Theory of thermally activated polaritonic chemistry

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Polaritonic chemistry is an emerging paradigm at the intersections of chemistry, materials science and photonics. Its main promise is to steer and control the properties of reactive processes such as yield, selectivity and rates through the coupling of molecules or molecular ensembles to confined electromagnetic fields.Such confined electromagnetic fields can be realised in various ways, for example by cavities enclosed by light-reflecting surfaces. Recent experiments in micro-cavities [Thomas et. al, Angew. Chem. 55, 11462 (2016)] report important modifications of thermal rate constants owing to the effect of confined electromagnetic modes coupled to molecular vibrations of the reactants and transition state. Currently, the mechanisms by which vibrationally coupled cavity-ensemble hybrid systems affect thermal chemical reactions are poorly understood. For example, experimental rate measurements involving molecules coupled to a cavity have been interpreted through the glass of traditional transition state theory, thus extracting, e.g., enthalpic and entropic contributions to the total thermal rate constant. However, these experimental interpretations are slippery, as a microscopic picture that explains the interactions and energy redistribution mechanisms in such systems, and a microscopic reaction rate theory that can explain those rates, are missing.The main aim of this project is hence to advance towards a theoretical understanding of thermally activated chemical reactions in vibrationally coupled cavity-molecular ensembles (VCE). This encompasses three main areas: (I) characterisation of the infrared spectroscopy of cavity-molecular ensembles and development of theoretical approaches to calculate the corresponding spectra; (2) development of a microscopic picture of the energy redistribution processes and couplings mediated by the cavity mode(s) and which have an effect in modifying its reactive properties and (3) calculation of chemical reaction rates that include the effects of the cavity coupling.Advances in these areas shall enable future progress, both experimental and theoretical, in the directions of steering and controlling chemical reactions in the presence of confined electromagnetic fields.