Appearance energies and the kinetic shift. Loss of HCN from the benzonitrile molecular ion

Measurement of the appearance energy of the [C6H4]+⋅ ion from benzonitrile molecular ions fragmenting in the second field free region of a reverse geometry double focusing mass spectrometer, gives a value free of any significant kinetic shift. The heat of formation of the [C6H4]+⋅ ion calculated using this appearance energy is 1348 kJ mol−1, which is consistent with the ion having the benzyne structure.