  We present a reaction/diffusion model for the formation of a lower polariton
condensate in a micro cavity containing an organic semiconducting molecular
crystalline film. Our model--based upon an anthracene film sandwiched between
two reflecting dielectric mirrors--consists of three coupled fields
corresponding to a gas of excitons created by an external driving pulse, a
reservoir of vibron states formed by the coupling between a ground-state
vibrational model and a cavity photon, and a lower polariton condensate. We
show that at finite temperature, the presence of the vibron reservoir can
augment the exciton population such that a lower critical pumping threshold is
required to achieve condensation.
