Raman spectra of captopril under high pressure

Abstract In the present study, a systematic investigation on vibrational properties of captopril (C 9 H 15 NO 3 S) single crystal under pressure is presented. At first, it is used density functional theory calculation in order to furnish the assignment of the normal modes as observed through Raman spectroscopy. In the second part of the paper, it is shown the Raman spectra of captopril for several pressures up to 6.7 GPa in the spectral range from 50 to 3300 cm −1 . The study indicates that the captopril molecules assumes the trans conformation in all pressure range investigated. The modes appearing in the low wavenumber region of the spectrum suggest the crystal undergoes a phase transition between 2 and 3 GPa. Additionally, a softening of the C O bond of both amide and carboxylic group is observed up to approximately 2.7 GPa and after this pressure a stiffiness is noted. Finally, is verified a disorder associated with the CH group during compression.