1. ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, OXON, U.K., Unilever Research and Development Laboratory, Port Sunlight, Quarry Road East, Bebington, Wirral, U.K., Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, U.K., and Oxford Centre for Industrial and Applied Mathematics, Mathematical Institute, University of Oxford, 24-29 St Giles, Oxford, U.K.