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.

8 pages, 2 figures. Astrophysical Journal Letter, in press

References in corpus (24)

• Binding energies: new values and impact on the efficiency of chemical desorption
• On the reservoir of sulphur in dark clouds : chemistry and elemental abundance reconciled
• Dust as interstellar catalyst I. Quantifying the chemical desorption process
• Resetting chemical clocks of hot cores based on S-bearing molecules
• Low sulfur depletion in the Horsehead PDR
• Sulfur depletion in dense clouds and circumstellar regions I. H2S ice abundance and UV-photochemical reactions in the H2O-matrix
• Interstellar Hydrides
• The IRAM-30m line survey of the Horsehead PDR: II. First detection of the l-C3H+ hydrocarbon cation
• Vacuum-UV spectroscopy of interstellar ice analogs. I. Absorption cross-sections of polar-ice molecules
• Sulphur-bearing molecules in diffuse molecular clouds: new results from SOFIA/GREAT and the IRAM 30 m telescope
• The IRAM-30m line survey of the Horsehead PDR: III. High abundance of complex (iso-)nitrile molecules in UV-illuminated gas
• Spatially resolved l-c3h+ emission in the horsehead photodissociation region: Further evidence for a top-down hydrocarbon chemistry
• The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH
• HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces
• H2CO in the Horsehead PDR: Photo-desorption of dust grain ice mantles
• Chemical complexity in the Horsehead photodissociation region
• The sulfur depletion problem: upper limits on the H2S2, HS2, and S2 gas-phase abundances toward the low-mass warm core IRAS16293-2422
• Polysulfanes on interstellar grains as a possible reservoir of interstellar sulphur
• The IRAM-30m line survey of the Horsehead PDR: I. CF+ as a tracer of C+ and a measure of the Fluorine abundance
• Deuterium fractionation in the Horsehead edge
• Study of the photon-induced formation and subsequent desorption of CH3 OH and H2 CO in interstellar ice analogs
• A new study of the chemical structure of the Horsehead nebula: the influence of grain-surface chemistry
• Far-Infrared detection of neutral atomic oxygen toward the Horsehead Nebula
• A study of singly deuterated cyclopropenylidene c-C3HD in protostar IRAS 16293-2422

Cited by in corpus (28)

• 2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules
• 2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules
• Modeling Sulfur Depletion in Interstellar Clouds
• Sulfur chemistry in protoplanetary disks: CS and H2CS
• Gas phase Elemental abundances in Molecular cloudS (GEMS). II. On the quest for the sulphur reservoir in molecular clouds: the $H_{2}S$ case
• Gas phase Elemental abundances in Molecular cloudS (GEMS) VII. Sulfur elemental abundance
• Efficiency of non-thermal desorptions in cold-core conditions. Testing the sputtering of grain mantles induced by cosmic rays
• Photoprocessing of H2S on dust grains: building S chains in translucent clouds and comets
• Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry
• Abundances of sulphur molecules in the Horsehead nebula. First NS+ detection in a photodissociation region
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IV. Observational results and statistical trends
• Bottlenecks to interstellar sulfur chemistry: Sulfur-bearing hydrides in UV-illuminated gas and grains
• The initial gas-phase sulfur abundance in the Orion Molecular Cloud from sulfur radio recombination lines
• Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains
• Quantifying the chemical desorption of H${}_2$S and PH${}_3$ from amorphous water ice surfaces
• AB Aur, a Rosetta stone for studies of planet formation (II): H${}_2$S detection and sulfur budget
• Quantitative inference of the $H_2$ column densities from 3 mm molecular emission: A case study towards Orion B
• Searches for Interstellar HCCSH and H${}_2$CCS
• Millimeter- and submillimeter-wave spectroscopy of thioformamide and interstellar search toward Sgr B2(N)
• Photochemistry of interstellar ice forming Complex Organic Molecules
• Binding Energies and Vibrational Spectral Features of S${}_n$ Species on Amorphous Water-ice Mantles: A Quantum Mechanical Study
• PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem
• The sulfur plume in the Horsehead nebula: New detections of S${}_2$H, SH${}^{+}$, and CO${}^{+}$
• First detection of HS2 in a cold dark cloud
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores
• Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula
• Molecules with ALMA at Planet-forming Scales (MAPS) XII: Inferring the C/O and S/H ratios in Protoplanetary Disks with Sulfur Molecules
• Synthesis and Spectroscopic Characterization of Interstellar Candidate Ethynyl Thiocyanate: HCCSCN