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Reports of altered chemical phenomena under vibrational strong coupling, including reaction rates, product distributions, intermolecular forces, and cavity-mediated vibrational energy transfer, have been met with a great deal of skepticism due to several irreproducible results and the lack of an accepted theoretical framework. In this work, we add some insight by identifying a UV–vis measurement artifact that distorts observed absorption peak positions, amplitudes, and consequently, chemical reaction rates extracted in optical microcavities. We predict and characterize the behavior of this artifact using the Transfer Matrix (TM) method and confirm its presence experimentally. We then present a correction technique whereby an effective molar absorption coefficient is assigned to an absorbing species within the cavity. These revelations have important implications for many existing examples of cavity-modified chemistry and establishing best practices for carrying out robust future investigations.

In this article, we developed a theory describing surface exciton polaritons (SEPs) that accounts for the spatial dispersion of the dielectric constant connected with exciton momentum. Due to strong coupling between light and bulk excitons in the frequency separation, ℏωLT, between the longitudinal and transverse excitons, the SEP is formed and behaves as partially light and partially matter. The dispersion of the SEP was found through a combined solution of Maxwell’s and Thomas-Hopfield’s equations. The analytical theory describes SEPs at any bulk exciton/vacuum interface and provides its complete dispersion if one knows ℏωLT, the exciton effective mass, M, and the high-frequency dielectric constant, κ∞. The presented theory is in excellent agreement with the only numerical modeling of this problem, which was conducted for SEPs at a ZnO/vacuum interface. Calculations show the spatial dispersion of the dielectric constant leads to rather small broadening of the photon-like quasi-particle and suggest using SEPs for long-range coherence transfer. The theory was used to describe SEP dispersion in CsPbCl3and CsPbBr3perovskites.