1. Department of Chemistry, Faculty of Engineering Science, and Research Center for Photoenergetics of Organic Materials, Osaka University, Toyonaka, Osaka 560, Japan
2. Department of Industrial Chemistry, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo‐ku, Tokyo 113, Japan
3. Research Center for Ultra‐High Voltage Electron Microscopy, Osaka University, Yamadaoka, Suita, Osaka 565, Japan