CHAPTER 3: Inelastic Scattering: Basic Theory

The chapter presents the basic quantum theory of inelastic molecular collisions. It focuses on atom–diatom collisions and shows how the conservation of total angular momentum may be used to reduce the complexity of the differential equations that need to be solved. The close-coupling equations that arise from expanding the wavefunction in a basis set are derived. The extraction of the S and T matrices from the asymptotic form of the wavefunction is discussed and the relationship of these matrices to the various cross sections is made clear. Both space-fixed and body-fixed coordinate systems are discussed and the different expressions for the cross sections in terms of the S and T matrices in the two reference frames are contrasted.