Pressure Effect on Inter- and Intramolecular Vibrations of the p-Xylene Crystals

Abstract

Abstract The Raman active inter- and intramolecular vibrations of the [1H10]- and [2H10]p-xylene crystals were studied under various pressures between 1 atm and 7.5 GPa. The pressure effect of the frequency of the Raman bands due to the intermolecular vibrations indicates that the coupling between the intramolecular torsional vibration of the methyl group and the intermolecular rotational vibrations takes place under about 1 and 2.5 GPa in the [1H10]- and [2H10]p-xylene crystals, respectively. The calculated pressure-induced frequency shift of the intramolecular vibrations explains fairly well the observed frequency shifts and supports the conclusion given in the previous work that the contribution of the first-order differential of the intermolecular potential to the pressure-induced frequency shift is vanishingly small when the potential is well approximated.