Application of Morse potential and improved deformed exponential-type potential (IDEP) model to predict thermodynamics properties of diatomic molecules

The thermal properties of three diatomic molecules such as hydrogen (H2), carbon monoxide (CO) and iodine (I2) are theoretically predicted. To this end, two different potential models are considered, Morse potential and improved deformed exponential-type potential (IDEP). The Schrödinger equation is analytically solved to obtain energy levels. For the Morse and IDEP potential models, the Laplace transformation and the Greene–Aldrich approximation and appropriate coordinate transformation are employed, respectively. In the former potential model, we have obtained energy eigenvalues by considering position-dependent effective mass. Using the energy levels of two models, the partition function is first determined. Second, thermal functions of the molecules such as heat capacity, enthalpy and entropy are obtained and compared with the available results. The calculated enthalpy using the two models for CO and I2 molecules is in excellent agreement in comparison with the available data in a wide temperature range. But, the obtained enthalpy of H2 molecule using the Morse potential at high temperatures does not agree excellently with the experimental data. The entropy of H2, CO and I2 using the two models is tin good agreement in comparison with the available data in a wide temperature range whereas the entropy of H2 at low temperatures does not agree excellently with the experimental data. Our theoretical results using the two potential models do not show a suitable prediction about the heat capacity at a constant pressure of H2, CO and I2 molecules, But the IDEP shows more agreement compared to the Morse potential.