We establish an analytical representation for the prediction of the molar Gibbs free energies of gaseous diatomic molecule substances. By comparing the predicted values to the experimental data for the gaseous phosphorus dimer, the availability of the Gibbs free energy calculation model is verified. The present model is related to three molecular constants and away from the need of lots of experimental spectroscopy data. (C) 2018 Elsevier Ltd. All rights reserved.