Dissociation of the hydrogen molecule by electron impact

Abstract

The electron-impact dissociation cross sections of the ${\mathrm{H}}_{2}$ molecule have been calculated for the processes leading to $\mathrm{H}(1s)+\mathrm{H}(1s)$ and to $\mathrm{H}(1s)+\mathrm{H}(2s)$ by means of the Born-Rudge and Born-Ochkur methods. In addition to direct excitation to the repulsive $b^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state for the first process, cross sections are also computed for excitation of the discrete levels of the $a{^{3}\ensuremath{\Sigma}_{g}}^{+}$, $c^{3}\ensuremath{\Pi}_{u}$, $d^{3}\ensuremath{\Pi}_{u}$, and $e{^{3}\ensuremath{\Sigma}_{u}}^{+}$ states in order to account for cascades. These two mechanisms are found to be of equal importance. The second process is found to proceed mainly through excitation of the ${B}^{\ensuremath{'}}{^{1}\ensuremath{\Sigma}_{g}}^{+}$ state except near the threshold where $e{^{3}\ensuremath{\Sigma}_{u}}^{+}$ is an important contributor. The theoretical cross sections are in reasonably good agreement with experimental data for the first process. The cross sections of the second process account for nearly two-thirds of the measured cross sections of $\mathrm{H}(2s)$-atom production by electron impact. The difference is attributed mainly to predissociation and dissociative excitation through the doubly excited states.