The formation of gas-phased aromatics such as benzene, toluene, and styrene has been elusive under the cold conditions of planetary atmospheres and the Interstellar Medium. We present reaction mechanisms and product branching ratios that show the formation of these aromatics is possible by the addition of ethnyl radical to unsaturated hydrocarbons, which serve as seeds to larger aromatic systems, including polycyclic aromatic hydrocarbons (PAHs). The reaction mechanism is proposed on the basis of the resulting Potential Energy Surface (PES) that includes all the possible intermediates and transition states that can occur, and all the products that lie on the surface. The B3LYP/6-311g(d,p) level of theory is employed to determine optimized electronic structures, zero-point energy, moments of inertia, and vibrational frequencies. They are followed by CCSD(T)/cc-vtz calculations, including extrapolations to complete basis sets (CBS) of the reactants and products. A RRKM study predicts single-collision rate constants and product branching ratios.

Formation of the first aromatic ring in cold planetary atmospheres and the ISM: An ab initio/RRKM study

245th National Meeting (2013)

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