Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Chem Phys. 2019 Mar 28;150(12):124507. doi: 10.1063/1.5088499.
Polarization-selective Two Dimensional Infrared (2D IR) and IR pump-probe spectroscopies have been performed on the hydrogen bonding glass forming liquid 2-biphenylmethanol doped with the long-lived vibrational probe phenylselenocyanate over a wide range of temperatures. The spectral diffusion seen in the 2D spectra was found to have a large polarization dependence, in large excess of what is predicted by standard theory. This anomaly was explained by decomposing the 2D spectra into hydrogen-bonding and non-bonding components, which exchange through large-angle orientational motion. By adapting chemical exchange theories, parameters for the component peaks were then calculated by fitting the polarization-dependent spectral diffusion and the pump-probe anisotropy. A model of highly heterogeneous exchange and orientational dynamics was used to explain the observed time dependences as a function of temperature on fast time scales. The experimental observations, the kinetic modeling, and physical arguments lead to the determination of the times for interconversion of slow dynamics structural domains to fast dynamics structural domains in the supercooled liquid as a function of temperature. The slow to fast domain interconversion times range from 40 ps at 355 K to 5000 ps at 270 K.
偏振选择性二维红外（2D IR）和红外泵浦探针光谱学已在氢键形成液体 2-联苯甲醇中进行，该液体中掺杂了长寿命振动探针苯硒氰，研究范围涵盖了很宽的温度范围。在二维光谱中观察到的光谱扩散具有很大的偏振依赖性，远远超过标准理论的预测。通过将二维光谱分解为氢键和非氢键成分，这一异常现象得到了解释，这两种成分通过大角度取向运动进行交换。通过适应化学交换理论，然后通过拟合偏振相关的光谱扩散和泵浦探针各向异性，计算了成分峰的参数。使用高度非均匀交换和取向动力学模型来解释在快速时间尺度上观察到的随温度变化的时间依赖性。实验观察、动力学建模和物理论证导致确定了在过冷液体中慢动力学结构域与快动力学结构域之间的相互转换时间作为温度的函数。慢到快的域相互转换时间范围从 355 K 时的 40 ps 到 270 K 时的 5000 ps。
