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 H-2(+) and D-2(+) 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) cm(2) 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.