2020/12/18 by N. Bulut, Niyazi Bulut, O. Roncero +59
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Ab initio #Astrochemistry #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Atmospheric chemistry and aerosols #Atomic physics #Chemistry #Context (archaeology) #Extrapolation #Galaxy #Interstellar cloud #Interstellar medium #Observable #Physics #Quantum #Reaction rate #Semiclassical physics #astro-ph.GA
paper · pdf · doi:10.1051/0004-6361/202039611
published as Astronomy & Astrophysics 646, A5 (2021) · 11 pages, 10 figures, accepted in Astronomy & Astrophysics
arxiv created 2020/12/18 · openalex publication_date 2020/12/19 · openalex created_date 2021/01/05 · arxiv updated 2021/02/05 · openalex updated_date 2026/08/05
Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O → CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150−400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures <150 K which are prevailing in the interstellar medium. Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS+O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T ~ 150−400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150–400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10 −15 cm 3 s −1 , which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, ζ H 2 , along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.