CAREER: Ultrafast and multidimensional vibrational spectroscopy of aqueous interfaces

在化学系化学结构、动力学和机理计划的支持下，密歇根州立大学的John McGuire教授和他的研究小组将研究振动弛豫、取向动力学以及水在水溶液界面上的振动模式之间的耦合。水的特性，如其异常高的沸点和热容，很大程度上来自于它的氢键网络。这种网络的特性通常是其动力学的产物，其特征是从皮秒到亚皮秒的时间尺度。界面处氢键网络的终止导致了不同于在整体中广泛测量的动力学。然而，到目前为止，绝大多数水界面的实验研究都集中在它们的静态性质上。通过激发水分子的非平衡分布，然后测量表面敏感和频响应，可以探测表面动力学。这为深入了解界面氢键网络提供了新的机会。麦奎尔教授的团队将使用新的多维和相敏技术来检测和频信号，以提高对弱表面非线性光学过程的灵敏度。研究将解决一系列化学和物理上重要的水界面的动力学性质的差异，包括疏水和亲水界面以及具有不同浓度的溶质(如盐)的水界面。了解水界面上的动力学和振动耦合将影响我们对水界面上一系列现象的理解，如溶剂化和电荷转移，这些现象是蛋白质折叠、电化学能量生成和储存、多相催化和大气化学等各种过程的核心。所开发的技术还将应用于其他界面和非中心对称块体系统的研究。参与这个项目的学生将接受振动和超快光谱学以及广泛应用于化学和物理系统研究的非线性光学技术的培训。通过高中教师参与研究和为K-12教师举办动手讲习班等活动，将向K-12学生传播科学发现的过程和结果以及对水的科学理解。

In this CAREER award, supported by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Professor John McGuire and his research group at Michigan State University will study vibrational relaxation, orientational dynamics, and couplings between vibrational modes of water at aqueous interfaces. The properties of water, such as its anomalously high boiling point and heat capacity, derive largely from its hydrogen-bond network. The properties of this network are often a product of its dynamics, which are characterized by picoseconds to sub-picosecond timescales. The termination of the hydrogen-bond network at interfaces leads to dynamics distinct from those widely measured in the bulk. However, to date, the vast majority of experimental studies of aqueous interfaces have focused on their static properties. By exciting a non-equilibrium distribution of water molecules and then measuring the surface-sensitive sum-frequency response, the surface dynamics can be probed. This offers the opportunity for new insights into the interfacial hydrogen-bond network. Professor McGuire's group will employ new multidimensional and phase-sensitive techniques for the detection of sum-frequency signals to enhance the sensitivity to weak surface nonlinear optical processes. Investigations will address the differences in the dynamical properties of a range of chemically and physically important aqueous interfaces including hydrophobic and hydrophilic interfaces and aqueous interfaces characterized by varying concentrations of solutes such as salts.Understanding dynamics and vibrational couplings at aqueous interfaces will impact our understanding of a broad range of phenomena at aqueous interfaces, such as solvation and charge transfer, that are central to such varied processes as protein folding, electrochemical energy generation and storage, heterogeneous catalysis, and atmospheric chemistry. The techniques developed will also find application in studies of other interfacial and non-centrosymmetric bulk systems. Students involved in this project will receive training in vibrational and ultrafast spectroscopy and nonlinear optical techniques broadly applicable to studies of chemical and physical systems. Through activities such as engagement of high school teachers in research and hands-on workshops for K-12 teachers, the process and results of scientific discovery and an appreciation for a scientific understanding of water will be disseminated to students in K-12.