IR and Raman spectra of liquid water: Theory and interpretation
IR and Raman spectra of liquid water: Theory and interpretation
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DOI：
10.1063/1.2925258
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发表时间：
2008-06-14
影响因子：
4.4
通讯作者：
Skinner, J. L.
中科院分区：
文献类型：
--
作者：
Auer, B. M.;Skinner, J. L.
几年前测量了液态水OH伸缩区的IR和拉曼（平行偏振和双偏振）光谱，但对它们的解释仍有争议。在某种程度上，这是因为纯液体的这种光谱的理论计算提出了一个艰巨的挑战，由于振动发色团之间的耦合和运动窄化的影响。最近，我们提出了一个电子结构/分子动力学方法计算光谱的稀HOD在液体D2 O，它依赖于从头计算簇提供一个地图从核坐标的分子在液体中的OH伸缩频率，过渡偶极子，和极化率。在这里，我们将这种方法扩展到计算生色团之间的耦合。从波动的本地模式的频率，过渡时刻，和耦合的轨迹，我们使用我们最近开发的时间平均近似计算线的形状。对红外和拉曼谱线形状的计算结果与实验结果吻合较好，并捕捉到了它们之间的显著差异。我们的分析表明，虽然发色团之间的耦合是相对温和的，但它产生的振动本征态的离域超过12个发色团，这对光谱有深远的影响。特别是，我们的研究结果表明，在平行偏振拉曼光谱在约3250波数的峰值是集体的性质。(c)2008年美国物理研究所。
IR and Raman (parallel- and perpendicular-polarized) spectra in the OH stretch region for liquid water were measured some years ago, but their interpretation is still controversial. In part, this is because theoretical calculation of such spectra for a neat liquid presents a formidable challenge due to the coupling between vibrational chromophores and the effects of motional narrowing. Recently we proposed an electronic structure/molecular dynamics method for calculating spectra of dilute HOD in liquid D2O, which relied on ab initio calculations on clusters to provide a map from nuclear coordinates of the molecules in the liquid to OH stretch frequencies, transition dipoles, and polarizabilities. Here we extend this approach to the calculation of couplings between chromophores. From the trajectories of the fluctuating local-mode frequencies, transition moments, and couplings, we use our recently developed time-averaging approximation to calculate the line shapes. Our results are in good agreement with experiment for the IR and Raman line shapes, and capture the significant differences among them. Our analysis shows that while the coupling between chromophores is relatively modest, it nevertheless produces delocalization of the vibrational eigenstates over up to 12 chromophores, which has a profound effect on the spectroscopy. In particular, our results demonstrate that the peak in the parallel-polarized Raman spectrum at about 3250 wavenumbers is collective in nature. (c) 2008 American Institute of Physics.