Collaborative Research: Detailed Mechanistic Pathways of Surface Catalysis using SERS Spectroscopy: A Joint Theoretical and Experimental Synergistic Approach

在化学系化学测量和成像（CMI）项目的支持下，南加州大学（USC）的Stephen Cronin教授和宾夕法尼亚州立大学（PSU）的Lasse Jensen教授将研究一种称为表面增强拉曼散射（SERS）的测量技术的物理机制。这项工作完成了理论和实验之间的循环，提供了催化反应过程中分子吸附在金属表面的详细量子力学图像。该项目使用基于一般sers的方法来研究与表面催化相关的反应机制，并朝着以亚微米空间分辨率成像催化表面化学反应性的目标发展。实验SERS光谱提供的信息在没有支持理论工作的帮助下，对潜在过程提供原子性的见解，这在一定程度上是有限的。因此，为了获得分子及其在表面上的反应的详细图像，包括分子与金属表面之间的电荷转移，区分物理吸附和吸附，建立关键的催化活性位点，确定表面结合的中间物质和催化反应的其他关键方面的相对重要性，在实验的同时进行理论计算是至关重要的。在本次合作项目中，由Stephen Cronin教授（USC）领导的实验研究小组将使用水浸透镜记录电化学工作条件下电极表面的SERS光谱，由Lasse Jensen教授（PSU）领导的理论研究小组将使用时间依赖密度泛函理论（TD-DFT）及相关方法模拟金属表面吸附的化学物质。理论计算和实验测量之间的直接对应有望为吸附质和金属表面之间电荷流动的基本假设提供可靠的测试。该团队正在测试他们的假设，即分子和金属表面之间的动态电荷流在SERS增强过程中起着重要作用，并可用于从依赖于模式的SERS增强因子中提取重要的化学信息。研究人员正在通过将产物形成与他们在电化学工作条件下记录的原位SERS光谱相关联来测试这一假设。他们还将检验一个假设，即SERS增强与催化活性相关或反相关。这一假设源于这样一种观点，即增强和催化活性都取决于给定的反应物或中间体与金属表面的结合程度，而这最终取决于发生在界面上的电荷转移量。此外，该团队计划根据他们了解到的动态电荷流和SERS活性之间关系的信息，使用不同振动模式的相对SERS增强来成像反应性和/或反应位点。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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 Measurement and Imaging (CMI) Program in the Division of Chemistry, Professors Stephen Cronin at the University of Southern California (USC) and Lasse Jensen at Pennsylvania State University (PSU) will investigate the physical mechanisms underlying a measurement technique called surface-enhanced Raman scattering (SERS). This work closes the loop between theory and experiment, providing a detailed quantum mechanical picture of the molecules adsorbed on metal surfaces during catalytic reactions. The project uses a general SERS-based approach to study reaction mechanisms associated with surface catalysis, and also toward the goal of imaging chemical reactivity of catalytic surfaces with sub-micron spatial resolution. The information provided by experimental SERS spectra is somewhat limited without the aid of supporting theoretical work to provide atomistic insight on the underlying processes. Therefore, it is crucial to carry out theoretical calculations in parallel with the experiments in order to obtain a detailed picture of the molecules and their reactions on surfaces, including the charge transfer between a molecule and the metal surface, to distinguish between physisorption and adsorption, to establish key catalytically active sites, and to identify surface-bound intermediate species and the relative importance of other key aspects of catalytic reactions. In this collaborative project, the experimental research group led by Professor Stephen Cronin (USC) will record the SERS spectra of electrode surfaces under electrochemical working conditions using a water immersion lens, and the theoretical research group led by Professor Lasse Jensen (PSU) will use time-dependent density functional theory (TD-DFT) and related methods to simulate adsorbed chemical species on metal surfaces. The direct correspondence between the theoretical calculations and experimental measurements in this effort promises to provide a robust test of the basic hypotheses underlying charge flow between the adsorbate and metal surface. The team is testing their hypothesis that dynamic charge flow between a molecule and the metal surface plays an important role in the SERS enhancement process and can be used to extract important chemical information from the mode-dependent SERS enhancement factors. The researchers are testing this hypothesis by correlating product formation with in situ SERS spectra that they record under electrochemical working conditions. They will also examine a hypothesis that the SERS enhancement is either correlated or anti-correlated with catalytic activity. This hypothesis stems from the idea that both the enhancement and the catalytic activity depend on the degree to which a given reactant or intermediate is bound to the metal surface, which is ultimately based on the amount of charge transfer that occurs at the interface. Additionally, the team plans to use the relative SERS enhancement of different vibrational modes to image reactivity and/or reactive sites based on the information they learn about the relationship between dynamic charge flow and SERS activity.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.