Mutual neutralization in low-energy H++H- collisions: A quantum ab initio study

The mutual neutralization of H+ and H- at low collision energies is studied by means of a molecular close-coupling approach. All degrees of freedom are treated at the full quantum level also taking into account the identity of the nuclei. The relevant (1)Sigma(+)(g) and (1)Sigma(+)(u) electronic states as well as the associated nonadiabatic radial couplings are calculated for internuclear distances between 0.5 and 50a(0). Following a transformation into a strictly diabatic basis, these quantities enter into a set of coupled equations for the motion of the nuclei. Numerical solution of these equations allows the cross sections for neutralization into the H(1)+H(n), n=1,2,3 final states to be calculated. In the present paper, results are reported for the collision energy region 0.001-100 eV, with special emphasis on the important energy region below 10 eV. The low temperature rate coefficient is obtained from a parametrization of the calculated cross section and is estimated to be valid over the range 10-10 000 K.