DYNAmics at ionic Water-air INterfaces: Synergy between SFG experiments and DFTMD simulations

发生在水界面的物理和化学过程已被证明在从大气气溶胶化学和多相催化到生物物理学和生物化学的各种领域发挥着突出作用。这一建议旨在获得水的结构和动力学的分子水平的信息，特别是在空气和离子溶液之间的界面。这样的见解与大气化学高度相关，例如，在气溶胶表面发生非均匀臭氧化学。尽管表面上很重要，但令人惊讶的是，人们对这些界面的动力学知之甚少。真正理解这种界面的反应性需要了解结构和能量流动动力学，这些特性将被当前的研究计划所揭示。实验和理论方法的独特结合将提供有关这些重要界面的新信息。待回答的问题包括：离子的存在如何影响界面处的结构弛豫动力学？离子通过与水分子的相互作用，诱导界面水的非均质性吗？在界面处能量传递的速度有多快？我们将集中讨论含卤化物盐的水溶液和酸性溶液。德国团队将使用表面敏感和频率产生（SFG）光谱对表面进行实验研究，该光谱探测界面的前几层单层。最近，德国团队对这项技术进行了扩展，包括时间分辨率和二维SFG，可以在亚皮秒的时间分辨率下获得界面水分子的动力学。虽然功能强大，但这些实验需要理论指导和支持，以实现对界面发生的物理和化学的详细理解。为此，法国团队将进行最先进的第一性原理分子动力学模拟。模拟将用于计算在界面处提供结构、动力学、振动能量松弛和化学反应性的轨迹。法国合作伙伴提供的基本输入是使用第一性原理MD计算SFG光谱，可以直接与实验测量光谱进行比较。通过理论和实验相结合的方法，结合两个领域最先进的技术，我们的目标是充分了解所研究的水界面的表面结构和动力学。我们相信这些结果对于理解与非均相化学相关的气溶胶上发生的反应至关重要。

Physical and chemical processes occurring at aqueous interfaces have been shown to play a prominent role in a variety of fields ranging from chemistry of atmospheric aerosols and heterogeneous catalysis to biophysics and biochemistry. This proposal aims at obtaining molecular-level information on the structure and dynamics of water at specifically the interface between air and ionic solutions. Such insights are highly relevant for atmospheric chemistry where, for instance, on the surface of aerosols heterogeneous ozone chemistry occurs. Despite of the apparent importance, surprisingly little is known about the dynamics of these interfaces. Truly understanding the reactivity of such an interface requires knowledge of both the structural and energy flow dynamics, properties that will be unraveled by the present research program. A unique combination of experimental and theoretical approaches will provide new information about these important interfaces. Questions to be answered include: how does the presence of ions affect the structural relaxation dynamics at the interface? Do ions, by interacting with water molecules, induce heterogeneity amongst the interfacial water? How fast is energy transferred at the interface? We will focus on aqueous solutions containing halide salts and on acidic solutions. The German team will experimentally study the surface using surface-sensitive sum-frequency generation (SFG) spectroscopy, which probes the first few monolayers of the interface. Recent extensions of this technique by the German team including time-resolved, and two dimensional SFG allow obtaining the dynamics of interfacial water molecules with sub-picosecond time resolution. Although powerful, these experiments require theoretical guidance and support to achieve detailed understanding of the physics and chemistry occurring at the interface. To this end, state of the art first-principles molecular dynamics simulations will be performed in the French team. Simulations will be used to calculate trajectories that provide the structure, dynamics, vibrational energy relaxation, and chemical reactivity, at interfaces. The essential input provided by the French partner is the use of first principle MD to calculate SFG spectra, which can be directly compared to the experimental measured spectra. With this combined theoretical and experimental approach with state-of-the-art techniques in both fields we aim to get a full understanding of the surface structure and the dynamics of the aqueous interfaces under study. We believe the results will be essential for understanding reactions occurring on aerosols relevant for heterogeneous chemistry.