Quantum Chemical Rovibrational Analysis of the HOSO Radical

syn-HOSO is the most stable form of hydrogenated sulfur dioxide, a possible intermediate in the creation of sulfuric acid. Recent work has characterized the structure and rotational constants, but the present work provides new insights into the vibrational spectra of this molecule. The central S-O bond is weaker than the terminal S-O bond, which allows for near-free rotation of the hydrogen atom. The stretches and the torsional modes are relatively bright infrared emitters/absorbers. The torsional mode is very low in frequency making it a potential target for terahertz observation. The other vibrational frequencies for HOSO are reduced relative to the corresponding frequencies in SO2, H2SO4, and the HOS radical making the infrared features of syn-HOSO likely red-shifted in mixed spectral observation, where oxygen, hydrogen, and sulfur are all found.