Negative-ion formation and mutual neutralization in atom-atom and ion-ion collisions below keV energies

Dynamics and cross-section values for ion-pair formation and its reverse process, mutual neutralization in atom-atom and ion-ion collisions are reviewed for hydrogen-hydrogen atom collisions and hydrogen-alkali atom collisions. For ion-pair formation process, the initial state shows a weak polarization potential, while the final ion-pair state arises from a strong Coulomb potential. Hence, the final state shows a series of avoided crossings with many intermediate states which correspond to electronic excited states of one of pairs. Therefore, the ladder climbing mechanism is the driving dynamics for ion-pair formation. This fact, that is, many sates are involved in dynamics, makes theoretical treatments more complex and cumbersome for an accurate description. We overview the current experimental and theoretical status of these processes.