Structure and Dynamics of Single-Crystalline Ice Ih Interfaces

2021 Fiscal Year Final Research Report

• Project/Area Number: 18H01934
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: Saitama University
• Principal Investigator: Yamaguchi Shoichi 埼玉大学, 理工学研究科, 教授 (60250239)
• Co-Investigator(Kenkyū-buntansha): 野嶋 優妃 埼玉大学, 理工学研究科, 助教 (90756404)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 氷 / 分光 / 表面 / 界面 / 非線形 / 和周波

Outline of Final Research Achievements

Among numerous crystalline phases of ice, the Ih phase is the most stable above 72 K at atmospheric pressure. It is well established that the orientations of water molecules in the bulk of ice Ih are statistical without long-range order. However, the orientational order of water at the surface of ice Ih has been enigmatic. Here we show that the surface of ice Ih at 100 K has hydrogen order with the OH group pointing upward to the air ("H-up" orientation). We applied nonlinear optical spectroscopy and theoretical modeling to the surface of isotopically pure and diluted ice Ih and observed OH stretch vibrational signatures attributed to H-up ordering. Furthermore, we found that this hydrogen order takes place despite more inhomogeneous microenvironment at the surface than in the bulk. Our results suggest the prominent role of the surface to allow the reorientation of water molecules for hydrogen ordering that is virtually prohibited in the bulk.

Free Research Field

物理化学

Academic Significance and Societal Importance of the Research Achievements

今回の研究で，氷Ihの表面はH-upの水素秩序構造を有することが分かったが，なぜそのような秩序が発生するのかは明らかでない．72 K以下のバルクでは，水素無秩序構造の氷Ihよりも水素秩序構造の氷XIの方が安定であることが知られているが，IhからXIへの相転移は欠陥の導入なしでは速度論的に不可能である．表面では水素結合ネットワークが切断され，水分子の並進と回転運動の自由度がバルクよりも大きく，フラストレーションがより小さい．それによって表面では水素秩序構造への“相転移”が速度論的に可能となっているのかもしれない．表面での秩序-無秩序転移の機構解明には，温度依存性の研究が将来的に重要になる．