Collisions among molecules can also be viewed as a problem in time-dependent quantum mechanics. The perturbation is the "interaction potential" and the time dependence arises from the movement of the nuclear positions.
Thumbnail: A simple schematic diagram of a two-particle scattering process. One particle is scattered on a single scattering center. The impact parameter and the differential cross section element and the solid angle element in the exit direction are marked. Their quotient is the differential cross section. Image used with permission (CC BY-SA 3.0; Vswitchs)