Low‐Frequency Vibrational Modes of Protic Molten Salts and Ionic Liquids: Detecting and Quantifying Hydrogen Bonds

The subtle balance between Coulomb forces, hydrogen bonds, and dispersion forces is important for the understanding of the unique properties of molten salts and ionic liquids. Vibrational modes with peak frequencies falling in the 140–180 cm−1 range of far-infrared spectra were assigned unequivocally to hydrogen bonds, which are local and directional in nature, but almost insensitive to the molecular weight of the ions.