Knowledge Bank

The visible and near ultraviolet absorption spectrum of acenaphthylene has been studied in the vapour phase, in the pure crystal, and as an oriented guest in acenaphthene, naphthalene, durene, and fluorene host crystals. Crystal spectra were measured with polarized light at low temperature; the pure crystal spectrum was interpreted in the light of an x-ray study which shows that the molecular and crystal $C2$ axes coincide. Sharp vibrational structure, dominated by a $1375cm-1$ progression polarized perpendicular to the $C2$ axis, is observed for the weak $4700\backslash AA$ system in the acenaphthene mixed crystal, although bands in the pure crystal spectrum are broad. Stronger systems at 3400 and 3$230AA$ are marked by moderately sharp vibrational bands in the vapour and mixed crystal spectra. The vibrational structure and polarizations of the various systems will be discussed.