1. Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 R1‐3 Nagatsuta, Midoriku, Yokohama 226‐8503, Japan, http://www.res.titech.ac.jp/~shinkin/
2. Present address: Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso‐cho, Showa‐ku, Nagoya 466‐8555, Japan