模拟二维红外拉曼光谱和拉曼光谱用于液态水的分子间和分子内模式,The Journal of Chemical Physics

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模拟二维红外拉曼光谱和拉曼光谱用于液态水的分子间和分子内模式
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-02-18 13:45:37 , DOI: 10.1063/1.4941842
Hironobu Ito ₁ , Yoshitaka Tanimura ₁

Affiliation

对液态水的二维（2D）红外拉曼光谱和2D拉曼光谱进行了完全经典的分子动力学（MD）模拟，以阐明使用极化水模型进行分子间和分子内振动光谱（POLI2VS）的模式-模式耦合机制。。该模型能够描述红外光谱和拉曼光谱。使用平衡-非平衡混合MD方法计算了二阶响应函数，该函数包括2D IR-Raman的一个分子极化率和两个分子偶极矩以及2D Raman光谱学的三个分子极化率。使用具有非线性系统-浴相互作用的多模式布朗振荡器（BO）模型分析获得的信号，该非线性系统-浴相互作用表示分子内OH拉伸，分子内HOH弯曲，液态水的氢键（HB）分子间自由运动和HB分子间振动（平移）运动。该模型是通过使用层次Fokker-Planck方程来应用的。通过BO模型可以精确地再现从MD模拟获得的2D光谱中峰轮廓的定性特征。这表明该模型捕获了分子间和分子内运动的基本特征。我们阐明了控制2D信号轮廓的机制，包括谐波模式-模式耦合，极化率和偶极矩的非线性以及液态水的振动相移过程，即使从MD模拟获得的2D谱峰重叠或不清楚。在所有2D光谱中均观察到由电非谐耦合（EAHC）和机械非谐耦合（MAHC）引起的模式耦合峰。我们发现，在OH拉伸和HB分子间振动模式之间的MAHC强度可与OH拉伸和HOH弯曲模式之间的强度相媲美。此外，我们发现这种OH拉伸和HB间的分子间振动耦合应在2D光谱中观察为非对角交叉峰。

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Simulating two-dimensional infrared-Raman and Raman spectroscopies for intermolecular and intramolecular modes of liquid water

Full classical molecular dynamics (MD) simulations of two-dimensional (2D) infrared-Raman and 2D Raman spectroscopies of liquid water were carried out to elucidate a mode-mode coupling mechanism using a polarizable water model for intermolecular and intramolecular vibrational spectroscopy (POLI2VS). This model is capable of describing both infrared and Raman spectra. Second-order response functions, which consist of one molecular polarizability and two molecular dipole moments for 2D IR-Raman and three molecular polarizabilities for 2D Raman spectroscopies, were calculated using an equilibrium-non-equilibrium hybrid MD approach. The obtained signals were analyzed using a multi-mode Brownian oscillator (BO) model with nonlinear system-bath interactions representing the intramolecular OH stretching, intramolecular HOH bending, hydrogen bonded (HB)-intermolecular librational motion and HB-intermolecular vibrational (translational) motion of liquid water. This model was applied through use of hierarchal Fokker-Planck equations. The qualitative features of the peak profiles in the 2D spectra obtained from the MD simulations are accurately reproduced with the BO model. This indicates that this model captures the essential features of the intermolecular and intramolecular motion. We elucidate the mechanisms governing the 2D signal profiles involving anharmonic mode-mode coupling, the nonlinearities of the polarizability and dipole moment, and the vibrational dephasing processes of liquid water even in the case that the 2D spectral peaks obtained from the MD simulation overlap or are unclear. The mode coupling peaks caused by electrical anharmonic coupling (EAHC) and mechanical anharmonic coupling (MAHC) are observed in all of the 2D spectra. We find that the strength of the MAHC between the OH-stretching and HB-intermolecular vibrational modes is comparable to that between the OH-stretching and HOH bending modes. Moreover, we find that this OH-stretching and HB-intermolecular vibrational coupling should be observed as off-diagonal cross peaks in the 2D spectra.

更新日期：2016-02-21

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