Sulfur Dioxide Sulfide (SSO2): The Elusive Isovalent Analogue of Sulfur Trioxide (SO3)
Mason McAnally, Xilin Bai, Yuheng Luo, Zesen Wang, Jinghui Lu, Ashanie Herath, Chaojiang Zhang, Jia Wang, Andrew M. Turner, Baoyu Song, Yang Pan, Tao Yang, Rui Sun, Ryan C. Fortenberry, Ralf I. KaiserAbstract
Sulfur dioxide sulfide (SSO2) has remained experimentally undetected despite repeated theoretical predictions of its stability. As a missing sulfur oxide isovalent to sulfur trioxide (SO3), SSO2 occupies a distinctive position at the boundary of formally hypervalent bonding, where replacing oxygen with sulfur perturbs a delocalized chalcogen-oxide framework. Here, we close this long-standing gap by identifying SSO2 in cryogenic SO2 ices processed by energetic electrons using tunable vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry and high-level quantum chemical computations. These studies reveal a broader sulfur oxide network including sulfur oxide peroxide (OSOO), 1,2,3-dioxathiirane 3-oxide (cyclic-S(O)OO), and disulfur monoxide (S2O). Our results establish sulfur-atom incorporation into SO2 as a viable condensed-phase route to a previously elusive sulfur oxide─SSO2─and highlight its unique molecular structure in sulfur-rich planetary and astrochemical environments.