1. Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6DX, U.K.
2. Department of Chemistry, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, U.K.
3. Department of Archaeology, University of Reading, Whiteknights, Reading RG6 6AB, U.K.
4. Department of Environmental Sciences, University of Basel, Bernoullistrasse 32, Basel 4056, Switzerland