Isotope effects in electron-impact dissociation of D(2)H(+)

Defrance, Pierre [UCL] Jureta, Jozo [UCL] Lecointre, Julien [UCL] Urbain, Xavier [UCL]

Absolute cross sections have been measured using the crossed electron-ion beams method for electron-impact dissociation of the D(2)H(+) molecular ion yielding H(+), D(+), HD(+) and D(2)(+) fragments. The collision energy ranges from a few eV up to 2.5 keV. Around the maximum, cross sections are found to be of a similar amplitude: (3.25 +/- 0.08) x 10(-17) cm(2) for H(+), (3.56 +/- 0.15) x 10(-17) cm(2) for HD(+) and (3.33 +/- 0.11) x 10(-17) cm(2) for D(2)(+), except for D(+) for which the maximum cross section is (4.62 +/- 0.09) x 10(-17) cm(2). Individual contributions for dissociative excitation (DE) and for dissociative ionization (DI) are determined for each product. Close analysis of present data brings into evidence isotope effects in the fragmentation pattern of the D(2)H(+) target. Ejection of the lightest isotope is generally favoured: for resonant DE (H(+) over D(+)), for DE (molecular ions D(2)(+) and HD(+), associated with ejection of H and D, respectively) and for dissociative ionization, but not for H(+) and D(+) produced via direct dissociative excitation. Present DE cross sections for D(2)H(+) are found to be significantly lower than those measured for D(3)(+), although those of DI agree well together.