1. State
Key Laboratory for Structural Chemistry of Unstable and Stable Species,
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
2. Department
of Chemistry, Tsinghua University, Beijing 100084, P. R. China
3. Department
of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, USA
4. Department
of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, USA