A double exponential Morse potential energy function for diatomic molecules

In this work, we have proposed and tested a double exponential Morse (DEM) potential energy function (PEF) which describes the interatomic interactions of diatomic molecules. The DEM PEF, composed of the remedy function to the Morse PEF, is used to describe the vibrational motion for the ground electronic states of Br₂ and Cl₂ molecules. Comparing the Morse and DEM potential energy functions (PEFs), only three experimental spectral constants like \(D_{e} ,\;\omega_{e} ,\;{\text{and}}\;r_{e}\) for both cases are needed to be taken into account. Furthermore, the potential energy curves (PECs) and the vibrational energy levels for the ground electronic states of Br₂ and Cl₂ molecules are calculated by the DEM potential, Hulburt–Hirschfelder (HH) potential, Morse potential, improved multiparameter exponential-type (IMPET) potential and Huxley–Murrell (HM) potential. The results reveal that the DEM potential fits the Rydberg–Klein–Rees (RKR) data much better against other potentials, especially in the medium-long range regions. The vibrational energy levels derived from the DEM PEF align more closely with the experimental data. Moreover, the DEM potential provides opportunities for theoretical calculations of reduced molar Gibbs free energy and the molar entropy in a temperature range of 100–6000 K.

Graphical abstract

Overview of the PECs for the ground electronic state of Br₂ molecule.