  We employ an exact quantum mechanical simulation technique to investigate a
model of cavity-modified chemical reactions in the condensed phase. The model
contains the coupling of the reaction coordinate to a generic solvent, cavity
coupling to either the reaction coordinate or a non-reactive mode, and the
coupling of the cavity to lossy modes. Thus, many of the most important
features needed for realistic modeling of the cavity modification of chemical
reactions are included. We find that when a molecule is coupled to an optical
cavity it is essential to treat the problem quantum mechanically in order to
obtain a quantitative account of alterations to reactivity. We find sizable and
sharp changes in the rate constant that are associated with quantum mechanical
state splittings and resonances. The features that emerge from our simulations
are closer to those observed in experiments than are previous calculations,
even for realistically small values of coupling and cavity loss. This work
highlights the importance of a fully quantum treatment of vibrational polariton
chemistry.
