Extraterrestrial Organic Molecules from [SiX](+) Ions: A Coupled Cluster Theory Inquest for Plausible Reaction Pathways

Abstract

The formation of organic molecules in the interstellar medium is still an elusive process. In recent times, numerous experimental and computational attempts have been made to understand the synthesis of extraterrestrial molecules. Herein, we report the possibility of the formation of organic molecules from simple silicon-containing diatomic molecules. The motivation of this work stems from the fact that several silicon-containing species have been detected in circumstellar envelopes of aging stars such as IRC+10216 (C.W. Leonis). Some organic molecules, such as methanol, ethylene, methylamine, hydrogen cyanide, ethylene, and so on, have also been observed in these chemically rich environments. However, there are no reports on the role of these silicon-containing species in the formation of organic molecules. With the help of "gold standard" quantum chemical calculations, that is, at the CCSD(T)/TZVPP level, reactions of SiX+ (X = C, N, O, and S) with the simplest organic molecule, methane, have been explored. The reaction pathway for each reaction has been proposed, and the corresponding potential energy curve has been deduced. The obtained results in the form of potential energy curves have been analyzed for the feasibility of corresponding reactions under circumstellar conditions. The potential energy curves (PEC) in most reactions show a downward cascade, indicating the thermodynamic favorability of the reactions and the feasibility of forming organic molecules from Si-containing diatomic molecules.