The high pressure response and structural stability of crystalline racemic (RS) ibuprofen up to 7 GPa are explored by Raman spectroscopy, employing diamond anvil cells for the pressure application and glycerol as the pressure transmitting medium. Two independent high pressure experiments were performed with practically identical results. Both intermolecular vibrations (associated with weak van der Waals interactions and hydrogen bonding between ibuprofen molecules) and intramolecular vibrations (associated with strong covalent bonding within the ibuprofen molecule) are monitored as a function of pressure, with the former being far more susceptible to volume contraction. The pressure dependence of the Raman peak frequencies undergoes two distinct changes at ~2 and ~6 GPa, indicating the occurrence of pressure-induced structural modifications of ibuprofen. Based on the high pressure Raman data for the intermolecular vibrations of the RS ibuprofen below 2 GPa, a zero pressure value for the bulk modulus of ~7.5 GPa is also extracted.
Siavou et al. (Sat,) studied this question.