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

El Ghazaly, Mohamed Ould Jureta, Jozo [UCL] Urbain, Xavier [UCL] Defrance, Pierre [UCL]

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 2psigma(u) repulsive state in the vicinity of their outer turning point. This observation is consistent with the measured vibrational population extending up to upsilon = 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 (1ssigma(g) --> 2psigma(u)), (1ssigma(g) --> 2ppi(u)) and (1ssigma(g) --> 2ssigma(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 2ppi(u) and 2ssigma(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.