Coupling between lattice and intramolecular modes in 9,10-dimethylanthracene: Raman spectra under pressure and quasi-harmonic lattice dynamics calculations

Raman phonon spectra of 9,10-dimethylanthracene crystals have been measured as a function of pressure in the range 0–10 GPa for both lattice and intramolecular modes. Quasi-harmonic lattice dynamics calculations have been used to analyze the effects of the vibrational degrees of freedom on the pressure dependence of the crystallographic structure and phonon wave numbers. We find that the coupling between lattice and intramolecular vibrations contributes significantly to the pressure dependence of the phonon spectra, which is accurately reproduced by the calculations. Vibrational effects on the structure, instead, are less significant.