  The modification of thermal chemical rates in Fabry-Perot cavities, as
observed in experiments, still poses theoretical challenges. While we have a
better grasp of how the reactivity of isolated molecules and model systems
changes under strong coupling, we lack a comprehensive understanding of the
combined effects and the specific roles played by activated and spectator
molecules during reactive events. In this study, we investigate an ensemble of
randomly oriented gas-phase HONO molecules undergoing a cis-trans isomerization
reaction on an ab-initio potential energy surface. Using the classical reactive
flux method, we analyze the transmission coefficient and determine conditions
that lead to accelerated rates within the collective regime. We identify two
main mechanisms at work: firstly, spectator molecules enhance the cavity's
ability to dissipate excess energy from the activated molecule post-reactive
event. Additionally, the interaction between spectator molecules and the cavity
gives rise to the creation of polaritonic modes. These modes then interact with
the activated molecule at a shifted resonance frequency.
