A potential model, which is represented by the overlap of electron clouds of interacting particles, has been applied to discuss the diabatic potential crossings which lead to one- and two-electron transitions in moderate-energy collisions of closed-shell particles. The crossings evaluated with the potential model interpret reasonably well both differential scattering experiments and ab initio calculations. In the model, the potential crossings originate from the hole(s) produced by the promotion of electron(s) in the outermost shell(s) of incident particle(s).