Improved thermodynamic modeling of linear triatomic molecules using a hyperbolic Pöschl-Teller oscillator

Abstract

Accurate characterization of thermodynamic properties at high temperatures is essential for modeling chemical systems. However, widely used methods such as NASA polynomials, which are based on the rigid-rotor harmonic oscillator (RRHO) approximation, often fail to capture anharmonic vibrational effects. This study develops computational models using the simplified Pöschl-Teller (SPT) potential to describe the symmetric stretching mode in linear triatomic molecules, while harmonic oscillators are used for the remaining vibrational modes. Analytical expressions for entropy, enthalpy, Gibbs free energy, and heat capacity are derived from the partition function. The models, along with NASA polynomial fits, are applied to CO 2 , CS 2 , and N 2 O, using NIST-JANAF data for benchmarking. The SPT models yield mean percentage absolute errors (MPAE) below 2% for enthalpy and heat capacity, and as low as 0.2% for entropy and Gibbs free energy. While NASA polynomials perform well for CO 2 , they show significant deviations at elevated temperatures for CS 2 and N 2 O. This study presents the first application of the SPT potential to linear triatomic molecules and demonstrates its effectiveness in improving thermodynamic characterization.