Vibrational spectra and molecular orientation with experimental configuration analysis in surface sum frequency generation (SFG)
Vibrational spectra and molecular orientation with experimental configuration analysis in surface sum frequency generation (SFG)
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表面和频生成 (SFG) 中的振动谱和分子取向以及实验构型分析
DOI：
10.1021/jp067062h
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发表时间：
2007-06-28
影响因子：
3.7
通讯作者：
Wang, Hong-Fei
中科院分区：
文献类型：
--
作者：
Gan, Wei;Wu, Bao-Hua;Wang, Hong-Fei
和频产生-振动光谱(SFG-VS)的最新发展表明，SFG-VS不仅是分子界面的光谱探针，而且是研究分子光谱的重要工具。通过偏振和对称性分析，证明了几套偏振选择规则对振动光谱的指认有明显的帮助。这是因为从分子界面或薄膜的SFG过程的相干性质和强烈的取向依赖性。在这项工作中，我们进一步讨论了在SFG-VS偏振分析中对实验组态的依赖。这样的实验和分析可以进一步提高SFG-VS作为识别光谱细节和重叠光谱特征的工具的能力，以及获得详细的分子取向信息的能力。在PPP极化组合中，SFG光谱的实验构型依赖性最显著，在SPS和SSP极化组合中不明显，这是因为PPP是四个不同磁化率张量元素组合的结果，而SSP和SPS都是单一张量元素。在SFG-VS研究中，过去避免了PPP频谱的这种复杂性，这在本工作中是非常有用的。在不同的实验构型下，研究了蒸汽/甲醇、蒸汽/乙醇和蒸汽/乙二醇界面上SFG-VS的光谱细节。对这些液体界面的强烈实验构型依赖性也表明它们具有良好的有序界面结构。这份报告中的概念和结论可能会在研究更复杂的分子界面和薄膜方面找到未来的应用。
Recent developments in sum frequency generation-vibrational spectroscopy (SFG-VS) have shown that SFG-VS is not only a spectroscopic probe of the molecular interfaces but also an important tool for studying molecular spectroscopy in general. It has been demonstrated that through polarization and symmetry analysis a few sets of polarization selection rules can explicitly help the vibrational spectral assignment. This worked because of the coherent nature and the strong orientational dependence of the SFG process from the molecular interfaces or films. In this work, we further discuss the dependence on the experimental configurations in the SFG-VS polarization analysis. Such experiment and analysis can further increase the ability of the SFG-VS as the tool for discerning spectral details and overlapping spectral features, as well as the ability to obtain detailed molecular orientational information. The experimental configuration dependence of the SFG spectra is most significant in the ppp polarization combination, less significant in the sps and ssp polarization combinations, due to the fact that ppp is the result of the combination of four different susceptibility tensor elements, while both ssp and sps are of a single tensor element. Such complexity of the ppp spectrum, which is very useful as demonstrated in this work, used to be avoided in the SFG-VS studies. The spectral details of the SFG-VS from the vapor/methanol, vapor/ethanol, and vapor/ethylene glycol interfaces are studied in different experimental configurations. The strong experimental configuration dependence observed for these liquid interfaces also indicated that they possess well-ordered interfacial structures. The concepts and conclusions in this report may find future applications in studying more complex molecular interfaces and films.