Modification of phonon spectra due to vibron self-trapping in molecular crystals

Possible modification of the phonon spectra due to the presence of small-polaron arising on account of vibron (amid-I quanta) self-trapping in hydrogen-bonded molecular chains is discussed. We predict that small-polaron effect should produce characteristic temperature variation of phonon frequencies and small-polaron binding energy. These effects should be observed in the experiments such as measurements of the speed of sound and infrared absorption spectra of molecular crystals which open an interesting possibility for the indirect confirmation of the existence of self-trapped states in molecular chains. Infrared absorption spectra may be especially interesting in that sense since the anticipated temperature variation of binding energy would be observed as a shift of the position of the unconventional (temperature dependent) peak in the IR absorption spectrum towards the position of the normal (temperature independent) one.