1. Department of Physics, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530
2. Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581
3. Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195
4. Division of Chemistry, Graduate School of Science, Hokkaido University, Kita 10, Nishi 8, Kita, Sapporo 060-0810