Processes for charge transfer into ${\mathrm{He}}^{2+}$ colliding with the atomic isotopes hydrogen (H), deuterium (D), and tritium (T) are theoretically studied at collision energies as low as 30 eV/amu. Probabilities and cross sections for electron capture into different shells of the projectile are calculated using an ab initio approach which solves the time-dependent Schrödinger equation. The results are interpreted in terms of radial and rotational couplings between molecular orbitals. The probabilities exhibit strong Stueckelberg oscillations for charge transfer into shells with the principal quantum numbers $n=2$ and 3 due to radial coupling mechanisms in specific ranges of the impact parameter. The total cross sections for charge transfer, evaluated for a given shell, differ by orders of magnitude, as different isotopes are used in the collisions. The isotope effect increases significantly for decreasing $n=3$, 2, and 1. This finding is attributed to the influence of the rotational coupling mechanism, which is strongly affected by the distance of closest approach between the collision partners.

• Received 30 November 2009

DOI:https://doi.org/10.1103/PhysRevA.81.052704