Fine and hyperfine excitations of CCS isotopologues induced by collisions with He - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2022

Fine and hyperfine excitations of CCS isotopologues induced by collisions with He

A Godard Palluet
F Lique

Résumé

The physical conditions in space are derived from the spectra captured by telescopes. The spectral analysis requires to know the population of molecular energy levels. In astrophysical media, where the local thermodynamic equilibrium conditions are rarely fulfiled, the competition between radiative and collisional processes must to be taken into account. Rate coefficients, which characterize collisional processes, are hence used to derive the abundances of the chemical species. They are preferentially obtained from scattering calculations performed on a potential energy surface (PES) which describe the interaction between the two colliders. The CCS(3Σ−) radical and its isotopologues have been detected in several dark molecular clouds, including TMC-1 and in the circumstellar enveloppe IRC+10216. 1,2 Rate coefficients for this radical do not exist in the literature. Hence, astrophysicists are currently using the ones of the OCS radical to infer the ones of CCS. 3 However, the CCS radical presents large fine structure splitting, which makes the estimation of the rate coefficients incorrect and the line modelisation difficult. 1 Therefore, the CCS rate coefficients must be accuratly determined. The PES used for the close coupling scattering calculations was obtained with the gold standard RCCSD(T) method and an aVQZ basis set with additional mid-bond functions. We provide accurate fine state-to-state rate coefficients for the 5 - 50 K range of temperature for the 12C12C32S, 13C12C32S, 12C13C32S and 12C12C34S isotopologues. The hyperfine structure of the 13C12C32S and 12C13C32S isotopologues had been taken into account to provide hyperfine resolved rate coefficients for the 5 - 20 K temperature range. The determination of CCS abundances derived from these rate coefficients could provide rich informations. Indeed, its abundance ratio with NH3 and 13C isotopologues could be usefull to characterize evolution stages of dark molecular clouds and the chemical processes forming this radical, respectively.
Fichier non déposé

Dates et versions

hal-03725320 , version 1 (16-08-2022)

Identifiants

  • HAL Id : hal-03725320 , version 1

Citer

A Godard Palluet, F Lique. Fine and hyperfine excitations of CCS isotopologues induced by collisions with He. Collisional excitation of (reactive) astrophysical molecules and its applications workshop, Jun 2022, Saint Florent, France. ⟨hal-03725320⟩
28 Consultations
0 Téléchargements

Partager

Gmail Facebook X LinkedIn More