Measured appearance energies of fragment ions produced by electron impact on

We have used mass spectrometric techniques to determine the appearance energies for the formation of small, singly charged fragment ions produced by controlled electron impact on under single collision conditions. The measured appearance energies range from 79 eV to 91 eV and show, within the experimental error bar of eV, little variation with the cluster size. This result is distinctly different from the behaviour of the previously measured appearance energies for the large fragment ions to and indicates that the small fragment ions are the result of a different fragmentation pathway.