1. Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Miyako‐dani 1‐3, Tadara, Tanabe‐cho, Tsuzuki‐gun, Kyoto 610‐03, Japan
2. Showa Denko Company, Limited, Chemical Research Laboratory, Oogi‐machi 5‐1, Kawasaki‐ku, Kawasaki 210, Japan