Bend Vibration of Surface Water Investigated by Heterodyne-Detected Sum Frequency Generation and Theoretical Study: Dominant Role of Quadrupole

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• 作者：Achintya Kundu ; Shogo Tanaka ; Tatsuya Ishiyama ; Mohammed Ahmed ; Ken-ichi Inoue ; Satoshi Nihonyanagi ; Hiromi Sawai ; Shoichi Yamaguchi ; Akihiro Morita ; Tahei Tahara
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：July 7, 2016
• 年：2016
• 卷：7
• 期：13
• 页码：2597-2601
• 全文大小：323K
• 年卷期：0
• ISSN：1948-7185

文摘

Heterodyne-detected vibrational sum frequency generation spectroscopy was applied to the water surface for measuring the imaginary part of second-order nonlinear susceptibility (Im χ⁽²⁾) spectrum in the bend frequency region for the first time. The observed Im χ⁽²⁾ spectrum shows an overall positive band around 1650 cm^–1, contradicting former theoretical predictions. We further found that the Im χ⁽²⁾ spectrum of NaI aqueous solution exhibits an even larger positive band, which is apparently contrary to the flip-flop orientation of surface water. These unexpected observations are elucidated by calculating quadrupole contributions beyond the conventional dipole approximation. It is indicated that the Im χ⁽²⁾ spectrum in the bend region has a large quadrupole contribution from the bulk water.