The Role of Resonant Coupling in Vibrational Sum-Frequency-Generation Spectroscopy: Liquid Acetonitrile at the Silica Interface
The Role of Resonant Coupling in Vibrational Sum-Frequency-Generation Spectroscopy: Liquid Acetonitrile at the Silica Interface
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DOI：
10.1016/j.molliq.2023.121315
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发表时间：
2023-01
影响因子：
6
通讯作者：
Amanda J. Souna;S. Cohen;Christopher A. Rivera;K. Manfred;B. Coasne;J. Fourkas
中科院分区：
文献类型：
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作者：
Amanda J. Souna;S. Cohen;Christopher A. Rivera;K. Manfred;B. Coasne;J. Fourkas
振动和频产生（VSFG）光谱是一种用于探测界面处分子组织的通用技术。人们越来越认识到，动力学现象，如重取向和分子间振动耦合，也可以影响VSFG光谱。二氧化硅/液体乙腈界面是一个有用的系统，更详细地探索这些影响。乙腈在该界面处的组织已经得到了很好的研究，并且已知在许多方面类似于支持的脂质双层。在这里，同位素稀释被用来探讨甲基对称伸缩共振分子间耦合的影响，该系统的VSFG光谱。VSFG光谱中的甲基伸缩区域在这个界面上显示蓝移，线宽的减少，并高于预期的强度稀释后，在氘代乙腈。我们证明了共振耦合通过红外跃迁影响VSFG光谱位移。使用分子模拟，我们表明，我们的实验观察是一致的甲基过渡偶极之间的共振耦合是一个显着的，但不是占主导地位的，所观察到的同位素稀释后的光谱位移的贡献。此外，我们的分子模拟表明，共振耦合占部分线宽和强度的变化。这些经典的分子动力学模拟也阐明了同位素稀释后的各向同性拉曼光谱在散装液体中的行为。我们进一步模拟了该系统中氰基伸缩链之间的共振耦合。这些模拟匹配的实验位移由于在散装液体中的CN拉伸的拉曼非重合效应的位移，但表明相应的共振耦合引起的位移在二氧化硅界面处的VSFG光谱是最小的。我们的实验和模拟结果表明，接近的界面可以引起实质性的变化，在液体中的振动的共振耦合。
Vibrational sum-frequency-generation (VSFG) spectroscopy is a versatile technique for probing molecular organization at interfaces. There is a growing recognition that dynamic phenomena, such as reorientation and intermolecular vibrational coupling, can also influence VSFG spectra. The silica/liquid acetonitrile interface is a useful system for exploring these effects in more detail. The organization of acetonitrile at this interface has been well studied, and is known to resemble that of a supported lipid bilayer in many ways. Here isotopic dilution is used to explore the influence of resonant intermolecular coupling of methyl symmetric stretches on the VSFG spectroscopy of this system. VSFG spectra in the methyl stretching region at this interface show a blue shift, a decrease in linewidth, and a higher-than-expected intensity upon dilution in deuterated acetonitrile. We demonstrate that resonant coupling influences VSFG spectral shifts through the infrared transition. Using molecular simulations, we show that our experimental observations are consistent with resonant coupling between methyl transition dipoles being a significant, but not the dominant, contribution to the observed spectral shift upon isotopic dilution. Furthermore, our molecular simulations demonstrate that resonant coupling accounts partially for changes in linewidth and intensity. These classical molecular dynamics simulations also elucidate the behavior of the isotropic Raman spectrum in the bulk liquid upon isotopic dilution. We further simulate the resonant coupling among cyano stretches in this system. These simulations match the experimental shift due to the Raman non-coincidence effect shift of the CN stretch in the bulk liquid, but suggest that the corresponding resonant-coupling-induced shift in the VSFG spectrum at the silica interface is minimal. Our experimental and simulation results indicate that proximity to an interface can cause substantial changes in the resonant coupling of vibrations in a liquid.