Gas phase Elemental abundances in Molecular cloudS (GEMS): III. Unlocking the CS chemistry: The CS+O reaction
Artikel i vetenskaplig tidskrift, 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.
Astrochemistry
ISM: Abundances
ISM: Clouds
Molecular processes
ISM: Molecules
Författare
N. Bulut
Firat Üniversitesi
O. Roncero
CSIC - Instituto de Fisica Fundamental (IFF)
A. Aguado
Universidad Autonoma de Madrid (UAM)
J. C. Loison
Université de Bordeaux
D. Navarro-Almaida
Observatorio Astronómico Nacional (OAN)
V. Wakelam
Université de Bordeaux
A. Fuente
Observatorio Astronómico Nacional (OAN)
Evelyne Roueff
Université Pierre et Marie Curie (UPMC)
R. Le Gal
Harvard-Smithsonian Center for Astrophysics
P. Caselli
Max-Planck-Gesellschaft
M. Gerin
Université Pierre et Marie Curie (UPMC)
K. M. Hickson
Université de Bordeaux
S. Spezzano
Max-Planck-Gesellschaft
P. Riviere-Marichalar
Observatorio Astronómico Nacional (OAN)
T. Alonso-Albi
Observatorio Astronómico Nacional (OAN)
R. Bachiller
Observatorio Astronómico Nacional (OAN)
I. Jimenez-Serra
Centro de Astrobiologia (CAB)
C. Kramer
Institut de Radioastronomie Millimétrique (IRAM)
B. Tercero
Observatorio Astronómico Nacional (OAN)
Observatorio de Yebes (IGN)
M. Rodríguez-Baras
Observatorio Astronómico Nacional (OAN)
S. G. Burillo
Observatorio Astronómico Nacional (OAN)
J.R. Goicoechea
CSIC - Instituto de Fisica Fundamental (IFF)
Sandra Treviño Morales
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
G. Esplugues
Observatorio Astronómico Nacional (OAN)
S. Cazaux
TU Delft
B. Commerçon
École Normale Supérieure de Lyon
J. C. Laas
Max-Planck-Gesellschaft
J. Kirk
University of Central Lancashire
V. Lattanzi
Max-Planck-Gesellschaft
R. Martín-Doménech
Harvard-Smithsonian Center for Astrophysics
G. Muñoz-Caro
Centro de Astrobiologia (CAB)
J. Pineda
Max-Planck-Gesellschaft
D. Ward-Thompson
University of Central Lancashire
M. Tafalla
Observatorio Astronómico Nacional (OAN)
N. Marcelino
CSIC - Instituto de Fisica Fundamental (IFF)
J. Malinen
Universität zu Köln
Helsingin Yliopisto
R. Friesen
National Radio Astronomy Observatory
B. M. Giuliano
Max-Planck-Gesellschaft
M. Agundez
CSIC - Instituto de Fisica Fundamental (IFF)
A. Hacar
Universiteit Leiden
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 646 A5Ämneskategorier
Oorganisk kemi
Atom- och molekylfysik och optik
Teoretisk kemi
DOI
10.1051/0004-6361/202039611