Formation and decomposition of distonic o-, m-, and p-benzyne radical cations from photolysis of Mg+(o-, m-, p-C6H4F2)

Distonic o-, m-, and p-benzyne radical cations (1-3) have been generated by a novel photolysis reaction of mass-selected Mg+-difluorobenzene complexes. The energy required for the formation of these radical cations is within 2.2 eV. The formation of o-benzyne cation is most facile. The benzyne radical cations dissociate further to yield ethyne and 1,3-butadiyne radical cation as major products given a sufficient amount of energy. The whole process involves only a single photon, and is very efficient. The calculated threshold for the formation of 1,3-butadiyne radical cation from Mg+(o-C6H4F2) is about 4.6 eV, quite comparable with the experimental estimate.