Gas-phase phenylium and acyclic [C6H5]+ isomers

The structures of [C₆H₅]⁺ species, formed from a variety of precursors, have been investigated by ion/molecule reactivity studies with pulsed ion cyclotron resonance mass spectrometry and by collision spectroscopy with mass-analyzed ion kinetic energy spectrometry. Formed by sequential ion/molecule reactions in gaseous acetylene, the [C₆H₅]⁺ species are present as a mixture of isomers, those that react with acetylene and those that do not. Ion-assisted dehalogenation reactions were used to establish that the unreactive [C₆H₅]⁺ isomer was the phenylium ion. These data were used to study and confirm collisional decomposition reactions postulated to be diagnostic of the acyclic and phenylium isomers. These diagnostic reactions were then used to study the composition of the [C₆H₅]⁺ isomers produced by electron ionization of a number of precursors. These results are contrasted with previous studies and the collision spectroscopy experiments are described in detail. The possible role of [C₆H₅]⁺ species in flame processes is discussed.