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

Abstract Sulfur dioxide and hypohalous acids (HOX, X=F, Cl, Br, I) are ubiquitous molecules in the atmosphere that are central to important processes like seasonal ozone depletion, acid rain, and cloud nucleation. We present the first theoretical examination of the HOX⋯SO 2 binary complexes and the associated trends due to halogen substitution. Reliable geometries were optimized at the CCSD(T)/aug‐cc‐pV(T+d)Z level of theory for HOF and HOCl complexes. The HOBr and HOI complexes were optimized at the CCSD(T)/aug‐cc‐pV(D+d)Z level of theory with the exception of the Br and I atoms which were modeled with an aug‐cc‐pwCVDZ‐PP pseudopotential. 27 HOX⋯SO 2 complexes were characterized and the focal point method was employed to produce CCSDT(Q)/CBS interaction energies. Natural Bond Orbital analysis and Symmetry Adapted Perturbation Theory were used to classify the nature of each principle interaction. The interaction energies of all HOX⋯SO 2 complexes in this study ranged from 1.35 to 3.81 kcal mol −1 . The single‐interaction hydrogen bonded complexes spanned a range of 2.62 to 3.07 kcal mol −1 , while the single‐interaction halogen bonded complexes were far more sensitive to halogen substitution ranging from 1.35 to 3.06 kcal mol −1 , indicating that the two types of interactions are extremely competitive for heavier halogens. Our results provide insight into the interactions between HOX and SO 2 which may guide further research of related systems.