Abstraction and insertion mechanisms in reactive collisions of H-2(+) and D-2(+) with O-

Integral cross-sections were measured for the associative ionisation and reactive ionisation in collisions of H2 + and D2 + with O- by means of a merged-beam set-up operating with keV beams. The magnitude of the reactive cross-sections is quite large (10-14 cm2 at 10 meV), and surpasses the associative ionisation by an order of magnitude. The observed ratio is discussed in terms of insertion and abstraction mechanisms that prevail in the case of atom-diatom inelastic collisions. These measurements may be relevant to the understanding of some astrophysical objects such as the comets, where the presence of the water cation was highlighted.