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.

Astrochemistry

ISM: Abundances

ISM: Clouds

Molecular processes

ISM: Molecules

Author

N. Bulut

Firat University

O. Roncero

CSIC - Instituto de Fisica Fundamental (IFF)

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

CSIC - Instituto de Fisica Fundamental (IFF)

Sandra Treviño Morales

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

G. Esplugues

Spanish National Observatory (OAN)

S. Cazaux

Delft University of Technology

B. Commerçon

Ecole Normale Superieure 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

CSIC - Instituto de Fisica Fundamental (IFF)

J. Malinen

University of Cologne

University of Helsinki

R. Friesen

National Radio Astronomy Observatory

B. M. Giuliano

Max Planck Society

M. Agundez

CSIC - Instituto de Fisica Fundamental (IFF)

A. Hacar

Leiden University

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 646 A5

Subject Categories

Inorganic Chemistry

Atom and Molecular Physics and Optics

Theoretical Chemistry

DOI

10.1051/0004-6361/202039611

More information

Latest update

3/22/2021