1. Department of Chemistry, University of Wales Cardiff, P.O. Box 912, Cardiff CF1 3TB, U.K., Physical Chemistry, Royal Institute of Technology, Stockholm, S100 44, Sweden, Kodak European Research, Headstone Drive, Harrow, Middlesex HA1 4TY, England, and Imaging Research and Advanced Development, Eastman Kodak Company, Rochester, New York 14650-2109