A Study of the Stabilities of Negative Ions

Abstract

The Magnetron technique, which had been developed for the measurement of electron affinities from observations on the equilibrium between neutrals, electrons, and ions at a heated metal surface, was applied to the measurement of electron affinities of both radicals and molecules. A series of metal hexafluorides was studied, which showed that they captured electrons directly to form negative ions of the type MF6. The relative electron affinities of these compounds were shown to be consistent with their relative oxidizing powers. Electron capture by the radicals C2H., CF3., SiF3., R1R2N., and R1R2P. (where R1 and R2 can be phenyl (Ph), methyl (Me), or hydrogen (H)) was studied to determine the effect the nature of the centre of acceptance and substitution at this centre had upon the electron affinity of the radical. The additional electron was shown to be localized as a lone pair on the atomic centre where the free valence lay, and the experimental electron affinity was compared to the calculated electron affinity of the atomic centre in the same valence state, as given by the method of Hinze and Jaffe. The disadvantage of the Magnetron technique lay in the fact that the identification of the ions was only indirect and, therefore, complex reactions, which gave rise to similar numbers of ions of differing mass, could have been misinterpreted in terms of a simple reaction. To overcome this, a surface ionization source was attached to an Atlas AMP 3 Quadrupole Mass Filter, which enabled direct identification of the ions to be made along with the usual Magnetron type measurements.