The HOX⋯SO₂ (X=F, Cl, Br, I) Binary Complexes: Implications for Atmospheric Chemistry.

Area of Science:

• Atmospheric Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Sulfur dioxide (SO2) and hypohalous acids (HOX) are key atmospheric molecules.
• These molecules influence ozone depletion, acid rain, and cloud formation.

Purpose of the Study:

• To theoretically investigate HOX⋯SO2 binary complexes for the first time.
• To analyze trends in these interactions based on halogen substitution.

Main Methods:

• High-level ab initio calculations (CCSD(T)) were used for geometry optimization.
• Focal point analysis (CCSDT(Q)/CBS) determined interaction energies.
• Natural Bond Orbital (NBO) and Symmetry Adapted Perturbation Theory (SAPT) analyzed interaction types.

Main Results:

• 27 HOX⋯SO2 complexes were characterized with interaction energies from 1.35 to 3.81 kcal/mol.
• Hydrogen-bonded complexes showed moderate interaction energies (2.62–3.07 kcal/mol).
• Halogen-bonded complexes exhibited greater sensitivity to halogen substitution (1.35–3.06 kcal/mol), indicating competitive interactions.

Conclusions:

• HOX⋯SO2 interactions are significant and influenced by halogen type.
• Hydrogen and halogen bonding are competitive, particularly with heavier halogens.
• Findings offer insights for future research on related atmospheric systems.