  In this article, we address the optomechanical effects in surface-enhanced
resonant Raman scattering (SERRS) from a single molecule in a nano-particle on
mirror (NPoM) nanocavity by developing a quantum master equation theory, which
combines macroscopic quantum electrodynamics and electron-vibration interaction
within the framework of open quantum system theory. We supplement the theory
with electromagnetic simulations and time-dependent density functional theory
calculations in order to study the SERRS of a methylene blue molecule in a
realistic NPoM nanocavity. The simulations allow us not only to identify the
conditions to achieve conventional optomechanical effects, such as vibrational
pumping, non-linear scaling of Stokes and anti-Stokes scattering, but also to
discovery distinct behaviors, such as the saturation of exciton population, the
emergence of Mollow triplet side-bands, and higher-order Raman scattering. All
in all, our study might guide further investigations of optomechanical effects
in resonant Raman scattering.
