Cavity-Vibration Mixed States: Chemistry in Etalons

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Molecules typically vibrate at frequencies that correspond to infrared light (the wavelength range important in night vision technologies). Etalons are optical devices that consist of two parallel reflective metal plates whose spacing corresponds to infrared wavelengths (roughly 1 micrometer to 1 millimeter). If molecules are placed inside an etalon with just the right spacing, their vibrational properties can change. The molecule+cavity system is called a "mixed state", an interesting combination of light and matter. Since molecular vibrations have very important roles in how molecules undergo chemical reactions, there is the possibility that by simply changing cavity spacings, we can change vibrational properties of the molecules as well as their reactivity. In this project supported by the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professor James Coe and his graduate students at The Ohio State University seek to demonstrate the feasibility of making mixed states of infrared etalon cavity modes and condensed phase vibrations to change reaction rates. "Chemistry in Etalons" would represent an entirely new field of chemistry, and may offer significant opportunities for producing chemicals more efficiently. The students involved in this project are gaining experience in both advanced optical spectroscopy and theoretical chemistry calculations. Professor Coe also plans to collaborate with professors at Cal State Dominguez Hills, which has an ethnically and economically diverse student body. The project begins with the construction of alignable and adjustable etalons in order to produce etalon fringes of variable width. The etalon is filled with a condensed phase material which has vibrations of interest. Etalon fringes are angle-tuned into resonance with the vibrations and an infrared transmission spectrum is recorded which enables the measurement of Rabi splittings--the energy difference between the mixed states of cavity and vibration. In order for the measured Rabi splittings to be related to fundamental quantum mechanical properties such as dipole derivatives, our models show that the etalon fringe width and vibrational transition width should be the same. Since vibrational features show a wide range of widths, there is a need to be able to carefully design etalons that match molecular vibrations. This project is focusing on: 1) the effect of etalon fringe width on measured Rabi splittings, 2) the conjugated double bond system of CO2 in water, and 3) broadened gas phase systems, all in order to establish the relation of these measurements to fundamental quantum mechanical properties. Finally, selected reactions are being studied within the wavelength-scale etalon cavity as informed by the previous results and as followed by infrared transmission spectra that allow assessment of whether the rates of reactions can be affected by mixed states of cavities and vibrations. While this project seeks fundamental insights into etalon-molecule mixed states, there is a potential for implications in a wide range of technological applications, including chemical and nanoparticle sensors, and even in heterogeneous catalysis (e.g., the etalon mirrors could serve as catalysts or catalyst supports).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.