Theory of profiles of hydrogen stretching infrared bands of hydrogen-bonded solids. Model of strong coupling between the high-frequency hydrogen stretching vibration and low-frequency phonons

A theory is developed to describe a broad IR absorption which appears in the range of a high-frequency stretching vibration of the X-H group involved in the hydrogen bond in solids. The theory is based on the anharmonic coupling mechanism between the high-frequency hydrogen stretching vibration. ν(XH), and low-frequency lattice phonons. The theory was constructed in the framework of the molecular exciton Davydov approach. Model calculations show that the strong anharmonic couplings between the high-frequency ν(XH) and low lattice vibration frequencies generate the broadness of the ν(XH) band.