1. Department of Applied Chemistry, China Agricultural University, Beijing 100193 (P.R. China), Fax: (+86) 10‐62733830
2. Department of Chemistry, University of Idaho, Moscow, ID 83844‐2343 (USA), Fax: (+1) 208‐885‐9146
3. Naval Research Laboratory, Code 6030, Washington, D.C. 20375‐5001 (USA)