1. Japan Broadcasting Corporation (NHK) Science and Technology Research Laboratories 1‐10‐11, Kinuta, Setagaya‐ku Tokyo 157‐8510 Japan
2. Department of Physics, Graduate School of Science Tokyo University of Science 1–3 Kagurazaka, Shinjuku‐ku Tokyo 162‐8610 Japan
3. Department of Chemistry School of Science Kyoto University Sakyo‐ku Kyoto 606‐8502 Japan