Reactions of cations derived from naphthalene with molecules and atoms of interstellar interest

The chemistry of naphthalene radical cation and its derivatives (C10Hn+, n = 6,7,8,9) has been studied with molecules and atoms of interstellar intere st in a selected ion flow tube. The radical cation C10H8+ is unreactive wit h H-2, CO, H2O, and NH3 but reacts with H, O, and N atoms. Adduct formation is the only channel detected in the case of reaction with H atoms, but add itional channels contribute in reactions between C10H8+ and O and N atoms; these latter reactions proceed through novel reaction pathways via C and CH abstraction, leading to the formation of the stable compounds CO and HCN, respectively. The closed-shell naphthylium cation C10H7+ is essentially unr eactive with atoms but associates via nucleophilic addition with most of th e molecules studied. The reaction kinetics are close to saturation in the a ccessible helium pressure range. The naphthyne radical cation C10H6+ does n ot react with H-2, CO, or H2O but forms an adduct with NH3 at a moderate ra te. Reactions with atoms were found to be very similar to those of C10H8+ T he implications of these results for the stability of polycyclic aromatic h ydrocarbon cations in the interstellar medium are briefly discussed.