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An inelastic neutron scattering, Raman, far-infrared, and molecular dynamics study of the intermolecular dynamics of two ionic liquids

Texto completo
Autor(es):
Lima, Thamires A. [1, 2] ; Paschoal, Vitor H. [2] ; Freitas, Rafael S. [3] ; Faria, Luiz F. O. [2] ; Li, Zhixia [1, 4] ; Tyagi, Madhusudan [5, 6] ; Ribeiro, Mauro C. C. [2]
Número total de Autores: 7
Afiliação do(s) autor(es):
[1] Univ Illinois, Beckman Inst Adv Sci & Technol, Urbana, IL 61801 - USA
[2] Univ Sao Paulo, Lab Espectroscopia Mol, Dept Quim Fundamental, Inst Quim, BR-05513970 Sao Paulo, SP - Brazil
[3] Univ Sao Paulo, Inst Fis, BR-05314970 Sao Paulo, SP - Brazil
[4] Univ Illinois, Dept Nucl Plasma & Radiol Engn, Urbana, IL 61801 - USA
[5] NIST, NIST Ctr Neutron Res, Gaithersburg, MD 20899 - USA
[6] Univ Maryland, Dept Mat Sci & Engn, College Pk, MD 20742 - USA
Número total de Afiliações: 6
Tipo de documento: Artigo Científico
Fonte: Physical Chemistry Chemical Physics; v. 22, n. 16, p. 9074-9085, APR 28 2020.
Citações Web of Science: 0
Resumo

The intermolecular dynamics in the THz frequency range of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, {[}N-1114]{[}NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, {[}N-1444]{[}NTf2], were investigated by a combined usage of inelastic neutron scattering (INS), Raman, and far-infrared (FIR) spectroscopies and the power spectrum calculated by molecular dynamics (MD) simulations. The collective dynamics of the simulated systems is also discussed by the calculation of time correlation functions of charge and mass currents that are projected onto acoustic- and optic-like motions. The INS and Raman measurements have been performed as a function of temperature in the glassy, crystalline, and liquid phases. The excess in the vibrational density of states over the expectation of the Debye theory, the so-called boson peak, is found in the INS and Raman spectra as a peak at similar to 2 meV (similar to 16 cm(-1)) and also in the direct measurement of heat capacity at very low temperatures (4-20 K). This low-frequency vibration is incorporated into the curve fits of Raman, FIR, and MD data at room temperature. Fits of spectra from these different sources in the range below 100 cm(-1) are consistently achieved with three components at ca. 25, 50, and 80 cm(-1), but with distinct relative intensities among the different techniques. It is proposed as the collective nature of the lowest-frequency component and the anion-cation intermolecular vibration nature of the highest-frequency component. The MD results indicate that there is no clear distinction between acoustic and optic vibrations in the spectral range investigated in this work for the ionic liquids {[}N-1114]{[}NTf2] and {[}N-1444]{[}NTf2]. The analysis carried out here agrees in part, but not entirely, with other propositions in the literature, mainly from optical Kerr effect (OKE) and FIR spectroscopies, concerning the intermolecular dynamics of ionic liquids. (AU)

Processo FAPESP: 19/00207-0 - Teoria do funcional da densidade aplicada a dinâmica vibracional de cristais de sistemas iônicos.
Beneficiário:Vitor Hugo Paschoal
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
Processo FAPESP: 15/16191-5 - Pesquisas em novos materiais envolvendo campos magnéticos intensos e baixas temperaturas
Beneficiário:Gennady Gusev
Linha de fomento: Auxílio à Pesquisa - Temático
Processo FAPESP: 15/05803-0 - Estrutura de líquidos iônicos em alta pressão
Beneficiário:Luiz Felipe de Oliveira Faria
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
Processo FAPESP: 16/21070-5 - Espectroscopia vibracional com resolução espacial
Beneficiário:Mauro Carlos Costa Ribeiro
Linha de fomento: Auxílio à Pesquisa - Temático
Processo FAPESP: 14/15049-8 - Estudo por espectroscopia Raman da transição vítrea de líquidos iônicos em alta pressão.
Beneficiário:Thamires Andrade Lima
Linha de fomento: Bolsas no Brasil - Pós-Doutorado
Processo FAPESP: 16/24241-5 - Estudo da dinâmica de líquidos iônicos formadores de vidro por espalhamento de neurons e raios-X
Beneficiário:Thamires Andrade Lima
Linha de fomento: Bolsas no Exterior - Estágio de Pesquisa - Pós-Doutorado