Pressure effect on vibrational frequency and dephasing of 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids

L. Pison, M. F. Costa Gomes, A. A. H. Padua, D. Andrault, S. Norman, C. Hardacre, M. C. C. Ribeiro*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

Raman spectra in the range of the totally symmetric stretching mode of the [PF6]− anion, νs(PF6), have been measured for 1-alkyl-3-methylimidazolium ionic liquids [CnC1im][PF6], for n = 4, 6, and 8, as a function of pressure at room temperature. The ionic liquids [C6C1im][PF6] and [C8C1im][PF6] remain in an amorphous phase up to 3.5 GPa, in contrast to [C4C1im][PF6], whichcrystallizes above ∼0.5 GPa. Equations of state based either on a group contribution model or Carnahan-Starling-van der Waals model have been used to estimate the densities of the ionic liquids at high pressures. The shifts of the vibrational frequency of νs(PF6) with density observed in [C6C1im][PF6] and in [C8C1im][PF6] have been calculated by a hard-sphere model of a pseudo-diatomic solute under short-range repulsive interactions with the neighboring particles. The stochastic model of Kubo for vibrational dephasing has been used to obtain the amplitude of vibrational frequency fluctuation, ⟨Δω 2⟩, and the relaxation time of frequency fluctuation, τ c , as a function of density by Raman band shape analysis of the νs(PF6) mode of [C6C1im][PF6] and [C8C1im][PF6].
Original languageEnglish
Article number054510
Pages (from-to)1-7
Number of pages7
JournalJournal of Chemical Physics
Volume139
Issue number5
DOIs
Publication statusPublished - 07 Aug 2013

Keywords

  • BAND-SHAPE-ANALYSIS
  • 1-BUTYL-3-METHYLIMIDAZOLIUM HEXAFLUOROPHOSPHATE
  • VOLUMETRIC PROPERTIES
  • COMPUTER-SIMULATION
  • RAMAN-SPECTROSCOPY
  • TEMPERATURE
  • SHIFTS
  • RELAXATION
  • PREDICTION
  • EQUATION

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry
  • Medicine(all)

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