1. Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Bunkyo‐ku, Tokyo 113, Japan
2. Department of Chemistry, Faculty of Science, Toho University, Funabashi, Chiba 274, Japan
3. Department of Physics, Faculty of Science, The University of Tokyo, Hongo, Bunkyo‐ku, Tokyo 113, Japan
4. Department of Applied Physics, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo‐ku, Tokyo 113, Japan