1. Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 300, R.O.C., Department of Physics, National Chung-Hsing University, Taichung, Taiwan 402, R.O.C., Department of Chemistry, National Central University, Chungli, Taiwan 320, R.O.C., and Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, R.O.C.