1. ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OPU, U.K., Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, U.K., School of Pharmacy, Kings College London, London, SE1 9NN, U.K., and Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, U.K.