Communication: The formation of CHe2+ by radiative association

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 HeX2+ 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 CHe2+ by radiative association is the center of this study. The question was addressed by means of numerical simulations using high level ab initio calculation...