Recent Updates of Gas-phase Chemical Reactions and Molecular Lines of SiS in CLOUDY

Shaw, Gargi; Ferland, Gary J.; Chatzikos, Marios

doi:10.3847/2515-5172/acc1ea

Cited by 2 publications

(1 citation statement)

References 43 publications

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“…It is also possible that certain rate coefficients with large positive values of β can diverge and be unphysical when extrapolated to temperatures much above the upper limit, T u , of the range over which the fit is made (see Shaw et al 2023 for a discussion of this issue in RATE12). This occurs only for NN reactions and we have identified 10 such reactions.…”

Section: Caveats and Limitationsmentioning

confidence: 99%

The UMIST Database for Astrochemistry 2022

Millar,

Walsh,

Van de Sande

et al. 2024

A&A

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Context. Detailed astrochemical models are a key component to interpret the observations of interstellar and circumstellar molecules since they allow important physical properties of the gas and its evolutionary history to be deduced. Aims. We update one of the most widely used astrochemical databases to reflect advances in experimental and theoretical estimates of rate coefficients and to respond to the large increase in the number of molecules detected in space since our last release in 2013. Methods. We present the sixth release of the UMIST Database for Astrochemistry (UDfA), a major expansion of the gas-phase chemistry that describes the synthesis of interstellar and circumstellar molecules. Since our last release, we have undertaken a major review of the literature which has increased the number of reactions by over 40% to a total of 8767 and increased the number of species by over 55% to 737. We have made a particular attempt to include many of the new species detected in space over the past decade, including those from the QUIJOTE and GOTHAM surveys, as well as providing references to the original data sources. Results. We use the database to investigate the gas-phase chemistries appropriate to both O-rich and C-rich conditions in TMC-1 and to the circumstellar envelope of the C-rich AGB star IRC+10216 and identify successes and failures of gas-phase only models. Conclusions. This update is a significant improvement to the UDfA database. For both the dark cloud and C-rich circumstellar envelope models, calculations match around 60% of the abundances of observed species to within an order of magnitude. There are a number of detected species, however, that are not included in the model either because their gas-phase chemistry is unknown or because they are likely formed via surface reactions on icy grains. Future laboratory and theoretical work is needed to include such species in reaction networks.

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Section: Caveats and Limitationsmentioning

confidence: 99%

The UMIST Database for Astrochemistry 2022

Millar,

Walsh,

Van de Sande

et al. 2024

A&A

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Revisiting the Gas-phase Chemical Rate Coefficients at High Temperatures in CLOUDY

2023

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A two-body gas-phase reaction rate coefficient can be given by the usual Arrhenius-type formula which depends on temperature. The UMIST Database for Astrochemistry is a widely used database for reaction rate coefficients. They provide fittings for coefficients valid over a particular range of temperatures. The permissible upper-temperature limits vary over a wide range: from 100 to 41,000 K. A wide range of temperatures occurs in nature; thus, it requires evaluating the rate coefficients at temperatures outside the range of validity. As a result, a simple extrapolation of the rate coefficients can lead to unphysically large values at high temperatures. These result in unrealistic predictions. Here we present a solution to prevent the gas-phase reaction coefficients from diverging at a very high temperature. We implement this into the spectral synthesis code CLOUDY which operates over a wide range of temperatures from CMB to 1010 K subject to different astrophysical environments.

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Recent Updates of Gas-phase Chemical Reactions and Molecular Lines of SiS in CLOUDY

Cited by 2 publications

References 43 publications

The UMIST Database for Astrochemistry 2022

The UMIST Database for Astrochemistry 2022

Revisiting the Gas-phase Chemical Rate Coefficients at High Temperatures in CLOUDY

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