Netsu Sokutei, 31 (1), p. 6, (2004)

小特集 -水-

水の多様性;ダイナミックスと反応性

Water; Dynamics and Reactions

最も一般的な液体であり多くの物理科学的な多様性を示す。その多様性の発現機構の源である水素結合のネットワークの構造変化とそれが引き起す化学反応の機構を探る。そのような「水の多様な特性の発現機構」に関係する次の三つの課題;① 水の中の水素結合ネットワークの構造変化の特性,特にその長時間変化の様相と,またネットワーク構造変化伴う水の中の集団運動・揺らぎを観測するための新しい実験法について,② 水の氷化の分子論的機構(水は如何にして結晶に凍るのか?)について,また③ 水や氷中のプロトン移動の機構について,の最近の研究について述べる。
Various aspects of Water Dynamics are discussed; (1) Fluctuation and relaxation in hydrogen bond network rearrangement and their observation, (2) Mechanism of water freezing, and (3) Proton transfer in liquid water and ice. Liquid water yields the intermittently collective motions accompanied with large fluctuations. Various relaxation processes associated with these collective motions in liquid water yield so-called 1/f spectra. We present the result of our analysis on a method, called 2-dimensional Raman/IR spectroscopy. This method will be able to deal with the mechanism of these intermittent collective motions. Upon cooling, water freezes into ice. This process is a most familiar phase-transition, occurring in many places in nature, but has never been successfully simulated by a computer simulation. We report the first successful simulation for the pure water freezing process, which gives a molecular level picture of, particularly, how an initial nucleus is created and grows. The proton transfer is a most basic reaction in chemistry and biochemistry. It is found that the mechanism of the proton transport in ice is completely different from that in liquid water. The repulsion from fourth coordinated water makes the facile proton transfer possible. The long range solvation is essential for the smooth transport of the proton in ice.