RT info:eu-repo/semantics/article
T1 Exploring chemical pathways for the interstellar molecule HOCS+: Preferential formation of the O-protonated carbonyl sulfide isomer
A1 Redondo Cristóbal, María del Pilar
A1 Barrientos Benito, María Carmen
A1 Sanz Novo, Miguel
A1 Rivilla, Víctor M.
K1 Datos moleculares
K1 Moléculas ISM
K1 Astroquímica
K1 ISM: objetos individuales: G+0.693-0.027
K1 2101 Cosmología y Cosmogonía
AB Context. The recent interstellar detection of the high-energy O-protonated carbonyl sulfide isomer (HOCS+) toward the molecular cloud G+0.693-0.027 contrasts with the non-detection of its lower-energy S-protonated counterpart, HSCO+, the global minimum in energy. This raises questions regarding the occurrence of selective formation pathways of these [H,C,S,O]+ isomers in space. Aims. In this work, we aim to explore the most likely gas-phase formation routes for both HOCS+ and HSCO+ beyond the direct protonation of OCS (i.e., HCS+ + OH, HCO+ + SH, HOC+ + SH, and HCO + SH+) to help rationalize previous observational results. Methods. We first explored the thermodynamic feasibility of the aforementioned reactions using high-level double-hybrid B2PLYPD3/aug-cc-pVTZ and CCSD(T)-F12/cc-pVTZ-F12 computations. For the reaction HCS+ + OH, found to be the most ther modynamically favorable, we characterized the stationary points on its corresponding potential energy surface (PES). In addition, we also used a composite approach to refine relative energies and employed the statistical rate theory and master equation simulations to estimate rate constants and branching ratios. Results. We show that HOCS+ is preferentially formed through the reaction of HCS+ with OH, providing a plausible chemical explanation for its interstellar presence and the non-detection of the low energy isomer. Nevertheless, while the branching ratio computed at a T Tkin(G+0.693) = 70-140 K is qualitatively consistent with the observations, its value is two orders of magnitude larger than the derived HOCS+/HSCO+ lower limit observational ratio (of 2.3). This suggests that if the upper limit of HSCO+ is close to the real abundance, additional formation pathways may also play a significant role in shaping the isomeric ratio. Conclusions. These results highlight that including all isomers in a given family, along with their isomer-preferential formation pathways, in astrochemical models, which are in many cases isomer-insensitive, is essential to understand their formation routes.
SN 0004-6361
YR 2025
FD 2025
LK https://uvadoc.uva.es/handle/10324/80100
UL https://uvadoc.uva.es/handle/10324/80100
LA eng
NO Astronomy & Astrophysics, 2025, (9 pp)
NO Producción Científica
DS UVaDOC
RD 20-dic-2025