1. State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry; Chinese Academy of Sciences; Beijing 100190 P.R. China
2. Beijing National Laboratory for Molecular Sciences; CAS Research/ Education Center of Excellence in Molecular Sciences; Beijing 100190 P.R. China
3. Present address: Department of Precision Instrument; Tsinghua University; Beijing 100084 P.R. China
4. University of Chinese Academy of Sciences; Beijing 100049 P.R. China