Molecular reorientations and intermolecular interactions: Raman spectra of the three crystalline phases of p‐dichlorobenzene

The three crystalline phases of p‐dichlorobenzene (DCB) are related to each other primarily by molecular reorientations. In order to examine the anisotropy in the crystal interactions, the effect of these molecular reorientations on the phonon dispersion and the internal vibrational exciton splitting is investigated with Raman spectroscopy. Isotopically mixed crystals (DCB‐h₄:DCB‐d₄) are used to measure the phonon dispersions and the vibrational exciton splittings. The results obtained show that these dynamic properties are highly sensitive to molecular reorientation, revealing an anisotropy in the crystal interactions. The anisotropy in the crystal interaction is also found to be mode selective.