Classical interpretation of probability oscillations in low-energy atomic collisions

We perform close-coupling molecular and classical trajectory Monte Carlo (CTMC) calculations of charge-exchange probabilities in low-energy H+, He2++H collisions. We consider head-on collisions with a zero impact parameter and study the dependence of the charge-exchange probability on the impact velocity. This probability exhibits oscillations generally understood as signatures of quantum phase effects. CTMC calculations with dimensionality reduced to one fairly reproduce the oscillations and show that these latter stem from the back and forth motion of the electron between the nuclear centers in the internuclear region. In three dimensions, the probability oscillations are generally washed out in the statistical CTMC framework because of the electron transverse degrees of freedom. However three-dimensional Bohmian trajectories ascertain the classical interpretation of the oscillations in a quantum framework.