1. International Solvay Institutes for Physics and Chemistry, C.P. 231, Boulevard du Triomphe, 1050 Brussels, Belgium
2. Theoretische Naturkunde, Free University of Brussels, Brussels, Belgium
3. Service de Chimie Physique, Universite Libre de Bruxelles, C.P. 231 Campus Plaine ULB, 1050-Bruxelles, Belgique
4. Departamento de Fisica, Universidade Federal do Espirito Santo, 29060-900 Vitoria ES, Brazil