Laser photodissociation of C₇H₇⁺ created through multiphoton ionization of para-chlorotoluene

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.