Photochemistry of Sulfur-species in ice mantles
G. M. Muñoz Caro,1 R. Martín-Doménech,1 H. Carrascosa,1 C. González-Díaz,1B.
Escribano,1 C. del Burgo,1 A. Fuente,1 Y.-J. Chen,2 A. Ciaravella,3 A. Jiménez-Escobar,3 C.
Cecchi-Pestellini,3 S. Cazaux4 and P. Caselli5
Centro de Astrobiología (CAB), INTA-CSIC, Spain
Department of Physics, National Central University, Taiwan
3Osservatorio Astronomico di Palermo, INAF, Italy
4
Faculty of Aerospace Engineering, Delft University of Technology, The Netherlands
5Max Planck Institute for Extraterrestrial Physics, Germany
12Sulfur chemistry is a trending topic in Astrochemistry. Several S-species are commonly detected in the gas
toward interstellar and circumstellar environments, such as SO2, SO, CS, OCS, H2S, C2S and H2CS, but
their total observed abundance in the dense interstellar medium is more than one order of magnitude lower
than the sulfur cosmic abundance. Refractory sulfur in dust grains is summoned to account for theS-depletion in dense clouds and protoplanetary disks. This refractory form of sulfur, however, remains amistery. Laboratory experiments involving irradiation of H2S in the ice, theoretical models, and thedetection of S2, S3 and S4 in comet 67P during the Rosetta mission, suggest that S-chains is a potential
source of refractory sulfur in the dust.
Figure 1 displays the thermal desorption of an irradiated H2S ice sample [1]. Each mass over charge(m/z) value corresponds to the molecular ion of a species or to a fragment of a larger species. The
desorption temperatures of Sx molecules are indicated by the solid vertical lines, while dashed lines indicate
the desorption of H2Sx species. Apart from the molecular ion of each species, the m/z values of the main
fragments used to confirm the presence of these species are displayed.
A brief overview of experiments mimicking the photochemistry of H2S and other S-bearing species in
the ice will be presented. We use the experimental data and modeling to interpret the observational results.
The study of S-species in the ice serves to prepare the observations of refractory sulfur and to interpret thegas phase observations accounting for the desorption of S from the ice. In addition to thermal desorption
when the dust temperature is high enough, other mechanisms were proposed for the release of solid
S-species to the gas phase, among them are chemical desorption [2] and photodesorption [3] . The lattermechanism will also be discussed in our presentation.

Figure 1: Desorption of S-photoproducts during warm-up of a previously UV-irradiated H2S ice layer,adapted from [1].

References[1]
S. Cazaux, H. Carrascosa, G. M. Muñoz Caro, P. Caselli, A. Fuente, D. Navarro-Almaida, & P.
Riviére-Marichalar “Photoprocessing of H2S on dust grains. Building S chains in translucent clouds and comets”,
2022, A&A 657, A100
[2]
Y. Oba, T. Tomaru, T. Lamberts, A. Kouchi, & N. Watanabe ¨An infrared measurement of chemicaldesorption from interstellar ice analogues¨, 2018, Nat. Astron. 2, 228[3]
A. Fuente, J. R. Goicoechea, J. Pety, R. Le Gal, R. Martín-Doménech, P. Gratier, V. Guzmán, E. Roueff, J.
C. Loison, G. M. Muñoz Caro, V. Wakelam, M. Gerin, P. Riviére-Marichalar, Th. Vidal ¨First detection ofinterstellar S2H¨, 2017, ApJL 851, L49