Strong intermolecular coupling between the HF stretching and H2O bending vibrations in HF:H2O binary amorphous solids: breakdown of the electrostatic description of the hydrogen bond.

The coupling mechanism between the HF stretching and H(2)O bending vibrations observed in the infrared spectra of HF:H(2)O binary amorphous solids is analyzed using a simple cluster model. The intermolecular vibrational coupling derived from electrostatic potentials is one order of magnitude smaller, and of the opposite sign, than that obtained from electronic structure-based potentials. This highlights the distinctively covalent character of strong H-bonds and unveils fundamental weaknesses of electrostatic descriptions of vibrational energy transfer in liquid water and aqueous solutions.