1. Department of Earth and Planetary Systems Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan, Advanced Science Research Center, Japan Atomic Energy Research Institute (JAERI), Tokai, Ibaraki 319-1195, Japan, and Center for Arts and Sciences, Musashi University and Nezu Institute of Chemistry, Toyotama-kami, Tokyo 176-8534, Japan