The crystal spectra of phenanthrene and phenanthrene- d 10 near 3400 Å

Abstract

The weak absorption system of phenanthrene near 3400 Å has been measured in the vapour, pure crystal, and mixed crystal spectra for both phenanthrene- h 10 and - d 10 . The assignment A 1 — A 1 is confirmed. Except for a small number of weak vibronic bands the pure electronic and vibrationally induced components have the same polarization, along the symmetry axis, showing that the perturbing vibration is totally symmetrical. The vapour spectra in 50 m paths at 90 °C show absorption envelopes similar to solution spectra, with a small number of sharp features of uncertain assignment. In the pure crystal the pure electronic origin band is split by 59 cm -1 , the same for both isotopic species within the experimental limits of ± 5 cm -1 . Frequencies, intensities, and polarization ratios are reported for pure crystals, and for mixed crystals in fluorene and biphenyl as hosts. The results are analysed and discussed in relation to previously studied vibrationally induced transitions in benzene and naphthalene.