1. State Key Laboratory of Heavy Oil Processing, China University of Petroleum (Beijing), 18 Fuxue Road, Beijing 102249, P. R. China
2. Faculty of Chemistry and Material Science, Langfang Teachers College, 100 Aiminxi Road, Langfang 065000, Hebei Province P. R. China
3. Department of Physics and International Centre for Quantum and Molecular Structures, Shanghai University, 99 Shangda Road, Shanghai 200444, P. R. China