1. Departamento de Quìmica, Universidade de Coimbra, P-3049 Coimbra Codex, Portugal and Fakultät für Chemie, Universität Bielefeld, Bielefeld, 33501 Germany
2. Institute of Atomic and Molecular Science, Taipei, Taiwan ROC 10764, and Department of Physics and Applied Mathematics, Soreq NRC, Yavne 81800, Israel