A flowing-afterglow method has been applied to optical spectroscopic studies on two types of ion-ion reactions between positive and negative ions. One is two-body and three-body ionic-recombination reactions leading to rare gas halide excimers (RgX*), and the other is two-body ion-ion neutralization reactions of NO⁺ with SF₆^- and C₆F₆^- leading to NO*. For the former recombination reactions, the electronic and vibrational state distributions of excimers, the relative formation rates of excimers and predissociation products, and the effects of the third-body atom in the three-body reactions are examined by isolating one of the spin-orbit state of rare gas ion, Rg⁺(^2p _1/2) or  Rg⁺(^2p _3/2). For the latter neutralization reactions, the dependence of internal state distributions of NO* on the negative ion is examined. On the basis of product state distributions, dynamical features of ion-ion reactions are discussed.