Spectroscopic Characterization of S₃O Isomers: Potential Contributor to the Unknown UV Absorber in Venus’s Atmosphere

A long-standing question about Venus’s atmosphere concerns the origin and distribution of the mysterious ultraviolet (UV) absorber, which is responsible for the absorption band observed in the near-UV and blue regions of Venus’s spectrum. In this work, we investigate the electronic structure of S3O isomers, their excited states, and their photoabsorption cross sections using quantum chemistry methods. Our results demonstrate that the cis- and trans-S3O isomers exhibit strong absorption in the 300–500 nm range, making them plausible candidates for the unknown near-UV absorber. The electronic spectrum of ring-S3O is featureless, whereas planar-S3O exhibits absorption around 300 nm. Additionally, spectroscopic data were generated using vibrational configuration interaction (VCI) for the most stable isomer and its isotopes to aid in their detection in the laboratory or the interstellar medium. This study provides valuable insights into the photochemistry of S3O isomers and the complex sulfur chemistry within Venus’s atmosphere.