1. Manchester Materials Science Centre, UMIST, Grosvenor Street, Manchester M1 7HS, U.K., Physical Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 157 71 Athens, Greece, Manchester Polymer Centre, Department of Chemistry, University of Manchester, Manchester M13 9PL, U.K., Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, U.K., and CCLRC, Daresbury Laboratory, Warrington, WA4 4AD, U.K.