Knowledge Bank

The expressions for vibrational absorption and circular dichrosim intensities are derived which require only the knowledge of molecular geometry and Sayvetz conditions. Three different cases are considered. (a). When partial charges are assumed to follow the nuclei, and charge flux is negligible, the dissymmetry factor for symmetric bending vibration is about two orders of magnitude larger than that for antisymmetric bending vibration. (b). When fixed partial charge contributions are negligible and charge flux along B-B bond is of the same order as that along A-B bond, the dissymetry factors for symmetric and antisymmetric bending vibrations are of the same magnitude, for molecules with $-60\ast$ dihedral angle. (c). When fixed partial charge contributions are begligible and charge flux along A-B bonds is greater than that along B-B bond, the dissymetry factors for symmetric and antisymmetric bending vibrations follow $tan2\Theta$ relation. The latter two points are also applicable to the two A-B streching vibrations. Details of the theoretical formulation and of the above summary will be discussed in this presentation.