Quantum collisions in semi-constrainted structures

The problem of a quantum particle moving in a narrow, bent two-dimensional channel is used to illustrate features of collisions in systems with semi-constrained structures. The collision theory of such systems is developed and, under certain general restrictions on the geometry, the following properties are rigorously established: (1) The (localized) Møller wave operator exist and the S operator is unitary in the scattering channels. (2) The singular spectrum is discrete in intervals away from the continuum thresholds. The discussion is based on a time-dependent approach.