Chemical Applications of Floquet State Spectroscopy

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With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Professor John Wright and his research group at the University of Wisconsin are developing a new technique called Floquet state spectroscopy. Floquet state spectroscopy is the fully coherent optical analogue of nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopy, which uses radio waves to interact with atoms and molecules, is used extensively in science and technology because of its ability to characterize complex samples. Floquet state spectroscopy promises similar capabilities using light, rather than radio waves, to interact with molecules. The goal of this project is to apply Floquet state spectroscopy to a range of chemical systems that are important in practical applications of chemistry. For example, Professor Wright and his team use the technique to determine how the atoms within a molecule must bend, twist, and stretch in order to change the bonds that hold the molecule together. This information forms the heart of synthetic chemistry because it identifies the mechanisms responsible for a reaction. The team also works with collaborators from academic, industrial, and government laboratories to demonstrate the unique capabilities of Floquet state spectroscopy for characterizing complex materials and to show how the technique can be applied in many fields of science and technology. The broader impacts of the project include wide dissemination of this new technology, student training opportunities, and a collaboration with Spelman College that engages minority students in summer research projects on Floquet state spectroscopy.Floquet state spectroscopy measures the response of a system based on simultaneously driven multiple vibrational and electronic molecular states. The resulting quantum mechanically entangled superposition state emits light according to the wavevector combinations of the Floquet states. Scanning the driving frequencies across resonances of a molecule results in multiplicative enhancements of the output light beams and thus provides a way to measure multidimensional spectra. A primary focus of this research project is using Floquet state spectroscopy to probe the mechanisms of chemical reactions. Creating a Floquet state that contains the same vibrational and electronic states as those driven by chaotic thermal motions allows direct observation and control of a reaction. Cobalamin and a Ru-Ru metal-metal complex are two model compounds that the team is using to test the ability of Floquet state spectroscopy to probe reaction mechanisms. In cobalamin, the challenge is to understand the factors responsible for the 12-orders of magnitude change in the scission rate of the C-Co bond upon binding with a substrate. In the ruthenium complex, the challenge is understanding the mechanism for the amination of C-H bonds. Dissemination of the technology includes working with collaborators to apply Floquet state spectroscopy for complex polymeric materials characterization, disposal of actinide nuclear waste in glasses, femtosecond stimulated Raman studies of photochemical reactions, and development of medical diagnostics for pancreatic cancer. Additional broader impacts include advanced training for graduate students as well as the efforts to broaden participation through the collaboration with Spelman College.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.