在巨觀狀態及奈米空間內水分子動力學之探討

Abstract

水在自然界無所不在，且對生物系統扮扮演重要的角色。在熱力學， 水也以許多反常的現象著名。這許多反常現象皆與水分子間的氫鍵有關， 在水内形成氫鍵網路。在巨觀液態的水中，氫鍵斷裂及形成不斷的以一兆 分之一秒（picosecond)的時間發生，這使液態水的結構與動力學極為複 雜。由於超快速光譜以及電腦模擬的技術快速發展，在過去二十年，對水 動力學的研究有許多新的進展。在實際的物質内，水並不是以巨觀狀態存 在，而是附在該物質的表面，或是充滿在一很小的空穴内。水在有限空間 内的動力學，是最近非常受注目且有興趣的研究題目，因為這題目對許多 的實際應用非常重要。

在這三年的計晝中，我將對在巨觀狀態及在奈米有限空間内的水分子 動力學研究。對水在巨觀狀態，我會集中在三個題目：（A)水的低頻拉曼 光譜，（B)水分子OH鍵定向的旋轉動力學與鬆弛，（C)氫鍵對水分子内 振動的效應，包括單一 OH鍵的伸縮振動，以及兩OH鍵間鍵角的振動。對 水在奈米有限空間内，我們將計算對應的物理量，以檢驗與在巨觀狀態下 的差異，以了解奈米有限空間對單一水分子的動力學。

Water is ubiquitous in nature and plays an important role in biological systems. Water is also well known for many anomalous behaviors in thermodynamics. These anomalies are related to the H-bonds among water molecules, which form a network in liquid water. Continually breaking and reforming on a picosecond time scale in bulk liquids, the H-bonds make the structure and dynamics of liquid water extremely complicated. With the advent of the techniques in ultrafast spectroscopy and molecular dynamics simulations, researches on water dynamics were much progressed in the past two decades. In real materials, water is not in the bulk form but attached to some substrates or filling a small cavities. Recently, water dynamics in confined space has attracted considerable interests, since it is related to many technological problems.

In this project of three years, I will investigate water molecular dynamics in bulk liquids and in nanoscale confinements. For bulk liquid water, I will focus on three topics: (A) the low-frequency Raman spectrum, (B) orientational relaxation dynamics of the OH-bond of water molecules and (C) the H-bond effects on intramolecular vibrations of water molecules, including the OH stretching and bending. For water in nanoscale confinements, we will calculate the corresponding quantities and compare them with those of bulk liquids so that the effects of confined spaces on the single-particle dynamics of water molecules are examined.