Vibrational Spectroscopy and Thermodynamic Properties of Ionic Liquids under High Pressure

Abstract

Due to promising applications of ionic liquids as alternative solvents, it has become necessary to improve the knowledge of their thermodynamic properties and its microscopic interpretation in terms of ionic interactions. Many spectroscopic techniques, complemented by computational simulations, have been used to evaluate ionic interactions in pure ionic liquids and solute-solvent interactions in ionic liquids solutions. In vibrational spectroscopy, the evaluation of pressure effects are especially useful to elucidate the role that different types of intermolecular forces play in structure and dynamics of liquids. In this project, results of frequency shift and vibrational relaxation of ionic liquids under high pressure will be analyzed by theories that relate the spectral changes to structural and dynamical parameters that depend on the liquid's density. On the other hand, equation of states of ionic liquids have been proposed relying on data obtained under MPa pressure range, while Raman and infrared spectroscopy experiments of high pressure liquids are usually taken within the GPa range. In this project, we will use molecular dynamics simulations to evaluate the extrapolation of equations of states of ionic liquids to the range of high pressures achieved in diamond anvil cells. The molecular dynamic simulations will also be used to calculate the time correlation functions involved in theories of vibrational relaxation in order to compare models and experimental vibrational spectra. Therefore, the computational simulations will have the double role of complementing thermodynamic data of ionic liquids and to evaluate the appropriateness of theories of vibrational spectroscopy of condensed phases.