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The appearance potentials of the vinyl ion as produced by electron impact from eight different compounds have been measured. The corresponding values of the heat of formation of the vinyl ion vary from 274 to 292 kcal/mole, with an average value of 281.5 kcal/mole. It is pointed out that no definitive explanation for the variation can be given. The heat of formation of the vinyl radical is found to be 82.3 kcal/mole, which leads to a value of 122 kcal/mole for the first C–H bond dissociation energy in ethylene. The ionization potential of the vinyl radical is 200.5 kcal/mole=8.69 ev.
F. H. Field (1953) studied this question.