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The Astrophysical Journal


The American Astronomical Society


Two reaction-rate-based kinetic models for condensation of carbon dust via the growth of precursor linear carbon chains are currently under debate: the first involves the formation of C2 molecules via radiative association of free C atoms, and the second forms C2 molecules by the endoergic reaction CO + C → C2 + O.Bothare followedby C captures until the linear chain eventually makes an isomeric transition to ringed carbon on which rapid growth of graphite may occur. These two approaches give vastly different results. Because of the high importance of condensable carbon for current problems in astronomy, we study these competing claims with an intentionally limited reaction rate network which clearly shows that initiation by C + C → C2 + γ is the dominant pathway to carbon rings. We propose an explanation for why the second pathway is not nearly as effective as its proponents calculated it to be.


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