  A quantum system composed of a molecule and an atomic ensemble, confined in a
microscopic cavity, is investigated theoretically. The indirect coupling
between atoms and the molecule, realized by their interaction with the cavity
radiation mode, leads to a coherent mixing of atomic and molecular states, and
at strong enough cavity field strengths hybrid atom-molecule-photon polaritons
are formed. It is shown for the Na$_2$ molecule that by changing the cavity
wavelength and the atomic transition frequency, the potential energy landscape
of the polaritonic states and the corresponding spectrum could be changed
significantly. Moreover, an unforeseen intensity borrowing effect, which can be
seen as a strong nonadiabatic fingerprint, is identified in the atomic
transition peak, originating from the contamination of the atomic excited state
with excited molecular rovibronic states.
