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 $\mathrm{H}\mathrm{}\left(1s\right)+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ and to $\mathrm{H}\mathrm{}\left(1s\right)+\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ by means of the Born-Rudge and Born-Ochkur methods. In addition to direct excitation to the repulsive $b{}_{}{}^3{}_{}{}^{}{\Sigma }_u_{}^{+}{}_{}{}^{}$ state for the first process, cross sections are also computed for excitation of the discrete levels of the $a{{}_{}{}^3{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}}^{+}$, $c{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$, $d{}_{}{}^3{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$, and $e{{}_{}{}^3{}_{}{}^{}\Sigma _u^{}{}_{}{}^{}}^{+}$ 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 $B^{\prime }{{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}}^{+}$ state except near the threshold where $e{{}_{}{}^3{}_{}{}^{}\Sigma _u^{}{}_{}{}^{}}^{+}$ 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 $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$-atom production by electron impact. The difference is attributed mainly to predissociation and dissociative excitation through the doubly excited states.