Energy distribution of fragments from H2 and H2+ dissociation by electron impact for the use in numerical models applied to negative ion sources

In negative hydrogen ion sources, the kinetic energy of the atoms is directly related to the negative ion yield at the caesiated converter, with a larger contribution from hot atoms. The energy distribution of hydrogen atoms is related to the formation process: either the kinetic energy release, resulting from dissociation of the hydrogen molecules or molecular ions, or the proton neutralization either in the volume or during reflection at walls. The interpretation of recent experimental measurements related to the translational energy distribution of atoms or positive ions could profit from accurate inclusion of the initial energy distribution in numerical models. In this work, we focus on the calculation of the kinetic energy release for the various dissociation channels due to electron impact on H2 and H+2, in the Franck -Condon and delta approximation. Since in negative ion sources non -equilibrium vibrational distributions of H2 are found, the energy distribution of fragments is calculated for all vibrational levels. The inverse cumulative distribution functions related to the main dissociation processes are given, as well as the cumulative distributions for all dissociation channels by electron impact, for simple implementation in Monte Carlo numerical simulations. Finally, the application of the method to few cases of interest for negative ion sources is discussed.