1. Central Research and Development, Experimental Station, Du Pont, Wilmington, DE 19880-0328, and Departments of Physics and of Chemistry, Ohio State University, Columbus, OH 43210-1106
2. Central Research & Development, Experimental Station, Du Pont, Wilmington, DE 19880-0328
3. Departments of Physics and of Chemistry, Ohio State University, Columbus, OH 43210-1106