Efficient Production of S${}_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions

Abstract

In this work, we reexamine sulfur chemistry occurring on and in the ice mantles of interstellar dust grains, and report the effects of two new modifications to standard astrochemical models; namely, (a) the incorporation of cosmic ray-driven radiation chemistry and (b) the assumption of fast, non-diffusive reactions for key radicals in the bulk. Results from our models of dense molecular clouds show that these changes can have a profound influence on the abundances of sulfur-bearing species in ice mantles, including a reduction in the abundance of solid-phase H${}_2$S and HS, and a significant increase in the abundances of OCS, SO${}_2$, as well as pure allotropes of sulfur, especially S${}_8$. These pure-sulfur species - though nearly impossible to observe directly - have long been speculated to be potential sulfur reservoirs and our results represent possibly the most accurate estimates yet of their abundances in the dense ISM. Moreover, the results of these updated models are found to be in good agreement with available observational data. Finally, we examine the implications of our findings with regard to the as-yet-unknown sulfur reservoir thought to exist in dense interstellar environments.

ApJ, accepted: 37 pages, 8 figures

References in corpus (19)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition
• Modeling Sulfur Depletion in Interstellar Clouds
• Sulfur chemistry in protoplanetary disks: CS and H2CS
• Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
• Modelling the sulphur chemistry evolution in Orion KL
• A new look at sulphur chemistry in hot cores and corinos
• Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H${}_2$O${}_2$ $\to$ H${}_2$O + OH
• H2S in the L1157-B1 Bow shock
• Interstellar Simulations Using A Unified Microscopic-Macroscopic Monte Carlo Model with a full Gas-Grain Network including Bulk Diffusion in Ice Mantles
• Search for Interstellar monohydric Thiols
• The Case of H${}_2$C${}_3$O Isomers, Revisited: Solving the Mystery of the Missing Propadienone
• On Simulating the Proton-Irradiation of O${}_2$ and H${}_2$O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity
• Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
• Tunneling Reaction Kinetics for the Hydrogen Abstraction Reaction H + H${}_2$S -> H${}_2$ + HS in the Interstellar Medium
• A new model of the chemistry of ionizing radiation in solids: CIRIS
• Sulfur Chemistry in L1157-B1