The extent of isomerization of [&Hlo]+' ions, with lifetimes of approximately 10-l1 and 10-6s has been investigated using field ionization, collisionally activated dissociation and charge stripping techniques. The [C9Hlo]+' ions which were investigated included the molecular ions of a-methylstyrene, P-methylstyrene, o-methylstyrene, m-methylstyrene, pmethylstyrene, indan, cyclopropylbenzene, allylbenzene and the product of water loss from 3-phenylpropanol. The field ionhation spectra of all the &Hlo hydrocarbons were different indicating that isomerization to a common ion structure had not occurred to a measurable extent for ions with lifetimes of approximately 10-l1 s. Collisionally activated dissociation and charge stripping results indicated that most of the [C&,]" ions continued to maintain unique ion structures (or mixtures of structures) at ion lifetimes of lO-'s. Possible exceptions are the [C,Hlo]+' ions from allylbenzene and cyclopropylbenzene which gave indistinguishable collisionally activated dissociation and charge stripping spectra.

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