Vibrations de valence C?H/C?D fondamentales et harmoniques de dérivés halogénés du méthane et du deutériométhane

The fundamentals and overtones of the C? H stretching vibrations of a number of halogenated methanes and deuteriomethanes are compared with a hypothetical model consisting of isolated groups. The anharmonicity constants are evaluated and lie between ?20 cm^?1 and ?130 cm^?1 for the C? H and C? D stretching vibrations. The value of the anharmonicity constant for a coupling between two different modes of vibration is always greater (in absolute numbers) than its value for an overtone of one frequency. The constant is larger for a symmetric mode than for an asymmetric mode in the case of a C? H vibration; the contrary is true for a C? D bond. Complex interactions between different vibrations often strongly modify the spectra of the overtones. It is shown, however, that the conception of an isolated group is helpful for evaluating the spectra of these substances.