Proton Order toward the Surface of Ice Ih Revealed by Heterodyne-Detected Sum Frequency Generation Spectroscopy
Proton Order toward the Surface of Ice Ih Revealed by Heterodyne-Detected Sum Frequency Generation Spectroscopy
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DOI：
10.1021/acs.jpclett.7b02198
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发表时间：
2017-10-19
影响因子：
5.7
通讯作者：
Yamaguchi, Shoichi
中科院分区：
文献类型：
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作者：
Nojima, Yuki;Suzuki, Yudai;Yamaguchi, Shoichi
使用外差检测和频率发生（HD-SFG）光谱，我们研究了单晶冰 I-h 的基底、主棱镜和副棱镜面的表面质子序。 130 K。所获得的光谱的复相位清楚地表明，HD-SFG 信号产生的二阶非线性偏振仅在表面产生。这表明表面质子沿着法线有序排列，而大部分质子仍然是无序的，正如众所周知的冰 I-h 一样。 HD-SFG 光谱中观察到的强正峰使我们能够确定表面质子序的“方向”为“H-up”，即 OH 基团的氢原子指向远离本体的方向，而与冰面无关。本研究中进行的可靠 HD-SFG 测量极大地增进了我们对冰 I-h 表面结构的理解。
Using heterodyne-detected sum frequency generation (HD-SFG) spectroscopy, we investigated surface proton order at the basal, primary prism, and secondary prism faces of single-crystalline ice I-h at ca. 130 K. The complex phase of the obtained spectra clearly indicates that second-order nonlinear polarization from which the HD-SFG signal arises is generated exclusively at the surfaces. This suggests surface proton ordering along the normal, whereas the bulk remains proton-disordered, as is well known for ice I-h. A strong positive peak observed in the HD-SFG spectra enables us to determine the "direction" of the surface proton order as "H-up", that is, the hydrogen atom of the OH group pointing away from the bulk, irrespective of the ice faces. Reliable HD-SFG measurements carried out in the present study have greatly advanced our understanding of surface structure of ice I-h.