The reaction of polycyclic aromatic hydrocarbon cations with hydrogen atoms: The astrophysical implications

The reaction of the naphthalene cation, C10H8+, with H atoms is exothermic by about 60 kcal mol(-1) and yields the 1-hydronaphthalene cation C10H9+. T he addition of a second H atom is exothermic by about 45 kcal mol(-1), lead ing to the 1, 2-dihydronaphthalene cation C10H10+, which has less aromatic character than the parent naphthalene cation. Such products have been ident ified from the C-H stretching modes of the unidentified infrared bands. The abstraction of H from the 1-hydronaphthalene cation is found to have littl e, if any, barrier. This suggests that the polycyclic aromatic hydrocarbon (PAH) cations can catalyze the recombination of H atoms in the gas phase. S ince the barrier to abstracting a deuterium is larger than hydrogen, reacti ons of hydrogen with PAH cations could enhance the degree of deuterium enri chment in PAHs.