1. Contribution from the Chemistry Department, SUNY Stony Brook, Stony Brook, New York 11794-3400, Dipartimento Scienze della Terra, Universitá di Modena, 41100 Modena, Italy, Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, and DuPont Central Research and Development (Contribution Number 7395), Wilmington, Delaware 19880-0262