to measurements near surfaces in attenuated total reflectance (ATR). Raman spectroscopy is therefore commonly used as an alternative to investigate the vibrational modes in the infrared given the lack of contribution from water molecules to the Raman spectra due to the different selection rules. In recent years, terahertz time-domain spectroscopy (THz-TDS), has emerged as a new tool that can be used, similar to FTIR, to probe the molecular vibrations due to permanent dipole changes but it has the advantage that it can also be applied in transmission when water is present in the sample given the slightly lower absorption of water at terahertz frequencies compared with the mid-infrared. THz-TDS has been proved to be a useful technique to study both amorphous and crystalline materials in the solid state, as it is sensitive to inter-and intra-molecular interactions within such systems . It has been successfully applied to investigate the properties of pure amorphous materials and crystals, and also phase transitions of polymorphs and even crystallisation from the amorphous to crystalline phase - . Additionally, the dielectric relaxation phenomena on picosecond time scales have been investigated with terahertz spectroscopy in polar liquids, such as alcohol, water, and their mixtures .