A trapped electron apparatus employing an R.P.D. electron gun has been built for electron impact studies of excitation and negative ion formation. It operates in the energy range from 0 to 25 eV with a resolution of 0.35 eV and a reproducibility of ± 0.17 eV. Preliminary studies of hydrogen indicate reproducible structure in the dissociative attachment process known to occur between 8 and 10.7 eV. Four resonances attributed to dissociative attachment in chlorine have been identified with peak values at 0, 1.75, 3.07 and 5.9 ± 0.17 eV. The first three resonances have the same dissociation limit, while the fourth is distinct and contains reproducible structure. At higher energies, an excitation process and ion pair formation have been identified. Similar dissociative attachment processes in bromine give rise to resonance peaks at 0.05, 0.98 and 3.30 ± 0.17 eV. AIl of the processes lead to the same dissociation products. For iodine, dissociative attachment peaks arise at energies of 0.28, 0.58 and 2.15 ± 0.17 eV. AIl three processes produce products in the same energy states. A sharp break at 8.27 ± 0.17 eV is attributed to the initiation of ion pair formation.

Goodings, J. (Supervisor)