Inelastic neutron scattering spectrum of p-terphenyl

The far infra-red1 and Raman2 spectra for single crystals of p-terphenyl have recently been taken. The assignments are ambiguous because more lines are observed in the optical experiments than could be expected from simple group theory arguments for an ordered crystal. We have taken the inelastic neutron scattering (i.n.s.) spectrum of polycrystalline p-terphenyl in order to throw light on these since the scattering and vibrational amplitude weighting if i.n.s. emphasizes quite different features to optical selection rules.