1. Department of Chemistry and BP Institute, University of Cambridge, Cambridge, Cambs CB2 1EW, U.K.
2. Institut Laue Langevin, 71 avenue des Martyrs, Grenoble 38000, France
3. ISIS Pulsed Neutron Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, STFC, Didcot, Oxon OX11 0QX, U.K.