A Possible Additional Formation Pathway for the Interstellar Diatomic SiS

Abstract

The formation of silicon monosulfide (SiS) in space appears to be a difficult process, but the present work shows that a previously excluded pathway may contribute to its astronomical abundance. Reaction of the radicals SH + SiH produces SiS with a submerged transition state and generates a stabilizing H _2 molecule as a product to dissipate the kinetic energy. Such is a textbook chemical reaction for favorable gas-phase chemistry. While previously proposed mechanisms reacting atomic sulfur and silicon with SiH, SH, and H _2 S will still be major contributors to the production of SiS, an abundance of SiS in certain regions could be a marker for the presence of SiH where it has previously been unobserved. These quantum chemically computed reaction profiles imply that the silicon-chalcogen chemistry of molecular clouds, shocked regions, or protoplanetary disks may be richer than previously thought. Quantum chemical spectral data for the intermediate cis - and trans -HSiSH are also provided to aid in their potential spectroscopic characterization.

Keywords

• Astrochemistry
• Interdisciplinary astronomy
• Neutral-neutral reactions
• Quantum-chemical calculations
• Shocks