Nihonyanagi Satoshi, Yamaguchi Shoichi, Tahara Tahei
Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University , 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan.
Chem Rev. 2017 Aug 23;117(16):10665-10693. doi: 10.1021/acs.chemrev.6b00728. Epub 2017 Apr 5.
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.
我们概述了利用时间分辨振动和频产生（VSFG）光谱对水在水相界面的超快动力学所开展的研究。受近期技术发展的推动，该研究领域发展迅速。在本综述中，首先描述了传统VSFG、外差检测VSFG以及各种红外泵浦/VSFG探测技术（即时间分辨传统VSFG、时间分辨外差检测VSFG及其向二维光谱的扩展）的原理和仪器装置。其次，按照二氧化硅/水、带电单分子层/水和空气/水界面的顺序，讨论了这些时间分辨VSFG技术在研究不同界面水的飞秒振动动力学方面的应用。这些研究表明，界面存在特定的水动力学，并且时间分辨VSFG光谱能够以界面选择性的方式明确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VSFG和二维外差检测VSFG通过对OH伸缩振动带中的烧孔以及随后在飞秒时间区域内的光谱扩散进行明确观测，揭示了氢键的不均匀性以及界面水的相关振动动力学。这些时间分辨VSFG研究也留下了一些有待讨论的问题。我们不仅描述了对界面水动力学所获得的确凿物理见解，还阐述了仍不清楚或存在争议的要点。还简要描述了一种利用紫外激发的新型实验。最后，给出了时间分辨VSFG光谱的总结和一些未来展望。
