Vibrations de valence C-H des alcanes et halogénures de t-butyle

The first and second harmonic C-H and C-D valence vibrations of alkanes and t-butyl halides have been measured. A model is proposed for the methyl and methylene groups, which allows the calculation of the anharmonicity constants of every vibrational mode and of the couplings between the modes. The already known large values (-100 to -150 cm-1) for the anharmonicity constants that couple the symmetrical with the asymmetrical triodes are confirmed. As compared with lower harmonics combination bands become predominant for the higher ones; they allow the application of a diatomic model to estimate higher harmonics and the energy of dissociation.