1. a Institute for Chemical Reaction Science, Tohoku University , Katahira, Aoba-ku, Sendai , Miyagi , 980-77 , Japan
2. b National Institute of Materials and Chemical Research , Higashi, Tsukuba , Ibaraki , 305 , Japan
3. c Hitachi Research Laboratory , Hitachi Ltd. , Kuji-cho, Hitachi , Ibaraki , 319-12 , Japan