1. Unilever Research and Development Laboratory, Port Sunlight, Quarry Road East, Bebington, Wirral, U.K.
2. ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, OXON, U.K.
3. Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford, U.K.
4. Institute Laue Langevin, 6 Rue Jules Horowitz, F-38042, Grenoble, Cedex 09, France