Kundu Achintya, Tanaka Shogo, Ishiyama Tatsuya, Ahmed Mohammed, Inoue Ken-Ichi, Nihonyanagi Satoshi, Sawai Hiromi, Yamaguchi Shoichi, Morita Akihiro, Tahara Tahei
Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Department of Chemistry, Graduate School of Science, Tohoku University , Sendai 980-8578, Japan.
J Phys Chem Lett. 2016 Jul 7;7(13):2597-601. doi: 10.1021/acs.jpclett.6b00657. Epub 2016 Jun 27.
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.
外差检测振动和频产生光谱首次应用于水面，用于测量弯曲频率区域二阶非线性极化率虚部（Imχ((2))）光谱。观测到的Imχ((2))光谱在1650 cm(-1)附近呈现出一个整体的正峰，这与之前的理论预测相矛盾。我们进一步发现，NaI水溶液的Imχ((2))光谱表现出一个更大的正峰，这显然与表面水的翻转取向相反。通过计算超出传统偶极近似的四极贡献，阐明了这些意外的观测结果。结果表明，弯曲区域的Imχ((2))光谱有来自体相水的大的四极贡献。
