Implementation of the sudden approximation eikonal method in ion-diatom collisions

We describe an implementation of the vibro-rotational sudden approximation eikonal (SEIKON) method to treat collisions between ions (atoms) and diatomic molecules at impact energies 50 eV amu(-1) < E < 1 keV amu(-1) such that a semiclassical eikonal approximation can be applied to treat the relative motion of the colliding species, and a close-coupling molecular expansion is able to accurately represent electronic transitions. Our method, which does not make use of Franck-Condon-type approximations, allows us to evaluate vibrationally resolved charge-transfer and excitation cross sections, as well as total cross sections for transitions to the vibrational continuum. The implementation is illustrated with calculations of cross sections for single-charge transfer, vibrational excitation, and transfer dissociation in Be4+ + H-2, D-2 and DT collisions. The validity of the Franck-Condon approximation for these reactions is studied.