preprints.org > chemistry and materials science > theoretical chemistry > doi: 10.20944/preprints202409.0045.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 30 August 2024 / Approved: 1 September 2024 / Online: 2 September 2024 (12:08:33 CEST)

I present in this paper Diatomic, an open-source Excel application that calculates molar ther-modynamic properties for diatomic ideal gases. This application is very easy to use and requires only a limited number of molecular constants, which are freely available online. Despite its sim-plicity, Diatomic provides methodologies and results that are usually unavailable in general quantum chemistry packages. This application uses the general formalism of statistical mechanics, enabling two models to describe the rotational structure and two models to describe the vibra-tional structure. In this work, Diatomic was used to calculate standard molar thermodynamic properties for a set of fifteen diatomic ideal gases. Special emphasis was placed on the analysis of four properties (standard molar enthalpy of formation, molar heat capacity at constant pressure, average molar thermal enthalpy and standard molar entropy), which were compared with ex-perimental values. The results obtained lead to the following main conclusions: (i) the theoretical model used to describe rotational structure has a small effect on the accuracy of the results, (ii) at moderate and high temperatures, the Morse model gives better results than the harmonic model, and (iii) at the lowest temperatures both models give similar results.

diatomic molecules; thermodynamic properties; open-source Excel application; statistical mechanics; quantum mechanics; classical limit; ideal gases

Chemistry and Materials Science, Theoretical Chemistry

* All users must log in before leaving a comment