Oscillations in gas-grain astrochemical kinetics

Dufour, Gwenaëlle; Charnley, Steven B.; Lindberg, Johan E.

doi:10.1093/mnras/stad110

Cited by 2 publications

(1 citation statement)

References 41 publications

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“…These oscillations are thought to occur due to the existence of bistable solutions (Dufour & Charnley 2019), related to autocatalytic processes in the gas phase. Moreover, they can lead to limit cycles and chemical relaxation oscillation solutions when coupled with the gas-grain exchange of key species (Dufour et al 2023), and they usually take place on timescales of interest for comparing models and observations.…”

Section: Chemical Modeling Of Hocs +mentioning

confidence: 99%

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺

Sanz-Novo,

Rivilla,

Jiménez-Serra

et al. 2024

ApJ

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We present the first detection in space of O-protonated carbonyl sulfide (HOCS+), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all K a = 0 transitions ranging from J lo = 2 to J lo = 13 of HOCS+ covered by our survey, we derive a column density of N = (9 ± 2) × 1012 cm−2, translating into a fractional abundance relative to H2 of ∼7 × 10−11. Conversely, the S-protonated HSCO+ isomer remains undetected, and we derive an upper limit to its abundance with respect to H2 of ≤3 × 10−11, a factor of ≥2.3 less abundant than HOCS+. We obtain an HOCS+/OCS ratio of ∼2.5 × 10−3, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of HOCS+ is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionization rates (10−15–10−14 s−1) are needed to reproduce the observed abundance of HOCS+. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find an HOCO+/HOCS+ ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.

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Section: Chemical Modeling Of Hocs +mentioning

confidence: 99%

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺

Sanz-Novo,

Rivilla,

Jiménez-Serra

et al. 2024

ApJ

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New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low- and high-metallicity values

Mendoza,

Costa,

Carvajal

et al. 2024

A&A

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Among the silicon-bearing species discovered in the interstellar medium, SiS and SiO stand out as key tracers due to their distinct chemistry and variable abundances in interstellar and circumstellar environments. Nevertheless, while the origins of SiO are well documented, the SiS chemistry remains relatively unexplored. Our objective is to enhance the network of Si- and S-bearing chemical reactions for a gas-grain model in molecular clouds, encompassing both low and high metallicities. To achieve this, we calculated the energies and rate coefficients for six neutral atom-diatom reactions involved in the SiCS triatomic system, with a special focus on the C+SiS and S+SiC collisions. We employed the coupled-cluster method with single and double substitutions and a perturbative treatment of triple substitutions (CCSD(T)) refined at the explicitly correlated CCSD(T)-F12 level. With these computational results in conjunction with supplementary data from the literature, we construct an extended network of neutral-neutral chemical reactions involving Si- and S-bearing molecules. To assess the impact of these chemical reactions, we performed time-dependent models employing the Nautilus gas-grain code, setting the gas temperature to 10 K and the H$_2$ density to 2times 10$^4$ cm$^ $. The models considered two initial abundance scenarios, corresponding to low- and high-metallicity levels. Abundances were computed using both the default chemical network and the constrained network, enriched with newly calculated reactions. The temperature dependence for the reactions involving SiS were modelled to the $k(T)= T/300 beta gamma/T) $ expression, and the coefficients are provided for the first time. The high-metallicity models significantly boost the SiS production, resulting in abundances nearly four orders of magnitude higher compared to low-metallicity models. Higher initial abundances of C, S, and Si, roughly sim 2, 190, and 210 times higher, respectively, contribute to this. Around the age of 10$^3$ yr, destruction mechanisms become relevant, impacting the abundance of SiS. The proposed production reaction S + SiC longrightarrow C + SiS, mitigates these effects in later stages. By expanding the gas reaction network using a high-metallicity model, we derived estimates for the abundances of observed interstellar molecules, including SiO, SO, and SO$_2$. We demonstrate the significance of both SiC+S and C+SiS channels in the SiS chemistry. Notably, the inclusion of neutral-neutral mechanisms, particularly via Si+HS and S+SiC channels, played a pivotal role in determining SiS abundance. These mechanisms carry a significance level on a par with that of the well-known and fast ion-neutral reactions.

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Oscillations in gas-grain astrochemical kinetics

Cited by 2 publications

References 41 publications

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺

New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low- and high-metallicity values

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Oscillations in gas-grain astrochemical kinetics

Cited by 2 publications

References 41 publications

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS+

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS+

New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low- and high-metallicity values

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Product

Resources

About

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺

Interstellar Detection of O-protonated Carbonyl Sulfide, HOCS⁺