Ab Initio Approach to the Structure, Vibrational Properties, and Electron Binding Energies of H₂S∙∙∙SO₂

The present study employs high-level ab initio calculations to investigate the structure, vibrational frequencies, and electronic properties of H₂S∙∙∙SO₂. The analysis of vibrational frequencies reveals an intramolecular vibrational energy transfer phenomenon, where energy from the stretching modes of H₂S is transferred to the ν1s mode of SO₂. At the CCSD(T)/aug-cc-pVQZ level, the interaction energy between H₂S and SO₂ is predicted to be 2.78 kcal/mol. Electron propagator theory calculations yield a HOMO-LUMO gap of 8.24 eV for H₂S∙∙∙SO₂. Furthermore, by utilizing ab initio results for the adiabatic ionization energy and electron affinity, the electrophilicity of H₂S∙∙∙SO₂ is estimated to be 2.01 eV. This value is similar to the electrophilicity of SO₂, suggesting comparable reactivity and chemical behavior. The non-covalent interaction (NCI) analysis of the H₂S∙∙∙SO₂ complex emphasizes the significant contribution of non-covalent van der Waals interactions in its energetic stabilization.