Comparative dielectric study of monohydric alcohols with terahertz time-domain spectroscopy

Using terahertz (THz) time-domain spectroscopy, we have measured the complex permittivity of 14 monohydric alcohols in the frequency range 0.2–2.5 THz, at temperatures ranging from 253 to 323 K. The molecular structures of these monohydric alcohols change systematically with the position of the OH group, the number of carbon atoms, and the structure of the carbon chain. The complex permittivity in the THz region contains the following three components: (i) a high-frequency tail of dielectric relaxation processes, (ii) a broad vibration mode around 1.2 THz, and (iii) a low-frequency side of an intermolecular vibration mode located above 2.5 THz. At low temperatures, the relaxation processes shift toward a low-frequency range, while a peak of the broad vibration mode, which is independent of temperature, is clearly observed around 1.2 THz. The present comparative study shows that there is a strong correlation between this mode around 1.2 THz and the molecular structures of monohydric alcohols.