| Popis: |
Using terahertz (THz) time-domain spectroscopy, we have measured the complex permittivity of seven pentanol isomers (1-pentanol, 2-pentanol, 3-pentanol, 2-methly-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, and 3-methyl-2-butanol) in the frequency range of 0.2–2.5 THz at temperatures from 253 to 323 K. For all samples, the complex permittivity contains the following three components: (i) a high-frequency side of dielectric relaxation processes, (ii) a broad vibration mode around 1.5 THz, and (iii) a low-frequency side of an intermolecular stretching mode located above 2.5 THz. At low temperatures, the relaxation process moves to a low-frequency range and a peak of the broad vibration mode, which is independent of temperature, is clearly observed around 1.5 THz. Spectra in the THz region change sensitively according to the molecular structure of the pentanol isomers. We have also observed the complex permittivity in the microwave range of 1 MHz–20 GHz. The behavior of the dielectric relaxation processes below GHz region much depend on the isomers. Our experimental data demonstrate that the molecular structures of the pentanol isomers influence all the molecular dynamics ranging from dielectric relaxation phenomena, which are due to reorientational motion of the molecules, to vibration dynamics within the hydrogen-bonded network structure. |
Full Text from ScienceDirect