An ultrafast vibrational study of dynamical heterogeneity in the protic ionic liquid ethyl-ammonium nitrate. I. Room temperature dynamics
An ultrafast vibrational study of dynamical heterogeneity in the protic ionic liquid ethyl-ammonium nitrate. I. Room temperature dynamics
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DOI：
10.1063/5.0044822
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发表时间：
2021-04-07
影响因子：
4.4
通讯作者：
Garrett-Roe, Sean
中科院分区：
文献类型：
--
作者：
Johnson, Clinton A.;Parker, Anthony W.;Garrett-Roe, Sean
利用超快二维红外光谱（2D-IR），以硫氰酸根（SCN-）为振动探针，研究了质子离子液体硝酸乙基铵（EAN）与水的氢键网络.在室温下在平行（ZZZZ）和垂直（ZZXX）偏振下进行2D-IR实验。在EAN中，SCN-的FTIR光谱中的非高斯线形表明两个子系综。从2D-IR光谱中提取的振动弛豫速率提供了两个子系综之间的动力学差异的证据。我们支持两个子合奏的解释与响应函数模拟的两个重叠的频带具有不同的振动弛豫速率，否则，类似的动态。光谱扩散的测量速率取决于极化，表明重定向诱导的光谱扩散（RISD）。一个模型的限制分子旋转（摆动在一个圆锥）充分描述了所观察到的光谱扩散EAN。在H2O中，RISD和结构光谱扩散都有相似的时间尺度。室温下动力学的完整表征为本系列论文II中的温度相关测量提供了基础。
Using ultrafast two-dimensional infrared spectroscopy (2D-IR), a vibrational probe (thiocyanate, SCN-) was used to investigate the hydrogen bonding network of the protic ionic liquid ethyl-ammonium nitrate (EAN) in comparison to H2O. The 2D-IR experiments were performed in both parallel (ZZZZ) and perpendicular (ZZXX) polarizations at room temperature. In EAN, the non-Gaussian lineshape in the FTIR spectrum of SCN- suggests two sub-ensembles. Vibrational relaxation rates extracted from the 2D-IR spectra provide evidence of the dynamical differences between the two sub-ensembles. We support the interpretation of two sub-ensembles with response function simulations of two overlapping bands with different vibrational relaxation rates and, otherwise, similar dynamics. The measured rates for spectral diffusion depend on polarization, indicating reorientation-induced spectral diffusion (RISD). A model of restricted molecular rotation (wobbling in a cone) fully describes the observed spectral diffusion in EAN. In H2O, both RISD and structural spectral diffusion contribute with similar timescales. This complete characterization of the dynamics at room temperature provides the basis for the temperature-dependent measurements in Paper II of this series.