1. Institut für Physikalische Chemie, Martin-Luther-Universität Halle-Wittenberg, Muehlpforte 1, D-06108 Germany, Dipartimento di Chimica e Chimica Industriale, Universita de Pisa, via Risorgimento 35, 56126 Pisa, Italy, and Chemistry Department, Moscow State University, Lenin Hills, 119992 Moscow, Russia