1. ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon 0X11 0QX, U.K., Unilever Research, Port Sunlight Laboratory, Quarry Road East, Bebington, Wirral L63 3JW, U.K., Physical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford 0X1 3QZ, U.K., and Chemistry Department, University of Surrey, Guildford, Surrey 9U2 5XH, U.K.