Recent results
Summary of up-to-date research result
(List of other research results: Papers)
We determined the complex dielectric constants of the liquid water isotopes by THz TD-ATR. †
Hiroyuki Yada, Masaya Nagai, Koichiro Tanaka "Origin of the fast relaxation component of water and heavy water revealed by terahertz time-domain attenuated total reflection spectroscopy"
Water is a significant material in scientific research and has been of interest to many scientists in physics, chemistry and biology. Over years of their study, some specificity has been revealed in its characteristics. For instance, it is proved that the highest density can be obtained at 4 C. Abnormally high mobility of proton is also observed compared to other liquids.
The origin of such properties is yet unclear, although it is assumed that they could be related with water dynamics, consisting of hydrogen bonding network itself which forms liquid water and hydrogen bonding vibration process per subpicosecond (ps=10-12 s).
However, recent research demonstrates that the vibration contributes significantly to the peculiar property of H2O rather than the network. Until today water dynamical structure study has been mainly performed by Raman spectroscopy and now it is strongly required to reveal the origin of the vibration. Recent advances of the ultrashort pulse technique allow us to perform THz time-domain spectroscopy (THz-TDS: THz=1012 Hz=33 cm-1=4.1 meV), which belongs to the infrared spectroscopy. This method detects the vibration more precisely and its real time measurement of the electric field enables to measure directly the time-correlation function of the subpicosecond region polarization, determines the complex dielectric constant without applying Kramers-Kronig transform and examines in detail even in the mode with small intensity, different from the traditional FTIR (Fourier transform infrared spectroscopy).
In fact, many researches have evaluated liquid water by THz time-domain spectroscopy. However, the limited frequency region (up to 2 THz) has been measured due to the fact that water highly absorbs terahertz waves. This technical insufficiency caused the delay in effective use of THz-TDS for analysis of water dynamical structure.
For this study, we established THz time-domain attenuated total reflection spectroscopy (THz TD-ATR) as an optical method to accurately measure within a wider THz frequency region the complex dielectric constants of the materials with high absorption such as liquid water. Especially we succeeded in developing a temperature adjuster specialized for total reflection spectroscopy and performed temperature-dependent measurement of the precise complex dielectric constants of water.