Role of potential curve crossing in subexcitation molecular collisions: Exact (two-state) computations vs decoupling approximations for resonance positions

Exact numerical solutions for two-state curve-crossing problems in the subexcitation region are presented and discussed in terms of various decoupling schemes. These provide an approximate, single-channel description of the problem. The energies of the bound states in the (decoupled) closed channel are used as approximations for the resonance positions. The transition from a weak to a strong coupling regime is discussed and a treatment of the resonances in the intermediate coupling region using a diabatic basis is provided.