Conformations of 1-Butyl-3-methylimidazolium Chloride Probed by High Pressure Raman Spectroscopy

Abstract

The behavior of 1-butyl-3-methylimidazolium chloride has been investigated byRaman spectroscopy as a function of hydrostatic pressure. Under ambient pressure tworotational isomers (GA and AA forms) of the 1-butyl-3-methylimidazolium cation coexist inthe ionic liquid state. As the supercooled liquid was compressed from ambient to 0.9 GPa,the contribution of the GA conformer decreases in intensity as the pressure was elevated. Anew high pressure phase is formed above the pressure of 1.5 GPa. This new high pressurephase of 1-butyl-3-methylimidazolium chloride arises from perturbed GA conformer, i.e.,distorted Crystal 2. Crystal 1 form (AA form) is known as a thermodynamically stable formunder ambient pressure. Nevertheless, crystal 1 form is switched to a metastable state underthe condition of high pressure.

Keywords

• Raman spectroscopy
• High pressure
• 1-Butyl-3-methylimidazolium chloride.