Fellows Alexander P, Duque Álvaro Díaz, Balos Vasileios, Lehmann Louis, Netz Roland R, Wolf Martin, Thämer Martin
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), 28049 Madrid, Spain.
Langmuir. 2024 Sep 3;40(35):18760-18772. doi: 10.1021/acs.langmuir.4c02571. Epub 2024 Aug 22.
The air-water interface is a highly prevalent phase boundary impacting many natural and artificial processes. The significance of this interface arises from the unique properties of water molecules within the interfacial region, with a crucial parameter being the thickness of its structural anisotropy, or "healing depth". This quantity has been extensively assessed by various simulations which have converged to a prediction of a remarkably short length of ∼6 Å. Despite the absence of any direct experimental measurement of this quantity, this predicted value has surprisingly become widely accepted as fact. Using an advancement in nonlinear vibrational spectroscopy, we provide the first measurement of this thickness and, indeed, find it to be ∼6-8 Å, finally confirming the prior predictions. Lastly, by combining the experimental results with depth-dependent second-order spectra calculated from ab initio parametrized molecular dynamics simulations, which are also in excellent agreement with this experimental result, we shed light on this surprisingly short correlation length of molecular orientations at the interface.
气-水界面是一种高度普遍的相界，影响着许多自然和人工过程。该界面的重要性源于界面区域内水分子的独特性质，其中一个关键参数是其结构各向异性的厚度，即“愈合深度”。这个量已经通过各种模拟进行了广泛评估，这些模拟得出的预测结果是，其长度非常短，约为6 Å。尽管目前还没有对这个量进行任何直接的实验测量，但这个预测值令人惊讶地被广泛接受为事实。利用非线性振动光谱学的一项进展，我们首次测量了这个厚度，结果发现其约为6 - 8 Å，最终证实了先前的预测。最后，通过将实验结果与从头算参数化分子动力学模拟计算出的深度相关二阶光谱相结合（这些光谱也与该实验结果高度吻合），我们揭示了界面处分子取向这种惊人的短关联长度。
