1. Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan
2. Japan Energy Co. Ltd., 3-17-35 Niizo-Minami, Toda, Saitama 335, Japan
3. The School of Chemistry, The University of Hull, Hull HU6 7RX, U.K.