Maryam Dehestani - Department of Chemistry, Shahid Bahonar of University of Kerman, Kerman, Iran
Motahare Shool - Department of Chemistry, Shahid Bahonar of University of Kerman, Kerman, Iran

The vibrational spectra of molecular systems show definite deviations from the predictions of the harmonic model. In order to interpret these experimental results satisfactorily, it is necessary to drop the assumption of infinitesimal displacement of the atoms and to use a more complex model in which terms higher than the second are retained in the potential function [1].