2024/02/23 by Miguel Sanz‐Novo, Sanz-Novo, Miguel, V. M. Rivilla +27 · 3 citations
Earth and Planetary Sciences · Physics and Astronomy · #Atmospheric Ozone and Climate #Atmospheric chemistry and aerosols #Astrophysics and Star Formation Studies
paper · pdf · doi:10.48550/arxiv.2402.15405
We present the first detection in space of O-protonated carbonyl sulfide (\chHOCS+), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all Ka = 0 transitions ranging from Jlo = 2 to Jlo = 13 of \chHOCS+ covered by our survey, we derive a column density of N = (9 ± 2)×1012 cm-2, translating into a fractional abundance relative to H2 of ∼7×10-11. Conversely, the S-protonated \chHSCO+ isomer remains undetected, and we derive an upper limit to its abundance with respect to H2 of ≤3×10-11, a factor of ≥2.3 less abundant than \chHOCS+. We obtain a \chHOCS+/OCS ratio of ∼2.5×10-3, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of \chHOCS+ is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionisation rates (10-15-10-14 s-1) are needed to reproduce the observed abundance of \chHOCS+. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find a \chHOCO+/\chHOCS+ ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.