81U05 $2$-body potential scattering theory [See also 34E20 for WKB methods]
81U10 $n$-body potential scattering theory
81U15 Exactly and quasi-solvable systems
81U20 $S$-matrix theory, etc.
81U30 Dispersion theory, dispersion relations
81U40 Inverse scattering problems 
81U99 None of the above, but in this section