The reactivity of ground-state carbon atoms with unsaturated hydrocarbons in combustion flames and in the interstellar medium

This article reviews recent crossed-beams and ab-initio studies of reactions of ground-state carbon atoms C(3P j ) with unsaturated hydrocarbons and their radicals. All reactions have no entrance barrier and are initiated via an addition of the carbon atom to the ~ system. With the exception of the carbon atom reaction with acetylene, which also shows a significant fraction of molecular hydrogen loss, these bimolecular collisions are dominated by an atomic carbon versus hydrogen atom exchange mechanism. In some systems, homolytic cleavages of carbon-carbon bonds present additional decomposition routes of typically a few per cent at the most. The impact-parameter-dependent chemical dynamics are interpreted in terms of statistical and non-statistical decomposition of reaction intermediates involved. The polyatomic reaction products are highly hydrogend-eficient resonance-stabilized free radicals. The latter are strongly suggested as suitable precursors to form the first (substituted) aromatic ring molecule, polycyclic aromatic hydrocarbon-like species and carbonaceous nanoparticles in combustion processes, chemical vapour deposition and the outflows of carbon stars.