A mass spectrometry/mass spectrometry investigation of the nature of [C₁₀H₁₀]^+˙, [C₉H₇]⁺ and [C₁₀H₈]^+˙ gas phase ions

Additional evidence for the rearrangement of the 1‐ and 3‐phenylcyclobutene radical cations, their corresponding ring‐opened 1,3‐butadiene ions and 1,2‐dihydronaphthalene radical cations to methylindenetype ions has been obtained for the decomposing ions by mass analysed ion kinetic energy spectroscopy (MIKES). The nature of the [C₉H₇]⁺ and [C₁₀H₈]^+˙ daughter ions arising from the electron ionization induced fragmentation of these [C₁₀H₁₀]^+˙ precursors has been investigated by collisionally activated dissociation (CAD), collisional ionization and ion kinetic energy spectroscopy. The [C₉H₇]⁺ produced from the various C₁₀H₁₀ hydrocarbons are of identical structure or an identical mixture of interconverting structures. These ions are similar in nature to the [C₉H₇]⁺ generated from indene by low energy electron ionization. The [C₁₀H₈]^+˙ ions also possess a common structure, which is presumably that of the maphthalene radical cation.