Total cross sections and kinetic energy release for the electron impact dissociation of H⁺₂and D⁺₂

Absolute total cross sections have been measured for electron impact dissociative excitation and dissociative ionization of H + 2 and D + 2 in the energy range 5–3000 eV. The vibrational population of the primary H + 2 beam has been analysed by dissociative charge exchange on a potassium target, and is in good agreement with the measurements of von Busch and Dunn (1972 Phys. Rev. A 5 1726). Kinetic energy release (KER) distributions have been extracted from momentum analysis of the released protons and deuterons at selected impact energies. A model calculation has been performed to interpret the different spectra. Below 100 eV, the distributions exhibit a sharp peak in the range 0–1 eV that is attributed to the dissociative excitation of high vibrational levels to the 2pσ u repulsive state in the vicinity of their outer turning point. This observation is consistent with the measured vibrational population extending up to v = 13, as confirmed by the appearance threshold of the dissociative ionization (DI) channel. The KER distributions exhibit a second contribution peaking between 1 and 5 eV, resulting from the admixture of the (1sσ g → 2pσ u ), (1sσ g → 2pπ u ) and (1sσ g → 2sσ g ) electronic transitions. A distinctive hump is also present around 9 eV, that coincides both with the maximum of the DI contribution, and with the high-energy shoulder of the 2pπ u and 2sσ g contributions. The present measurements are in qualitative agreement with the previous results of Caudano and Delfosse, and are fairly well reproduced by our first-order model.