Cavity-Controlled Vibrational Dynamics and Chemical Reactivity with Quantum Strong Coupling

化学的核心目标是发现控制化学反应结果的新方法。 分子所处的环境可以决定分子如何甚至是否会发生化学反应。 溶于水中的盐酸（HCl）很容易分解成H+和Cl-离子，但溶于乙腈（C2 H3 N）等有机溶剂时基本保持完整。 有些反应只有在完全没有溶剂分子的情况下才能发生;因此化学家们通常会创造出比外太空更“空”的真空环境。 在这个项目中，由化学结构，动力学和机制-化学系的一个项目资助，密歇根大学的Kevin Kubarych教授和他的学生正在探索一种新的环境，这种环境在自然界中不存在，但也能够极大地改变化学反应的过程。研究人员发现，通过将反应分子放置在由两个平行镜子形成的空间内（它们的间隔非常小，大约是一根头发的宽度！）控制化学反应的力不同于装置外部的力。 该装置被称为光学谐振器，它可以以类似于将收音机调谐到正确频率以接收给定电台的方式进行调谐。 从事该项目的研究生研究人员正在从外部控制腔，以改变镜子之间分子的行为，最终目标是控制腔中发生的反应。学生们在实验科学和量子力学理论方面获得了宝贵的经验，这为理解分子和光学谐振腔之间的相互作用提供了框架。 除了对博士生进行正式培训外，该项目还需要为高中生开发量子力学教育模块。 Kubarych教授和他的学生正在为密歇根数学和科学学者开发一个为期两周的课程模块，该课程旨在让高中生接触数学和科学中令人兴奋的新概念和基本概念。这些模块允许学生通过动手实验和计算机模拟来学习激光和量子力学的基本概念。该项目采用超快二维红外光谱来跟踪最基本的化学转变之一的平衡动力学，围绕C-C单键旋转，而靶分子（1-氟-2-异氰酸基-乙烷）被限制在专门设计的扫描法布里-珀罗样品腔内。 核心假设是目标分子和腔形成光和物质的混合体（极化激元），并且腔条件可以提供控制化学反应的外部手段。 通过比较反应动力学以及腔内外异构体之间的平衡，可以确定反应能量面中强耦合的影响。 改变分子浓度允许直接控制与腔的耦合，并且使用压电换能器调谐腔长度允许腔谐振的系统变化。除了直接研究极化激元控制的基态化学反应性外，该项目还旨在测试强耦合下化学动力学的基本概念。具体来说，该项目致力于多模耦合、非均匀加宽以及强耦合改变非谐波耦合（表现为费米共振）的能力等新概念。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

A central goal of chemistry is to discover new ways to control the outcome of chemical reactions. The environment in which a molecule exists can determine how or even if the molecule will undergo a chemical reaction. Hydrochloric acid (HCl) dissolved in water readily dissociates into H+ and Cl- ions but remains largely intact when dissolved in an organic solvent like acetonitrile (C2H3N). Some reactions occur only in the complete absence of solvent molecules; chemists thus routinely create vacuum environments that are more “empty” than outer space. In this project, funded by the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professor Kevin Kubarych and his students at the University of Michigan are exploring a new type of environment that does not exist in nature, but which is also capable of dramatically altering the course of a chemical reaction. Researchers have discovered that by placing reacting molecules within a space formed by two parallel mirrors (their separation is very small, the width of roughly one human hair!) the forces that govern the chemical reaction are different than those outside of the device. The device is called an optical resonator and it can be tuned in a manner similar to how one tunes a radio to the right frequency to pick up a given radio station. The graduate student researchers working on this project are externally controlling the cavity to change the behavior of molecules between the mirrors, with the ultimate goal of controlling the reactions that occur in the cavity. The students are gaining valuable experience in experimental science and quantum mechanical theory, which provides the framework for understanding the interactions between molecules and optical resonator cavities. In addition to the formal training of doctoral students, the project also entails the development of educational modules in quantum mechanics for high school students. Professor Kubarych and his students are developing a two-week course module for the Michigan Math and Science Scholars, a program to expose high school students to exciting new and fundamental concepts in math and science. The modules allow students to learn about lasers and basic concepts in quantum mechanics via hands-on experiments and computer simulations.This project employs ultrafast, two-dimensional infrared spectroscopy to track the equilibrium kinetics of one of the most fundamental chemical transformations, rotation about a C-C single bond while the target molecule (1-fluoro-2-isocyanato-ethane) is confined within a specially designed scanning Fabry-Perot sample cavity. The central hypothesis is that the target molecule and cavity form a hybrid of light and matter (polaritons), and that the cavity conditions may provide an external means for controlling chemical reactions. By comparing the reaction kinetics as well as the equilibrium between the isomers inside and outside of the cavity, it is possible to determine the influence of strong coupling in the reaction energy surface. Varying the molecule concentration allows direct control over the coupling to the cavity and tuning the cavity length using piezoelectric transducers enables systematic variation of the cavity resonance. In addition to direct investigations of polariton-controlled ground state chemical reactivity, this project also aims to test basic concepts in chemical dynamics under strong coupling. Specifically, the project addresses new concepts in multi-mode coupling, inhomogeneous broadening, and the ability of strong coupling to alter anharmonic coupling manifested as Fermi resonances.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.