Department of Chemistry and Biochemistry , University of California , San Diego La Jolla, California 92093 , United States.
J Phys Chem B. 2018 Nov 29;122(47):10754-10761. doi: 10.1021/acs.jpcb.8b09910. Epub 2018 Nov 15.
A quantitative characterization of intermolecular and intramolecular couplings that modulate the OH-stretch vibrational band in liquid water has so far remained elusive. Here, we take up this challenge by combining the centroid molecular dynamics formalism, which accounts for nuclear quantum effects, with the MB-pol potential energy function, which accurately reproduces the properties of water across all phases, to model the infrared (IR) spectra of various isotopic water solutions with different levels of vibrational couplings, including those that cannot be probed experimentally. Analysis of the different IR OH-stretch line shapes provides direct evidence for the partially quantum-mechanical nature of hydrogen bonds in liquid water, which is emphasized by synergistic effects associated with intermolecular coupling and many-body electrostatic interactions. Furthermore, we quantitatively demonstrate that intramolecular coupling, which results in Fermi resonances due to the mixing between HOH-bend overtones and OH-stretch fundamentals, is responsible for the shoulder located at ∼3250 cm of the IR OH-stretch band of liquid water.
迄今为止，人们仍难以对调节液态水中 OH 伸缩振动带的分子间和分子内耦合进行定量描述。在这里，我们通过组合质心分子动力学形式理论（该理论考虑了核量子效应）和 MB-pol 势能函数（该函数准确地再现了所有相态下水的性质）来应对这一挑战，从而对具有不同振动耦合程度的各种同位素水溶液的红外（IR）光谱进行建模，包括那些无法通过实验探测的光谱。对不同的 IR OH 伸缩线形状的分析为液态水中氢键具有部分量子力学性质提供了直接证据，这种性质通过与分子间耦合和多体静电相互作用相关的协同效应得到了强调。此外，我们还定量地证明了，由于 HOH 弯曲泛频和 OH 伸缩基频之间的混合而导致的费米共振的分子内耦合，是液态水 IR OH 伸缩带中位于约 3250cm 处的肩峰的原因。
