1. Department of Physics, Federal University of Minas Gerais, Brazil
2. Fritz-Haber-Institute of the Max-Planck Society, Faradayweg 4-6, 14195 Berlin, Germany
3. Institut für Chemie, Humboldt-Universität zu Berlin, 10099 Berlin, Germany
4. Hamilton College, Clinton, New York 13323, USA
5. Grinnell College, Grinnell, Iowa 50112, USA
6. Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, Brazil