Raman phonon spectra and lattice dynamics of 7-methoxycoumarin under pressure

Raman phonon spectra of 7-methoxycoumarin in the lattice phonon region have been measured in the range 0–5 GPa. A model atom-atom Buckingham potential has been determined to calculate structural parameters and Raman-active lattice phonons at ambient conditions and under pressure up to 14 GPa. The agreement with experiment is satisfactory. Results are discussed with reference to the mechanism of the non-topochemical photodimerization which is confirmed to occur via defect sites of the crystal rather than as a phonon-assisted process.