Theoretical Study of Molar Entropy and Gibbs Free Energy for HCl and DCl

Abstract Molecular molar entropy and Gibbs free energy are pivotal for understanding the thermodynamic and kinetic properties of molecular systems, facilitating the optimization of chemical reactions and phase transitions. In this work, we integrated experimental spectral constants (De, re, ωe, ωeχe, Be, αe) and Rydberg-Klein-Rees (RKR) data, and constructed the potential energy curves (PECs) for the ground electronic states of HCl and DCl molecules using the variationally improved Hulburt-Hirschfelder (VIHH) potential model. The complete set of rovibrational energy levels for the ground electronic states of HCl and DCl is obtained by solving the one-dimensional Schrödinger equation. Finally, the molar entropy and the reduced Gibbs free energy of these two molecules in the temperature range of 100 to 6000K are calculated within the framework of quantum statistical theory. Our results demonstrate that the PECs and vibrational energy levels derived from the VIHH model align closely with experimental values, and the calculated thermodynamic properties are consistent with data from the National Institute of Standards and Technology.