Computational Investigation of the Structural, Vibrational, Electronic, and Thermodynamic Properties of Carbon Disulfide (CS₂) Using the PM3 Semi-Empirical Method

Abstract

Carbon disulfide (CS₂) is a linear molecule that has attracted significant attention in computational chemistry because of its distinctive structural, vibrational, electronic, and thermodynamic characteristics. In the present work, these properties were systematically investigated using the PM3 semi-empirical method implemented in HyperChem 8.0 and WinMOPAC 7.21. Geometry optimization was first performed to obtain the equilibrium molecular configuration and assess its structural stability. The optimized structure yielded an equilibrium C=S bond length of 1.422001 Å and a minimum total energy of −258.92169 eV. A potential energy curve was then constructed to estimate the bond dissociation energy, giving a value of 151.03 kcal/mol  6.55 eV) using conversion 1 eV = 23.0605( kcal/mol. Electronic structure calculations produced a HOMO–LUMO energy gap of 8.210 eV, suggesting that the molecule possesses high electronic stability together with relatively low chemical reactivity. Vibrational frequency calculations were also carried out to identify the characteristic infrared-active modes, while molecular electrostatic potential and charge density analyses were employed to examine the distribution of electron density and the most reactive regions of the molecule. In addition, the temperature dependence of the heat of formation, enthalpy, entropy, and heat capacity was evaluated to describe the thermodynamic behavior of CS₂. Overall, the calculated results indicate that the PM3 semi-empirical approach provides consistent and reliable predictions for the structural, vibrational, electronic, and thermodynamic properties of carbon disulfide, demonstrating its usefulness as a computationally efficient method for investigating small molecular systems.