title: Communication: The formation of CHe(2+) by radiative association.
abstract: The detection of ArH(+) has revived the interest in the search for noble gas containing species. Despite helium being the second most abundant element in the universe (He/H ∼ 1/10), it has never been observed in any other form than that of a neutral/ionized atom in the interstellar medium. Because He is the "most noble" gas, its non-observation as part of neutral molecular systems is understandable. It is more surprising for charged species, especially HeH(+) whose spectral signatures are well documented in the laboratory. The purpose of this work was to find a simple positive ion containing He, and likely to be observed as an alternative to undetected HeH(+). Among the HeX(2+) diatomics formed with first row atoms, we focused on X = C because of both its relative abundance and the magnitude of its ionization potentials with respect to He. The formation of CHe(2+) by radiative association is the center of this study. The question was addressed by means of numerical simulations using high level ab initio calculations of the CHe(2+) potential surface, followed by a quantum chemical determination of the rate coefficients for the corresponding radiative association in the range of 10 to 1000K. The radiative association path shows a potential well deep enough to accommodate 20 vibrational levels, and no barrier to oppose the reaction. The rate coefficient varies from ∼4.5 × 10(-20) cm(3)s(-1) to ∼2.5 × 10(-22) cm(3)s(-1) for the temperatures considered. The present study suggests that the existence of this species has to be searched for mainly in highly irradiated regions.
authors.affiliation: Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ. Paris 06, UMR - CNRS 7616, F-75005 Paris, France.
authors.forename: E
authors.initials: E
authors.lastname: Zicler
authors.affiliation: Institut Lumière Matière, UMR5306 Université Lyon1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex, France.
authors.forename: M-C
authors.initials: MC
authors.lastname: Bacchus-Montabonel
authors.affiliation: Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ. Paris 06, UMR - CNRS 7616, F-75005 Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Pauzat
authors.affiliation: Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ. Paris 06, UMR - CNRS 7616, F-75005 Paris, France.
authors.forename: P
authors.initials: P
authors.lastname: Chaquin
authors.affiliation: Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ. Paris 06, UMR - CNRS 7616, F-75005 Paris, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Ellinger