Discussion of Results and General Conclusions
In the modern version of the theory largely developed by M, V. Vol’kenshtein, a distinction is made between mechanical and electro-optical anharmonicity when considering overtones and composite frequencies. Mechanical anharmonicity means a deviation of the potential-energy function from the qua’dratic relationship. Electro-optical anharmonicity means a nonlinear dependence of the electrical moment or polarizability on the normal vibrational coordinates. The numerical values of the overtone frequencies are determined by the mechanical anharmonicity, and their electro-optical properties (intensity and polarization) by both the mechanical and electro-optical anharmonicities. In the presence of mechanical anharmonicity the concept of normal coordinates and normal vibrations loses its meaning. Nevertheless, for purposes of calculation one usually employs normal coordinates as a zero approximation, introducing anharmonic corrections as perturbations.
KeywordsPolyatomic Molecule Molecular Vibration Harmonicity Coefficient Fermi Resonance Anharmonicity Constant
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