1. Geosciences and Chemistry Departments, State University of New York, Stony Brook, New York 11794-2100, NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, and Central Research and Development, DuPont Company, Experimental Station, P.O. Box 80262, Wilmington Delaware 19880-0262