SiS formation in the interstellar medium through Si+SH gas phase reactions

Abstract

Silicon monosulfide is an important silicon bearing molecule detected in circumstellar envelopes and star forming regions. Its formation and destruction routes are not well understood, partially due to the lack of a detailed knowledge on the involved reactions and their rate coefficients. In this work we have calculated and modeled the potential energy surface (PES) of the HSiS system employing highly accurate multireference electronic structure methods. After obtaining an accurate analytic representation of the PES, which includes long-range energy terms in a realistic way via the DMBE method, we have calculated rate coefficients for the Si+SH$\to$SiS+H reaction over the temperature range of 25-1000K. This reaction is predicted to be fast, with a rate coefficient of $\sim 1\times 10^{-10}\mathrm{c}{\mathrm{m}}^3{\mathrm{s}}^{-1}$ at 200K, which substantially increases for lower temperatures (the temperature dependence can be described by a modified Arrhenius equation with $\alpha =0.770\times 10^{-10}\mathrm{c}{\mathrm{m}}^3{\mathrm{s}}^{-1}$, $\beta =-0.756$ and $\gamma =9.873\mathrm{K}$). An astrochemical gas-grain model of a shock region similar to L1157-B1 shows that the inclusion of the Si+SH reaction increases the SiS gas-phase abundance relative to \ce{H2} from $5\times 10^{-10}$ to $1.4\times 10^{-8}$, which perfectly matches the observed abundance of $\sim 2\times 10^{-8}$.

11 pages, 7 figures. Accepted for publication in The Astrophysical Journal

References in corpus (7)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• The 2014 KIDA network for interstellar chemistry
• The abundance of SiS in circumstellar envelopes around AGB stars
• Si-bearing molecules towards IRC+10216: ALMA unveils the molecular envelope of CWLeo
• Condensation of MgS in outflows from carbon stars
• Sulfur Chemistry in L1157-B1
• Seeds of Life in Space SOLIS. IX. Chemical segregation of $\mathrm{S}{\mathrm{O}}_2$ and SO toward the low-mass protostellar shocked region of L1157

Cited by in corpus (3)

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• First detection of silicon-bearing molecules in $\eta$ Car
• Confirmation of the outflow in L1451-mm: SiO line and CH${}_3$OH maser detections