Direct Observation of the Entire Exciton Band of the First Excited Singlet States of Crystalline Benzene and Naphthalene

The density-of-states functions for the exciton bands of the first excited singlet states of crystalline benzene and naphthalene have been determined experimentally. The experimental density functions were derived from spectral data involving exciton-band↔exciton-band transitions. The experimental results for naphthalene have been compared with calculations based on the octopole model. Using a Frenkel dispersion relation and various sets of coupling constants, density functions have been calculated and compared with the experimental results. For benzene these calculations show that the “optically forbidden” Au component lies between 37 815 and 37 875 cm−1. From the temperature dependence of transitions, phonon contributions have been estimated. It is found that the experimentally derived density function is temperature independent below ∼30°K.