Fragmentation of negative ions formed in collisions of alkali atoms and halogen molecules

Abstract

Total cross sections have been measured for the production of negative halogen ions in collisions between alkali atoms and homonuclear halogen molecules at relative energies from threshold up to about 20 eV. By means of a mass spectrometer the cross sections for negative parent-ion and fragment-ion production could be measured separately. These measurements confirm the previously measured adiabatic electron affinities of the homonuclear halogen molecules. The fragment- and parent-ion cross sections are about equally large. It was found that the general behaviour of the fragment-ion cross sections is characteristically dependent on the alkali collision partner: the potassium cross sections peak sharply at energies just above threshold; the sodium cross sections, however, have a smooth maximum at higher energies. This could be explained qualitatively by a simple model.