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Advances in Condensed Matter Physics
Volume 2015, Article ID 176067, 11 pages
http://dx.doi.org/10.1155/2015/176067
Research Article

An Infrared Spectroscopy Study of the Conformational Evolution of the Bis(trifluoromethanesulfonyl)imide Ion in the Liquid and in the Glass State

1CNR-ISC, UOS La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy
2Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
3Dipartimento di Chimica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy

Received 9 April 2015; Revised 16 July 2015; Accepted 26 July 2015

Academic Editor: Fajun Zhang

Copyright © 2015 Oriele Palumbo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We measure the far-infrared spectrum of N,N-Dimethyl-N-ethyl-N-benzylammonium (DEBA) bis(trifluoromethanesulfonyl)imide (TFSI) ionic liquid (IL) in the temperature range between 160 and 307 K. Differential scanning calorimetry measurements indicate that such IL undergoes a glass transition around 210 K. DFT calculations allow us to assign all the experimental absorptions to specific vibrations of the DEBA cation or of the two conformers of the TFSI anion. We find that the vibration frequencies calculated by means of the PBE0 functional are in better agreement with the experimental ones than those calculated at the B3LYP level, largely used for the attribution of vibration lines of ionic liquids. Experimentally we show that, in the liquid state, the relative concentrations of the two conformers of TFSI depend on temperature through the Boltzmann factor and the energy separation, H, is found to be 2 kJ/mol, in agreement with previous calculations and literature. However, in the glassy state, the concentrations of the cis-TFSI and trans-TFSI remain fixed, witnessing the frozen state of this phase.