Liquid acetonitrile at a silica surface is known to organize in a manner that, in some respects, resembles a supported lipid bilayer. Here we use broadband vibrational sum-frequency generation (VSFG) spectroscopy to study how this organization depends on temperature. We find that VSFG spectra in the methyl-stretching region of the spectrum decrease in magnitude and shift to the blue for all polarization combinations (SSP, SPS, and PPP) as the temperature is raised from 25 to 60 °C. The observed decrease in intensity with increasing temperature is unexpected and suggests that the dynamics of the second sublayer of acetonitrile molecules plays an important role in the spectral behavior of this system. We propose that the decrease in intensity with increasing temperature arises largely from the more static first sublayer becoming more disordered. This picture is supported by the observed blue shift at high temperature, which is consistent with faster reorientation-induced spectral diffusion. The rapid dynamics and average orientation of the second sublayer are biased by the first sublayer, but this bias is not influenced substantially by increasing the temperature.

中文翻译：

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温度对二氧化硅/液体界面上乙腈组织的影响

已知在二氧化硅表面上的液体乙腈以某种方式组织，该方式在某些方面类似于负载的脂质双层。在这里，我们使用宽带振动和频生成（VSFG）光谱来研究这种组织如何依赖温度。我们发现，随着温度从25°C升高到60°C，对于所有极化组合（SSP，SPS和PPP），在光谱的甲基拉伸区域中的VSFG光谱的幅度都减小，并变为蓝色。观察到强度随温度升高而降低是出乎意料的，这表明乙腈分子第二亚层的动力学在该系统的光谱行为中起着重要作用。我们提出强度随温度升高而降低的主要原因是，更静态的第一子层变得更加无序。此图片得到高温下观察到的蓝移的支持，这与更快的重新定向诱导的光谱扩散相一致。第二子层的快速动力学和平均取向被第一子层偏置，但是该偏置基本上不受温度升高的影响。