Isotope effects in electron-impact dissociation of D2H+

Abstract

Absolute cross sections have been measured using the crossed electron–ion beams method for electron-impact dissociation of the D2H+ 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) × 10−17 cm2 for H+, (3.56 ± 0.15) × 10−17 cm2 for HD+ and (3.33 ± 0.11) × 10−17 cm2 for D+2, except for D+ for which the maximum cross section is (4.62 ± 0.09) × 10−17 cm2. 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 D2H+ 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 D2H+ are found to be significantly lower than those measured for D+3, although those of DI agree well together.