Time-dependent study of collinear H-+H2(v) collisions

It has recently been shown [A. K. Belyaev and A. S. Tiukanov, Chem. Phys. Lett., 1999, 302, 65] that the electron detachment process occurring during the reactive or inelastic H− + H2 encounter preferentially takes place from the first excited state of H3−. The present paper investigates the possibility of this process occurring at a relatively low collision energy (Ecoll<2.5 eV) by tunnelling through that first excited electronic state. We use a two-state coupled wavepacket approach restricted to the collinear geometry, where the detachment probability is accounted for by a negative imaginary potential. The calculation is carried out using both the adiabatic representation and a diabatic representation. It is shown that the tunnelling effects efficiently populate the electron detachment channel even in energy domains where the first excited H3− state is energetically closed.