Chemical Applications of Floquet State Spectroscopy

About This Grant

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor John Wright at the University of Wisconsin-Madison is developing a new technology called Floquet state spectroscopy. It will allow synthetic chemists to use lasers to discover the vibrational modes and electronic states that control their chemical reactions. Floquet state spectroscopy fulfils a dream for creating an optical analogue of NMR that can also coherently control chemical reactions. NMR itself is based on controlling Floquet states. Floquet states are a non-equilibrium, non-adiabatic entanglements of multiple quantum states where the couplings between states changes the states. NMR uses the entangled and coupled nuclear spins of 1H, 13C, etc. to control the spin states, so flipping the spin on a 13C will change the frequency of the neighboring 1H. In the same way, Floquet state spectroscopy uses entangled molecular vibrational and electronic states where the coupling is much stronger and even controls the molecular structure. Professor Wright and his students will employ higher order Floquet state spectroscopy to investigate the multidimensional potential energy surfaces of cobalamin and methyl-cobalamin including their Co-C and Co-N axial ligand stretch motions that are involved in both the photodissociation, and the 12 orders of magnitude increase in the enzymatic rate of the Co-C bond scission. Their work will have a Broad Impact on, not only the field of synthetic chemistry, but also much of modern technology because understanding the factors that control a technology at the most fundamental quantum mechanical level are also central for understanding how that technology can be advanced. The development of new quantum information technologies is an important example of how the long coherence times of a Floquet state can advance quantum science. Floquet state spectroscopy is closely related to coherent multidimensional spectroscopy (CMDS). Just as NMR can be performed using frequency or time domain methods, so also can CMDS. Time domain CMDS itself has become popular because its femtosecond bandwidth can measure the free induction decay of single quantum coherences on ultrafast time scales. However, the short pulse bandwidth strongly limits multidimensional spectral features to narrow ranges and the brightest transitions. Floquet state spectroscopy uses higher order quantum coherences to create multidimensional spectra over the entire range of electronic and vibrational resonances. The Floquet state is interrogated by scanning the excitation frequencies across molecular resonances. The resonant enhancements of the higher order quantum coherence amplitudes are multiplicative, so even weak spectral features become visible. By driving the Floquet state over long time periods compared to the time scales for molecular atomic motion, the entanglement and coupling between states in the Floquet state results in changes in the electron distribution, the bond energies, the molecular structure of the electronic state, and the molecular fundamentals, overtones, and combination band modes. These include the same modes that form the basis for coherent control of chemical reactions. Rather than using the thermally driven vibration modes that drive reactions, Floquet states can coherently drive and control the same modes and the reactions. The multiplicative resonance enhancements that occur in higher order processes allow the observation of the anharmonicities of the higher order overtones and combination bands that are needed to directly measure the higher potential energy surfaces that control molecular reactions. Dissemination of the Broader Impact technology has been enhanced by collaborations with UW-Madison synthetic chemistry Professors Thomas Brunold and John Berry and theoretical chemistry Professor Yang Yang. 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.