Oxide–water interfaces host a wide range of important reactions in nature and modern industrial applications; however, accurate knowledge about these interfaces is still lacking at the molecular level owing to difficulties in accessing buried oxide surfaces. Here we report an experimental scheme enabling in situ sum-frequency vibrational spectroscopy of oxide surfaces in liquid water. Application to the silica–water interface revealed the emergence of unexpected surface reaction pathways with water. With ab initio molecular dynamics and metadynamics simulations, we uncovered a surface reconstruction, triggered by deprotonation of surface hydroxylated groups, that led to unconventional five-coordinated silicon species. The results help demystify the multimodal chemistry of aqueous silica discovered decades ago, bringing in fresh information that modifies the current understanding. Our study will provide new opportunities for future in-depth physical and chemical characterizations of other oxide–water interfaces.

氧化物-水界面在自然界和现代工业应用中具有广泛的重要反应;然而，由于难以接近埋藏的氧化物表面，在分子水平上仍然缺乏关于这些界面的准确知识。在这里，我们报告了一种实验方案，能够对液态水中的氧化物表面进行原位和频振动光谱分析。应用于二氧化硅-水界面揭示了与水的意外表面反应途径的出现。通过从头计算分子动力学和元动力学模拟，我们发现了由表面羟基化基团的去质子化触发的表面重建，这导致了非常规的五配位硅种类。这些结果有助于揭开几十年前发现的二氧化硅水性多峰化学的神秘面纱，带来新的信息，改变目前的理解。我们的研究将为未来其他氧化物-水界面的深入物理和化学表征提供新的机会。