CF+ excitation in the interstellar medium

Benjamin Desrousseaux (1) , François Lique (1) , Javier R. Goicoechea (2) , Ernesto Quintas-Sánchez (3) , Richard Dawes (4)

1 LOMC - Laboratoire Ondes et Milieux Complexes
2 CSIC - Consejo Superior de Investigaciones Cientificas [España] = Spanish National Research Council [Spain]
3 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
4 Department of Chemistry, Missouri University of Science and Technology, 142 Schrenk Hall, 400 West 11th Street, Rolla, Missouri 65409, United States

The detection of CF+ in interstellar clouds potentially allows astronomers to infer the elemental fluorine abundance and the ionization fraction in ultraviolet-illuminated molecular gas. Because local thermodynamic equilibrium (LTE) conditions are hardly fulfilled in the interstellar medium (ISM), the accurate determination of the CF+ abundance requires one to model its non-LTE excitation via both radiative and collisional processes. Here, we report quantum calculations of rate coefficients for the rotational excitation of CF+ in collisions with para- and ortho-H2 (for temperatures up to 150 K). As an application, we present non-LTE excitation models that reveal population inversion in physical conditions typical of ISM photodissociation regions (PDRs). We successfully applied these models to fit the CF+ emission lines previously observed toward the Orion Bar and Horsehead PDRs. The radiative transfer models achieved with these new rate coefficients allow the use of CF+ as a powerful probe to study molecular clouds exposed to strong stellar radiation fields.

Mots clés: ISM: general; masers; scattering; molecular data; radiative transfer

Domaines: Astrophysique [astro-ph]

Benjamin Desrousseaux, François Lique, Javier R. Goicoechea, Ernesto Quintas-Sánchez, Richard Dawes. CF+ excitation in the interstellar medium. Astronomy and Astrophysics - A&A, 2021, 645, pp.A8. ⟨10.1051/0004-6361/202039823⟩. ⟨hal-03045973⟩