1. Instituto de Quimica Fisica “Rocasolano”, CSIC, C/Serrano 119, 28006 Madrid, Spain
2. Dow Corning Corporation, P.O. Box 995, Mail 128, Midland, Michigan, 48686-0995
3. Department of Chemistry, University of Reading, Whiteknights, P.O. Box 224, Reading RG6 6AD, U.K.