Very low energy scattering in HH+ and HD+

Differential and total cross sections for elastic scattering and resonant–near-resonant charge exchange have been computed for H+–H(1s) and H+–D(1s) collisions in the energy range 0 to ~0.1 eV, using a rigorous quantum mechanical formulation of slow collision theory in which all spurious couplings of the perturbed stationary states (PSS) theory are removed. Orbiting and shape resonances are described and compared in the two systems, and in addition the distinctive features of the HD+ case, such as the appearance of several Feshbach resonances in the region below the D+–H(1s) threshold, are identified and discussed. Most of the effects of the isotopic H(1s)–D(1s) splitting disappear at collision energies near the end of this range.