1. Contribution from the Institute of Chemical Physics, Department of Chemistry, University of Tartu, Jakobi 2, 51014 Tartu, Estonia, and Institute of Advanced Material Science, Kyushu University, Kasuga 816, Japan, and Institute for Fundamental Research of Organic Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan