1. Department of Physics, University of Warwick, Coventry CV4 7AL, U.K.
2. GSK R&D, Stevenage, Hertfordshire SG1 2NY, U.K.
3. GSK R&D, Collegeville, Pennsylvania 19426, United States
4. Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.