CHAPTER 3: Low-energy Scattering in Crossed Molecular Beams

This chapter is devoted to the experimental observation of neutral molecular collisions (reactive or inelastic scattering) at low energies, corresponding to thermal mean values (<E> = 3/2 RT) at temperatures in the near-cold domain (1–50 K). Basic notions are given on the dynamics of molecular collisions and on the experimental approaches used to study such processes using molecular beam techniques. A special emphasis is given on the link from the measurements (what can be detected) to the physical quantities of interest (what information can be deduced). Examples are also given of quantum resonances recently observed in reactive as well as inelastic collisions at low energies.