Recent experiments conducted by a team of researchers from Japan have unveiled significant insights into the behavior of solid sulfur dioxide (SO2) in the interstellar medium. The study, published on November 15, 2024, indicates that SO2 can undergo reactions with hydrogen atoms in amorphous solid water (ASW) at low temperatures.
During the experiments, approximately 80% of the deposited SO2 was lost from the substrate after just 40 minutes of exposure to hydrogen atoms at temperatures ranging from 10 to 40 K. Even at 60 K, about 50% of the SO2 was lost, although no definitive reaction products were detected at that time.
Quantum chemical calculations revealed that hydrogen atoms preferentially attach to the sulfur atom in solid SO2, leading to the formation of the radical HSO2. Subsequent reactions involving HSO2 produced various sulfur-bearing species, including HS(O)OH, the radical S(O)OH, HO-S-OH, HS-OH, and hydrogen sulfide (H2S).
In co-deposition experiments that combined hydrogen and SO2, the formation of H2S, HS(O)OH, and/or HO-S-OH was confirmed. However, the yields of these sulfur-bearing species were insufficient to account for the total loss of the initial SO2 reactant, suggesting that some products may have desorbed into the gas phase after formation.
This research indicates that while a portion of SO2 in icy mantles may remain unreacted and avoid hydrogenation, the remainder transforms into other species, some of which are subject to chemical desorption. The findings hold potential implications for understanding the chemical processes in the interstellar medium and could inform future studies on the formation of complex organic molecules in space.