , Hannover , FRG