1. Instituto de Fisica, Universidade de Sãw Paulo, Caixa Postal 20516, CEP 01498, São Paulo, SP, Brazil
2. Institute for Nuclear Sciences, University of Gent, Proeftuinstraat 86, B-9000 Gent, Belgium
3. Department of Chemistry, University of Antwerp UIA, Universiteitsplein 1, B-2610 Antwerp-Wilrijk, Belgium