We present an overview of studies on the ultrafast dynamics of water at aqueous interfaces carried out by time-resolved vibrational sum frequency generation (VSFG) spectroscopies. This research field has been growing rapidly, stimulated by technical developments achieved recently. In this review, first, the principles and instrumentations are described for conventional VSFG, heterodyne-detected VSFG, and various IR-pump/VSFG-probe techniques, namely, time-resolved conventional VSFG, time-resolved heterodyne-detected VSFG, and their extension to two-dimensional spectroscopy. Second, the applications of these time-resolved VSFG techniques to the study of the femtosecond vibrational dynamics of water at various interfaces are discussed, in the order of silica/water, charged monolayer/water, and the air/water interfaces. These studies demonstrate that there exists water dynamics specific to the interfaces and that time-resolved VSFG spectroscopies can unambiguously detect such unique dynamics in an interface-selective manner. In particular, the most recent time-resolved heterodyne-detected VSFG and two-dimensional heterodyne-detected VSFG unveil the inhomogeneity of the hydrogen bond and relevant vibrational dynamics of interfacial water through unambiguous observation of hole-burning in the OH stretch band, as well as the subsequent spectral diffusion in the femtosecond time region. These time-resolved VSFG studies have also left several issues for discussion. We describe not only the obtained conclusive physical insights into interfacial water dynamics but also the points left unclear or controversial. A new type of experiment that utilizes UV excitation is also described briefly. Lastly, the summary and some future perspectives of time-resolved VSFG spectroscopies are given.

中文翻译：

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振动和频率产生谱研究水界面的超快动力学

我们提出了对水在水界面的超快动力学研究的概述，该研究是通过时间分辨振动和频率产生（VSFG）光谱学进行的。在最近取得的技术发展的带动下，该研究领域发展迅速。在这篇综述中，首先，介绍了常规VSFG，外差检测VSFG和各种IR泵/ VSFG探针技术的原理和仪器，即时间分辨的常规VSFG，时间分辨的外差检测VSFG及其它们的扩展到二维光谱学。其次，按二氧化硅/水，带电单层/水和空气/水界面的顺序，讨论了这些时间分辨的VSFG技术在各种界面上水的飞秒振动动力学研究中的应用。这些研究表明，存在着特定于界面的水动力学，并且时间分辨的VSFG光谱学可以以界面选择性的方式明确地检测到这种独特的动力学。特别是，最新的时间分辨外差检测的VSFG和二维外差检测的VSFG还通过清楚地观察OH拉伸带中的空穴燃烧，揭示了氢键的不均匀性和界面水的相关振动动力学。作为飞秒时间范围内的后续频谱扩散。这些时间分辨的VSFG研究还留下了一些问题需要讨论。我们不仅描述了获得的关于界面水动力学的确凿的物理见解，而且还描​​述了不清楚或有争议的观点。还简要介绍了利用紫外线激发的新型实验。最后，给出了时间分辨VSFG光谱学的总结和未来的展望。