1. Beijing National Laboratory for Molecular Sciences; State Key Laboratory of Rare Earth Materials Chemistry and Applications; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 P. R. China
2. Canadian Neutron Beam Centre; Chalk River Laboratories; Chalk River ON K0J 1J0 Canada
3. ISIS Neutron Facility; STFC Rutherford Appleton Laboratory; Chilton Oxfordshire OX11 0QX UK
4. Institute of Physics Chinese Academy of Sciences; Beijing 100190 P.R. China
5. School of Chemistry; University of Nottingham University Park; Nottingham NG7 2RD UK