1. Department of Chemical Physics, Lund University, Box 124, S-221 00 Lund, Sweden, Department of Chemistry, University of Connecticut, U-60, 55 North Eagleville Road, Storrs, Connecticut 06269-3060, and Department of Chemistry, Faculty of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662-8501, Japan