Theory of the profiles of hydrogen stretching infrared bands of hydrogen-bonded solids: Fermi resonance effect and strong coupling between the high-frequency hydrogen stretching vibration and low-frequency phonons

A theory is developed to describe the profiles of hydrogen stretching infrared bands of hydrogen-bonded solids taking into account the anharmonic coupling between the high-frequency stretching vibration, ν(XH), and low-frequency lattice phonons as well as a Fermi resonance between states involving the ν(XH) stretching and an overtone or combination of some internal modes. The theory was constructed in the framework of the extended molecular exciton Davydov approach.