Journal of the American Society for Mass Spectrometry 2009-01-01

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

Anne-Marie Boulanger, David M P Holland, David A Shaw, Paul M Mayer

Index: J. Am. Soc. Mass Spectrom. 20(1) , 20-4, (2009)

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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.