Z. Naturforsch. 2017; aop Kevin Gooniah, Hanshika Jhurree, Dooshika Shiwpursad, Lydia Rhyman, Ibrahim A. Alswaidan, Veikko Uahengo, Radhakhrishna Somanah and Ponnadurai Ramasami* Structural, Spectroscopic, and Energetic Parameters of Diatomic Molecules Having Astrophysical Importance https://doi.org/10.1515/zna-2017-0176 Received May 24, 2017; accepted August 6, 2017 Abstract: This research investigates molecular parameters such as equilibrium structure, dipole moment, rotational constant, harmonic frequency, adiabatic electron affin- ity, atomisation energy, and ionisation potential of some identified diatomic molecules in interstellar/circumstel- lar medium. A theoretical understanding of the molecular properties of the investigated molecules is obtained using the popular B3LYP hybrid density functional with four basis sets: 6-311++G(2df,2pd), 6-311++G(3df,3pd), cc-pVTZ, and aug-cc-pVTZ. The computed data conform very well with available experimental and theoretical results. The accuracy of the B3LYP functional on the studied molecu- lar systems are ±0.006 Å for the bond length, ±0.044 D for the dipole moment, ±0.854 GHz for the rotational con- stant, ±59 cm −1 for the harmonic frequency, ±2.03 kcal/mol for the electron affinity, ±4.74 kcal/mol for atomisation energy, and ±3.19 kcal/mol for ionisation potential. Keywords: Astrophysical; DFT; Diatomic Molecules; Spectroscopy. 1 Introduction The study of diatomic molecules in physical sciences is of intrinsic worth because these molecules are the build- ing blocks of large molecules [1]. Interstellar diatomic molecules can be identified through their electronic, vibrational, and rotational spectra observed in different spectral regimes [2]. Quantum chemical approach can provide insight on the underlying interstellar chemistry of the identified and possible astromolecules, especially when highly reactive molecules are difficult to investigate in the laboratory [3]. Molecular parameters such as equilibrium structure, dipole moment, rotational constant, harmonic frequency, electron affinity, atomisation energy, and ionisation poten- tial are of special interest for astrochemistry. The acquaint- ance of the equilibrium dipole moment is crucial for the determination of the abundances of interstellar molecules [4]. The computation of harmonic frequencies is of great significance for the interpretation of complex experimen- tal spectra and its comparison with observed frequencies has enabled the identification of several unusual mole- cules [5]. A further key property is electron affinity, which provides insight on several molecular thermochemical properties [6] as well as the abundance of anions for astro- nomical detection [7]. The ionisation potential governs the formation of charged species that play a vital role in ion– molecule collisions occurring in interstellar space. When combined with thermochemical data, accurate values of ionisation potentials can provide precise bond energies for both neutral and cationic species [8]. Larsson et al. [9] detected the oxygen diatomic mole- cule, which is an important coolant of the dense inter- stellar medium. Another detected diatomic molecule is *Corresponding author: Ponnadurai Ramasami, Computational Chemistry Group, Faculty of Science, Department of Chemistry, University of Mauritius, Réduit 80837, Mauritius; and Department of Applied Chemistry, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa, E-mail: p.ramasami@uom.ac.mu Kevin Gooniah: Faculty of Science, Department of Physics, University of Mauritius, Réduit 80837, Mauritius; and Computational Chemistry Group, Faculty of Science, Department of Chemistry, University of Mauritius, Réduit 80837, Mauritius Hanshika Jhurree and Dooshika Shiwpursad: Computational Chemistry Group, Faculty of Science, Department of Chemistry, University of Mauritius, Réduit 80837, Mauritius Lydia Rhyman: Computational Chemistry Group, Faculty of Science, Department of Chemistry, University of Mauritius, Réduit 80837, Mauritius; and Department of Applied Chemistry, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa Ibrahim A. Alswaidan: Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia Veikko Uahengo: Department of Chemistry and Biochemistry, University of Namibia, Mandume Ndemufayo Road, Windhoek, Namibia Radhakhrishna Somanah: Faculty of Science, Department of Physics, University of Mauritius, Réduit 80837, Mauritius