Interstellar Ice Chemistry Yields Elusive Sulfinothioic Acid (HS(O)SH)

Area of Science:

• Astrochemistry
• Chemical Physics
• Planetary Science

Background:

• Low-oxidation-state sulfur oxyacids are vital but elusive interstellar chemistry intermediates.
• Sulfinothioic acid (HS(O)SH), the simplest of these, has not been detected in space or isolated on Earth.
• The S-S(O) motif's presence in biological systems hints at potential astrobiological relevance.

Purpose of the Study:

• To achieve the first laboratory synthesis of sulfinothioic acid under astrophysically relevant conditions.
• To identify and characterize this molecule using advanced analytical techniques.
• To explore the formation pathways of sulfur oxyacids in cold interstellar environments.

Main Methods:

• Formation of sulfinothioic acid in sulfur dioxide (SO2)-water (H2O) ices at 5 K under ultrahigh vacuum.
• Irradiation of ices using galactic cosmic-ray proxies.
• Identification via isomer-selective photoionization reflectron time-of-flight mass spectrometry.
• Utilizing isotopic labeling for confirmation.

Main Results:

• Successful synthesis and identification of sulfinothioic acid in laboratory ice.
• Demonstration that energetic particle irradiation can drive the formation of this molecule.
• Confirmation of a previously unrecognized class of astrochemically accessible sulfur oxyacids.

Conclusions:

• Establishes a missing link in interstellar sulfur chemistry.
• Reveals that radical-mediated, non-equilibrium processes driven by energetic particles are key to forming sulfur oxyacids in cold interstellar environments.
• Highlights the potential astrobiological significance of these newly accessible molecules.