Electric quadrupole contribution to the nonresonant background of sum frequency generation at air/liquid interfaces.
Electric quadrupole contribution to the nonresonant background of sum frequency generation at air/liquid interfaces.
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DOI：
10.1063/1.3586811
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发表时间：
2011-05
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影响因子：
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通讯作者：
S. Yamaguchi;K. Shiratori;A. Morita;T. Tahara
中科院分区：
文献类型：
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作者：
S. Yamaguchi;K. Shiratori;A. Morita;T. Tahara
研究了在电子和振动非共振条件下，电四极子对空气闪烁液界面和频产生的贡献。外差探测的电子和频产生光谱的空气闪烁液体界面显示，非共振χ（（2））（二阶非线性极化率）有一个负的符号和几乎相同的值为所有研究的八种液体。这一结果是合理的基础上的理论表达式的χ（（2））考虑到电四极贡献。得出结论，SFG的非共振背景主要是由于界面非线性极化具有四极贡献。虽然这种非线性极化是局域在界面上的，但它不仅依赖于界面处的四极极化，而且依赖于体相的四极极化。这意味着非共振χ（（2））的符号与界面分子的“上”与“下”排列无关，因为非共振χ（（2））具有四极原点。
We study an electric quadrupole contribution to sum frequency generation (SFG) at air∕liquid interfaces in an electronically and vibrationally nonresonant condition. Heterodyne-detected electronic sum frequency generation spectroscopy of air∕liquid interfaces reveals that nonresonant χ((2)) (second-order nonlinear susceptibility) has a negative sign and nearly the same value for all eight liquids studied. This result is rationalized on the basis of the theoretical expressions of χ((2)) with an electric quadrupole contribution taken into account. It is concluded that the nonresonant background of SFG is predominantly due to interfacial nonlinear polarization having a quadrupole contribution. Although this nonlinear polarization is localized at the interface, it depends on quadrupolar χ((2)) in the bulk as well as that at the interface. It means that the sign of nonresonant χ((2)) bears no relation to the "up" versus "down" alignment of interfacial molecules, because nonresonant χ((2)) has a quadrupolar origin.