1. Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204
2. Laboratoire d'Etudes des Propiétés Electroniques des Solides, CNRS, BP 166, 38042, Grenoble Cedex 9, France
3. Instituto de Fisica, Universidade Federal Fuluminense, Campus da Praia Vermelha, Niteroi, 24210-340, Brazil