1. Department of Physics, National Taiwan University, Taipei 106, Taiwan, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, National Synchrotron Radiation Research Center, Science Industrial Park, Hsinchu 300, Taiwan, Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan, and Institutes of Chemistry, Academia Sinica, Taipei 115, Taiwan