Theoretical Investigation of Cl₂, ClO and Cl₂O Molecules

In this work, we have investigated the electronic properties of the ground and excited states of the Cl₂Cl₂ dimer, the ground state of ClO diatomic molecule, and the potential energy surface of the Cl2OCl2O triatomic molecule. These systems attract and receive attention from experimentalists and theorists because of their relationship with the stratosphere and ozone depletion. In order to achieve an accurate description of molecular interactions between involved atoms and molecules, we adopt a theoretical approach using numerical simulations with various highly correlated ab initio techniques and extended basis sets. Then, the potential energy curvesPotential energy curves are computed as a function of the internuclear distances and orientations. The spectroscopic constants are extracted and compared with previous theoretical and experimental studies. Our results, Configuration Interaction CI and Multireference Configuration Interaction MRCI with correction of DAVIDSON, are found to be in good agreement with the experimental data. For the triatomic system Cl₂O, the potential energy surfaces (PESs) are computed for fixed internuclear distance between chlorine atoms and different angular orientations within the Jacobi coordinates system. We used very efficient ab initio methods, MRCI and MRCI with corrections of Davidson and Pople. These PESs exhibit significant anisotropy where the dependence on the orientation is noticed. We carried out our numerous calculations using MOLPRO software, to solve the Schrödinger equation using the variational principle to determine the wave functions and the associated eigenvalues, while being in the Born Oppenheimer approximation to treat nuclear and electronic motion separately. Therefore, Hartree–Fock method is always the first prediction, and then we applied various post-Hartree–Fock methods to consider the electronic correlation.