The nature of the C7H7+ ion created through resonant dissociative multiphotoionization of para-chlorotoluene by an ultraviolet (UV) laser was investigated thanks to its interaction with a second laser beam. The dissociation pattern corresponding to one or several photon absorption could be observed. Cross section for the one-photon absorption in the 265/530 nm range revealed the presence of the tropylium and benzyl isomers and suggested they possessed substantial internal energy. This was confirmed by the study of the C7H7+ + hv⇒C 5H5++C2H2 reaction, and more precisely of its rate and of the kinetic energy released. A ladder switch mechanism for the three-photon dissociative ionization of para-chlorotoluene leading to C7H7+ is shown to agree with our results.
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