1. Department of Chemistry, University of Wales Cardiff, P.O. Box 912, Cardiff CF1 3TB, U.K.
2. Physical Chemistry, Royal Institute of Technology, Stockholm, S100 44 Sweden
3. Kodak European Research, Headstone Drive, Harrow, Middlesex HA1 4TY, England
4. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, England