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

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

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.