Rashmi Richa, Paesani Francesco
Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States.
Materials Science and Engineering, University of California San Diego, La Jolla, California 92093, United States.
J Am Chem Soc. 2025 Jan 15;147(2):1903-1910. doi: 10.1021/jacs.4c14610. Epub 2025 Jan 3.
Ice interfaces are pivotal in mediating key chemical and physical processes such as heterogeneous chemical reactions in the environment, ice nucleation, and cloud microphysics. At the ice surface, water molecules form a quasi-liquid layer (QLL) with properties distinct from those of the bulk. Despite numerous experimental and theoretical studies, a molecular-level understanding of the QLL has remained elusive. In this work, we use state-of-the-art quantum dynamics simulations with a realistic data-driven many-body potential to dissect the vibrational sum-frequency generation (vSFG) spectrum of the air/ice interface in terms of contributions arising from individual molecular layers, orientations, and hydrogen-bonding topologies that determine the QLL properties. The agreement between experimental and simulated spectra provides a realistic molecular picture of the evolution of the QLL as a function of the temperature without the need for empirical adjustments. The emergence of specific features in the experimental vSFG spectrum suggests that surface restructuring may occur at lower temperatures. This work not only underscores the critical role of many-body interactions and nuclear quantum effects in understanding ice surfaces but also provides a definitive molecular-level picture of the QLL, which plays a central role in multiphase and heterogeneous processes of relevance to a range of fields, including atmospheric chemistry, cryopreservation, and materials science.
冰界面在介导关键的化学和物理过程中起着关键作用，如环境中的多相化学反应、冰核形成和云微物理学。在冰表面，水分子形成一个准液态层（QLL），其性质与本体不同。尽管有大量的实验和理论研究，但对QLL的分子水平理解仍然难以捉摸。在这项工作中，我们使用具有现实数据驱动多体势的先进量子动力学模拟，从决定QLL性质的单个分子层、取向和氢键拓扑结构的贡献方面剖析空气/冰界面的振动和频产生（vSFG）光谱。实验光谱和模拟光谱之间的一致性提供了一个现实的分子图像，即QLL随温度变化的演变，而无需进行经验调整。实验vSFG光谱中特定特征的出现表明，表面重构可能在较低温度下发生。这项工作不仅强调了多体相互作用和核量子效应在理解冰表面中的关键作用，还提供了一个明确的QLL分子水平图像，QLL在与一系列领域相关的多相和异质过程中起着核心作用，包括大气化学、低温保存和材料科学。
