NEW ASPECT ON RELAXATION AND VIBRATION OF WATER AND LIQUID IN THz FREQUENCY REGION

(1)用<18><18>基于多重随机电报（MRT）模型的弛豫函数和两个阻尼振子函数对水的四种同位素（H_2O、D_2O、H_2^ O、D_2^ O）在太赫兹频段的低频拉曼光谱进行了拟合。MRT模型有效地包含了热浴的惯性效应和记忆效应。从拟合分析的190 cm-1模式被分配到一个四面体状结构的四个水分子和50 cm-1的峰值由水分子之间的弯曲状运动和MRT弛豫模式的一个组件的氧原子的拉伸运动。(2)H-水（H_2O，H_2^ O）的弛豫时间<18>总是比D-水（D_2O，D_2^ O）的弛豫时间短<18>。弛豫时间的Arrhenius图表明，在300 K左右，斜率发生变化. (3)通过将乙醇光谱和水光谱简单相加，分析了乙醇/水二元混合物在太赫兹波段的低频拉曼光谱的浓度依赖性。虽然在40 cm-1以上，每个观察到的光谱很好地再现了一个和谱，低于40 cm-1的弛豫分量是占主导地位的是从来没有适合的和谱，并显示出系统的偏差。偏差的积分强度在约0.6水摩尔分数处显示出最大值。实验获得的朗道-普拉泽克比的浓度依赖性，这是瑞利分量对布里渊双重峰的比率，显示在约0.8水摩尔分数的最大值。该浓度与超声衰减实验中浓度波动的最大值相吻合。通过与甲醇、正丙醇、正丙醇等醇类的比较，讨论了这些醇/水二元混合物的微观均匀性。

(1) Low-frequency Raman spectra of four water isotopes (H_2O, D_2O, H_2^<18>O, D_2^<18>O) in the THz frequency region are well fitted by a relaxation function based on a Multiple Random Telegraph (MRT) model and two damped oscillator functions. The MRT model effectively includes the inertia effect and memory effect of the heat bath. From the fitting analysis the 190 cm-1 modes are assigned to a stretching motion of oxygen atoms in a tetrahedral-like structure of four water molecules and the 50 cm-1 peaks are composed both by a bending-like motion between water molecules and a component of the MRT relaxation mode.(2) The relaxation times of H-waters (H_2O, H_2^<18>O) are always shorter than those of D-water (D_2O, D_2^<18>O). The Arrhenius plot of the relaxation times show that the slope is changed at about 300 K.(3) Concentration dependence of low-frequency Raman spectra of ethanol/water binary mixture in the THz frequency region are analyzed by a simple addition of ethanol spectrum and water spectrum. Although above 40 cm-1 each observed spectrum is well reproduced by a sum spectrum, below 40 cm-1 where a relaxation component is dominant is never fitted by a sum spectrum and shows a systematic deviation. The integrated intensity of the deviation shows a maximum at about 0.6 water mole fraction. Concentration dependence of the experimentally obtained Landau-Placzek ratio which is the ratio of the Rayleigh component against the Brillouin doublets show a maximum at about 0.8 water mole fraction. This concentration coincides to the maximum of concentration fluctuation from the ultra-sonic attenuation experiment. Comparing the results among other alcohol such as methanol, 1-propanol and 1-propanol, the microscopic homogeneity of these alcohol/water binary mixtures is discussed.