Terahertz Time-Domain Spectroscopy and Low-Frequency Raman Scattering of Crystalline and Glassy Pharmaceutical Indapamide

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on crystalline and glassy states of pharmaceutical indapamide (IND). We have determined the real and imaginary part of the complex dielectric constants and the imaginary part of the Raman susceptibility in the THz region. Several phonon peaks have been observed in the crystalline IND and the mutual exclusion principle of infrared and Raman spectroscopy holds in the measured frequency range. In a glassy state of IND, a broad absorption peak has been observed in both the THz and the Raman spectra with different spectral shape, and this disagreement indicates that the far-infrared and Raman light-vibration coupling constants are different in the glassy IND. A clear boson peak has been observed in the Raman spectra of the glassy IND at about 0.5 THz.