1. Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192-03, Japan
2. Earth Science Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan
3. Commissariat ä l'Energie Atomique, Centre d'Etudes Nucliaires de Cadarache, F-13108 Saint-Paul-les-Durance, France