The theory of non-reactive scattering in systems with arbitrary angular momenta in the BF frame was developed Launay,
and was recently recalled in the context of scattering calculations for He-perturbed shape of HD
rovibrational resonances (see Stankiewicz et al) and O2-perturbed resonances of HCl
(see Olejnik et al).
We briefly summarize it in this section: