1. Mobil Research and Development Corporation, P. O. Box 480, Paulsboro, New Jersey 08066, Department of Chemistry, Weiss School of Natural Sciences, Rice University, P. O. Box 1892, Houston, Texas 77251, Central Research Laboratory, Mobil Research and Development Corporation, P. O. Box 1025, Princeton, New Jersey 08540, Bruker Analytische Messtechnik GMBH, Silberstreifen, D-76287 Rheinstetten, Germany, and Department of Radiology, Southwestern Medical Center at Dallas, University of Texas, 5801 Forest Park...