Sulfurous Acid: Predicting a Spectrum and Setting the Surface Straight

Sulfurous acid is hypothesized to be a nucleation center for aerosols, but its isolation and characterization have been described as one of the greatest challenges of inorganic chemistry. Consequently, most information about sulfurous acid has come from the more than twenty theoretical studies examining it. However, none of them have performed a comprehensive examination of this surface, and the studies are plagued by problems ranging from basis sets that predict wrong Lewis structures to discrepancies in activation barriers of up to 40 kcal/mol. To aid in the possible gas-phase characterization of this molecule, we (1) identify previously unknown stationary points, (2) use focal point analysis to provide definitive enthalpies and explain contradictions in previous literature, and (3) use VPT2, with an effective Hamiltonian treatment of Fermi resonances, to predict a reliable infrared spectrum for the spectroscopically relevant species.