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 distinct properties from the bulk. Despite numerous experimental and theoretical studies, the 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 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.

中文翻译：

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从和频生成谱的量子模拟中剖析空气/冰界面的分子结构


冰界面在介导关键的化学和物理过程方面发挥着关键作用，例如环境中的非均相化学反应、冰成核和云微物理学。在冰表面，水分子形成准液态层 （QLL），其特性与冰块不同。尽管进行了大量实验和理论研究，但对 QLL 的分子水平理解仍然难以捉摸。在这项工作中，我们使用最先进的量子动力学模拟，具有逼真的数据驱动的多体潜力，根据决定 QLL 特性的单个分子层、取向和氢键拓扑产生的贡献，剖析空气/冰界面的振动和频产生 （vSFG） 频谱。实验光谱和模拟光谱之间的一致性提供了 QLL 随温度变化的真实分子图，而无需进行经验调整。实验 vSFG 光谱中特定特征的出现表明，表面重构可能发生在较低温度下。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方面的关键作用，而且还提供了 QLL 的明确分子水平图景，QLL 在与大气化学、低温保存和材料科学等一系列领域相关的多相和非均相过程中发挥着核心作用。