1. College of Chemistry, Chemical Engineering and Materials Science; Soochow University; Suzhou 215123 P.R. China
2. Department of Physical Science; Hiroshima University; Higashihiroshima Hiroshima 739-8526 Japan
3. Department of Physics; Beihang University; Beijing 100191 P.R. China
4. Beijing Synchrotron Radiation Facility; Institute of High Energy Physics; Chinese Academy of Sciences; Beijing 100049 P.R. China