Summary

As an alternative to naturally occurring negative ion discrimination, we have used electric dissociation to discriminate between isobars, by destroying the weaker negative ion of a pair. This technique also permits the determination of the properties of the quantum states and the binding energy of some weakly bound negative ions (Ca, Tm, Dy and Yb), some of which had not been studied previously (Tm, Dy, Yb). During the course of this study, it was also established that some very weakly bound negative ions (Dy and Yb) are destroyed by weak electric fields such as those in tandem accelerators. This fact was used to verify the theory of electric dissociation by the comparison of the dissociation probability under different field configurations and gradients. The results regarding the lanthanide elements indicate that in all three cases the extra electron occupies a p orbital which does not follow the ''natural' ' filling of the periodic table. The study of Ca- concluded that the lowest states are the 4s(2)4p P2 J = 1/2, 3/2 states with binding energy of 21.0 +/- 2.5 meV and a spin-orbit splitting in the range 0.4-.5 meV with a maximum probability at 0.75 meV. The ordering of the levels has not yet been established