Re-examination of the theoretical interpretations of the spectra of crystalline benzene and naphthalene

In order to explain the crystal spectra of naphthalene and benzene, a theory is presented in which the combined effects of charge delocalization and interactions via transition octupole moment coupling are important. Charge delocalization, achieved by means of configuration interaction of the lowest crystal chargetransfer states with the lowest singlet neutral exciton state, is predicted to explain most of the environmental shift and to contribute approximately one-third of the Davydov splitting. The transition-octupole- transitionoctupole interactions, on the other hand, are predicted to induce the remaining two-thirds of the splitting and to determine the polarization ratios for the different Davydov components. Either of the two interactions alone shows drawbacks if it is used to explain the spectra, but when combined, the two interactions lead to a theory in good agreement with experiment.