Semiclassical approximation for off-shell T-matrix elements for molecular collisions

A semiclassical approximation is given for off-shell T-matrix elements for collisions between systems with internal degrees of freedom. The derivation is based on the approaches of Miller and Marcus to semiclassical dynamics and the result generalizes an expression given by Korsch for off-shell T-elements for potential scattering, obtained from the WKB approximation. The approximation proposed provides a simple physical interpretation for the off-shell quantities and can be calculated by practical methods. The result has potential applications to various multiple collision problems and especially to calculations of collision-induced dissociation of polyatomic molecules.