Exciton–Photon Coupling in Crystalline Anthracene

The form of the exciton–photon dispersion curve in an infinite crystal of anthracene is predicted by calculating the positions of the k = 0 polariton and Coulombic exciton levels for each vibronic level of the 3800-Å free molecule transition. Intermolecular interactions are restricted to dipole–dipole interactions and the 2500-Å system treated as if it were a single level. An exact classical solution of the problem posed here is employed in the calculations thereby circumventing perturbation theory. A slightly improved calculation of the dipole Davydov splitting is also reported.