1. Department of Chemistry, Moscow State University, Moscow, 119899 GSP, Russia; Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow B-334, Russia; Division of Thermochemistry, Chemical Center, University of Lund, S-221 00 Lund, Sweden; Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104; and Department of Physics, Washington University, St. Louis, Missouri 63130