Boyer Mark A, Marsalek Ondrej, Heindel Joseph P, Markland Thomas E, McCoy Anne B, Xantheas Sotiris S
Department of Chemistry , University of Washington , Seattle , Washington 98195 , United States.
Charles University , Faculty of Mathematics and Physics , Ke Karlovu 3 , 121 16 Prague 2, Czech Republic.
J Phys Chem Lett. 2019 Mar 7;10(5):918-924. doi: 10.1021/acs.jpclett.8b03790. Epub 2019 Feb 14.
The structure of hydrogen bonded networks is intimately intertwined with their dynamics. Despite the incredibly wide range of hydrogen bond strengths encountered in water clusters, ion-water clusters, and liquid water, we demonstrate that the previously reported correlation between the change in the equilibrium bond length of the hydrogen bonded OH covalent bond and the corresponding shift in its harmonic frequency in water clusters is much more broadly applicable. Surprisingly, this correlation describes the ratios for both the equilibrium OH bond length/harmonic frequency and the vibrationally averaged bond length/anharmonic frequency in water, hydronium water, and halide water clusters. Consideration of harmonic and anaharmonic data leads to a correlation of -19 ± 1 cm/0.001 Å. The fundamental nature of this correlation is further confirmed through the analysis of ab initio Molecular Dynamics (AIMD) trajectories for liquid water. We demonstrate that this simple correlation for both harmonic and anharmonic systems can be modeled by the response of an OH bond to an external field. Treating the OH bond as a Morse oscillator, we develop analytic expressions, which relate the ratio of the shift in the vibrational frequency of the hydrogen-bonded OH bond to the shift in OH bond length, to parameters in the Morse potential and the ratio of the first and second derivatives of the field-dependent projection of the dipole moment of water onto the hydrogen-bonded OH bond. Based on our analysis, we develop a protocol for reconstructing the AIMD spectra of liquid water from the sampled distribution of the OH bond lengths. Our findings elucidate the origins of the relationship between the molecular structure of the fleeting hydrogen-bonded network and the ensuing dynamics, which can be probed by vibrational spectroscopy.
氢键网络的结构与其动力学紧密相连。尽管在水团簇、离子 - 水团簇和液态水中遇到的氢键强度范围极其广泛，但我们证明，先前报道的氢键合的OH共价键平衡键长变化与其在水团簇中谐波频率相应位移之间的相关性具有更广泛的适用性。令人惊讶的是，这种相关性描述了水、水合氢离子水和卤化物水团簇中平衡OH键长/谐波频率以及振动平均键长/非谐波频率的比率。对谐波和非谐波数据的考虑得出相关性为 -19 ± 1 cm/0.001 Å。通过对液态水的从头算分子动力学（AIMD）轨迹的分析，进一步证实了这种相关性的基本性质。我们证明，这种适用于谐波和非谐波系统的简单相关性可以通过OH键对外场的响应来建模。将OH键视为莫尔斯振子，我们推导出解析表达式，该表达式将氢键合的OH键振动频率的位移与OH键长的位移之比与莫尔斯势中的参数以及水的偶极矩在场依赖投影到氢键合的OH键上的一阶和二阶导数的比率相关联。基于我们的分析，我们开发了一种从OH键长的采样分布重建液态水AIMD光谱的方案。我们的研究结果阐明了短暂氢键网络的分子结构与随之而来的动力学之间关系的起源，这可以通过振动光谱进行探测。
