Ionized o-, m-, and p-difluorobenzene dissociate through ring-opened intermediates: A TPEPICO investigation

Abstract

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 DeltaS(double dagger) for each ion (ca 100 J K(-1) mol(-1)) suggests a ring-opened structure for these transition states.

Long Bonds and Short Barriers: Ionization and Isomerization of Alkyl Nitriles

“…The energy difference between pentanenitrile and 3b is 9.64 eV (G3//B3-LYP value, Table 10). To test this hypothesis, this energy difference was used to convert photon energy to ion internal energy of 3b, and the four competing dissociation channels were modeled in the manner described in a series of previous publications 29,30,[44][45][46][47][48] (Figure 8). Each channel is characterized by an activation energy, E 0 , and entropy, ∆ ‡ S. The derived best theoretical fits to the experimental data were obtained by adjusting E 0 and the estimated transition-state vibrational frequencies for each channel.…”