Chlorine-Sulfur Isomers as Parents of ClS2 and SCl2 on Venus: Spectroscopy and Photochemistry of ClSSCl, SSCl2, and (ClS)2

Chlorine-sulfur photochemistry has emerged as a key component of the complex atmospheric chemistry of Venus and a promising avenue for explaining the sulfur cycle of the planet. A theoretical study of ClSSCl, SSCl2, and (ClS)2 isomers was performed to elucidate their stability, spectroscopy, and photochemistry, with implications for their potential presence in the upper atmosphere of Venus. The ClSSCl and SSCl2 isomers are thermodynamically stable, with significant Cl-S and S-S bond dissociation energies (>47 kcal/mol), which suggests resistance to thermal dissociation. In contrast, the cyclic (ClS)2 isomer is a metastable species with a weak Cl-S bond, which indicates that it is likely a transient intermediate or prereaction complex. Excited states and photoabsorption cross-sectional analysis revealed that ClSSCl exhibits strong UV absorption at approximately 240 nm, thereby resulting in specific, rapid photodissociation channels. Conversely, SSCl2 displays broad absorption across the near-UV‒visible range of ~340 nm, with a high density of interacting states, which leads to complex and slow photodissociation dynamics. These results establish ClSSCl and SSCl2 as plausible candidates for detection in the Venusian atmosphere and, critically, as potential photochemical parent molecules for the ClS2 and SCl2 species, thus providing an accurate spectroscopic and photochemical roadmap for their future observation and simulation.