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Fermi-resonance wave in a two-layer system

The next natural step is the discussion of Fermi resonance effects in molecular crystals. Let molecules having Fermi resonance between intramolecular vibrations form a molecular crystal due to weak (van der Waals) forces. Then the individual molecular vibrational excitations discussed above become coupled to each other and form collective Fermi resonance bands. We shall consider here a simple two-layer ID model with intermolecular interaction only between nearest neighbors (see Fig. 9.6). [Pg.257]

Fermi resonance coupling between molecular vibrations leads to the interaction of these linear modes with each other, which gives rise to mixed waves. To obtain their dispersion law, we again introduce the intensity [Pg.258]

These expressions define the dispersion laws of normal modes arising from linear plane waves due to the nonlinear Fermi resonance interaction. It is important that the nonlinearity leads to the dependence of the dispersion laws on the intensity I of vibrations. Such a dependence gives rise to soliton solutions discussed in the following sections. [Pg.259]

The relations (9.44) can be considered as a good enough approximation only in the limit of large intensity [Pg.259]

Nevertheless, as we saw in the preceding section, semiclassical formulas give exact enough results even in the quantum region I h. More exact relations can be easily derived by means of a quantum-mechanical treatment (9 10). [Pg.259]


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