High pressure and temperature effects on the molecular crystal 2‐amino‐5‐methyl‐1,3,4‐thiadiazole

We report a detailed study of 2‐amino‐5‐methyl‐1,3,4‐thiadiazole (C3H5N3S) using Raman and infrared spectroscopy techniques combined with density functional theory at the condensed phase and for the isolated molecule in gas phase. This information provides the vibrational mode assignments, which wil...

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Bibliographic Details
Published in:	Journal of Raman spectroscopy Vol. 49; no. 10; pp. 1713 - 1721
Main Authors:	de Toledo, Thiago A, Bento, Ricardo R F, Cunha, Thiago R, Pizani, Paulo S
Format:	Journal Article
Language:	English
Published:	Bognor Regis Wiley Subscription Services, Inc 01-10-2018
Subjects:	2‐amino‐5‐methyl‐1,3,4‐thiadiazole Anharmonicity Density functional theory DFT calculations Discontinuity Doppler effect External pressure High pressure Infrared spectroscopy phase transition Phase transitions Pressure Pressure effects Raman spectra Raman spectroscopy Red shift Spectrum analysis Temperature effects thiadiazole Thiadiazoles Wavelengths
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Summary:	We report a detailed study of 2‐amino‐5‐methyl‐1,3,4‐thiadiazole (C3H5N3S) using Raman and infrared spectroscopy techniques combined with density functional theory at the condensed phase and for the isolated molecule in gas phase. This information provides the vibrational mode assignments, which will give a basis for the better understanding of the changes in the Raman spectra due to the temperature (from 10 to 413 K) and pressure (up to 9.2 GPa at room temperature) variation. The anharmonic effects in the Raman spectra of C3H5N3S were identified in the temperature range 10–393 K, corresponding to wavenumber shift, changes in the line intensity, and linewidth. The crystal undergoes to phase transition in the temperature range 403–413 K, as indicated by the discontinuity in the dω/dT of several Raman bands in external and internal mode region. As pressure increases, a notable change in the Raman spectra occurs at 1.6 GPa, suggesting a second‐order phase transition attributed to splitting, discontinuity in the dω/dP, and red shift of the external and internal Raman modes. All changes in the Raman spectrum were reversible after releasing pressure. We report a detailed study of 2‐amino‐5‐methyl‐1,3,4‐thiadiazole using Raman and infrared spectroscopy techniques combined with density functional theory at the condensed phase and for the isolated molecule in gas phase. This information provides the vibrational mode assignments, which will give a basis for the better understanding of the changes in the Raman spectra due to the temperature (from 10 to 413 K) and pressure (up to 9.2 GPa at room temperature) variation.
ISSN:	0377-0486 1097-4555
DOI:	10.1002/jrs.5451