scieee AI-readable full text Open interactive document viewer

Origin and fate of interstellar S-bearing molecules: insights from observations and experiments

Julia, Santos

Publisher
Zenodo
DOI
10.5281/zenodo.17108829
Repository
zenodo.org
Language
en

Abstract

The observed sulfur content in dense interstellar clouds and protostellar environments constitutes only a small fraction of the expected cosmic value, with the bulk of its reservoir remaining unknown. One hypothesis is that the missing sulfur is locked away in or beneath the icy mantles that shroud interstellar dust grains, challenging its observation. This distinctive feature of sulfur-bearing species makes them critical for understanding the evolution of volatile and refractory components during star and planet formation. In this presentation, I will showcase recent laboratory experiments on interstellar ice analogues that offer particularly promising new pathways to S-bearing organics. We find that SH radicals can initiate a prolific sulfur reaction network under interstellar conditions, leading to the formation of CH3CH2SH, CH2CHSH, HSCH2CH2SH, H2S2, OCS, and tentatively CH3CHS and CH2CS. Computational calculations further elucidate key reaction routes in this network. I will also present ALMA observations of gaseous SO2 and OCS towards 26 MYSOs from the ALMAGAL survey, compared with literature ice data—including JWST observations. These species are particularly relevant since they are major carriers of gaseous sulfur and the only sulfurated molecules detected in ices to date. Such comparisons provide powerful information on the chemical and physical environments of these molecules and their potential inheritance by planetesimals.

Full text

Julia C. Santos PhD candidate Leiden Observatory The!origin!and!fate!of!interstellar! sulfur-bearing!molecules: Insight from observations and experiments Harold Linnartz, Ewine van Dishoeck, Ko-Ju Chuang, Martijn van Gelder, Pooneh Nazari, Joan Enrique-Romero, Thanja Lamberts Towards a complex sulfur chemistry methanethiol! (CH3SH) Rodriguez-Almeida+2021 Cernicharo+2021Kolenisková+2014Linke+1979 ethanethiol! (CH3CH2SH) thioformic acid! (CH(O)SH) thioketene! (CH2CS) thioacetaldehyde! (CH3CHS) Agúndez+2025 Towards a complex sulfur chemistry Calmonte+2016 ESA/Rosetta/NAVCAM methanethiol! (CH3SH) Rodriguez-Almeida+2021 Cernicharo+2021Kolenisková+2014Linke+1979 ethanethiol! (CH3CH2SH) thioformic acid! (CH(O)SH) thioketene! (CH2CS) thioacetaldehyde! (CH3CHS) Agúndez+2025 In 67P: [H2S]/[H2O] ~ 1% Cernicharo+2021 Kolenisková+2014 ethanethiol (CH3CH2SH) thioketene (CH2CS) Molpeceres & Rivilla 2022 C2H2 as a carbon backbone C2H2 + SH ( +H ) ? thioacetaldehyde! (CH3CHS) Agúndez+2025 Towards a complex sulfur chemistry Part 1: S-COMs formation from SH + C2H2 Santos et al., 2024, ACS Earth Space Chem. 8, 1646 Experiments reveal a prolific ice S network Santos et al., 2024, ACS Earth Space Chem. 8, 1646 Part 1: S-COMs formation from SH + C2H2 T = 10 K! P ~ 5 x 10-10 mbar Figure credit: Dr. Kruczkiewicz H2S + H SH + H2 C2H2 + SH ( +H ) ? 60 80 100 120 140 160 0 2×10-11 4×10-11 6×10-11 8×10-11 Intensity (A) Temperature (K) m/z: 32 45 46 47 58 59 60 62 66 CH2CS* CH3CHS* CH2CHSH + CH3CH2SH HSCH2CH2SH H2S2 Santos et al., 2024, ACS Earth Space Chem. 8, 1646 Part 1: S-COMs formation from SH + C2H2 T = 10 K! P ~ 5 x 10-10 mbar Figure credit: Dr. Kruczkiewicz C2H2 + H2S + H Experiments reveal a prolific ice S network Vinyl mercaptan and ethanethiol 100 120 140 0.0 5.0×10-12 1.0×10-11 1.5×10-11 Intensity (A) Temperature (K) m/z: 60 58 47 62 46 a) b) c) 46 47 58 60 62 0 50 100 Exp. Ref. 117 K 121 K C2H2:H2S:H = 1:5:10 CH2CHSH 46 47 58 60 62 0 50 100 Exp. Ref. Relative intensity m/z CH3CH2SH 0.000 0.001 0.002 1600 1500 1400 1300 1200 0.000 0.001 CH3CH2SH CH2CHSH C2H2 + H2S + H (10 K) C2H2 + H C2H2 + H2S + H (100 K - 140 K) CH3CH2SH std C2H6C2H4 C2H2 + C2H6 a) b) Wavenumber (cm-1) Absorbance x 0.1 vinyl mercaptan! CH2CHSH ethanethiol! CH3CH2SH QMS IR 10 K Santos et al., 2024, ACS Earth Space Chem. 8, 1646 Part 1: S-COMs formation from SH + C2H2 100 - 140 K Molecules with 2 S atoms are also formed 1,2-ethanedithiol! SHCH2CH2SH 0 5×10-12 1×10-11 2×10-11 120 140 160 180 0 2×10-13 4×10-13 Intensity (A) m/z: 47 60 46 59 58 61 158 K a) b) c) Temperature (K) m/z: 94 46 47 58 59 60 61 94 0 40 80 120 Relative intensity m/z Exp. Ref. HSCH2CH2SH Santos et al., 2024, ACS Earth Space Chem. 8, 1646 Part 1: S-COMs formation from SH + C2H2 Our subset: 26 line-rich MYSOs ALMAGAL: > 1000 dense clumps M > 500 M☉d < 7.5 kpc Band 6 Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas Sample selection from ALMAGAL Sergio Molinari and the ALMAGAL team Compact emission from the hot core Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(OCS) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(OCS) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(OCS) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(OCS) / N(CH3OH) ice vs gas CO + S → OCS! CO + HS → HSCO! HSCO + H → OCS + H2 ice e.g., Santos+2024 A&A, 690, A24 Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(OCS) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(SO2) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(SO2) / N(CH3OH) ice vs gas Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas N(SO2) / N(CH3OH) ice vs gas Cernicharo+2021 Kolenisková+2014 ethanethiol (CH3CH2SH) thioketene (CH2CS) Molpeceres & Rivilla 2022 C2H2 as a carbon backbone C2H2 + SH ( +H ) ? thioacetaldehyde! (CH3CHS) Agúndez+2025 Can we form 2-carbon S-COMs? Towards a complex sulfur chemistry But what can we see in ices?OCS and SO2 Rocha+2024 Boogert+1997 Protostars What can we learn by comparing ice and gas? Compact emission from the hot core Fixed Tex: < 2.5 factor difference on relative abundances Santos et al., 2024, A&A, 689, A248 Part 2: OCS and SO2 ice vs gas 34SO2 and O13CS 1 line each The case of H2S NASA/JPL-Caltech/R. Hurt S HS H2S + H + H The case of H2S NASA/JPL-Caltech/R. Hurt H2S Jimenez-Escobar+2011 Cosmic [H2S]/[H2O] = 2.7%! S HS H2S + H + H CH3OH Towards more sulfur chemical complexity Lahuis+2010 Gaseous C2H2 in hot cores sublimated from ices? Tsuge+2024 C2H2 ice formation in clouds via C diffusion + hydrogenation? McGuire2022 The interstellar chemical inventory McGuire2022 The interstellar chemical inventory As of February 2025:! 332 molecules (CDMS) McGuire2022 The interstellar chemical inventory 300 350 2040 As of February 2025:! 332 molecules (CDMS) McGuire2022 Cosmic S/H ~1.35 x 10-5 Asplund+2009