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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Probing Microstructure of Acetonitrile-Water Mixtures by Using Two-Dimensional Infrared Correlation Spectroscopy
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Probing Microstructure of Acetonitrile-Water Mixtures by Using Two-Dimensional Infrared Correlation Spectroscopy

机译：二维红外相关光谱技术研究乙腈-水混合物的微观结构

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摘要

Acetonitrile-water mixtures are a unique model system for implementing a new family of coherent two-dimensional (2D) vibrational spectroscopy-doubly vibrationally enhanced (DOVE) four wave mixing (FWM) spectroscopy for structure analysis of hydrogen-bonded systems. These mixtures often have a heterogeneous microstructure that consists of acetonitrile (CH_3CN) or water clusters. There are two types of CH_3CN environments in mixtures-free CH_3CN species and hydrogen-bonded CH_3CN species. To design new DOVE-FWM experiments and interpret DOVE-FWM spectra, it is crucial to have a complete structure information regarding this model system. In this work, we have used a highly sensitive spectroscopic method, 2D infrared (IR) correlation spectroscopy for probing structure information of the mixtures (a 50:50 mol % CH_3CN-H_2O solution, a 50:50 mol % CH_3CN-D_2O solution and a 38:62 mol % CH_3CN-D_2O solution) under temperature perturbation. In addition to two cross-peaks at 2253 and 2259 cm~(-1), corresponding to the C ≡ N stretch of free acetonitrile molecules and hydrogen-bonded acetonitrile molecules, respectively, the 2D correlation spectra show a new feature at 2256 cm~(-1) which has not been observed by conventional IR and Raman spectra in these mixtures. The second derivatives of the IR spectra also show this new feature whose intensity increases with temperature, whereas the features at 2253 and 2259 cm~(-1) become weaker. Correspondingly, a new feature appears at about 3168 cm~(-1) for the combination band of the C ≡ N stretch and the C-C stretch, whereas the combination band of the free CH_3CN species is centered at 3164 cm~(-1), and 3171 cm~(-1) for the hydrogen-bonded CH_3CN species. The new feature may be related to an intermediate microstructure between clusters of acetonitrile molecules and hydrogen-bonded acetonitrile molecules associated with clusters of water molecules. The results will provide useful structural and spectral information for the design of new 2D DOVE-FWM experiments and the molecular structure modeling of the mixtures.
机译：乙腈-水混合物是一种独特的模型系统，可用于实施新的相干二维（2D）振动光谱学-双振动增强（DOVE）四波混合（FWM）光谱学，用于氢键合系统的结构分析。这些混合物通常具有由乙腈（CH_3CN）或水簇组成的异质微观结构。无混合物的CH_3CN物种和氢键的CH_3CN物种有两种类型的CH_3CN环境。为了设计新的DOVE-FWM实验并解释DOVE-FWM光谱，拥有有关此模型系统的完整结构信息至关重要。在这项工作中，我们使用高灵敏度光谱法，二维红外（IR）相关光谱法探测混合物的结构信息（50:50 mol％CH_3CN-H_2O溶液，50：50 mol％CH_3CN-D_2O溶液和在温度扰动下加入38:62 mol％的CH_3CN-D_2O溶液）。除了分别在2253和2259 cm〜（-1）处的两个交叉峰（分别对应于游离乙腈分子和氢键合乙腈分子的C≡N延伸）之外，二维相关光谱在2256 cm〜处具有新特征。 （-1）尚未通过常规IR和拉曼光谱在这些混合物中观察到。红外光谱的二阶导数也显示出这种新特征，其强度随温度而增加，而在2253和2259 cm〜（-1）处的特征变弱。相应地，C≡N延伸和CC延伸的结合带在约3168 cm〜（-1）处出现一个新的特征，而游离CH_3CN物种的结合带以3164 cm〜（-1）为中心，和氢键的CH_3CN物种为3171 cm〜（-1）。新特征可能与乙腈分子簇和与水分子簇相关的氢键合乙腈分子之间的中间微观结构有关。结果将为新的2D DOVE-FWM实验的设计和混合物的分子结构建模提供有用的结构和光谱信息。

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