We formulate scattering in one dimension due to the coupled Schrödinger equation in terms of the S matrix, the unitarity of which leads to constraints on the scattering amplitudes. Levinson’s theorem is seen to have the form η(0)=π(nb+1/2n−1/2N), where η(0) is the phase of the S matrix at zero energy, nb the number of bound states with nonzero binding energy, n the number of half‐bound states, and N the number of coupled equations. In view of the effects due to the half‐bound states, the threshold behaviour of the scattering amplitudes is investigated in general, and is also illustrated by means of particular potential models.

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