1. Department of Chemistry and Institute of Colloid and Surface Science, Clarkson University, Potsdam, New York 13676
2. Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 and Department of Physics, Graduate School and University Center of City University of New York, New York, New York 10036
3. Brookhaven National Laboratory, Department of Applied Science, Upton, New York 11973