Molecule-radiation and molecule-molecule processes in condensed media: a microscopic QED theory Original Research Article

A microscopic QED theory has been developed for the description of molecule-radiation and molecule-molecule processes in condensed molecular media. Adopting a polariton model, an explicit normal-mode expansion has been derived for the operator of the local displacement field. (It is the local displacement operator that describes the coupling of the individual molecules with the field.) The expansion manifestly embodies refractive influences, including, inter alia, local field contributions. To this end, the local field effects intrinsically emerge within the present formalism that systematically treats Umklapp processes; in addition, the theory accomoddates an arbitrary number of molecular levels contributing to the refractive index. The mode expansion is applicable for the investigation of a variety of molecule-radiation and molecule-molecule processes in condensed phases. In the present study, medium-induced modifications are analysed for spontaneous emission and linear absorption; application to the two-centre (bimolecular) processes are also discussed.