纳米二氧化硅孔隙中水的红外，拉曼和二维红外光子回波谱的模拟,The Journal of Chemical Physics

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纳米二氧化硅孔隙中水的红外，拉曼和二维红外光子回波谱的模拟
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-05-20 15:24:45 , DOI: 10.1063/1.4949766
Paul C. Burris ₁ , Damien Laage ₂ , Ward H. Thompson ₁

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振动光谱法通常用于表征纳米密闭液体，并探究封闭框架对液体结构和相对于相应的大体积流体动力学的影响。但是，仍不清楚从这些测量中可以获得什么分子水平的信息。在本文中，我们通过使用分子动力学（MD）模拟来再现亲水性（羟基封端）中的水的线性红外（IR），拉曼光谱和二维红外（2D-IR）光子回波光谱，从而解决了这一问题。二氧化硅中孔。为了简化光谱，D ₂中同位素稀释的HOD的OH延伸区考虑O。一种经验映射方法用于从MD模拟获得OH振动频率，跃迁偶极子和跃迁极化率。模拟的线性IR和拉曼光谱与文献中报道的介孔二氧化硅中水的实测光谱具有良好的一般一致性。限制作用对水谱的主要影响是最接近孔隙界面的OH基团的振动蓝移。蓝移可以归因于在OH基团和二氧化硅氧受体之间形成的较弱的氢键（H键）。非密码子效应极大地减少了这些OH部分对线性IR光谱的贡献，但是这些较弱的H键在拉曼光谱中很明显。尚未测量2D-IR光谱，因此，本结果代表了一种预测。

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Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D₂O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. The simulated spectra indicates that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.

更新日期：2016-05-21

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