1. Department of Chemistry, University of Liverpool, Robert Robinson Laboratory, Crown Street Liverpool, Liverpool L69 7ZD, U.K., Laboratoire CRISMAT-ENSICAEN, UMR6508, 6 Bd du Maréchal Juin, 14050 Caen Cedex, France, Clarendon Laboratory, Department of Physics, Oxford University, Parks Road, Oxford OX1 3PU, U.K., ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, U.K., and Department of Chemistry, University of Houston, 136 Fleming Building, Houston, Texas 77204-5003