1. Department of Chemistry The University of Tokyo Hongo 7-3-1 Bunkyo-ku Tokyo 113-0033 Japan
2. Present address: Institute for Solid State Physics The University of Tokyo Kashiwanoha 5-1-5 Chiba 277-8581 Japan
3. Department of Chemistry Tohoku University Aoba-ku Sendai 980-8578 Japan
4. JST ERATO Isobe Degenerate π-Integration Project Hongo 7-3-1 Bunkyo-ku Tokyo 113-0033 Japan