1. Department of Chemistry, Graduate School of Science, Hokkaido University North 10, West 8, Kita‐ku, Sapporo, Hokkaido 060‐0810, Japan, Fax: +81‐11‐706‐3447, http://barato.sci.hokudai.ac.jp/~cc/
2. Electrical Engineering and Computer Sciences, University of California at Berkeley Berkeley, CA 94720, USA