An ion-trapping technique has been used in the determination of the full kinetic shift for normal fragment ions. As expected, significant kinetic shifts are found for the production of daughter ions from benzonitrile, benzene and touluene, while that involved in the decomposition of ethylene is essentially zero. Appearance potentials determined at long trapping-times are in general agreement with thermo—chemical values. The dependence of kinetic shift on ion source residence-time is discussed in terms of experimentally derived rate-coefficient versus energy data.