1. Contribution from the Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716-2522, and Department of Physics, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010-2899