  We demonstrate a macro-coherent regime in molecular exciton-polariton
systems, where nonequilibrium polariton Bose--Einstein condensation coexists
with macroscopically occupied vibrational states. Strong vibronic coupling in
molecules induces an effective optomechanical interaction between cavity
polaritons and vibrational degrees of freedom of molecules, leading to
vibrational amplification in a resonant blue-detuned configuration. This
interaction maps out properties of the condensate to vibrational states,
offering a novel approach to achieve vibrational condensation with potential
applications in cavity-controlled chemistry, nonlinear and quantum optics.
