1 Ocak 2023 Dergi makalesi Açık Erişim

Rocha, Carlos M. R.; Roncero, Octavio; Bulut, Niyazi; Zuchowski, Piotr; Navarro-Almaida, David; Fuente, Asuncion; Wakelam, Valentine; Loison, Jean-Christophe; Roueff, Evelyne; Goicoechea, Javier R.; Esplugues, Gisela; Beitia-Antero, Leire; Caselli, Paola; Lattanzi, Valerio; Pineda, Jaime; Le Gal, Romane; Rodriguez-Baras, Marina; Riviere-Marichalar, Pablo

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{
  "DOI": "10.1051/0004-6361/202346967", 
  "abstract": "<p>Context. Carbon monosulphide (CS) is among the few sulphur-bearing species that have been widely observed in all environments, including in the most extreme, such as diffuse clouds. Moreover, CS has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. Therefore, a complete understanding of its chemistry in all environments is of paramount importance for the study of interstellar matter.</p>\n<p>Aims. Our group is revising the rates of the main formation and destruction mechanisms of CS. In particular, we focus on those involving open-shell species for which the classical capture model might not be sufficiently accurate. In this paper, we revise the rates of reactions CH + S -&gt; CS + H and C-2 + S -&gt; CS + C. These reactions are important CS formation routes in some environments such as dark and diffuse warm gas.</p>\n<p>Methods. We performed ab initio calculations to characterize the main features of all the electronic states correlating to the open shell reactants. For CH+S, we calculated the full potential energy surfaces (PESs) for the lowest doublet states and the reaction rate constant with a quasi-classical method. For C-2+S, the reaction can only take place through the three lower triplet states, which all present deep insertion wells. A detailed study of the long-range interactions for these triplet states allowed us to apply a statistic adiabatic method to determine the rate constants.</p>\n<p>Results. Our detailed theoretical study of the CH + S -&gt; CS + H reaction shows that its rate is nearly independent of the temperature in a range of 10-500 K, with an almost constant value of 5.5 x 10(-11) cm(3) s(-1) at temperatures above 100 K. This is a factor of about 2-3 lower than the value obtained with the capture model. The rate of the reaction C-2 + S -&gt; CS + C does depend on the temperature, and takes values close to 2.0 x 10(-10) cm(3) s-(1) at low temperatures, which increase to similar to 5.0 x 10(-10) cm(3) s(-1) for temperatures higher than 200 K. In this case, our detailed modeling - taking into account the electronic and spin states - provides a rate that is higher than the one currently used by factor of approximately 2.</p>\n<p>Conclusions. These reactions were selected based on their inclusion of open-shell species with many degenerate electronic states, and, unexpectedly, the results obtained in the present detailed calculations provide values that differ by a factor of about 2-3 from the simpler classical capture method. We updated the sulphur network with these new rates and compare our results in the prototypical case of TMC1 (CP). We find a reasonable agreement between model predictions and observations with a sulphur depletion factor of 20 relative to the sulphur cosmic abundance. However, it is not possible to fit the abundances of all sulphur-bearing molecules better than a factor of 10 at the same chemical time.</p>", 
  "author": [
    {
      "family": "Rocha", 
      "given": " Carlos M. R."
    }, 
    {
      "family": "Roncero", 
      "given": " Octavio"
    }, 
    {
      "family": "Bulut", 
      "given": " Niyazi"
    }, 
    {
      "family": "Zuchowski", 
      "given": " Piotr"
    }, 
    {
      "family": "Navarro-Almaida", 
      "given": " David"
    }, 
    {
      "family": "Fuente", 
      "given": " Asuncion"
    }, 
    {
      "family": "Wakelam", 
      "given": " Valentine"
    }, 
    {
      "family": "Loison", 
      "given": " Jean-Christophe"
    }, 
    {
      "family": "Roueff", 
      "given": " Evelyne"
    }, 
    {
      "family": "Goicoechea", 
      "given": " Javier R."
    }, 
    {
      "family": "Esplugues", 
      "given": " Gisela"
    }, 
    {
      "family": "Beitia-Antero", 
      "given": " Leire"
    }, 
    {
      "family": "Caselli", 
      "given": " Paola"
    }, 
    {
      "family": "Lattanzi", 
      "given": " Valerio"
    }, 
    {
      "family": "Pineda", 
      "given": " Jaime"
    }, 
    {
      "family": "Le Gal", 
      "given": " Romane"
    }, 
    {
      "family": "Rodriguez-Baras", 
      "given": " Marina"
    }, 
    {
      "family": "Riviere-Marichalar", 
      "given": " Pablo"
    }
  ], 
  "container_title": "ASTRONOMY & ASTROPHYSICS", 
  "id": "270264", 
  "issued": {
    "date-parts": [
      [
        2023, 
        1, 
        1
      ]
    ]
  }, 
  "page": "13", 
  "title": "Gas phase Elemental abundances in Molecular cloudS (GEMS) VIII. Unlocking the CS chemistry: The CH plus S \u2192 CS + H and C<sub>2</sub> + S \u2192 CS plus C reactions", 
  "type": "article-journal", 
  "volume": "677"
}