1. Department of Physics, University of Guelph, Guelph, Ontario, N1G 2W1, Canada, National Research Council, Steacie Institute for Molecular Sciences, Chalk River, Ontario, K0J 1J0, Canada, Raman Research Institute, Bangalore 560 080, India, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria