1. Chemical Engineering Department; Federal University of Santa Maria-UFSM; 1000, Roraima Avenue, 97105-900 Santa Maria RS Brazil
2. Unité de Recherche de Physique Quantique; UR 11 ES 54, Faculté des Sciences de Monastir Tunisie
3. Institute of Chemistry; Federal University of Rio Grande do Sul; UFRGS, Porto Alegre RS Brazil