Dissociative Ionization ofH2: A Study of Angular Distributions and Energy Distributions of Resultant Fast Protons

Protons with energies between 2 and 14 eV have been observed from dissociative ionization of ${\mathrm{H}}_2$ using a rotatable collision chamber in conjunction with a small 60° sector magnetic spectrometer, and using electrons with energies ranging from threshold to 1500 eV. The degree of anisotropy in the angular distribution of protons is found to be dependent on electron energy. The anisotropy is analyzed in terms of selection rules and in terms of electron scattering using an analogy with dissociative excitation. The effects of the anisotropy and its electron energy dependence on measurements of cross sections and the energy distribution of protons is investigated. The energy distribution of protons is measured as a function of electron energy, and quite good agreement is found with predictions of the Franck-Condon principle. This is in rather sharp contrast with results of previous investigators.