1. Physical and Theoretical Chemistry Laboratory University of Yaoundé 1 P.O. Box 812 Yaoundé Cameroon
2. Computational Chemistry Laboratory High Teacher Training College University of Yaoundé 1 P.O. Box 47 Yaoundé Cameroon
3. Sorbonne Université CNRS Laboratoire de Chimie Théorique CC 137-4, place Jussieu 75252 Paris CEDEX 05 France