1. Departament of Physics and Chemistry, São Paulo State University, CEP 15385-000, P.O.
Box 31, Ilha Solteira, SP, Brazil
2. Department of Physics, Federal University of São Carlos, CEP 13565-905,
São Carlos, SP, Brazil
3. Department of Physical Chemistry, São Paulo State University, CEP 14801-970, P.O.
Box 355, Araraquara, SP, Brazil