The neutral exciton model for triplet factor-group splittings in aromatic crystals

The calculation of triplet factor-group splitting in benzene, naphthalene and anthracene crystals has been reexamined. Substantially revised values of the two-centre exchange integrals in the neutral exciton model give much improved agreement with experiment in benzene; the need for refinements such as ion-pair contributions is marginal. In naphthalene and anthracene the new values are little altered. Thus, in benzene and naphthalene the neutral exciton model appears to be adequate; in anthracene the previously noted disagreement with experiment remains.Multicentre intermolecular integrals can be neglected in the examples studied, and are unlikely to be important in other aromatic crystals.