  The semiclassical Wigner treatment of bimolecular collisions, proposed by Lee
and Scully on a partly intuitive basis [J. Chem. Phys. 73, 2238 (1980)], is
derived here from first principles. The derivation combines E. J. Heller's
ideas [J. Chem. Phys. 62, 1544 (1975); 65, 1289 (1976); 75, 186 (1981)], the
backward picture of molecular collisions [L. Bonnet, J. Chem. Phys. 133, 174108
(2010)] and the microreversibility principle.
