Gas phase Elemental abundances in Molecular cloudS (GEMS): III. Unlocking the CS chemistry: The CS+O reaction
Journal article, 2021
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 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, ζH2, along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.
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 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, ζH2, along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.
ISM: Molecules
Molecular processes
Astrochemistry
ISM: Clouds
ISM: Abundances
Author
N. Bulut
Firat University
O. Roncero
Spanish National Research Council (CSIC)
A. Aguado
Universidad Autonoma de Madrid (UAM)
J. C. Loison
University of Bordeaux
D. Navarro-Almaida
Spanish National Observatory (OAN)
V. Wakelam
University of Bordeaux
A. Fuente
Spanish National Observatory (OAN)
Evelyne Roueff
Pierre and Marie Curie University (UPMC)
R. Le Gal
Harvard-Smithsonian Center for Astrophysics
P. Caselli
Max Planck Society
M. Gerin
Pierre and Marie Curie University (UPMC)
K. M. Hickson
University of Bordeaux
S. Spezzano
Max Planck Society
P. Riviere-Marichalar
Spanish National Observatory (OAN)
T. Alonso-Albi
Spanish National Observatory (OAN)
R. Bachiller
Spanish National Observatory (OAN)
I. Jimenez-Serra
Centro de Astrobiologia (CAB)
C. Kramer
Institut de Radioastronomie Millimétrique (IRAM)
B. Tercero
Spanish National Observatory (OAN)
Yebes Observatory
M. Rodríguez-Baras
Spanish National Observatory (OAN)
S. G. Burillo
Spanish National Observatory (OAN)
J.R. Goicoechea
Spanish National Research Council (CSIC)
Sandra Treviño Morales
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
G. Esplugues
Spanish National Observatory (OAN)
S. Cazaux
Delft University of Technology
B. Commerçon
École Normale Supérieure de Lyon
J. C. Laas
Max Planck Society
J. Kirk
University of Central Lancashire
V. Lattanzi
Max Planck Society
R. Martín-Doménech
Harvard-Smithsonian Center for Astrophysics
G. Muñoz-Caro
Centro de Astrobiologia (CAB)
J. Pineda
Max Planck Society
D. Ward-Thompson
University of Central Lancashire
M. Tafalla
Spanish National Observatory (OAN)
N. Marcelino
Spanish National Research Council (CSIC)
J. Malinen
University of Cologne
University of Helsinki
R. Friesen
National Radio Astronomy Observatory
B. M. Giuliano
Max Planck Society
M. Agundez
Spanish National Research Council (CSIC)
A. Hacar
Leiden University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 646 A5Subject Categories (SSIF 2011)
Inorganic Chemistry
Atom and Molecular Physics and Optics
Theoretical Chemistry
DOI
10.1051/0004-6361/202039611