Piezomodulated Raman spectroscopy of molecular crystals: An experimental method for study of the anharmonic properties of solids

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Abstract
Consideration of phonon-phonon coupling induced by strain serves as impetus for developing a theoretical structure for piezomodulated Raman spectroscopy which can be used for experimental realization of the coupling. The direct relation of the coupling constant to generalized stress Gruneisen parameters is shown. These describe the crystal’s anharmonic properties such as the thermal expansivity and the temperature dependence of the phonon energies. Numerical calculations are performed for anthracene crystal which exemplify the use of the stress Gruneisen parameters as sensitive measures of anisotropy of intermolecular interactions. Further development shows how the measurement can be used to determine these parameters and how piezomodulated Raman spectroscopy can be exploited to examine the anharmonicity of the lattice.