Ionized o-, m-, and p-Difluorobenzene Dissociate Through Ring-Opened Intermediates: A TPEPICO Investigation

Threshold photoelectron photoion coincidence (TPEPICO) experiments have shown that o-, m-, and p-difluorobenzene ions dissociate via a common, ring-opened intermediate and not via ionized p-difluorobenzene. Rice-Ramsperger-Kassel-Marcus (RRKM) modeling of the experimental breakdown curves yields activation energies for the initial isomerization of 4.48 ± 0.05, 4.55 ± 0.05, and 4.68 ± 0.05 eV for o-, m-, and p-difluorobenzene, respectively. These values place each ion at a similar absolute energy and thus similar transition states. A large positive ΔS‡ for each ion (ca 100 J K−1 mol−1) suggests a ring-opened structure for these transition states