  The formation of silicon monosulfide (SiS) in space appears to be a difficult
process, but the present work is showing 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 in order to aid in their potential spectroscopic characterization.
