Modified Scarf-type interaction potential for vibrational energy eigenvalues and chemical equilibrium constants of selected diatomic molecules

Accurate interaction potentials play an important role in the determination of vibrational, thermodynamic, and chemical equilibrium properties of diatomic molecules. In this work, a modified Scarf-type (MST) interaction potential is proposed and applied to the determination of vibrational energy eigenvalues and chemical equilibrium constants. An explicit expression for the vibrational energy eigenvalues is obtained from the radial Schrödinger equation using the parametric Nikiforov–Uvarov method. The resulting energy spectrum is subsequently employed in the determination of thermodynamic and chemical equilibrium properties. Validation against experimental and reference data demonstrates the reliability of the proposed model. Comparisons of the MST potential with Rydberg–Klein–Rees data for Br 2 , N 2 , PO, SO, and CO, and Born-Oppenheimer potential data for HeH + , yield MPAD values of 2.009%, 1.865%, 0.245%, 2.972%, 1.028%, and 1.268%, respectively. The calculated vibrational energy eigenvalues for Br 2 , N 2 , PO, SO, and CO also agree closely with the corresponding experimental RKR energies, with MPAD values of 2.669%, 1.997%, 0.547%, 1.860%, and 0.736%, respectively. Comparisons with NIST-JANAF thermochemical data further reveal close agreement for the chemical equilibrium constants of BrF, NO, PO, and SO, with MPAD values below 2% for BrF and NO and similarly favorable agreement for PO and SO at moderate and high temperatures. These findings establish the MST interaction potential as a useful framework for molecular spectroscopy, thermodynamic modeling, and chemical equilibrium studies of diatomic molecules.