Dependence of electron-capture probabilities on the initial-state magnetic quantum numbers in ion-atom collisions

Close-coupling calculations have been carried out for ion-atom collisions to show that electron-capture probabilities depend strongly on the magnetic quantum number of the initial target state if 2 the quantization axis is chosen to be perpendicular to the scattering plane. In the natural frame of reference, the probability for electron capture is largest for ${\mathit{m}}_{\mathit{i}}$=-l substates and decreases rapidly with increasing ${\mathit{m}}_{\mathit{i}}$, while states with positive values of ${\mathit{m}}_{\mathit{i}}$ have negligible probabilities. This propensity rule results from the rotation of the electron cloud with the internuclear axis in the collision. We have shown further that this propensity rule can be interpreted classically and have carried out classical-trajectory Monte Carlo calculations to confirm the same qualitative results.