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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Water Dynamics: Vibrational Echo Correlation Spectroscopy and Comparison to Molecular Dynamics Simulations
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Water Dynamics: Vibrational Echo Correlation Spectroscopy and Comparison to Molecular Dynamics Simulations

机译：水动力学：振动回波相关光谱法和分子动力学模拟的比较

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摘要

The dynamics of water are examined using ultrafast IR stimulated vibrational echo correlation spectroscopy. The OD hydroxyl stretch of HOD in H_2O is probed with 45-fs pulses that have sufficient bandwidth (>400 cm~(-1)) to span the entire broad spectrum. High-quality 2D correlation spectra are obtained having the correct phase relations across the broad hydroxyl band. The correlation spectra are found to evolve on multiple time scales. The time evolution of the vibrational echo correlation spectrum reflects the structural evolution of the hydrogen bond networks. The extended vibrational lifetime of the OD hydroxyl stretch of HOD in H2O facilitates the measurement of hydrogen bond dynamics for longer times than possible in previous studies of the OH stretch. Molecular dynamics simulations/electronic structure calculations are used to obtain the time correlation functions (TCF) for two water models, TIP4P and SPC/E. The TCFs are inputs to full time-dependent diagrammatic perturbation theory calculations, which yield theoretical correlation spectra. Quantitative comparison with the data demonstrates that the two water models somewhat overemphasize the fast fluctuations in water and do not contain a slow enough component to account for the slowest fluctuations. Fits to the data using a phenomenological triexponential TCF yield a slowest component of ～2 ps, and TIP4P and SPC/E have slowest components of <1 ps. The TCF obtained from the water models and the triexponential TCF reproduce the linear absorption line shape equally well, but all miss to some extent the asymmetric "wing" on the low-energy side of the line. Therefore, the time dependence of the vibrational echo correlation spectra provides a good test for the TCF, but the absorption spectrum does not.
机译：使用超快红外激发振动回波相关光谱法检查水的动力学。用具有足够带宽（> 400 cm〜（-1））的45-fs脉冲探测HOD在H_2O中的OD羟基延伸。获得了在宽羟基带上具有正确相位关系的高质量2D相关光谱。发现相关光谱在多个时间尺度上演化。振动回波相关谱的时间演化反映了氢键网络的结构演化。与以前的OH拉伸研究相比，HOD OD OD拉伸在水中的振动寿命延长，有利于氢键动力学的测量。使用分子动力学模拟/电子结构计算来获得两个水模型TIP4P和SPC / E的时间相关函数（TCF）。 TCF是完整的与时间相关的图解扰动理论计算的输入，从而产生了理论上的相关光谱。与数据的定量比较表明，这两种水模型在某种程度上过分强调了水的快速波动，并且没有包含足够慢的分量来说明最慢的波动。使用现象学三指数TCF拟合数据时，最慢分量为〜2 ps，而TIP4P和SPC / E的最慢分量为＜1 ps。从水模型获得的TCF和三指数TCF可以很好地重现线性吸收线的形状，但都在某种程度上错过了线低能量侧的不对称“机翼”。因此，振动回波相关光谱的时间依赖性为TCF提供了很好的测试，但吸收光谱却没有。

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