Intramolecular and Low-Frequency Intermolecular Vibrations of Pentacene Polymorphs as a Function of Temperature

Single crystals of pentacene with different morphologies (polymorphs C and H ) have been studied by Raman spectroscopy as a function of temperature from 79 to 300 K. All Raman active lattice modes and a range of low-frequency intramolecular modes have been identified and assigned. The experiments are compared with quasi harmonic lattice dynamics (QHLD) calculations of the crystallographic structures and vibrational frequencies as a function of temperature. Experiments and calculations both indicate that the two polymorphs are stable over a wide temperature range.