Broadband spectral measurements on liquid water with oxygen-isotopes from megahertz to mid-infrared region

2016 Fiscal Year Final Research Report

• Project/Area Number: 26410015
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Physical chemistry
• Research Institution: Kobe University
• Principal Investigator: Tominaga Keisuke 神戸大学, 分子フォトサイエンス研究センター, 教授 (30202203)
• Co-Investigator(Renkei-kenkyūsha): SAITO Shinji 分子科学研究所, 理論・計算分子科学研究領域, 教授 (70262847) ; TANI Masahiko 福井大学, 遠赤外領域開発研究センター, 教授 (00346181)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 複素誘電率 / 誘電緩和 / 分子間振動 / デバイ緩和 / 水素結合 / H2(18O) / 水 / テラヘルツ

Outline of Final Research Achievements

We measured complex dielectric spectra of three liquid water, H2O, D2O, H2(18O), and their temperature dependence from 0℃ to 50℃. The dielectric spectra were analyzed in terms of several model functions, which are sum of Debye relaxation functions and underdamped modes. We especially paid attention to the THz spectral component. We found that this component consists of one Debye relaxation in the lower frequency side and one underdamped mode in the higher frequency side. The relaxation component shows temperature dependence, and activation enthalpy is the same as that of the slow Debye component. This implies that the fast relaxation mode is associated with hydrogen bond making and breaking processes. We also performed molecular dynamics simulation and normal mode analysis to understand the low-frequency modes of liquid water. We found that the underdamped mode is due to distorted intermolecular bending mode.

Free Research Field

物理化学