Potential energy curves, partition functions and line intensities of HF and HCl molecules under the improved Hulburt‐Hirschfelder quantum mechanical anharmonic oscillator model

Abstract

An improved Hulburt‐Hirschfelder (IHH) quantum mechanical anharmonic oscillator model which describes the exact analytical potential energy curves (PECs) of diatomic molecules is presented. The IHH analytical potential function that involves a variable parameter, four empirically determined low‐order molecular vibrational and rotational spectral constants and the dissociation energy was applied to the ground electronic states of HF and HCl, yielding a good agreement between the Rydberg‐Klein‐Rees (RKR) potential energy points and the calculations. Correspondingly, with the determined IHH PECs, the partition functions at temperatures 300–6000 Kelvin (K) and rovibrational line intensities are evaluated, and coincide well with those quoted in the HITRAN2020 database compilation. The methodology could be valuable for the detection of molecules in interstellar clouds using infrared spectroscopy, as well as thermochemical reactions.

A method for predicting the entropy and Gibbs free energy of ICl and BrCl gases based on an improved Hulburt-Hirschfelder potential

“…Based on equation (1), a formula has been obtained after adding the hyperbolic cosine function q with an adjustable variational parameter λ that can be used to adjust the converging behavior in the asymptotic and dissociation region for the model, and can be expressed as [18] s s…”

“…The study of the thermodynamic properties of diatomic molecules gas has attracted great attention in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. It is applicable in the fields of material science, engineering science, chemical engineering, food chemistry, medicine and agriculture.…”

“…However, it should be noted that we did not calculate other thermodynamic properties such as entropy and Gibbs free energy. In this work, an improved Hulburt-Hirschfelder (IHH) potential energy model [18] developed recently for potential energy curves, partition functions and line intensities of diatomic molecules was applied to calculate entropy and Gibbs free energy for the ground electronic state of BrCl and ICl molecules. The results in this work show that the developed model is suitable for accurately predicting the molar entropy and reduced molar Gibbs free energy of some gaseous substances.…”

A variationally improved Hulburt-Hirschfelder analytical potential energy function for diatomic molecules

“…The HH potential is often regarded as the classical model compared with some other potentials. In order to improve the flexibility of HH potential and to reduce the error with experimental data, a hyperbolic cosine function is added to the HH potential to generate the IHH APEF [20] denoted as…”

“…Recently, a preliminary improved Hulburt-Hirschfelder (IHH) APEF is proposed [20], where the goal is to reach the optimal value of the adjustable parameter λ for the APEF construction, and it accomplished good results in simulating the PECs for the ground electronic states of HF and HCl. Whereas, there is a shortcoming that a small non-physical barrier appears in the asymptotic and dissociation region of the IHH curves of some molecules (e.g., ClO [21]).…”