The Rich Chemistry of Ionized Methanol With Sulfur Dioxide: Pathways to Prebiotic and Elusive Species in Earth's Atmosphere and Space

Sulfur dioxide (SO2) and methanol (CH3OH) are key components in both atmospheric and astrochemical environments, where ionizing radiation can initiate complex reaction networks. Here we investigate the ion chemistry of the CH3OH•+ + SO2 system by combining synchrotron experiments with theoretical analysis. The methanol radical cation CH3OH•+, generated at different photon energies, reacts efficiently with SO2, leading to an abundant distribution of ionic and neutral products. The reaction proceeds through rapid pathways involving the formation of the bound adduct [HOCH2O(H)SO]•+, which acts as a key intermediate governing the subsequent chemistry. Rearrangement and fragmentation of this ion lead to the formation of several species of chemical relevance. The formation of CH2O is particularly relevant because of its significant role in atmospheric oxidation processes and its importance as a prebiotic molecule detected in various interstellar environments. In addition, the formation of sulfur-containing molecules such as HOSOH•+, HOSO•, and CH2OSO•+ is of interest because these species are involved in sulfur oxidation chemistry, aerosol precursor formation, and contribute to the chemistry of sulfur in planetary environments and in the interstellar medium. The results indicate that the reaction of CH3OH•+ with SO2 can efficiently generate reactive molecules capable of initiating further chemical transformations.