Dissociative excitation and recombination ofH3+

Measurements of the cross sections for the electron-impact dissociative excitation of ${\mathrm{H}}_3^{+}$ as a function of electron energy are reported. Sharp structures are observed close to the excitation thresholds for the upper states of the ion, and these are interpreted as Feshbach resonances. Direct excitation appears to play a subordinate role at the energies studied. The implication of these findings applied to previous measurements of the dissociative recombination of ${\mathrm{H}}_3^{+}$ is discussed.