Investigations of Concentrated Salt and Acid Solutions Using Ultrafast Nonlinear Spectroscopy

在化学系化学结构、动力学和机理(CSDM-A)计划的支持下，斯坦福大学的Michael Fayer教授正在开发尖端的超快光谱，以研究溶剂化离子和质子的动力学和结构。盐和酸溶液在自然界中很常见，在技术应用中也很重要。直接研究水中离子的挑战是，离子/水的动力学发生在极短的时间尺度上，只有万亿秒，或者比相机快门速度快10亿倍。Fayer教授和他的学生将发展超快红外和可见光光谱方法，并用它们来研究浓盐和酸性溶液。他们的发现将增强对重要离子/水系统的基本知识，并使人们更好地理解复杂的电解液，例如正在开发的用于电池储能的电解液。除了通过与学术界、政府实验室和工业界共享信息和技术而产生的直接科学影响外，该项目还将为下一代顶尖科学家提供研究机会，并为国家的科学、技术、工程和数学(STEM)工作队伍做出贡献。费耶尔小组将使用超快红外非线性光谱方法，特别是二维红外(2D IR)、偏振选择泵浦-探测器(PSPP)和超快光学外差探测光学克尔效应(OHD-OKE)实验来探测高浓度盐和酸溶液。盐溶液通常被称为“盐中之水”。它们的水分子太少，不能完全溶剂化离子，例如，四个水分子对应一个离子对。酸性溶液也会有很高的浓度。在酸性溶液中，氢离子取代了盐溶液中的阳离子。虽然氢离子是一种阳离子，但它可以通过转移一个质子来改变它对水分子的同一性。盐溶液和酸溶液是由扩展的离子/水网络组成，而不是水合离子。实验将作为离子浓度和温度的函数进行。此外，还将研究单原子离子和多原子离子之间的差异以及它们的相对大小的影响。上面提到的方法是一套相互关联的工具，将用于检查相同系统的不同方面，使人们能够从根本上了解动力学、结构和整体属性之间的关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professor Michael Fayer of Stanford University is developing sophisticated ultrafast spectroscopies to study the dynamics and structure of solvated ions and protons. Salt and acid solutions are common in nature and important in technological applications. The challenge in directly investigating ions in water is that the ion/water dynamics occur on exceedingly short time scales, trillionths of a second, or a billion times faster than a camera shutter speed. Professor Fayer and his students will advance ultrafast infrared and visible spectroscopic methods and use them to study concentrated salt and acid solutions. Their discoveries will enhance basic knowledge of important ion/water systems and lead to better understanding of complex electrolytes, such as those being developed for use in batteries for energy storage. In addition to the direct scientific impact through the sharing of information and technologies with academia, government laboratories, and industry, the project will provide research opportunities for the next generation of top scientists and contribute to the Nation's science, technology, engineering, and mathematics (STEM) workforce.The Fayer group will employ ultrafast infrared nonlinear spectroscopic methods, particularly two-dimensional infrared (2D IR), polarization selective pump-probe (PSPP), and ultrafast optical heterodyne detected optical Kerr effect (OHD-OKE) experiments to probe highly concentrated salt and acid solutions. The salt solutions are frequently referred to as “Water in Salt”. They have far too few water molecules to fully solvate the ions, e.g., one ion pair for four water molecules. The acid solutions will also have very high concentrations. In the acid solutions, hydronium replaces the cation found in salt solutions. While hydronium is a cation, it can change its identity to a water molecule by transferring a proton. The salt and acid solutions are composed of extended ion/water networks rather than hydrated ions. The experiments will be conducted as a function of ion concentration and temperature. In addition, the differences between monatomic and polyatomic ions and the effects of their relative sizes will be investigated. The methods mentioned above are a set of interrelated tools that will be used to examine different aspects of the same systems, enabling a fundamental understanding of the relationships among dynamics, structure, and bulk properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.