1. Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, I-35131 Padova, Italy, Physics Department, Hunter College of CUNY, 695 Park Avenue, New York, New York 10021, and Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kakurazaka, Shinjuku-ku, Tokyo 162-8601, Japan