Transient studies of vibration-cavity polaritons

Vibration-cavity polaritons, which are produced by strong coupling between an optical cavity and a molecular vibration, have been shown to modify chemical reaction rates and branching ratios. However, the underlying mechanisms for the observed effects are poorly understood. In order to gain insight into how these polaritons might alter molecular processes, we have used ultrafast pump-probe and two-dimensional infrared (2DIR) spectroscopies to characterize coherent and incoherent polariton excited state behaviors. Our earlier studies on tungsten hexacarbonyl (W(CO)₆) strongly coupled to a Fabry-Pérot cavity demonstrated that much of the response is due to reservoir or uncoupled excited state absorption as well as polariton contraction. In recent studies, we have used 2DIR and spectrally filtered pump-probe studies on the nitroprusside anion (Fe(CN)₅NO^2-) in methanol to determine the transition frequencies and dynamics of polariton excited states allowing us to extract polariton dephasing timescales, which follow those of the cavity and molecule, as well as incoherent polariton population which decays at a significantly longer timescale. These studies reveal novel aspects of vibration-cavity polaritons that may reveal how they impact energy transfer, photophysics, and chemistry.