First detection of interstellar S2H

Abstract : We present the first detection of gas phase S2H in the Horsehead, a moderately UV-irradiated nebula. This confirms the presence of doubly sulfuretted species in the interstellar medium and opens a new challenge for sulfur chemistry. The observed S2H abundance is ~5x10$^{-11}$, only a factor 4-6 lower than that of the widespread H2S molecule. H2S and S2H are efficiently formed on the UV-irradiated icy grain mantles. We performed ice irradiation experiments to determine the H2S and S2H photodesorption yields. The obtained values are ~1.2x10$^{-3}$ and <1x10$^{-5}$ molecules per incident photon for H2S and S2H, respectively. Our upper limit to the S2H photodesorption yield suggests that photo-desorption is not a competitive mechanism to release the S2H molecules to the gas phase. Other desorption mechanisms such as chemical desorption, cosmic-ray desorption and grain shattering can increase the gaseous S2H abundance to some extent. Alternatively, S2H can be formed via gas phase reactions involving gaseous H2S and the abundant ions S+ and SH+. The detection of S2H in this nebula could be therefore the result of the coexistence of an active grain surface chemistry and gaseous photo-chemistry.
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Astrophysical Journal Letters, 2017, 851 (2), pp.id. L49. 〈10.3847/2041-8213/aaa01b〉
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https://hal.archives-ouvertes.fr/hal-01661652
Contributeur : Marie-Paule Pomies <>
Soumis le : mardi 12 décembre 2017 - 09:36:23
Dernière modification le : lundi 24 septembre 2018 - 16:04:03

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Asuncion Fuente, Javier R. Goicoechea, Jérôme Pety, Romane Le Gal, Rafael Martín-Doménech, et al.. First detection of interstellar S2H. Astrophysical Journal Letters, 2017, 851 (2), pp.id. L49. 〈10.3847/2041-8213/aaa01b〉. 〈hal-01661652〉

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