Isotopic mixed crystal exciton spectra in the far infrared: Naphthalene

Abstract

The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene- h 8 and d 8 were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B 3u, A u and B 1u vibrational exciton bands were found to be in the separated band limit. The lowest energy B 3u “butterfly” mode with its large (15 cm −1) exciton splitting was found to agree well with CPA calculations of mixed crystal spectra. A peak at 185 cm −1 was also assigned as a peak in the vibrational exciton density-of-states of the B 3u mode.