Competition between inter- and intra- molecular energy exchanges in a simple quantum model of a dimer

We propose a fully quantum model to describe the dynamics of a possible radiationless energy transfer process between identical and nearly localized molecules or monomers coupled through a dipole-dipole term. The system is studied as an environmentally isolated dimeric pair and we find that its dynamics exhibits a competition between the process ruling out the transfer of energy among different degrees of freedom of a given monomer and the one steering the intermolecular passage of excitations from a monomer to the other one. Such a competition is quantitatively characterized investigating on the temporal behaviour of quantum covariances of some couples of appropriate observables having a clear physical meaning.