Dense Low-Energy Landscapes of C2H6S2 and their Implications for Interstellar Sulfur Chemistry

Abstract The molecular inventory of sulfur-containing species in the interstellar medium remains poorly constrained, particularly for polysulfur organic species. Here, a comprehensive ab initio exploration of the C2H6S2 potential energy surface reveals a dense low-energy region containing numerous sulfur-containing structures with diverse bonding patterns and conformational flexibility. High-level jun-ChS + VPT2 calculations reproduce the available experimental rotational constants with a mean absolute error of approximately 0.2%, providing reliable spectroscopic reference data for future laboratory spectroscopic investigations. A total of 57 local minima were identified, including seven isomers within 30 kcal·mol–1 of the global minimum. Ethyl hydrodisulfide and dimethyl disulfide are the most stable structures, whereas geminal and vicinal dithiols remain nearly degenerate, suggesting that several neutral isomers may be thermodynamically accessible. In contrast to their oxygen analogues, the low-energy sulfur isomers exhibit strong energetic crowding and shallow torsional potentials, generating large conformational manifolds with temperature-dependent populations. Despite this structural diversity, computed ionization potentials remain confined to a narrow interval (8.10–9.38 eV).