CF${}^{+}$ excitation in the interstellar medium

Abstract

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.

References in corpus (7)

• Compression and ablation of the photo-irradiated cloud the Orion Bar
• The chemistry of ions in the Orion Bar I. - CH+, SH+, and CF+: The effect of high electron density and vibrationally excited H2 in a warm PDR surface
• Discovery of Interstellar CF+
• [CII] emission from L1630 in the Orion B molecular cloud
• HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
• Herschel / HIFI spectral line survey of the Orion Bar - Temperature and density differentiation near the PDR surface
• Widespread Galactic CF+ absorption: detection toward W49 with the Plateau de Bure Interferometer

Cited by in corpus (1)

• Bottlenecks to interstellar sulfur chemistry: Sulfur-bearing hydrides in UV-illuminated gas and grains