In this thesis, reactive scattering processes involving the H₂ reaction complex are studied ab initio and fully quantum mechanically. These processes have in common that they involve highly excited electronic states, which could be either bound or resonant. Non-adiabatic couplings, which can be significant both at small and large internuclear distances, need to be included to account for the interaction between the bound electronic states. In addition, the electronic resonant states interact with the ionization continuum at small internuclear distances, which may cause the collision complex to autoionize. In this work, a model is developed which incorporates these different coupling mechanisms. By introducing a quasidiabatic model at small internuclear distances, resonant states and couplings to the ionization continuum are incorporated. The quasidiabatic model is combined with a strict diabatic description, which rigorously incorporates non-adiabatic couplings among the bound electronic states. Nuclear dynamics are solved for using a close-coupling approach in a strict diabatic representation, where a non-local complex potential is included to account for loss into the ionization continuum. With this model, various reactive scattering processes can systematically be studied using the same set of potential energy curves and couplings. The model is applied in studies of H⁺+H^- mutual neutralization, H(1s)+H(ns) and H⁺+H^- associative ionization as well as dissociative recombination and resonant ion-pair formation in electron collisions with HD⁺. Cross sections and branching ratios are compared with results from previous experiments and theoretical studies.