Nonadiabatic formulation of the slow-atomic-collision problem in the finite electronic basis

The resonating-group method developed for nuclear collisions is used to obtain equations describing the collisions of slow atoms. On one hand, these equations correctly take into account the indistinguish- ability of electrons and scattering boundary conditions and therefore are free from the drawbacks of conventional equations in the adiabatic electronic basis. On the other hand, they retain the form of the latter equations and therefore are in agreement with the generally accepted picture of heavy-particle motion in the fields of adiabatic electronic potentials accompanied by nonadiabatic transitions. The general theory is illustrated by considering the interaction of two ground-state hydrogen atoms in the Heitler-London electronic basis.