Ultrafast dynamics of pyrrolidinium cation ionic liquids

Hideaki Shirota, Alison M. Funston, James F. Wishart, Ed Castner

Research output: Contribution to journalArticle

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Abstract

We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N -butyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 14 + NTf2-), N -methoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bromide P 1EOE +, and N -ethoxyethyl- N -methylpyrrolidinium dicyanoamide P 1EOE + DCA-). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P 14 +, P 1EOM +, and P 1EOE + paired with the NTf2- anion. The other group of liquids consists of the P 1EOE + cation paired with each of the three anions NTf2-, Br-, and DCA-. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (~2 ps) and intermediate (~20 ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750 cm-1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2- anion. The intermolecular vibrational line shapes between 0 and 150 cm-1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape.

Original languageEnglish
Article number184512
JournalJournal of Chemical Physics
Volume122
Issue number18
DOIs
Publication statusPublished - May 8 2005

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Ionic Liquids
Cations
cations
Imides
liquids
Anions
imides
Relaxation time
anions
time constant
line shape
relaxation time
Liquids
Molecular dynamics
Kerr effects
Spectroscopy
Viscosity
bromides
oscillators
viscosity

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Ultrafast dynamics of pyrrolidinium cation ionic liquids. / Shirota, Hideaki; Funston, Alison M.; Wishart, James F.; Castner, Ed.

In: Journal of Chemical Physics, Vol. 122, No. 18, 184512, 08.05.2005.

Research output: Contribution to journalArticle

Shirota, Hideaki ; Funston, Alison M. ; Wishart, James F. ; Castner, Ed. / Ultrafast dynamics of pyrrolidinium cation ionic liquids. In: Journal of Chemical Physics. 2005 ; Vol. 122, No. 18.
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abstract = "We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N -butyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 14 + NTf2-), N -methoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bromide P 1EOE +, and N -ethoxyethyl- N -methylpyrrolidinium dicyanoamide P 1EOE + DCA-). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P 14 +, P 1EOM +, and P 1EOE + paired with the NTf2- anion. The other group of liquids consists of the P 1EOE + cation paired with each of the three anions NTf2-, Br-, and DCA-. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (~2 ps) and intermediate (~20 ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750 cm-1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2- anion. The intermolecular vibrational line shapes between 0 and 150 cm-1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape.",
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AB - We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N -butyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 14 + NTf2-), N -methoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P 1EOE + NTf2-), N -ethoxyethyl- N -methylpyrrolidinium bromide P 1EOE +, and N -ethoxyethyl- N -methylpyrrolidinium dicyanoamide P 1EOE + DCA-). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P 14 +, P 1EOM +, and P 1EOE + paired with the NTf2- anion. The other group of liquids consists of the P 1EOE + cation paired with each of the three anions NTf2-, Br-, and DCA-. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (~2 ps) and intermediate (~20 ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750 cm-1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2- anion. The intermolecular vibrational line shapes between 0 and 150 cm-1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape.

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