Related Experiment Video
Updated: Jun 16, 2026

Synthesis of Ionic Liquid Based Electrolytes, Assembly of Li-ion Batteries, and Measurements of Performance at High Temperature
Published on: December 20, 2016
Infrared spectroscopy of ionic liquids: quantitative aspects and determination of optical constants
Thierry Buffeteau1, Joseph Grondin, Jean-Claude Lassègues
1Institut des Sciences Moléculaires, UMR 5255, CNRS, Université Bordeaux I, 351 Cours de la Libération, 33405 Talence Cedex, France.
Abstract:
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.
Related Concept Videos
Infrared (IR) Spectroscopy: Overview
Different compounds display unique properties due to their...
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
According to Hooke's law, the vibrational frequency is directly proportional to the...
Applications of IR Spectroscopy: Overview
IR Spectroscopy: Molecular Vibration Overview
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
IR and UV–Vis Spectroscopy of Carboxylic Acids
However, the stretching absorptions for the C=O bond vary depending on the structure of carboxylic acids. The C=O bond of the free carboxylic acids shows a higher stretching frequency, 1760 cm−1, while H-bonded carboxylic acids (dimers) exhibit stretching absorptions at a lower frequency, 1710 cm−1. The C=O bond of the...
IR Absorption Frequency: Delocalization
In IR spectroscopy,...

