Nonadiabatic reaction dynamics to silicon monosulfide (SiS): A key molecular building block to sulfur-rich interstellar grains

Abstract

Sulfur- and silicon-containing molecules are omnipresent in interstellar and circumstellar environments, but their elementary formation mechanisms have been obscure. These routes are of vital significance in starting a chain of chemical reactions ultimately forming (organo) sulfur molecules—among them precursors to sulfur-bearing amino acids and grains. Here, we expose via laboratory experiments, computations, and astrochemical modeling that the silicon-sulfur chemistry can be initiated through the gas-phase reaction of atomic silicon with hydrogen sulfide leading to silicon monosulfide (SiS) via nonadiabatic reaction dynamics. The facile pathway to the simplest silicon and sulfur diatomic provides compelling evidence for the origin of silicon monosulfide in star-forming regions and aids our understanding of the nonadiabatic reaction dynamics, which control the outcome of the gas-phase formation in deep space, thus expanding our view about the life cycle of sulfur in the galaxy.

Experimental and theoretical study of the low-temperature kinetics of the reaction of CN with CH2O and implications for interstellar environments

“…In these sources, initial abundances are molecular and reflect those in dust grain ice mantles which evaporate in the hot gas surrounding a massive young star. Our initial fractional abundances are taken from Doddipatla et al 81 Although these values are specific to these objects, our results are likely appropriate to other hot core/corino sources. Fig.…”

Quasiclassical Trajectory Study of the Si + SH Reaction on an Accurate Double Many-Body Expansion Potential Energy Surface

“…Although the rate coefficients currently available in the KIDA 13 and UMIST 14 databases involving this species are related to reactions involving ions, there has been a recent effort to investigate neutral−neutral processes for its formation and destruction both computationally 15−19 and experimentally. 20 Rosi et al 17 recently reported rate constants for the Si + SH reaction based on a Langevin-type capture model and the Rice−Ramsperge−Kassel−Marcus (RRKM) unimolecular reaction. Using density functional theory (DFT) 21 and the coupled-cluster method including single and double electronic excitations and a perturbative correction for triples (CCSD(T)), 22 they characterized the reaction pathways on the doublet state of SiSH using the aug-cc-pV(T+d)Z Dunning-type basis set 23,24 and calculating the harmonic vibrational frequencies with DFT using the B3LYP functional.…”

“…For astrochemical modeling, it is necessary to have accurate rate constants for the involved reactions. Although the rate coefficients currently available in the KIDA and UMIST databases involving this species are related to reactions involving ions, there has been a recent effort to investigate neutral–neutral processes for its formation and destruction both computationally − and experimentally . Rosi et al recently reported rate constants for the Si + SH reaction based on a Langevin-type capture model and the Rice–Ramsperge–Kassel–Marcus (RRKM) unimolecular reaction.…”

The Si + SO2 collision and an extended network of neutral–neutral reactions between silicon and sulphur bearing species

“…Contrary to the fairly well understood SiO chemistry, SiS formation and reactivity is still an open research topic, and new neutral-neutral reactions are being investigated recently, both theoretically (Rosi et al 2018;Paiva et al 2020;Mota et al 2021) and experimentally (Doddipatla et al 2021). Bridging these two major silicon bearing species, the OSiS molecule has also received attention, and Esplugues et al (2013) have provided an upper limit for its column density in Orion KL.…”