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Hydrostatic pressure and temperature effect on the Raman spectra of the molecular crystal 2-amine-1,3,4-thiadiazole

Texto completo
Autor(es):
de Toledo, T. A. [1] ; da Costa, R. C. [2] ; Bento, R. R. F. [1] ; Pizani, P. S. [3]
Número total de Autores: 4
Afiliação do(s) autor(es):
[1] Univ Fed Mato Grosso, Inst Fis, BR-78060900 Cuiaba, MT - Brazil
[2] Univ Fed Campina Grande, Ctr Ciancias & Tecnol Agroalimentar, BR-58840000 Pombal, PB - Brazil
[3] Univ Fed Sao Carlos, Dept Fis, BR-13565905 Sao Carlos, SP - Brazil
Número total de Afiliações: 3
Tipo de documento: Artigo Científico
Fonte: Journal of Molecular Structure; v. 1156, p. 127-135, MAR 15 2018.
Citações Web of Science: 2
Resumo

The structural, thermal and vibrational properties of the molecular crystal 2-amine-1,3,4-thiadiazole (ATD) were investigated combining X-ray diffraction, infrared spectroscopy, Raman scattering (in solid and in solution) and thermal analysis as experimental techniques and first principle calculations based on density functional theory using PZ, BLYP in condensed-phase and B3LYP/cc-pVTZ in isolated molecule methods. The structural stability and phonon anharmonicity were also studied using Raman spectroscopy at different temperatures and hydrostatic pressures. A reasonable agreement was obtained between calculated and experimental results. The main difference between experimental and computed structural and vibrational spectra occurred in the intermolecular bond distance N-H center dot center dot center dot N and stretching modes of NH2. The vibrational spectra were interpreted and assigned based on group theory and functional group analysis assisted by theoretical results, which led to a more comprehensive knowledge about external and internal modes at different thermodynamic conditions. As temperature increases, it was observed the line-width increases and red-shifts, indicating a phonon anharmonicity without a temperature induced phase transition in the range 10-413 K. However, ATD crystal undergoes a phase transition in the temperature range 413-475 K, as indicated by thermal analysis curve and Raman spectra. Further-more, increasing pressure from ambient to 3.1 GPa, it was observed the splitting of the external Raman bands centered at 122 cm(-1) (at 0.2 GPa), 112 cm(-1) (1.1 GPa), 93 cm(-1) (2.4 GPa) in two components as well as the appearance of new band near 50 cm(-1) at 1.1 GPa, indicating a possible phase-transition. The blue-shift of the Raman bands was associated to anharmonicity of the interatomic potential caused by unit cell contraction. (C) 2017 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 13/07793-6 - CEPIV - Centro de Ensino, Pesquisa e Inovação em Vidros
Beneficiário:Edgar Dutra Zanotto
Linha de fomento: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs