Isotopic mixed crystal exciton spectra in the far infrared: Naphthalene

The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene-h8 and d8 were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B3sub(u), Asub(u) and B1sub(u) vibrational exciton bands were found to be in the separated band limit. The lowest energy B3sub(u) 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 B3sub(u) mode. (orig.)