Semiclassical nearside–farside theory for inelastic and reactive atom–diatom collisions

We generalise the semiclassical nearside–farside (NF) theory of elastic angular scattering for an atom–atom collision from a central potential, to a general atom–diatom inelastic or reactive collision. The contribution of a classical trajectory to the N or F scattering subamplitude is found by projecting the atom–diatom Jacobi vector onto the (fixed) plane perpendicular to the total angular momentum vector and then monitoring its precession angle during the course of the collision. The theoretical tools used are a primitive semiclassical approximation for a reduced rotation matrix element expressed in terms of a type-2 classical generating function, the Poisson sum formula and the stationary phase method.