Ito Hironobu, Hasegawa Taisuke, Tanimura Yoshitaka
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyoku, Kyoto 606-8502, Japan.
J Chem Phys. 2014 Sep 28;141(12):124503. doi: 10.1063/1.4895908.
Recently, two-dimensional (2D) THz-Raman spectroscopy has been used to investigate the intermolecular modes of liquid water. We examine such 2D spectroscopy signals by means of full molecular dynamics (MD) simulations. In this way, we carry out a detailed analysis of intermolecular interactions that play an essential role in many important chemical processes. We calculate 2D Raman-THz-THz (RTT), THz-Raman-THz (TRT), and 2D Raman signals for liquid water, methanol, formamide, acetonitrile, formaldehyde, and dimethyl sulfoxide using an equilibrium-non-equilibrium hybrid MD simulation algorithm originally developed for 2D Raman spectroscopy. These signals are briefly analyzed in terms of anharmonicity and nonlinear polarizability of vibrational modes on the basis of the 2D Raman signals calculated from a Brownian oscillator model with a nonlinear system-bath interaction. We find that the anharmonic contribution is dominant in the RTT case, while the nonlinear polarizability contribution is dominant in the TRT case. For water and methanol, we observed vibrational echo peaks of librational motion in the 2D TRT signals. The predicted signal profiles and intensities that we obtained provide valuable information that can be applied to 2D spectroscopy experiments, allowing them to be carried out more efficiently.
最近，二维（2D）太赫兹-拉曼光谱已被用于研究液态水的分子间模式。我们通过全分子动力学（MD）模拟来检验此类二维光谱信号。通过这种方式，我们对在许多重要化学过程中起关键作用的分子间相互作用进行了详细分析。我们使用最初为二维拉曼光谱开发的平衡-非平衡混合MD模拟算法，计算了液态水、甲醇、甲酰胺、乙腈、甲醛和二甲亚砜的二维拉曼-太赫兹-太赫兹（RTT）、太赫兹-拉曼-太赫兹（TRT）和二维拉曼信号。基于从具有非线性系统-浴相互作用的布朗振子模型计算出的二维拉曼信号，从振动模式的非谐性和非线性极化率方面对这些信号进行了简要分析。我们发现，在RTT情况下非谐贡献占主导，而在TRT情况下非线性极化率贡献占主导。对于水和甲醇，我们在二维TRT信号中观察到了平动的振动回波峰。我们获得的预测信号轮廓和强度提供了可应用于二维光谱实验的有价值信息，从而使实验能够更高效地进行。
