Infrared spectroscopy of ionic liquids: quantitative aspects and determination of optical constants.
The infrared (IR) spectra of ionic liquids involving 1-butyl-3-methylimidazolium (BMI) and the (CF(3)SO(2))(2)N(-), BF(4)(-), or PF(6)(-) anions, recorded in the transmission and attenuated total reflection (ATR) modes, exhibit strong differences in the most intense anion absorption profiles. These distortions come from optical effects and make difficult any quantitative analysis of, for example, the antisymmetric stretching vibrations of the BF(4)(-) and PF(6)(-) anions. A method is proposed to determine the optical constants, from which any type of experimental spectrum can be simulated. It is then possible to use the anion vibrational bands as spectroscopic probes of the local interactions occurring in the neat ionic liquids and in solutions. This is illustrated by a direct identification of ion pairs and separated ions in the IR spectra of BMI-PF(6) solutions.
Institut des Sciences Moléculaires, UMR 5255, CNRS, Université Bordeaux I, 351 Cours de la Libération, 33405 Talence Cedex, France.
Thierry
T
Buffeteau
Joseph
J
Grondin
Jean-Claude
JC
Lassègues