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We will focus on approaches which make use of light-matter interactions to alter the chemical behavior of a target molecular species. This is done through cavity coupling to a molecular vibration. Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity and energy relaxation. Here, we demonstrate frequency domain results for vibrational bands strongly coupled to optical cavities. We experimentally and numerically describe strong coupling between a Fabry-Pérot cavity and several molecular species (e.g., poly-methylmethacrylate, thiocyanate, hexamethyl diisocyanate). We investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of a urethane monomer. Rabi splittings are in excellent agreement with an analytical description using no fitting parameters. We show that coupling strength is a function of molecule/cavity mode overlap by systematically altering the position of a molecular slab throughout a first order cavity with results agreeing well with analytical and transfer matrix predictions. Further, remote molecule-molecule interaction will be explored by placing discrete and separated molecular layers throughout a cavity. In addition to establishing that coupling to an optical cavity modifies the energy levels accessible to the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied in steady state and dynamically.
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