Acetonitrile Liquid Phase Modeling by the Quantum Cluster Equilibrium Theory

Abstract

This work aims to investigate liquid acetonitrile clusters considering the modified rigid-rotor harmonic oscillator and frequency corrections in the quantum cluster equilibrium (QCE) theory. To carry out this study, acetonitrile isomers with size n ranging from 1 to 12 are considered. Those isomers are generated using the flexible and rapid ABCluster generator distributions while avoiding poor symmetry. After that, geometry optimization and frequency calculations are performed on the selected structures to serve as inputs for applying the quantum cluster equilibrium theory. The temperature range covering the liquid acetonitrile, going from T = 200 to 400 K, is considered with the rigid rotor harmonic oscillator cutoff values of 50 and 100 cm⁻¹. The results show that the population of liquid acetonitrile is dominated by dodecamers, trimers, dimers, and tetramers, as identified in previously studied structures, across the range of liquid acetonitrile temperatures. The thermodynamic properties, such as the entropy and enthalpy of vaporization obtained by the QCE theory, have been compared to the experiment, yielding a relatively good agreement depending on the cluster set considered. Furthermore, based on the predicted population of the liquid acetonitrile, the infrared spectrum has been calculated at 298 K.